Archive for the ‘Heaf gun’ Category

The Heaf gun.

This is an instrument used for testing for tuberculosis and is called a Heaf test or a Sterneedle test.

There was also the Tine test which is a similar procedure

Named after Professor Frederick Roland George Heaf, born in Desborough in the UK of German parents.

A Heaf gun was used to inject multiple samples of testing serum under the skin at once. The needle points were dipped in tuberculin purified protein derivative (PPD) and pricked into the skin. There are a couple of versions, but they all work in a similar way.

This article is now of historical value only as Heaf testing stopped in about 2005. These days they use the Mantoux test

The main one described below is made by East’s of Oxford, the same firm that make the East Radcliffe ventilator.
They consist of a spring-loaded plunger, six short sharp needles on the nose of the instrument and a plate with six holes for the needles to pass through.
Some can be altered to be 20 pin versions for vaccinations.
The unit is adjusted for depth of needle penetration by turning a small knob at the top (1 or 2 mm), placed in position on the patient’s skin and pressed down, at a given pressure of around 4 lbf for the 6 pin version and 7.5 lbf for the 20 pin version the internal plunger suddenly retracts allowing the disc to do the same, this allows the needles to pass through to puncture the skin surface.
The maintenance of these is quite easy, in essence it is a matter of keeping the moving parts clean so that they operate in a smooth way when fired, and in addition keeping the needle points sharp on those models that have that sort of needle arrangement.

There is one type that has the needles mounted on a magnetic plate, the advantages of this is that a number of plates can be kept sterilised, the idea of the makers is that they are thrown away when the needle tips get blunt.
I think that you should be able to sharpen them quite a few times before you need to throw them away.
It is vital that if you do try to sharpen the disposable type or the fixed needle type, that you do it properly, not only with respect to the sharpness of the needles but to make sure that they are all the same length.

Maintenance of the East Heaf gun.
The needle assembly can be unscrewed from the firing mechanism.

Here is my photo of one.

After unscrewing the blue part, see photo below, and by pushing in the plate, (In the photo below of the blue one, you can see the plate on the right hand end where the needles are), the shaft to which it is fitted comes into view revealing a groove with a clip around it which stops the plate falling out in use.
Remove this with care and the small screw in the side, the plate can now be withdrawn leaving the pins exposed for attention.
The small countersunk screw in the side runs in a slot in the shaft and makes sure that the holes in the plate and the needles line up.
The body of the assembly is made from aluminium and may need cleaning out from time to time, the plate shaft will also need a clean.
These two operations must be done as carefully as possible to avoid damage to either part.
A little watch oil on the shafts is all you need, though they should run well dry.
Avoid taking the firing mechanism apart as it has two ball bearings and springs in it which are a fiddle to get back in place.
If it is not firing smoothly try squirting a little light lubricating oil (watch oil) in through the hole in the side and working it to and fro.
Should you feel that you have to take the mechanism apart do so as follows:

a. Unscrew the two bolts showing on the top of the unit.
As you do so hold on to the assembly to prevent it from springing apart.

b. Slowly allow the two halves to come apart, but hold the unit in the palm of your hand so that the two springs don’t shoot out sideways.
Take care that the ball bearings don’t fall out.
To re-assemble it, slide the shaft back in to about the right position, make sure the balls are in place, slide the two springs into their holes, replace the firing spring and slide together.
You will have to hold the two springs in their holes and slide the two halves together at the same time.
Retighten the two top bolts.

Photos of two types of Heaf gun, the blue one is the one I have described above.

East of Oxford Heaf gun

Allen and Hanbury heaf gun

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