Archive for the ‘Oxford inflating bellows’ Category


Oxford inflating bellows 1

This is a hand-operated bellows unit for inflating the lungs, it consists of an inlet connection and valve, the bellows in the middle, an outlet valve and outlet connection, the valve consists of a disk of metal that lifts by air flow and falls by gravity, there is also an oxygen inlet connection and tap.
You will see a magnet in a holder, under the bellows this is used to immobilise the outlet valve when a non-rebreathing valve such as the AMBU valve is in use.


The bellows was first designed for use with a simple spring-loaded expiratory valve.
This arrangement works well with spontaneous respiration, but for artificial respiration is less satisfactory for this reason a non- re-breathing valve as mentioned above is preferred.
Compression of the bellows during artificial respiration will produce a full deflection of the flap valves during inspiration, in order to draw the flaps back and hence permit the patient to expire to the atmosphere, a very small amount of air must pass back up the corrugated tube towards the bellows.
If the outlet flap valve of the bellows unit is not immobilised, air will be unable to pass back and the non-rebreathing valve will stick in the inspiration position.
So the magnet MUST be fitted if a non-rebreathing valve is being used.
This shows the magnet holding the expiratory valve open.(The bellows has been removed to make it easier to see)

magnet holding vslve open

The bellows can be changed from an adult one to a paediatric one just by unscrewing it from the base. The paediatric bellows has a full stroke capacity of about 400 ml, making it easier to ventilate children.
The bellows removed.


The bellows should be inspected regularly as you would with all pieces of equipment with bellows in them, you can’t really service anything unless you find one of the following faults

1. cracks in the bellows.
you can change the whole thing base plates and all or just the bellows.
To replace the bellows proceed as follows;
remove the bottom plate first by taking out the 4 small screws, and levering off the plate which has been cemented on with BOSTICK.
Loosen the inner bottom plate.
Access can then be gained to hold the ball ended bolt that is attached to the top plate.
Holding the bolt with pliers or a spanner, unscrew the hand knob on top of the bellows, releasing the bolt, spring and bottom plate.
The old bellows can then be pulled off the top plate.
Clean all the old cement off the end plates.
Insert the inner top plate into the bellows, apply a small but continuous ring fillet of BOSTICK to the groove in the outer top plate, position this on the bellows and insert the hand knob.
Enter the spring into the bellows from the outer end, apply the ball ended bolt and tighten the knob.
BOSTICK can then be applied to this thread for sealing, also care must be taken to keep the bellows and plates concentric during tightening.
Stretch the bellows over the inner lower plate and position the ring on the bellows edge in the groove in the plate.
Apply BOSTICK to the groove in the outer bottom plate and to the thread of the 4 small screws.
Assemble the bottom plate with the screws, again ensuring concentricity
of the rubber in the grooved end plates.
Allow the BOSTICK at least one hour to dry before testing the bellows for leaks.

My note: If you do not have Bostick you can use silicone sealer.

2. Check the glass domes for cracks.
To replace the glass domes proceed as follows, Note that the metal clamp rings are not inter-changeable between inlet and outlet valves.
Always use new gaskets (firms recommendation, not mine, unless they are obviously badly damaged) with new glasses and tighten the fixing screws in rotation, a little at a time, so as not to stress the glass unevenly.
Always ensure that the magnetic disk valve is installed in the outlet valve assembly, after dismantling the valve body.

3. The magnet should be fitted to its support to check that it lifts the outer valve clear of theĀ valve seating.
If it does not, check that the magnet is OK and that the disc is the correct one and is attracted to a magnet.

4. After replacing the magnet in its storage holder, block the inlet port with a cork or your hand and attempt to extend the bellows. This tests the outlet valve.

5. It should not be possible to extend the bellows more than 2.5 Cm in 1 minute.
Transfer the cork or your hand to block the outlet port and attempt to compress the bellows, this is testing for leaks in the inlet valve, again, movement should not exceed 2.5 Cm in 1 minute.
Remove the cork.

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