Archive for the ‘Vaporisers’ Category

The Afya ether vaporiser.

There now follows the description of an anaesthetic system made by the German firm of DRAGER, along the same lines as the Penlon E.M.O vaporiser.
I was unable to get any comprehensive maintenance instructions out of the firm despite a polite letter in German, written by my brother who lives in Berlin,  the reply to which was also in German which took me a great deal of time to translate.
In essence, they said that it was too complicated for anyone to service but themselves.
This sort of comment is not very helpful and is an insult to intelligent technicians who, with the proper information and tools, can do most things.
As a result, I have done the best I can for you by copying the description and instructions for use manual.
Where it does not alter the meaning I have left words and lines out to shorten things a bit.
First here is the address of Drager:
Dragerwerk A. G. Lubeck,
Postfach 1339.
Moislinger allee 53/55,
D 2400, Lubeck 1.
West Germany.

Section 1.
General, Intended use.

Modern operating techniques place stringent demands on anaesthesia which are met by the types of compressed gas-operated anaesthetic apparatus in general use in hospitals today.
There are however many areas and situations where it is either impossible or difficult and unreliable to have a supply of anaesthetic gas (N2O) and oxygen in steel cylinders.
As a result, a call was made for anaesthetic apparatus which makes it possible by using a mixture of Ether and air to perform inhalation anaesthesia in all areas of surgery.
This call led to Dragerwerk A.G. developing the AFYA anaesthesia system, (Afya is the Swahili word for health).
It is designed in accordance with the modular principle and permits optimum use either in a fixed situation like a hospital or mobile use.
The heart of the module is the ether vaporiser CATO 12, which, like the associated breathing accessories, operates on the semi-open principle using the draw over method.
In view of the fact that the system has, to all intents and purposes, no dead space, the ether concentrations (adjustable in Vol.%) can be matched in all phases of anaesthesia to the clinical indications and requirements.
If oxygen is available, the appropriate fittings can be used to enrich the mixture of ether and air with oxygen.
Whatever the combination, the system makes it possible at any point during anaesthesia to switch from spontaneous breathing to assisted or controlled manual ventilation without any settings having to be altered.
Naturally, such ventilation can also be performed without anaesthesia.
For mobile use, the vaporiser and necessary accessories can be put in a metal case for safe transportation.

Fig 1 shows the modules together with the transportation case.


The shown parts are listed below:
1. Light alloy transportation case.
2. CATO 12 ether vaporiser.
3. Connecting valve.
4. Corrugated tube 1m long, 22 mm diameter.
5. Corrugated tube 1m long, 13 mm diameter.
6. Connection port for respiratory bag.
7. Respiratory bag, large.
8. Respiratory bag, small.
9. Anaesthesia respiration valve for adults and children.
10. Anaesthesia respiration valve PAEDI for new-born babies and infants.
11. Connection piece for PAEDI valve.
12. Face masks for adults and children, 3 sizes.
13. Rendell-Baker masks for infants and new born babies, 4 sizes.
14. Guedal mouth tubes, 8 sizes, 00 – 6.
15. Catheter connection, 21 sizes, 1. 5 – 13 mm diameter.
16. Drainage piece.
17. Intubation kit.
18. AMBU mini foot operated suction pump.
19. Tin with spare parts.

Section 2.
Ether vaporiser CATO 12.

Sub section 1.

Fig 2 shows a schematic section through the vaporiser. Figs 3 and 4 clearly illustrate the individual controls.



The vaporiser is provided with a water tank as a heat accumulator in order to offset the cold generated during vaporisation.
The ether concentration (infinitely variable between 2 and 20 vol. %) is set using the rotary knob 15 taking account of the temperature reading on the thermometer 9.

Sub section 2.
Preparation of the vaporiser for anaesthesia.

1. Unscrew lock nut 16 marked WATER and pour NOT MORE THAN 1. 5 litres using a
funnel. The water should be at approximately room temperature.
Close the filler port again.
In daily use it is not necessary to change the water, it can remain in the vaporiser for any
length of time.
The water need only be emptied prior to transportation.
This is accomplished using the drainage piece as shown in figure 5.

2. Unscrew ether filler screw 1 and pour in the ether through the funnel.

If ether is to be topped up during anaesthesia the rotary metering knob 15 and the on/off knob should be turned to 0 !

Approximate quantities required for filling:

Upon initial commissioning (wicks in vaporiser dry)  370ml (up to max)  240ml (up to min)

With continuous use (wicks soaked through) (between min and max. ) 270ml.

Screw filler back in place again.
The ether level can be continuously monitored during anaesthesia by way of the ether sight glass 2. The level must never exceed the max mark and should not drop below the min mark.

3. Move the on/off knob setting to 0.

Sub section 3.
Setting of Ether concentration.

1. Set on/off knob 4 to 1. the rotary metering knob 15 cannot be moved so long as this knob is in the ‘O’ position.

2. Read off temperature on built in thermometer 9.

3. Set desired ether concentration using rotary metering knob 15.                                             When making this setting, the chosen concentration (sloping curves on tapered scale 10) must be made to intersect with the temperature reading on the vertical scale. In the example given in Fig 6,the settings are as follows:

Temperature 20c, concentration 4 vol. %.

Fig 6.


Key to Figs 2 – 6.
1. Filler funnel with screw plug.
2. Ether sight glass.
3. Ether drain valve.
4. On/Off knob.
5. Water container.
6. Ether container.
7. Vaporiser chamber.
8. Wick fabric.
9. Thermometer.
10. Concentration adjustment scale.
11. Metering cone.
12. Bypass throttle.
13. Pressure compensation chamber.
14. Inlet connection to atmospheric air.
15. Rotary metering knob.
16. Lock nut ( water filler port ).
17. Threaded connection for breathing systems.

Sub section 4.
After use.

1. Turn rotary metering knob 15 in an anti-clockwise direction as far as the stop.

2. Set On/Off knob 4 to 0. This knob can only be moved when the rotary metering knob has been turned in an anti-clockwise direction as far as the stop. In the ‘O’ setting the pressure inside the vaporising chamber is relieved through as small hole.

3. At the end of each working day the residual liquid ether is removed via the drain valve.

3. Fig 4.


Residual ether should not be re-used. The ether soaked up by the vaporiser wicks can be removed by ventilating the vaporiser with the respiratory bag in the maximum setting (20 vol.%).
This should be done prior to lengthy stoppages.

4. The water is drained using the drainage piece.



After removing the lock nut 16, the drainage piece is inserted into the filler port and gently squeezed using two fingers. Briefly blowing once into the upward facing drainage piece is sufficient to cause the water to drain off through the tubing, (siphon principle).
The water must never be tipped out!

5. Procedure to be adopted should the device have been tilted.
If a CATO 12 filled with anaesthetic agent is tilted, liquid anaesthetic may get into the metering unit regardless of whether the device is switched On or Off (knob 4).
This may lead to either an excessive or insufficient concentration.
If a filled CATO 12 is inadvertently tilted more than 45 degrees, the device must be kept completely opened (i.e. concentration setting 20 vol.%) for at least 30 minutes, without gas flow and standing in a normal position. It must then be flushed as follows:

1. Approximately 20 strokes of the respiratory bag at a setting of 20 vol.%.

2. Approximately 50 strokes of the respiratory bag at a setting of 0 vol.% whereby the On/Off knob is in position 1.

3.Approximately 50 strokes of the respiratory bag at a setting of 0 vol.% whereby the On/Off knob is in position 0. After flushing, the CATO 12 is serviceable again. Up to a tilt of 45 degrees the concentration is not affected. If there is a danger of the device being tilted to a greater degree during transportation, the anaesthetic agent should be removed from the CATO12.

6. The CATO 12 ether vaporiser is a precision instrument. Any checks and repairs which may need to be required must only be performed at Dragerwerk A.G. or by its authorised field services.

Note, my comments.
The manual makes no comment on how often the unit should be checked, I should imagine that it would go on a long time (years) before anything needed doing to it.
As a guide you really need an anaesthetic gas tester to check the output about twice a year.
Deviations from the set figures found by the test should be reported to the anaesthetists, leave them to decide what to do, but get them to sign the service sheet if they want to continue to use it.

Section 3.
The breathing systems and their combination.

Sub section 1.

The CATO 12 ether vaporiser is designed such that accessories to meet the requirements of various usage modes can be connected. Thus every situation has its own tailor made anaesthetic apparatus.
The required combination can be put together and made ready for operation in a few minutes without the need for tools.
Disassembly likewise presents no problems. The various combination possibilities are shown in Figs 7 – 11, with the individual photographs being accompanied in each case by a schematic drawing.

Sub section 2.
Combination ‘A’  Figs 7 and 7a.

This set up is intended for outpatient use and permits the following applications at any desired place of use:
1. Ether – air anaesthesia in the semi-open system in accordance with the draw over method with spontaneous breathing.

2. With switching potential at any time from spontaneous breathing to assisted or controlled manual ventilation.

3. Assisted or controlled manual ventilation ( without ether ) for resuscitation purposes.
The dimensions and performance data of the anaesthesia respiration valve 4, the corrugated tubes 3 and 5 and the respiratory bag 7 are meant for adults and children.

Sub section 3
Combination B Figs 8 and 8a.

The principle and mode of use of this set up correspond to that of combination ‘A’, however the anaesthesia respiration valve 9 (paedi valve), the corrugated tubes 8 and 10 and the respiratory bag 11 are meant for infants and new-born babies.

Key to Figs 7 – 8a.


fig7 copy







1. CATO 12 ether vaporiser.
2. Connecting valve.
3. Corrugated tube, 1m long 22 mm dia.
4. Anaesthesia respiration valve.
5. Corrugated tube, 1m long 22 mm dia.
6. Connection port for respiratory bag.
7. Respiratory bag, large.
8. Corrugated tube, 1m long 13 mm dia.
9. PAEDI ventilation valve with 9a adapter.
10. Corrugated tube 1m long 13 mm dia.
11. Respiratory bag, small.

