How To Repair A Blood Pressure Cuff Machine

Sphygmomanometers.
This is rather a long word which could be a joke but is the proper name for blood pressure machines. (sphygmos being the Greek word for pulse)

There are three types;
1. Mercury.
2. Aneroid.
3. Electronic.

The terminal, the electronic, we can forget about.
They are used in theatres and on some wards, only on the whole are a waste of coin for those with little to spend. In that location is more than to become incorrect and volition exist expensive to repair if they do so.
The second is the aneroid, these are compact and portable but practise suffer in that they are hands damaged and can go out of calibration without you realising it.
Aneroid units screwed to a wall or fastened to an anaesthetic auto are fairly rubber from impairment and should work well, but should be checked from time to time against a mercury blazon.
The first on the list, the mercury is past far the best. Easy to expect afterwards and incessantly accurate.
Take care if you take to maintain them, do non handle mercury, do not breath in the fumes or the blackness pulverisation that may be found in the tube or reservoir. Over a menstruum mercury and its oxide are toxic.

Maintenance of these: Should be done once a year.
The Aneroid blazon.
The first thing to check is that the pointer is at zilch, on some it volition autumn to a 0 effigy on others information technology will rest within an ellipse or square at the bottom of the dial.
In general terms if this is then it will probably be giving you authentic readings.
To check this you should connect it to a mercury machine with a 'Y' piece and note down the figures from both on a piece of newspaper.
If the pointer is non at zero, remove the 'glass', gently remove that pointer and put it back on in the right position.
Have intendance removing the hand they are made of thin metal and bend easily. Find a couple of small spiral drivers put one nether each side of the central boss and lever gently upwards.
Take care to notation where it goes when information technology comes off, it may fly off unexpectedly and get lost.
If when y'all permit the air out of the cuff the needle moves in a jerky manner y'all may demand to lubricate the machinery inside.
Over again remove the 'glass', face and pointer and lubricate the pivot points inside with a little light oil.
Having checked the accuracy against a mercury B.P. machine look at your figures, if they agree within a few mm all the way upwardly the scale it is o.thousand.
If they do not agree there are 2 possibilities:
one. The linear fault, here the error is the same all the way up the scale, say +10.

Mercury Aneroid

50 lx
seventy fourscore
100 110
150 160

2. The Non Linear mistake, here the mistake might be -20 at the lower end, getting less as you get up, correct at say seventy, and getting greater every bit it gets higher till at 150 it might exist reading 170.

Mercury Aneroid

xxx 10
50 twoscore
seventy seventy
100 110
150 170

as you can see the mistake is irresolute as you go up the scale.

Correcting these errors is very difficult going and can accept a dandy bargain of time. To do this you have to accept off the 'glass', paw and face.

From there information technology depends upon the make how y'all adjust the errors.
The one I describe is a common one made past Accoson and may requite you a guide as to the principles.

Below is my photo of the insides.

Within you will run across a disc shaped corrugated bellows, then a lever organization which changes the up and down movement of the bellows to a rotary movement of the pointer.
Part of the machinery is a pin resting on the curved inner side of a triangle with the heart (of the triangle) cutting away.
What happens is that when the pivot (which is resting on the bellows) is moved by the bellows expanding, it acts confronting the side of the triangle. This moves around and the teeth on the finish of the triangle engage on a cog which moves the pointer around.

At that place is a fine coiled spring to return the mitt to null when the pressure is released, take intendance not to impairment this spring.

It is non easy to describe and I could understand if yous had to read it a few times to get the hang of it.
Try pressurising it with your blood pressure cuff and bulb and picket what happens.
Now for the adjustment, and it involves bending the pin mentioned above –

VERY SLIGHTLY

If yous accept a linear mistake you have to bend the pivot either towards or abroad from the side of the triangle depending on which fashion you are correcting.
If the error is not-linear yous must bend the pivot parallel to the side of the triangle.
Information technology is very much a instance of trial and fault, a slight bend with a small pair of pliers, put the face and manus back on and re-test.
If the error is still there repeat information technology.
This volition have to be done many times earlier you become the direction and the amount of curve correct.
I can just stress again that each curve has to be done very gently, one time you lot get within two-3 mm Hg I would consider yourself lucky and exit it alone.
The merely other precaution I would take is to open the window, I have known people get so frustrated at doing this that they throw it out.
Leaks then along in the safety parts will be dealt with in the department on the mercury B.P. car.

The Mercury type.
Showtime a quick description of a common configuration in mercury BP machines.
The whole unit is held in a box. Attached to the lid will be the scale, normally 300 mm long sometimes 270. Information technology is held in place in a groove in the reservoir at the bottom and by a spring tensioned metal cap at the top.
In the cap at the summit is a leather washer held in place past a large short screw.
The graduated tube is held at the bottom in a hole in the top of the reservoir and at the elevation by the spring cap. The leather washer is pressed on to the tiptop of the tube.
The reservoir holds the mercury. The reservoir has a tubing connector on it for connecting the gage to. Under the tubing connector is another leather washer held in identify by a spiral cap.
These two washers allow the air in and out but prevent the mercury from escaping.
The mercury should be of sufficient quantity to be level with the zero marker on the tube.

The get-go matter to do when y'all demand to cheque one of these is to wrap the cuff around a round object well-nigh the size of a drinks can, connect it to the B.P. machine and inflate the cuff.
Cheque that the mercury goes up the tube, have it to the top of the scale so that information technology reaches the leather washer at the top, brand sure it does non leak out.
Slowly debunk the cuff and check that the mercury goes back to the nix point.