Sub Section 4
Combination C and D (figs 9 and 9a, 10 and 10a)

For stationary use in hospitals, it is appropriate to mount the CATO 12 ether vaporiser on the trolley made for the purpose and secure it in position using the central screw provided.
The breathing accessories and thus the fields of application are the same as those for combinations A and B.
If oxygen cylinders are available the quality of the anaesthesia can be significantly improved by enriching the ambient air sucked in by the patient (or the respiratory bag) with oxygen.
This is achieved most economically by way of the ancillary oxygen fixtures illustrated in Figs 9 and 10.
Pressure reducer 15 with flow control valve, flowmeter, safety valve, supply pressure gauge and second ( pressure ) outlet for bronchial aspiration.
Oxygen connection piece 12.
Oxygen reservoir tubing 13.
The O2 metering ( variable between 0 and 15 l.p.m. ) depends upon the patient’s minute volume and the O2 concentration considered suitable by the anaesthetist.

Key to figs 9 – 10a.

Fig 9


                                                                                                             Fig 9a


Fig 10


Fig 10a


1. CATO 12 ether vaporiser.
2. Connecting valve.
3. Corrugated tube, 1m long 22 mm dia.
4. Respiration valve.
5. Corrugated tube, 1m long 22 mm dia.
6. Connection port for respiratory valve.
7. Respiratory bag, large.
8. Corrugated tube, 1m long 13 mm dia.
9. PAEDI respiration valve with 9a adapter.
10. Corrugated tube, 1m long 13 mm dia.
11. Respiratory bag, small.
12. O2 connection piece.
13. O2 reservoir tube.
14. O2 connection tube.
15. O2 pressure reducer with flowmeter.
16. O2 cylinder.
17. Trolley.

Sub Section 5.
Combination E, ( Figs 11 and 11a ).                                                                                                                              Fig 11


Fig 11a


In the case of major and thus lengthy operations, monitoring of respiration/ventilation is extremely important.
For this purpose a number of optional accessories and measuring instruments can be supplied with and attached to the AFYA system.
They are all illustrated in Figs 11 and 11a and the individual breakdown is as follows:

Valve chamber ( item 18 in Fig 11a ).
This is screwed into the vaporiser in place of the connecting valve ( item 2 in Fig 7 ).
It contains the inspiratory valve 19, the expiratory valve 20 and under the expiratory valve, the expiratory valve control 18a, i.e. in another form the complete valve set contained in the respiration valve ( item 4 in Fig 7 ) or in the PAEDI valve.
The use of this valve chamber 18 makes it possible to prevent air exhaled by the patient from escaping in an uncontrolled manner into the open air, in that it is routed through the Y piece 22 and the second corrugated tube 3, into the measuring instruments 24 and 25 and only then via the expiratory control valve 18a into the open air.
It is thus possible to make use of measuring instruments and devices described in the following.

Drager Minute Volumeter ( item 25 in Fig 11 ).
This device is designed to measure and continually monitor the tidal volume.
It is screwed into position between the valve chamber 18 and the expiratory valve 20. With both spontaneous breathing and ventilation it measures each expiratory stroke, i.e. the tidal volume.
Monitoring the volume with the stop button for a period of 1 minute is a simple way of obtaining the minute volume.
My Note: I’m not sure what they mean by – monitoring with the stop button- but in any case  I think it means allowing the meter to register the breaths for 1 minute and taking a reading in litres at the end of that time.

Respiratory pressure gauge ( item 24 in fig 11 ).
This is likewise screwed into position between the valve chamber 18 and the expiratory valve 20 ( below the Volumeter ).
With every ventilatory stroke it indicated the inspiratory pressure in the breathing system.
The magnitude of the inspiratory pressure can be limited by using the pressure relief valve 21. The pressure gauge also makes it possible to detect whether the expiratory phase (which always takes place spontaneously) is continued as far as zero pressure.

Relief valve ( item 21 in Fig 11 ).
This is permanently attached to the valve chamber 18 and limits the level of respiratory pressure as desired. Settings between 10 and 40 mbar are possible.

Respiratory bellows ( item 23 in Fig 11 ).
These can be connected in place of the respiratory bag 7 or 11.
There permanent position on the trolley coupled with the unambiguous upward and downward movement makes easy manual ventilation in many cases. Ventilation is effected only with the fresh gas mixture sucked in via the O2 connection piece 12.
There is no re-breathing of the exhaled gas; the gas exhaled escapes via the expiratory control valve 18a into the open air.

Key to Figs 11 and 11a.
1. CATO 12 ether vaporiser.
3. Corrugated tubes 1m long 22 dia.
5. Corrugated tube 1m long 22 dia.
6. Connection port for respiratory bag.
7. Respiratory bag large.
11. Respiratory bag small.
12. O2 connection piece.
13. O2 reservoir tube.
14. O2 connection tube.
15. O2 pressure reducer with flowmeter.
16. O2 cylinder.
17. Trolley.
18. Valve chamber with
18a. Expiratory control valve
19. Inspiratory valve.
20. Expiratory valve.
21. Relief valve.
22. Y piece.
23. Respiratory bellows.
24. Respiratory pressure gauge.
25. Minute volumeter.
26. Anaesthesia timer/sphygmomanometer.
27. Sucker.
28. Connecting are for item 26.

Section 4.
Further accessories

Sub – section 1.
Anaesthesia timer ( item 26 Fig 11 )

During anaesthesia the timer makes all time dependent measurements easy.
1. Normal time measurement.
2. Stopwatch function: 1 revolution = 30 secs.
3. Pulse rate measurement.
4. Respiratory rate measurement.
This timer has an 8-day clock.

Sub – section 2.
Sphygmomanometer ( item 26 in Fig 11 ).

This is an aneroid type to which any cuff may be connected.

Sub – Section 3.                                                                                                                                         Sucker. ( item 27 Fig 11 ).

The sucker is a valuable supplement to the anaesthesia apparatus.
It is, however, reliant on the oxygen cylinders since it operates on the injector principle.
The generated maximum vacuum is – 6m WG (-0.6 bar), with an oxygen consumption of 6 l.p.m.

Sub – Section 4.
Ambu Foot operated sucker ( item 18 Fig 1 ).

The Ambu foot operated sucker is valuable whenever compressed oxygen or other vacuum is not available.
It is thus part of the AFYA transportation case. ( this is made by the Danish firm of AMBU who make a lot of resuscitation equipment ).

Section 5.
Notes on caring for the system.

Sub – Section 1.
Ether vaporiser CATO 12.

The CATO 12 is described in detail in section 2. It requires no maintenance other that external cleaning with a damp cloth and if necessary a disinfectant.

Sub – Section 2.
Connecting valve.

The connecting valve 2 can be easily disassembled without the need for tools.
All the parts can be washed in the usual manner and if necessary disinfected by immersing then in an appropriate liquid disinfectant.
The disc valve is made of high grade, surface ground porcelain and will not be effected by chemicals, though it can be broken if badly handled.
Care should be taken during cleaning to ensure that the valve seat is not damaged as leaks will occur.

Sub – Section 3.
Valve chamber ( item 18 in Fig 11a ).

The valve chamber contains not only the relief valve 21 but also the expiratory control valve 18a. The latter can be disassembled without tools for cleaning, washing and if necessary cold sterilising and then re – assembled.
The valve chamber itself together with the permanently attached relief valve should be properly rinsed and if necessary subjected to cold sterilising.
Before installing the expiratory control valve all parts should be properly dried otherwise they may stick.

Sub – Section 4.
Inspiratory valve and expiratory valve ( item 19, 20 in Fig 11 ).
The inspiratory and expiratory valves are similar to the connecting valve. See sub 2 for details.

Sub – Section 5.
Anaesthesia respiration valve ( item 4 Fig 7 ).
Fig 12 shows the disassemble valve.

Fig 12


These components should always be cleaned after use (and at least at the end of the working day) in warm soapy water and then disinfected in a liquid disinfectant.
If there is a risk of cross infection they can be boiled.
When cleaning, care should be taken to ensure that the small spring loaded inspiratory valve in the centre of the main diaphragm is not damaged.
Only assemble the respiration valve when all parts are dry.
When performing assembly work take particular care to ensure that the parts are installed in the sequence and position shown.

Sub section 6.                                                                                                                                           Paedi respiration valve (Item 9 in fig8)

The Paedi respiration valve is a practice proven product manufactured by Ambu international.

Sub section 7.                                                                                                                                           Tubes, masks and respiratory bags.

These are made from high grade anti static rubber. At the end of the day they should be cleaned with warm soapy water and then disinfected. They should be stored in a dark well ventilated and cool spot.

Sub – Section 8
Minute Volumeter 3000 ( item 25 Fig 11 ).
This requires a certain amount of care if it is to always function reliably.
It must be cleaned at the end of each working day.

To do so, allow hot water from the tap to run through from top to bottom, it can then be briefly centrifuged and dried on a Drager Volumeter drying unit.
My Comments: this method of drying sounds rather complicated to me, they do say that you can use a hair dryer to do it, if you do take care not to get it to hot, hold the unit in your hand and allow the hot air to blow through, if you find your hand getting to hot the hair dryer is to close.
If necessary it can be sterilised at 120C  in any super heated steam steriliser using standard procedures. Such sterilisation is performed subsequent to the cleaning procedure described above. In such cases drying can be despised with.

The bearings should be re-lubricated after 30-steam sterilisations, or every three months.
My comments: They say to use the lubrication set provided, when that has run out try to get some watch oil from a watch repair shop.
They also say that any repairs can only be done by Drager, not having seen the inside (or outside) of one I can’t say if this is true or not. However, at a guess, I would treat it like the Wrights respirometers written about in another section, or take it to a local watch repair man.
Sub – Section 9.
Respiratory pressure gauge ( item 24 Fig 11 ).

Clean with a damp cloth from time to time, if there is a danger of infection it can be steam sterilised like the Volumeter.
You must allow it to cool to room temperature before use.
Prior to use check the zero setting and adjust if necessary using the knurled adjusting ring.

Sub – Section 10.
Anaesthesia timer ( item 26 Fig 11 ).
This should require very little maintenance, if you are not happy about doing watch type repairs take it to a local watch repair shop.

Sub – Section 11.
Sphygmomanometer. ( item 26 Fig 11 ).

Repair as the aneroid sphygmomanometer described else where. Do not steam sterilise.

Sub – Section 12.
Pressure reducer. ( item 15 Fig 9 – 11 ).

The pressure reducer with blow off valve, flow control valve, flowmeter and pressure gauge (for displaying cylinder contents) requires no maintenance other than an occasional wipe with a damp cloth. Before changing cylinders the sealing ring is to be checked and replaced if damaged.

After some years they may need attention for leaks, Drager say to send them back to them, I would try to buy the parts and do it yourself.
Check the seal from time to time.

Sub – Section 13.
Sucker ( item 27 Fig 11 ).
When using the sucker care is to be taken to ensure that the secretions collector does not become over full.
The overflow of secretions to the injector is prevented by the float valve ( ping pong ball ) in the sealing cap of the collector.
At the end of the working day or in the event of acute danger of infection after each patient, those parts coming into contact with the secretions should be cleaned and disinfected.
The collector is to be properly rinsed and disinfected cold, i.e. in a liquid disinfectant.
If necessary it can be sterilised in super heated steam (observe temperature indicated on collector).
The same also applies to the secretions sight glass (glass tube at the patient end of secretions suction hose), the secretion aspiration hose itself and the sealing cap.
The ping pong ball can only be cold sterilised.

My Note: if the ping pong ball gets squashed but not punctured, they can sometimes be made round again by holding them in warm to hot water.

Sub section 14. Ambu foot pump.
I have written of this in another article.

Here is a list of spare parts and their numbers:
Cato 12 ether vaporiser
Sealing ring M 18789.

Connecting valve
Set of sealing rings (5). M 22155.
Set of valve discs (3) M 23249.
Set of transparent caps (5) M 22171.

Anaesthesia respiration valve.
Sealing ring. M 11345.
Diaphragm. M 11023.
Valve diaphragm. M 11140.

Valve chamber.
Diaphragm. M 18679.
Sealing ring. M 9257.

Inspiratory and expiratory valve.
Set of sealing rings (5)
Set of Valve discs (3).
Set of transparent caps (5).
numbers as for Connecting valve see above.

Respiratory pressure gauge and Volumeter.
Sealing ring. M 9257.
Sucker Sealing cap. M 22884.
Set of ping pong balls (3). M 22147.(or buy them in a local sports shop).
Set of caps (5) (under ping pong ball).M 20003.

Secretions jar. M 20091.
Set of secretion sight glasses (5). M 22150.

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The chances are you will never see one of these, they came set up for Ether, Trilene and Halothane.

The Boyle bottle ether vaporiser has two controls. The lever to the left of the picture, on the upstream side of the vaporiser, permits a proportion of the gas from the flowmeters to be ducted through the vaporiser or to bypass it. The control is uncalibrated but has extreme markings of ‘OFF’ and ‘ON’ and permits continuous proportional adjustment. The rod at the top of the vaporiser, known as the ‘plunger’, controls the extent to which the incoming gas is delivered to the liquid ether. Within the vaporiser bottle, it terminates in a cap that advances over the up-turned u-shaped gas inlet tube. In use, the lever is progressively rotated from OFF until it is fully ON. The plunger, initially fully raised, is progressively lowered. Gas is directed to pass more closely over the liquid ether surface and is ultimately bubbled through the liquid ether. This is the maximum setting possible. The rate of vaporisation causes rapid cooling so that the vapour concentration begins to diminish. The cooling can be delayed by filling the accessory water bath with water at room temperature. Without the water bath, the bottle will chill until frost forms on the glass to the level of the liquid ether. Depth of anaesthesia is judged clinically. The ‘U’ shaped inlet tube within the vaporiser and the cap of the plunger are made from un-plated copper. This is considered to protect the ether from degradation.



Below is an exploded diagram of the various parts.


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If you have a phone with a camera, take photos as you go to remind yourself where parts go.

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I am not sure who wrote this little piece, but thanks.

Photographs by me.

An anaesthetic vaporiser is a device generally attached to an anaesthetic machine which delivers a given concentration of a volatile anaesthetic agent.

Anaesthetic vaporiser
The design of these devices takes account of varying ambient temperature, fresh gas flow and agent vapour pressure

Historical vaporisers
Historically, ether (the first volatile agent) was first used by John Snow’s inhaler (1847) but was superseded by the use of chloroform (1848). Ether then slowly made a revival (1862–1872) with regular use via Kurt Schimmelbusch’s “mask”, a narcosis mask for dripping liquid ether. Now obsolete, it was a mask constructed of wire, and covered with cloth.
Pressure and demand from dental surgeons for a more reliable method of administrating ether helped modernise its delivery. In 1877, Clover invented an ether inhaler with a water jacket, and by the late 1899 alternatives to ether came to the fore, mainly due to the introduction of spinal anaesthesia. Subsequently, this resulted in the decline of ether (1930–1956) use due to the introduction of cyclopropane, trichloroethylene, and halothane.                                                                                                 By the 1980s, the anaesthetic vaporiser had evolved considerably; subsequent modifications lead to a raft of additional safety features such as temperature compensation, a bimetallic strip, temperature-adjusted splitting ratio and anti-spill measures.

Modern vaporisers
There are generally two types of vaporisers: plenum and draw over. Both have distinct advantages and disadvantages. A third type of vaporiser is exclusively used for the agent desflurane.

Plenum vaporisers
The plenum vaporiser is driven by positive pressure from the anaesthetic machine and is usually mounted on the machine. The performance of the vaporiser does not change regardless of whether the patient is breathing spontaneously or is mechanically ventilated. The internal resistance of the vaporiser is usually high, but because the supply pressure is constant the vaporiser can be accurately calibrated to deliver a precise concentration of volatile anaesthetic vapour over a wide range of fresh gas flows.                                                                                                                                                                                                     The plenum vaporiser is an elegant device which works reliably, without external power, for many hundreds of hours of continuous use, and requires very little maintenance.
The plenum vaporiser works by accurately splitting the incoming gas into two streams. One of these streams passes straight through the vaporiser in the bypass channel. The other is diverted into the vaporising chamber. Gas in the vaporising chamber becomes fully saturated with volatile anaesthetic vapour. This gas is then mixed with the gas in the bypass channel before leaving the vaporiser.

The performance of the plenum vaporiser depends extensively on the saturated vapour pressure of the volatile agent. This is unique to each agent, so it follows that each agent must only be used in its own specific vaporiser. Several safety systems, such as the Fraser-Sweatman system, have been devised so that filling a plenum vaporiser with the wrong agent is extremely difficult. A mixture of two agents in a vaporiser could result in unpredictable performance from the vaporiser.
Saturated vapour pressure for any one agent varies with temperature, and plenum vaporisers are designed to operate within a specific temperature range. They have several features designed to compensate for temperature changes (especially cooling by evaporation). They often have a metal jacket weighing about 5kg, which equilibrates with the temperature in the room and provides a source of heat. In addition, the entrance to the vaporising chamber is controlled by a bimetallic strip, which admits more gas to the chamber as it cools, to compensate for the loss of efficiency of evaporation.
The first temperature-compensated plenum vaporiser was the Cyprane ‘FluoTEC’ Halothane vaporiser, released onto the market shortly after Halothane was introduced into clinical practice in 1956.

Draw over vaporisers
The draw over vaporiser is driven by negative pressure developed by the patient, and must therefore have a low resistance to gas flow. Its performance depends on the minute volume of the patient: its output drops with increasing minute ventilation.
The design of the draw over vaporiser is much more simple: in general it is a simple glass reservoir mounted in the breathing attachment. Draw over vaporisers may be used with any liquid volatile agent (including older agents such as diethyl ether or chloroform, although it would be dangerous to use desflurane). Because the performance of the vaporiser is so variable, accurate calibration is impossible. However, many designs have a lever which adjusts the amount of fresh gas which enters the vaporising chamber.
The draw over vaporiser may be mounted either way round, and may be used in circuits where re-breathing takes place, or inside the circle breathing attachment.
Draw over vaporisers typically have no temperature compensating features. With prolonged use, the liquid agent may cool to the point where condensation and even frost may form on the outside of the reservoir. This cooling impairs the efficiency of the vaporiser. One way of minimising this effect is to place the vaporiser in a bowl of water.
The relative inefficiency of the draw over vaporiser contributes to its safety. A more efficient design would produce too much anaesthetic vapour.                                                                                                                                                                               The output concentration from a draw over vaporiser may greatly exceed that produced by a plenum vaporiser, especially at low flows. For the safest use, the concentration of anaesthetic vapour in the breathing attachment should be continuously monitored.
Despite its drawbacks, the draw over vaporiser is cheap to manufacture and easy to use. In addition, its portable design means that it can be used in the field or in veterinary anaesthesia.