Inflate the cuff again merely cease halfway up, watch what the mercury does, it should come to a terminate as soon every bit you stop pumping.
If when y'all stop pumping the mercury carries on going up at that place is a problem ( the same volition happen when allowing the air out of the gage), those not very experienced at taking claret pressures may non get this trouble because they let the air out slowly and thus the trouble is less serious.
You can allow for a little farther rise or fall subsequently you lot have stopped pumping but to much and the auto could be giving y'all loftier blood pressure results.
How loftier depends upon how blocked the leather disc is and how apace y'all let downward the gage.
Why is this so? well, in simple terms, it is because the leather disc at the top is blocked or besides thick and is not allowing the air in or out speedily enough. (less likely is the leather disc in the cap of the reservoir being blocked or very perished tubing is stuck together restricting the motion of air).
What happens when the mercury is going down is that the air is non able to get into the tube rapidly enough, information technology is held back slightly because the leather washer is blocked or as well thick, this means that the pressure in the gage is slightly less than the column of mercury reads, thus the high reading.

At that place is a cure for this problem, turn the B.P. machine on its side (with the reservoir downwards) remove the calibrated tube, the top function which holds the tube is sprung then lift it up to take the tube out. Where the acme of the tube rested there is a washer and then the leather disc, remove these carefully.
Take the leather disc and brand sure that information technology is clean, if having cleaned information technology, reassembled and re-tested the problem still exists, endeavour it without the disc in place, exercise not pump the mercury to the top because information technology will fountain out. You should find that the mercury stops equally soon as you lot stop pumping. If it does stop every bit information technology should then the problem is with the top leather disc, if the problem yet exists and then the fault lies elsewhere, either the leather disc at the pinnacle of the reservoir or a tubing problem betwixt the cuff and the machine.
If after cleaning the elevation leather disc at that place is still a trouble and so it may be that the disc is to thick, this is something that will always take been there. Remove the disc again and while holding it betwixt finger and pollex scrape it thinner with a scalpel blade.
Proceed information technology turning around otherwise, you volition distort the shape of information technology.
If this still does not better matters try some other material in its place.
The idea of the seal is to let air in and out but not to let the mercury out.
If after every endeavor you fail to better it the user volition only have to let the cuff down slowly.

Other problems.
The mercury drops before you open the release valve. Unless it is a very fast leak it is not that much of a problem because yous let the air out anyhow when you accept the claret pressure.
The obvious cause of this is a leak in the organisation, first cheque that the tubing and the cuff are not perished and that the connections are not loose.
The virtually likely cause is a leak in the ane fashion valve of the pressure release valve.
To go at this, remove the inflation seedling, in the pressure level relief valve you will run across a slice of rubber with a hole in it (different makes may have different means of doing the aforementioned matter), pull this out with a pair of forceps.
Some times you have to remove a fine mesh filter to become at the one-way valve.
Clean this while it is out otherwise information technology makes it hard to inflate the gage.
The older valves were a piece of tube with a small ball bearing in the finish and a slit in the side of the tube, the newer ones had the split at the cease, this lets the air into the gage only non out of it. Either way you will probably notice fluff and things stuck in information technology, this volition keep information technology slightly open so giving you the leak. Clean information technology out so that the lips close together.
Re-gather the valve and bulb and test, it should have cured the problem.
The release valve itself may exist leaking, there is petty that you can do about this as almost are made so that you cannot accept them autonomously.

Muddied mercury and/or tube.
First a discussion of caution.
Mercury is considered to be a hazardous chemic, its dangers prevarication in prolonged exposure to the fumes given off likewise as the mercury itself and the black mercuric oxide powder which forms after a while.
Accept intendance to store all waste mercury in plastic bottles with a trivial water on pinnacle, the h2o stops the fumes.
When cleaning a B.P. machine of the black powder do so in a smoke cabinet or outside.
Mercury volition, in time, oxidise and commencement to turn to a blackness pulverisation, this will stick to the side of the tube and make readings hard.
From time to time the tube will need to be cleaned, you should empty out the reservoir and make clean that at the same time.
Keep as follows (do this outside if you can):

Remove the tube, if it is dingy you will accept to clean it, the official ways of cleaning is with a long pipe cleaner longer than the tube, a piece of twisted wire with soft fibres woven into the twists. You probably won't have one so you will have to get a pocket-sized slice of cloth and push it through with a thin stick or metal rod.

To clean the reservoir. Get out the tube in place, remove the top of the reservoir, make clean the sealing washer in the meridian, remove the mercury from the reservoir by pouring it into a make clean canteen.
Remove the tube and clean it. Make clean the reservoir past blowing out the blackness powder and wiping the inside with a cloth.
Supersede the tube, refill the reservoir to the nada signal on the tube, spiral the tiptop back on re-connect the tubes and cuff and examination.

Rubber cuffs and tubes, repairs to.
Should you find a pigsty in the gage it should be replaced, if a new i is non available it can be patched with a patch from a bicycle repair outfit.
New cuffs (and other rubber products) should be stored in a cool, dark and dry out place. If you have any silicone oil, rub a lite smear of that on before you put them away. Talcum powder rubbed on to it will help, merely non both together.
Tubing on B.P. machines e'er seems to crack where it is ofttimes bent, for example near connections.
Quite ofttimes information technology is possible to cutting off a short length to make a good leak-complimentary connection again.

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