Dual-circuit gas-vapour blender
The third category of vaporiser (a dual-circuit gas-vapour blender) was created specifically for the agent desflurane. Desflurane boils at 23.5C, which is very close to room temperature. This means that at normal operating temperatures, the saturated vapour pressure of desflurane changes greatly with only small fluctuations in temperature. This means that the features of a normal plenum vaporiser are not sufficient to ensure an accurate concentration of desflurane. Additionally, on a very warm day, all the desflurane would boil, and very high (potentially lethal) concentrations of desflurane might reach the patient.
A desflurane vaporiser (e.g. the TEC 6 produced by Datex-Ohmeda) is heated to 39C and pressurised to 200kPa (and therefore requires electrical power). It is mounted on the anaesthetic machine in the same way as a plenum vaporiser, but its function is quite different. It evaporates a chamber containing desflurane using heat, and injects small amounts of pure desflurane vapour into the fresh gas flow. A transducer senses the fresh gas flow.
A warm-up period is required after switching on. The desflurane vaporiser will fail if mains power is lost. Alarms sound if the vaporiser is nearly empty. An electronic display indicates the level of desflurane in the vaporiser.
The expense and complexity of the desflurane vaporiser have contributed to the relative lack of popularity of desflurane, although in recent years it is gaining in popularity.

A selection of early vaporisers.

An early ether vaporiser made by Coxiter.


A slightly later Boyle’s Trilene vaporiser.

More or less gas was directed down the wide bore metal tube you can see in the glass bottle. The vertical chrome rod with the flat top could be moved up and down by the anaesthetist, on the other end is the wide bore tube where the gas comes out of the bottom of it, if you push the tube right down under the Trilene fluid level you got a higher anaesthetic concentration, the more you lifted the end of the wide bore tube to the surface of the liquid or out of it the lower the concentration given.


Next we have the Emotril.


The one below is the Medrex halothane vaporiser made by Airmed.


The Cardiff inhaler for Penthrane, this was made by Cyprane.


The Cyprane portable ether draw over vaporiser


Cyprane MkIII halothane vaporiser


Penlon’s EMO ether vaporiser.


Penlon’s OMV vaporiser’s, OMV 50 tri-services (L), OMV 30 (R) both draw over vaporisers.



Goldman’s vaporiser.

goldmans (1)

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This is another type of vaporiser that is some times found on BRITISH OXYGEN anaesthetic machines. Again they are not used so much these days but in case you do still use them, the following tells you all about them.

Below a Halox and the calculator.


The HALOX vaporiser is a `copper kettle’ type in which the vapour strength is controlled by regulating a flow of oxygen through the liquid.
A separate flowmeter is provided, from which oxygen is fed to the vaporiser emerging from a sintered glass diffuser immersed in the liquid halothane.
A thermometer is fitted to indicate the temperature of the halothane.
Each HALOX vaporiser is supplied with a simple slide rule calculator relating halothane concentration, at a known temperature and flow rate, to oxygen through halothane flowmeter reading.
The calculator enables the anaesthetist to measure accurately the exact amount of halothane vapour being added to the gas stream, this being important during closed circuit techniques and low minute volume operation.

The halox vaporiser should be serviced as follows;
1. Remove the glass bottle and examine it for cleanliness and damage, replace if required.

2. Examine the bottle sealing washer for serviceability, replace as necessary.

3. Examine the body for cleanliness, damage and security of attachment of components.

4. Examine the sintered glass filter and thermometer for serviceability, replace as necessary.

5. Refit glass bottle.

6. Examine halox slide rule calculator for serviceability and stowage for security of

This will just involve testing along with the other items on the back-bar of the anaesthetic machine, for leaks and so on.
An actual check on the accuracy of the instrument can only be done with the proper anaesthetic gas analyser.
As with the other old vaporisers the chances are that you won’t be able to buy any spares for them if parts do break, you will have to use old badly damaged ones to keep the better ones in service. see drawing.
See the section on anaesthetic machines for the back-bar testing procedure.
As with the Ether vaporiser parts may not be available still here are the part numbers:

Halox Halothane vaporiser (part number 310751).

Diagram of a Halox.



Item Name Part number
1. Screw, 10 BA x 3/32 in, Round head. 430454
2. Cage assembly 310862
3. Cage end 310843
4. Non-return valve assembly 311648
5. Washer 310842
6. Hex, stem 310853
7. Sealing washer 310840
8. Male cage mount assembly 310673
9. O ring 310676
10. O ring 108202
11. O ring 310676
12. B.S. adult/Paediatric outlet 310675
13. O ring 108202
14. Cage end 310843
15. Screw, 10 BA x 3/32 in, round head 430454
16. Washer 310842
17. O ring 108103
18. Gas distribution tube 310839
19. Thermometer 310845
20. Halothane bottle 50-100 ml 310857

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Cleaning a Mk 2 vaporiser.
In 1960 the design of the control valve was modified, this modification allows the control valve to be dismantled for cleaning without altering the calibration, they are identified with the letter ‘A’ added to the serial number. It may be before or after the number.

mkII fig1

The instruction book from which these instructions are taken from say that all others (that is the ones without the ‘A’) should be returned to the firm for cleaning.


1. remove the back cover 47015 (fig 2.)


Having removed the four screws the back cover may still stick to the main body, this is due only to the stickiness of the shellac on the joint.
A slight tap will allow it to be removed and as it comes away a spring, 47059 (fig 3) will also come out.

2. Carefully withdraw the bypass valve, 47057 (fig 30) and place this in a position where it will not be damaged.

3. Put the dial of the fluotec to the off position and by using the special circlip pliers, the circlip ‘T’ is removed.
This will release spring, 47049 (fig 3) (my note, take great care removing the circlip so as not to damage it, you may need to re-use it).


4. Remove the spring indicator, 47014 (fig 4) by taking out the 2 screws ‘J’ and ‘W’

5. Remove screw ‘W’ and then the spiral peg, 47020, can be removed from the spiral (figs 4 and 5).



6. The spindle,47041 (fig 5) can be completely removed by turning and pulling the dial, 47024 (fig 5). If the spindle is at all tight in the body, put a few drops of Fluothane into the spindle bore at point ‘D’ (fig 6).

Allow the liquid to soak into the bore for about an hour and then it will be found that the spindle can be removed easily. However, if the spindle is still tight then repeat the procedure.
If this fails, the spindle removing tool (T9) may be used.

It will be found in the cleaning kit alongside the cleaning rod and is a short round piece of metal with a hole in one end. (there is no picture of this in the handbook, but you are unlikely to have the kit anyway). I would imagine it is a piece of round brass with a shallow hole drilled in one end which is a little bit larger in size than the spindle end, you tap this gently with a light hammer, if you cannot make one tap it out from the rear using a piece of wood or plastic and again with a light hammer. DO NOT tap straight on to the spindle itself.
Great care must be taken not to bend the spindle or damage the bore.

7. The bore of the control valve should then be cleaned. Moisten the felt of the cleaning rod with Fluothane, if you do not have the rod use a piece of cloth on a thin wooden stick.
Take care not to scratch the bore.
Clean the spindle with a cloth soaked in Trilene.
When the Trilene has evaporated, blow away any cloth fibres that may have been left behind.
Now smear the bearing surfaces of the spindle with a thin coating of ‘Vaseline’, (petroleum jelly), probably available from your pharmacy.

8. Re-insert the spindle (fig 5) into the body and work it in and out a few times to make sure that it is quite free and working smoothly.
If not, remove the spindle, re-clean the bore and the spindle, re-grease and re-fit.
Note. the amount of petroleum jelly must be kept to a minimum.
9. Having made the spindle work freely in the bore, the re-assembly can begin by pressing the dial, 47024, as far into the body as it will go.

10. Insert the spring, 47049 (fig 6), large diameter first, over the end of the spindle.
Compress the spring with the spring compressor (fig 7)

and fit a new circlip by means of the circlip pliers whilst the spring is compressed. (my note. if you do not have a new one, fit the old one if it is in good condition).
Make sure the clip is firmly in the groove in the spindle (figs 6 and 7).

11. Rotate the spindle, 47041, until the spiral is directly under the hole ‘B’ (fig 5).

12. Carefully fit the spiral peg, 47020, into the hole ‘B’ (fig 5) and into the spiral, making sure that it enters the spiral correctly without any interference.

13. Hold the spiral peg, 47020, in position and rotate the dial, 47024, to make sure that it moves freely. Replace screw ‘W’.

14. Refit the spring indicator, 47014, by means of screws ‘W’ and ‘J’ noting that the screw ‘W’ is the longer one and should be fitted nearer the dial.

15. Carefully clean and replace the bypass valve, 47057, (fig3). Note: This valve is fitted with a timing sleeve which is held in position by a large circlip ‘B’, but should never be dismantled. because it is a timing sleeve which is set dimensionally to suit its particular ‘Fluotec’ and is not interchangeable.

16. Clean the joint face of the rear cover, 47015, (fig 3) and also the appropriate face of the valve body.

17. Take a new joint, reference 47040, and coat each side with a thin layer of Shellac which has been dissolved in methylated spirits to give a thin solution. Insert the larger diameter of the spring, 47059, into the recess in the rear cover, 47015, and the small diameter of the spring over the raised portion of the bypass valve, insert the four screws and tighten down evenly.
My note: If you do not have a new gasket, you might try a motor repair shop for some thin gasket material, the Shellac is the sort of thing you might find in a watch repair shop.

18. The assembly is now complete and the dial should be operated a few times to make sure that the action is quite smooth.

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A simple and reliable addition to the E.M.O for limited dosages of halothane, anaesthetic agent.
They have no controls.
Halothane is poured into the measuring dish on the top, this has a capacity of about 3 cc.
The wick unit is removed from the bottom and placed in the dish, the wick will absorb the halothane, and it is then replaced on the bottom of the unit and will immediately deliver vapour to the patient.
The unit is normally left attached to the E.M.O, it gives about 2% halothane at 4 l.p.m.
The only maintenance that you can do is to make sure the wick is in good condition and that the tapers are not damaged where it plugs into the E.M.O.

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Mk 3 Vaporisers.
more photographs by me in the illustrated version of this article.


This is a very easy vaporiser to clean.
Remove 4 grey plastic caps at each corner and with a 4mm hexagonal key, undo the 4 bolts holding the top on. Clean off the deposits on the brass face of the top and also the bottom part.
Use Halothane, Trilene or Ether.
Blow away any fibres that may have been left behind by the cleaning cloth, no lubrication required, re-assemble the top, tighten the 4 bolts and replace the grey caps.
As a general rule DO NOT use any abrasive cleaning compounds, and NEVER under any circumstances use wire wool or sandpaper.If, however, you do get one really stubborn bit you can use a metal polish but you MUST clean away any remaining polish afterwards with Halothane, Trilene or Ether, if you don’t it will continue to slightly abrade after reassemble and every time you turn the top.

Trouble with the click stops on the control knob:
Remove the two screws holding on the circular plate on top of the control knob, remove the plate.
Undo the large screw in the centre and remove it along with its washer, lift off the control knob. Remove the woodruff key (the small half-round piece of metal that keys the top to the spindle).
The click stops are provided by the small nylon pip at the front, there is a spring underneath it, it will either be stuck or the spring is weak or missing. Repair as necessary.
The sprung pip at the rear is to balance the front one.
The orange off position release button is on a spring held on by one screw.
Replace the woodruff key with the top part into the groove more than the bottom part otherwise you will have difficulty getting the top back in place. It may need a little juggling and a tap with a soft hammer or a piece of wood to get the top on.
Replace the large central screw and washer and the top cover and two screws.

To get to the wick, turn the unit on its side and undo the 4 screws underneath the lip of the unit, pull the top away complete with the wick assembly.
Inside you will see 4 bolts which hold on the filler unit and the sight glass unit.
These should not be disturbed unless you have to replace the seals, sometimes, if the unit has been dropped, they may work loose. Tighten them with a spanner, do not over tighten or you may damage the seals.
The drain cock may be removed by loosening it a few turns and undoing two countersunk screws.
There is a seal on the end of the shaft, do not damage it. Unless you have a replacement there will be little you can do to it.

If you do not have one use a piece of wood. Do not use a metal hammer, not that it won’t work but simply that it will damage the chrome.

Re-assemble in the reverse order and test.
Check that the taper connections at each end are round, if not make an anvil, slightly smaller than the hole in the connector, out of a piece of wooden stick, hold it in a vice and tap the connector round with a soft hammer, i.e. one with a nylon or similar head. If you do not have one use a piece of wood. Do not use a metal hammer, not that it won’t work but simply that it will damage the chrome.

I’ve just found a little piece in the operators manual for the Mk3 vaporiser made by CYPRANE, or OHMEDA (BRITISH OXYGEN) as it is now called, there are quite a few of these vaporisers around so it is worth setting it out in case it is of any use to you but I do stress that it is written for the Mk3 vaporiser sold by CYPRANE and more than likely won’t apply to other vaporisers.
The checking method below can be used where specialist equipment is not available for checking the calibration.
The characteristics of the vaporiser is such that if the vaporiser is correct at one setting it should be satisfactory at all other settings.
1. Check that the vaporiser has been filled and has been at an ambient temperature of 22c for at least three hours.

2. With the vaporiser securely mounted, open the drain until no more liquid will run
out and then close the drain.

3. Check that the dial is turned off and carefully and quickly refill with a measured
amount of anaesthetic agent without spilling, use 70ml, close the drain securely.

4.Leave the vaporiser at about 22C for 1 hour to ensure that the temperature
has stabilised.

5. Set a flow rate of 5lpm. of oxygen.

6. Turn dial to 2 %, note the time and check that the flow rate is still 5lpm.-readjust as appropriate.

7. Leave the vaporiser at this setting for 30 minutes, check the flow rate now and again, turn vaporiser off and turn the oxygen off.

8. Drain until no more liquid will come out and measure the amount of liquid drained off.

The amount of liquid consumed in ml should be in accordance with the table below.
Make sure that you exhaust the gas outside.
Fluotec 13.5
Enfluratec 15.5
Isotec 15.5

It should be appreciated that the above test method is designed to be quick and easy under ordinary hospital conditions and that the method is somewhat imprecise.
Nevertheless, it would be unusual for measured liquid consumption to vary from that given above by more than 25%.
This is a simple procedure and although the firm say it is imprecise, it is worth doing if you have no other means of testing.
In general terms, it is recommended that vaporisers are returned to their makers or agents from time to time.
If you have your own analyser you should check the output on a regular basis.
If you find that the error is more than +/- 10% of the dial setting, (at 2%, 1.8 ~ 2.2), the unit should be returned to the makers for re-calibration.
Any errors you find should be reported to the anaesthetist, let him decide if the unit is fit to be used.

Cutaway diagram.

Tec 3 Cut_Away

Tec 3 Schematic

Tec 3 Sump_Valve Assy 01

Thanks to General Anaesthetic services and in particular, Andrew Wall for the above diagrams.

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O.M.V. (Oxford Miniature Vaporiser)


Photographs and drawing in the illustrated version.
The description below might not be the same as for your vaporiser due to the age and model, however, it will be substantially the same.

This is a small Vaporiser which can be used without an anaesthetic machine for giving cheap and simple anaesthetics.
It works in a similar way to the large Vaporiser except that it does not have a temperature compensation device in it.
Instead, there is a chamber underneath filled with anti-freeze to help stabilise the internal temperature.
There are few things to go wrong with these units.
The most likely is that in time it will become stiff to operate the pointer.
This comes about because of deposits of thymol left behind by the anaesthetic agents.
So knowing how to clean it when required (or better still, before required) will be of great value.

It is a job which is easy enough with instruction, but one which must be done with care and careful thought and not rushed.
The only tools you need are a small watch makers screwdriver and a medium screwdriver (flat bladed) and the setting tool described below.

There are two cleaning procedures, the simple one and the less simple one.

If the control being stiff is the problem there is no need to dismantle the whole thing and clean the wicks. In this case use the simple procedure below.

The simple one.

This should be done as soon as the unit feels stiff, doing it then might prevent having to do the more difficult procedure.

The only thing you need for this is a rubber bung or similar to block the inlet and some cleaning fluid, ether or methylated spirits.
With ether this is best done outside to avoid the fumes and falling asleep.
Place the bung into the inlet; turn the Vaporiser on to its side with the outlet port pointing upwards.
Pour cleaning fluid into the inlet whilst moving the pointer to and fro.
The Vaporiser should be completely filled and allowed to stand for 5 minutes before emptying.
Once empty the vaporiser should be left open while air is blown through it for 15 – 20 minutes, this will rid it of any smells.
From time to time you may find that this does not free it up properly and you will have to go through the more difficult procedure.

The more difficult procedure.                                                                                                                                    This is done if you have to do a serious clean if the above procedure does not solve your stiff rotor problem if concentrations are falling off or there is an internal problem.
Apart from a few simple tools, you will need a setting gauge shown in fig A1.2.
Actually, the one shown and sold by the firm is a great deal more complicated than it needs to be.
For almost all models all you need is a piece of brass or stainless steel rod, ordinary steel will do except that in time it may go rusty, it needs to be 1/8 inch or 3.15 mm in diameter.
Cut off about 150mm and bend a right angle at one end, make the arm of the bend about 10mm long. Remove any rough edges.

If concentrations are going off and leaks are not a problem, it could be that the wicks are clogged with thymol, that is the main reason for wanting to remove the regulator and clean the wicks.

Clear your bench off, prepare your tools, all three of them.
You are now ready for the major cleaning procedure.
1. Remove the pointer- remove screw (13) and washer (32), lift off the pointer and abutment washer (33), remove scale.
Place in a safe place.

2. Remove lid – take out the three screws (53), and lever the lid off the body.
Note: These screws are rather short and with a fine thread, treat them very carefully otherwise you WILL strip the thread on the screw or the vaporiser.
If this does happen all is not lost, you will have to tap a new thread into the body and fit a larger screw, The tapping is done with a thread tap which you may have in your maintenance department or try a local engineering firm.

3. Remove M6 nut (35) and washer (36) and remove off – line hook (16).
Remove two screws (34), and take off tenon block (39) and clamp (40).

4. Remove 4 screws (27) and washers (28). Lift out regulator assembly (6), ‘O’ seal (21) and clamp ring (22).
Place all the screws in a safe place.

5. Part fill the vaporising chamber with cleaning fluid, (ether or alcohol), agitate gently to wet all parts of the wicks.
Allow to soak for 2 – 3 minutes repeating the agitation several times. Scrub with a toothbrush if necessary.
Throw away the liquid.
Repeat the process until the liquid appears clean.
Turn the chamber over and allow to dry completely.

6. If indicator glass is still dirty after the above process, remove the 4 screws (42) securing it, lift out the glass and wipe clean. Do not do this lightly, if you damage the seals and have no replacements you will be in trouble.

7. If after cleaning the wicks, corrosion is present on the wick e.g. rusty patches, reassemble the Vaporiser and return it to the manufacturers for replacement of the wicks. (their comments not mine)

8. Regulator – to dismantle.
Note: This description mentions an idler pinion, some models have only the rack and the pinion on the end of the pointer, others will have a pinion between that on the pointer and the rack this is the mentioned idler pinion. This is used to reverse the direction of the rack and slide valve relative to the pointer and scale.

Remove inlet and outlet cones (4 screws each Nos 25 and 26) gaskets (24) and obdurator assembly (19).
Remove 2 screws (23) securing the rack (20). Lift off rack and spacers. Note that the plastic sleeves inside the spacers must be retained. Note also the relative positions of the ports and the direction of the cone of the slider.
If there are no marks on the rack and pinion, mark across both with a pencil to assist in re-assembly.
Remove the slide valve by pushing from the outlet end of the regulator housing, if it is stiff use a wooden or plastic stick and a light hammer to tap it out, do not use metal as this will damage the machined surfaces.
Soaking the assembly in ether or alcohol will usually dissolve any deposits that may be causing the stiffness.
Wash the slide valve and regulator housing in cleaning fluid and dry with a clean cloth.
Pay particular attention to the sliding surfaces.
NEVER, NEVER clean the surfaces with sand paper, metal polish may be used to remove stubborn dirt but wash it off properly with alcohol or ether to remove any polish that may have been left behind.
Re-fit the slide valve to the housing.
Do not use oil or grease, check for smooth motion from one end to the other. Check the location of ports and the direction of the cone, re-assemble rack with spacers and screws, lining marked tooth on the rack between two marked teeth on the idler pinion, and the same time the marked teeth on the idler and the pointer pinion. (see fig 2.1).

9. Backlash and adjustment.
Backlash can develop between the rack and pinion and idler or between idler and pinion.
A tappet screw (29) is provided to adjust the engagement of the former.
The pinion (37) is mounted in an eccentric bush and engagement with the idler is adjusted by slackening the lock screw (30), rotating the eccentric bush using a 3mm bar in the hole provided until the engagement is correct and then tightening to lock screw.

10. Re-assemble regulator to body.
The special P.T.F.E. coated ‘O’ ring (21) which seals the assembly must be examined for damage and replaced if necessary.
Separate the clamp ring and regulator housing by removing 4 screws (27) and washers (28).
Insert the clamp ring into the body with the 4 screws at 45 degrees to the regulator housing looking from the top.
Immerse the ‘O’ ring in warm water (40oC to 60oC) for a few minutes to soften it.
Place the ‘O’ ring on top of the clamp ring.
Insert the regulator housing assembly using the 3mm bar to line up the screw holes in the clamp ring and the regulator housing, insert the draw screws into 2 diagonally opposite holes to draw the clamp ring into the body (hand tight only).
Insert 2 screws (27) and washers (28).
Remove the 2 draw screws, insert the 2 remaining screws and washers. Tighten all 4 screws evenly and fully, making sure that the regulator is pressed home fully into the body without gaps between the inlet and outlet square sections.

Note: This procedure can be done differently if you do not take apart the clamp ring and seal when removing the regulator from the body. When taking apart do not completely remove the four screws, just slacken them off.
When replacing you must be careful not to damage the ‘o’ seal when pushing the regulator into place in the body. Tease it in with your fingers.

11. Examine the obdurator assembly to ensure that the adjustment screws are sealed.
If the seal is broken, return the unit to the makers. (their comments not mine)
Assemble gaskets (24), obdurator assembly and inlet connector with 4 screws to the regulator housing.
Check that the obdurator is lined up with the slide valve.
Assemble gasket and outlet connector to regulator housing.

12. Leak test main body seal.
Ensure slide valve is open, block outlet connector, pressurise to about 180 mmHg through the inlet connector.
Run a small amount of cleaning fluid (ether or alcohol) into the joints between the regulator assembly and the body.
Check for bubbles.
Tighten screws or replace ‘O’ ring if necessary to obtain a leak free joint.
Tip out the surplus liquid and allow to dry.

13. Re-assemble tenon block, clamp, off line mounting block, lid and pointer. There is no need to replace the three screws that hold the top in place, but make sure the holes are lined up for the pointer checking procedure.

Do not fit the scale at this point.

Check pointer setting.

Do this by inserting the setting gauge (omv1) through the outlet port, (see fig 2.2) with the pointer set between ’50’ and ’60’ on the engraved scale on the lid.
Move the pointer until no further movement is possible. The pointer should indicate ’35’ on the engraved scale.
A positional error of +/- 1mm is acceptable, this allows for slackness due to old age.
If the gear train has been wrongly re-assembled, an error of 7.5o will be introduced per tooth, so errors are easy to detect.
Remove setting gauge, assemble the outlet connector and gasket (24), fit the scale back in place.
After completing the check then put in the three screws that hold the top in place.

Leak testing.
Equipment required for this test:

a. Source of compressed gas at about 200 mm Hg.
The book does say a source of compressed gas, however, I would advise you do not try to use gas from a pressurised cylinder, this is best provided by a blood pressure machine inflation bulb or an oxford inflating bellows.

b. Rubber bungs to fit the inlet and the outlet of the vaporiser.
One of which should have a steel or plastic tube through the middle with a diameter of about 6mm.

c. A reservoir of about 4 litres capacity (or so) capable of withstanding 200 mm Hg pressure.

d. A pressure gauge that reads about 200 mm Hg, a blood pressure machine would do nicely.

e. Liquid soap solution and a small paint brush.

f. Ether or Methylated spirits.

g. A stopwatch.

h. A pair of clamping forceps.

i. Some rubber tube to fit the connector in the rubber bung.
This procedure should be carried out if the unit has been reported to be giving low concentrations or is using excessive quantities of liquids.

The Vaporiser is connected to the reservoir, pressure gauge and compressed air source as shown in Drawing No 1
Air is pumped into the system until the pressure is reading 210 mm Hg, the air supply is them clamped off with the forceps.
The pressure in the system will fall slowly and the time taken for the fall from 200 mm Hg to 190 mm Hg is recorded by the stopwatch.
The check is carried out with:
1. The pointer set to the off position to test the connectors and the top end of the regulator housing.
2. The control pointer in the ‘3.5’ position to test the vapour chamber joints generally.

3. The control pointer to the OFF position and the filler held open to test the vapour seals.

Acceptance values.
1.30 seconds or more.
2.30 seconds or more.
3.15 seconds or more.

If the Vaporiser does not pass this test, the position of the leak is best found by brushing the suspected joints with soap solution whilst maintaining the pressure.
It will show by bubbles forming at the site of the leak.
Do not apply soap solution to the opening around the rack where it could enter the slide valve, it will dry up and cause the slider to stick.
Note: There is always a certain amount of leakage from the slide valve, but this can be ignored if the test figures given earlier are obtained.

Specific repairs.

1. Level indicator and filler unit, to fit a new indicator glass.
Remove 4 screws (42) take off retainer, old glass, seal and centring ring. When fitting a new glass always fit new seals.
Glasses vary a little in thickness, three seals are provided in the spare parts kit and sufficient seals should be used to obtain a good compression on the glass when the retainer is screwed back into place. Check again for leaks.

2. To fit a new drain seal.
Remove drain screw.
Use pin spanner (A1.3) to unscrew the old drain seat assembly (49) from filler block.
Discard old assembly and seal.
Fit new assembly and seal (52), tighten securely.
Leak test again.

3. To fit a new back seal.
If a leakage develops between the filler block and the body, remove level indicator glass.
With a screwdriver, lever out the engraved back plate of the level indicator, this will expose the heads of 2 socket screws (47).
If tightening does not cure the leak, remove the screws, lift off the filler block and fit a new seal (48) between the block and the body.
Re-assemble all parts and leak test.
4. To replace the complete base.
The top is fixed to the base using ‘Araldite 100’, an adhesive.
If this joint is broken due to a fall, the same adhesive should be used to re-affix the base.
Clean off the old adhesive before re-affixing and ensure that the recess in the base is aligned with the water filling screw (12).

The firm advises that the unit should go back to the factory every 2 years, I should leave this to the judgment of the anaesthetist.
For many hospitals this will not be practical, cleaning as required and treating the unit with care should ensure a long life.

Should the sight glass break and you do not have an official replacement and are unlikely to be able to get one, you will have to make your own. I did this once for a different reason. In this case we were doing some experiments on the vapouriser and wanted to measure the temperature inside. I made a glass out of some window glass, shaping it on a grinding wheel, then drilling a hole in it for the temperature probe to go through.
Do wear goggles and a mask when doing this.

Calibration procedure.
These instructions are for trained personnel using the equipment listed below:-

1. A supply of dry, clean compressed air, with a pressure regulating system producing
15 – 45 psig.

2. A flowmeter with a needle valve control to produce a measured flow of 4 – 6 lpm with 5% accuracy. (My comments: most flowmeters can manage this accuracy).

3. A fresh gas supply tube to connect the flowmeter outlet to a cagemount female taper connector to fit the vaporiser inlet.

4. A mixing chamber with a cagemount fitting to fit the vaporiser outlet, with an exhaust port for 22 mm tubing and a sampling port for 6 mm tubing (part number MH561)

5. 22mm tubing to the disposal system. (My comments: out of the window / to a scavenging system or suitable filter or sit outside in the sun.)

6. A Riken gas analyser, model 18, calibrated 0 – 6% halothane. (My comments: or other similar).

Caution: The sampling tube between 4 and 6 must be of nylon, PTFE, or similar material which does not absorb anaesthetic vapours. The use of rubber or other such materials may cause large errors in measurement. Short lengths of rubber may be used to join nylon tubing to the analyser and the sampling tee.

Choice of agent:
If the vaporiser is known to be dedicated to a specific agent, it should be calibrated to that agent.
If the vaporiser is used with various agents, it should be calibrated using halothane, as that agent gives the highest numerical scale values and therefore maximum accuracy of measurement.
The design features of the vaporiser which determine the relative output of the various agents at a specific setting of the control are dependent upon agent, temperature and pressure.
These three factors can be considered individually as follows.

1. The halothane in air Riken analyser can be used for other agents by multiplying the readings by the factors given below to give true Vol %. These factors are determined by the relative refractive indices of the vapour.

Agent Factor
Halothane 1.00
Enflurane 1.05
Isoflurane 1.06
Chloroform 1.14
Trichloroethylene 0.88
Methoxyflurane 0.86
Di ethyl ether 0.92

2. Temperature.
Calibration should be carried out at 20oC +/- 2oC. Within this range a temperature correction factor is not required, given the accuracy of measurement available.

3. Pressure.
Normal variations in barometric pressure due to weather changes are not significant given the accuracy of measurement available, but altitude may produce significant effects, as shown below.

Correction factor
Barometric pressure

610 m (2000ft)
x 0.9
910 mbar

1229 m (4000ft)
x 0.84
850 mbar

1830 m (5000ft)
x 0.8
813 mbar

Calibration procedure.

1. Connect the fresh gas directly to the mixing chamber (bypass the vaporiser).

2. Set a flow of 4 lpm and take several readings with the Riken to establish a true and consistent zero.
3. If necessary, flush the reference cell of the Riken with air and ensure that that this cell is equilibrated to atmospheric pressure.

Note; This is most important if the Riken analyser has itself been moved from one altitude to another.

4. Fill the vaporiser approximately three quarters full with the selected agent (see choice of agent) and attach the appropriate scale.

5. Allow the vaporiser to stand with the control at zero for 30 minutes to ensure all temperatures are equilibrated.

6. Connect the vaporiser to the fresh gas inlet and the mixing chamber.

7. Turn on an air flow of 4 lpm and allow the vaporiser to stand for 4 – 5 minutes with the control at zero.

8. Take a series of readings at various control settings with the Riken and record the results on the record sheet (see below). Each time squeeze the sample bulb a minimum of 3 times starting at the given time on the sheet.

Acceptance figures.
The readings, when corrected, should be within 20% of scale. a greater degree of depression than the above indicates that the wick system has been incorrectly assembled or that it is clogged up.

9. After calibration, drain the vaporiser chamber and connect the unit to an air supply.

10. With the control set full on and the exhaust system attached, blow air through until the smell of anaesthetic agent has been removed.

Halothane contains thymol as an additive and it is not possible to get rid of the smell of this substance.

11. Close the vaporiser control to zero before passing the unit for use or storage.

Inspection sheet:
Service at:
Serial number of unit:
Agent used:


Riken reading.
Correction factor (agent).
Vol %

After all this you will realise that you cannot do anything to adjust a vaporiser out of calibration, (unless as they say, the wick has been incorrectly assembled or the wick needs cleaning.).

The E.M.O, the O.M.V and OXFORD BELLOWS, amongst other things, are made by the English firm of PENLON, they are a very helpful firm who are interested in making good quality equipment suitable for use all over the world.
In the unlikely event of you having to send something back to them here is their address.

Penlon ltd.
OX 14 3PM

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E.M.O. (ether vaporiser)
Epstein – Macintosh – Oxford.

Below is a link to EMO maintenance in pictures;

EMO maintenance in pictures


Use and maintenance.

This is a sophisticated vaporiser of low internal resistance for use with Ether and air.
It will give percentages from 2 to 20.
It has a water jacket which helps keep the internal temperature stable. It has only two moving parts, the concentration rotor and the temperature compensator; these are set in the factory and should not be touched except in an emergency and then only after reading the service book.

The tests shown below are only to assist you in deciding if the unit is safe to operate.
There are very few repairs you can do without the service book and spares, however these are such well made units that if they are looked after they should not give trouble for years.

Some simple tests on the E.M.O.

1. Level indicator.
With the ether compartment empty, slowly turn the vaporiser over and check that the indicator moves freely, and falls to the full position and then returns to the empty position when it is turned back.

When filling it up, check that the quantity of ether you put in is as follows.
When the wicks are dry, it will be found that 150 – 200 ml of ether can be poured in before the level indicator lifts from the empty position. A further 300 ml will be required to raise the level indicator to the ‘F’ (full) position. DO NOT OVERFILL.

2. Closing mechanism.
Turn the control to the transit position and connect the outlet of an oxford inflating bellows or other hand ventilating equipment to the inlet of the vaporiser.
Block the outlet of the unit and gently pressurise it.
There should be no escape of air through the filler or through the top of the closing mechanism.

3. Filler.
With the bellows still connected as above and the outlet blocked, open the control knob to 10 and gently apply pressure to the system.
There should be no leakage through the filler.

4. Safety release valve. (this is combined with the closing mechanism)
With the control knob set to 12 and the oxford bellows connected to the outlet of the vaporiser, block the inlet and check that the operation of the bellows draws air in through the safety valve.

5. Temperature compensating unit.
The position of the compensating indicator will show if the unit is in good working order.
It consists of a rod with a black and red band and a metal top.
At 20oC – 25oC the metal top and the black band should show, at temperatures above 32oC the red band will begin to show.
If only the metal band can be seen at 20oC – 25oC the compensating unit is faulty.

6. Water compartment.
If the water used to fill the compartment is suspected to contain high concentrations of salts or chlorine, it is advisable to empty and refill this compartment from time to time.

Some notes on making your own distilled water.
The simple way to make distilled water is to have a water reservoir with sides on it and with a piece of glass angled over the top, leave it in the sun, the water will condense on the glass and run down into an angled water trap and then into a bottle, this is a fairly crude method but will produce better water for your water compartment.
Otherwise you can boil water in a kettle and collect the steam on a glass sheet and let it run into a bottle.

Some simple repairs.
There are a number of repairs that you can do on these units, however, most will need special tools, spare parts and a service book.
For the most part, if the machine is looked after you will have very few problems.
The one that you will have, due to the passage of time, is a stiff or seized rotor. This can be cured by following the instructions below.
When it is necessary to gain access to the interior of the E.M.O inhaler, the lid and pointer are removed as an assembly by the following sequence of operations. (see drawing 2.15)

1. Remove handle, 2 screws.

2. Remove ether label on the boss of the pointer, 2 screws.

3. Remove 3 spring dowels, use special tool EMO No5 or a pair of small pointed pliers or mosquito forceps.

4. Set control knob to 6% scale marking, remove plug in the handle of the control knob. Using a hexagon allen key, EMO tool No 6. Insert it through the hole from which the plug was taken, unscrew and remove 1 allen screw.

5. Remove ‘O’ ring and spring under ether label and keep in a clean position.

6. Remove 5 screws from around the rim of the lid and 3 screws near the centre. The closing mechanism may also be left attached to the lid.

Access can now be obtained to the rotor if this has become stiff or seized, and to the air inlet port if the closing mechanism has been leaking. Any dirt or foreign bodies should be carefully removed from the mixing chamber.
Removal of control pointer.
If it is necessary to remove the control pointer because of major damage or leaks, the lid must first be removed from the E.M.O.
The pointer is then released by removing the circlip (9), and the various sealing washers shown. When reassembling great care must be taken to replace the washers in the positions shown, and new plastic and rubber parts should always be fitted (if you have them).

Vaporising chamber.
If access is required to the vaporising chamber, the lid pointer assembly must first be removed.
Empty any liquid ether out of the vaporising chamber, remove the water drain plug and empty the water jacket.
Remove all screws around the edge of the mixing chamber, 15 in all, after which the mixing chamber can be lifted off the vaporising chamber. Remove the upper gasket and the three insulating sleeves, and then lift the vaporising chamber out of the water jacket.
The Mk 1 E.M.O. has a cast aluminium water jacket, the Mk 2 has a stainless steel pressed jacket and an aluminium clamp ring which will be free when the screws around the edge have been removed.
In both cases there is a gasket between the vaporising chamber and the water jacket.

To replace the vaporising chamber complete.
Dismantle as above and reassemble by reversing the operation using new gaskets.

Parts required:
Complete vaporising chamber with wicks. 60200.
Gasket lower. 60209
Insulating spacers, set of 3. 60109.
Fibre washers for screws, set of 8. 0100.

When reassembling the following points must be carefully checked:
1. All parts must be properly clean.

2. As the fixing screws around the edge are irregularly spaced, care is necessary to position the gaskets correctly so that all the holes are aligned. It may be necessary to turn the gaskets over to meet this condition. The upper gasket has 3 enlarged holes into each of which an insulated spacer must be fitted. New spacers should be used if the old ones were damaged with dismantling. Careful placing of the upper gasket and the use of spacers ensures that none of the fixing screws make metal contact between the vaporising chamber and the water jacket.
If available, an insulation tester should be used to check electrical insulation after assembly, one probe being held in contact with the water jacket, one with the vapour chamber (most easily reached through the temperature compensating well).

3. The fixing screws should be tightened gradually working alternately on one side and then on the opposite side of the inhaler, in a similar manner to the cylinder head nuts on a car.
They should be finally secured as tightly as possible with a normal screwdriver of the correct size to fit the head.

4. The 8 screws inside the mixing chamber must have fibre washers beneath their heads to ensure sealing. Any damaged washers should be replaced.

Rotor stiff.
If the action of the rotor is stiff it may be removed by twisting and lifting, washed in ether, re-lubricated with a small amount of pure Vaseline (petroleum jelly) and replaced.
Do not disturb either the centre screw or the 3 hexagonal socket screws indicated on the drawing. Ensure that the steel ball is in position at the base of the liner in which the rotor fits.
After re-assembling the complete inhaler check the rotor settings as set out below.

Checking the adjustment of the rotor.
Preparation for adjustment.
The inhaler should have the temperature compensating unit removed as set out below and the top plate of the control knob removed as well, together with the ‘O’ seal and the central spring which will be found below it. The spring dowel marked ‘E’ in fig 1 must not be removed.
A special gauge is required which may be obtained from the manufacturers or made locally to the dimensions shown in fig 2.
Special note: Before carrying out the checks and adjustments set out overleaf, make sure that the rotor is pressed home fully in the inhaler. This is normally performed by the spring which has to be removed, and after every movement of the rotor it must be pressed down to ensure that it has not lifted.

Removal of the temperature compensating unit.
Retained in the inhaler by 3 screws which expand rubber sealing sleeves when tightened.
To remove it from the inhaler slacken all three screws by 3 – 4 turns. Tap the heads of the screws down flush with a piece of wood or plastic. Grip the top of the unit and twist or wriggle slightly to break the grip of the rubber seals.
The unit should now lift out.
It may be necessary to repeat the slackening process if the inhaler has been in use for some time.
DO NOT remove the screws completely as parts may be lost in the inhaler.

Method of checking adjustment of the rotor.

Note: The rotor is correctly adjusted before leaving the factory, and should normally not be interfered with in any way.

These instructions are given for use in cases where dismantling has been necessary for servicing and must be stuck to in detail.
The rotor has both vertical and angular adjustment relative to the vapour port.
Vertical adjustment is effected by adjustment screw A which is locked by nut B.
Angular adjustment is provided by slackening 3 screws C and D. Screw C is a clamp only, those marked D have coned ends and by slackening one slightly and tightening the other, fine adjustments to the pointer can be made. (see fig 1)

To re-fit.
Make sure the three screws are slack, slide the unit into the inhaler body, check that the top plate is fitting correctly to the inhaler without gaps, and tighten the three screws.
To check the vertical adjustment.
Set the pointer at 4%. Insert the gauge into the temperature compensating well holding the long leg vertically. The short leg can then be entered into the vapour port until the mark on the side of the gauge is level with the edge of the temperature compensating well.
At this point the width of the gauge in the rotor is 0.100″ (2.54mm) and the gauge should fit the gap between the rotor and the liner without slackness.

To adjust the rotor vertically, if necessary (fig 3).
Slacken nut ‘B’, screw OUT the adjuster ‘A’ and press down on the rotor. Screw IN the adjuster ‘A’ until the gauge, when applied as above, indicated that the gap is 0.100″.

To check the angular adjustment (fig 4).
Set the pointer at the figure ‘1’ of the 10% mark. Insert the gauge as before but check that the gap between the main step of the rotor and the edge of the port is as in fig 4.
This dimension should be 0.125″. (3.15mm).

To adjust rotor if the angular position is incorrect.
Turn pointer until gap is wide enough to insert gauge as shown in fig 4, then turn pointer back until gauge is gripped. Slacken screws ‘C’ and ‘D’ (fig 1) and set pointer to the ‘1’ of the 10% mark, making sure that the rotor does not move. Tighten screw ‘C’ finger tight only and make final adjustment to the ‘1’ by tightening screws ‘D’ a little at a time. Tighten screw ‘C’ fully.
Remove gauge and re-check the gap as set out above.

Rotor seized.
If the rotor has become immovable, a small quantity of penetrating oil should be applied round the edge of the upper surface and through the ether port, reached via the temperature compensator well. Gentle warmth helps the action of the penetrating oil, which may take several hours to release the joint.
Using no undue force, grip the rotor boss with EMO tool No 2 or put the top back on and use the pointer (a temporary pin can be put in place instead of the spring dowels).
Attempt to turn and lift the rotor.
If it is still immovable, unlock and remove the central lock nut and tighten the central screw. This will lift the rotor in the casing and help break the point of seizure. Repeat the process of oiling, twisting and lifting until the rotor is completely removed.
At no time should undue force be used. The inhaler may be damaged permanently unless great care is taken.
In case of difficulty return the unit to the manufacturer.
The cause of the seizure is either a foreign substance in the ether, such as lacquer off the ether cans, or the use of ether which has decomposed and contains aldehydes, In the latter case the liner may show considerable corrosion which must be carefully removed by scraping with a suitable steel tool.
On no account use sandpaper, emery cloth or steel wool which may leave abrasive particles behind.
The rotor should be cleaned with metal polish, lubricated and re-assembled as described later.

If you are unable to get any penetrating oil make your own. Mix ether and a light oil in a 50/50 mixture.

Temperature compensating unit.
If you suspect a fault with this unit as a result of the test earlier, the following procedure may be carried out.
Remove the compensator following the instructions given earlier.
If the room temperature is above 21oC, put the canister part of the unit into iced water for about a minute. Remove it from the water and with finger and thumb around the lower sealing ring, press first up then down on the stepped valve disc ‘X’. This should move against springs in each direction, but if the E.M.O. has been left out of use for sometime in an extreme temperature it may have become stuck on its spindle. Firm pressure will generally release it.
If it cannot be released the whole unit will have to be replaced.

Now immerse the canister in iced water as before and watch that the whole stem and disc ‘X’ move down and the visual indicator also falls.
Now put the canister in fairly hot water, 40oC, and check that the stem, disc and indicator rise.
The disc should completely block the hole in the lower sealing ring and the indicator should rise until the red part is visible through the glass.
Transfer back to the cold water once again and check that the movement is now correct.
Replace the unit back into the E.M.O.

NOTE: On no account touch either the two nuts at the top of the stem or the grub screw at the top of the can. These control basic adjustments which have been correctly set at the factory.

Closing mechanism.
Retained in the inhaler by 2 dogs operated by screws (marked A on the drawing).
To release the unit, unscrew these by 2 or 3 turns only, tap the top of the unit lightly with a piece of wood or the plastic handle of a screwdriver to break the grip of the sealing washer.
A further turn on each screw should then release the dogs and the complete unit can be lifted out.
To reassemble the closing mechanism to the inhaler, make sure that the dogs are turned in fully and insert the unit into its seating, checking that the tongue provided on the inhaler fits into the slot in the closing mechanism body.

Tighten the 2 screws by one turn, lift the unit to check that both dogs are engaged properly and then tighten screws fully.

The part number of a complete replacement unit is: 60900.
spare parts are as follows:
Item 1. Body sealing washer. 60923.
Item 2. Relief valve washer. 60924.
Item 3. Valve assembly. 60930.
Item 4. Split pin. 092.
To fit new valve assembly.
Remove split pin (4) and small washer. Discard split pin (keep it if you have no other). Using a pair of fine pliers disengage the spring wire (6) from the hole in the valve stem.
Remove the complete valve stem assembly and fit new unit by reversing the above procedure. Use a new split pin if you have one.

To fit a new relief washer.
Pull down spring (8) and hold the spindle (7) inside it. By pressing the spindle away from the closing mechanism body the top end can be disengaged and the washer then readily replaced.
To fit a new body sealing washer.
Remove 2 screws (A) and dogs and adjusting screw (B). Remove the old washer by stretching it over the body; fit the new washer in the same manner. Reassemble dogs and screws (A) and (B). Check with the drawing for the correct position.
The dogs should be a tight fit on screws (A). Re-adjust unit as described below.

Adjustment of unit fitted to inhaler.
After fitting a new unit adjustment may be required to ensure correct seating of the valve. Screw (B) is provided for this purpose.
Turning this screw clockwise will increase the closing pressure on the valve.
The screw should be adjusted so that the control pointer can operate the closing mechanism without undue force, and the valve closes soundly when checked as set out earlier.

Level indicator.

This is retained in the unit by 3 screws.
The part number for a replacement unit is 60600

Items 1 & 2. Top assembly with glass. 60601/12.
Items 3 & 7. Indicator pole and assembly. 60608.
Item 4. Gasket. 60616.
Item 5. Screw. 0145.
Item 6. Case assembly. 60604.
Item 8. Glass float with wire. 60613.
New glasses are not supplied separately as this item is sealed into the metal top with a special cement.

This is retained in the unit by screw thread. A special split screwdriver is necessary for removal. Tool number E.M.O.1.
Replacement unit. 60500.
Spare gasket. (item 5). 60517.

To fit a new float glass.
The wire on the glass float is crimped into the tube No7. To release the old wire, squeeze the tube across the direction of the crimping and pull the wire out with a straight pull.

Insert the wire on the new float, and crimp the tube lightly with a pair of pliers.
Fit the level indicator assembly in to the empty E.M.O. and check the position of the indicator when the float is resting on the bottom of the empty ether chamber. Adjust so the indicator is level with the two arrows on either side of ‘E’ by pulling or pushing the float as required.
When the position is satisfactory, crimp the tube in a second place more heavily to secure the float wire.
Here are a few other problems you may come across and what to do about them:
1. Ether escaping, although the control is closed for transit.
a. Broken level glass, replace.
b. Broken indicator glass on the temperature compensating unit, replace compensator.
c. Closing mechanism not shutting, adjust or replace mechanism unit.

2. Concentrations initially appear to be higher than normal but drop off quickly after use.
a. Temperature compensator not operating, carry out checks as above.
b. Filler left open, close.

3. Concentrations appear to be lower than normal.
a. Leak in the circuit, find and cure.
b. Relief valve on closing mechanism stuck open. Carry out checks on safety valve as in 4 above.
Replace as necessary.
c. Overfilled with ether so that the vaporising surface is too small. Pour out the excess ether and check the level indicator.
d. Temperature compensator not working, check as above.

4. Level indicator fails to rise when the ether is added but moves freely when the unit is inverted.
a. Broken float, replace level indicator.

5. Level indicator sticks at any point and will not move when the inhaler is inverted.
a. Float caught by a frayed wick. Remove the unit and cut away the frayed ends of the wick with a pair of scissors.
b. Caught by collapsed ether compartment due to gas build up in the water jacket owing to the use of impure water. Return to the maker or their local agents for repair.

Cleaning and sterilising.
No antiseptic solutions must be used to clean the inhaler. The outside may be cleaned by wiping over with a damp cloth or where it is more seriously contaminated one damped in ether.

Sterilising is not normally necessary as the inhaler is used on open circuit, protected from contamination by non return valves. If special circumstances make it necessary to sterilise, the only suitable method is the use of Ethylene Dioxide gas.
Excessive heat due to boiling or autoclaving would render the inhaler useless.

When storing an E.M.O, O.M.V or Oxford bellows cover them to keep out the dust
(not a plastic bag, they may sweat) and put a bung into the inlet and outlet to prevent insects getting inside and building nests or dying.

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