Re: Diagnosing valve plate problems
Peter:
Pumping the compressor down can do a compressor valve check. If it will not pump down, or pumps down slowly, one or more suction valves may be bad.
If the compressor pumps down and off but the pressure on the suction side rises rapidly, one or more discharge valves are bad, the pressure relief valve is leaking, or you have a blown gasket. If the compressor is going off on the oil pressure control you may have a broken oil pump shaft or an oil pressure-regulating valve that is stuck. Most low oil pressure problems are a result of worn bearings causing a loss in pressure around the bearing surfaces.
Other causes for low oil pressure are high temperature and oil dilution. A broken oil pump shaft results in zero or no oil pressure and maybe a result of a bearing failure allowing the compressor crankshaft to bounce and snap the oil pump shaft.
I believe most technicians agree that replacement compressors fail at a rate several times higher than original equipment compressors. It is the service technician's responsibility to determine not only the reason the unit isn't cooling, "compressor is shorted to ground", but also what caused it to fail and to correct any system faults. Keep in mind that few compressors you replace actually ware out due to age. When you're called
To fix a system with a bad compressor, try to remember that the bad compressor is most likely a result.
Some of us have seen compressors that have been running for thirty or forty years but most of what we change have less than ten years running time. Most failures fall into just a few categories such as the loss of lubrication, which is probably number one and many things can cause this, but most are system faults rather than compressor defects. Any system fault will eventually show up in the compressor.
Roger
:cool:
Re: Diagnosing valve plate problems
Quote:
Originally Posted by shogun7
Peter:
Some of us have seen compressors that have been running for thirty or forty years but most of what we change have less than ten years running time. :cool:
Those compressor aren't fabricated anymore because they all have a MTBF and MTBO of +/- 10 years.
I worked in the past century in another business for some time and we had to deal with that.
For example: a Briggs and Straton engine on a lawnmower has a MTBF of 200 hours (yes, only 200 hours).
Business must running and a compressor that last more then 10 years is not good for the business. Therefore, if compressor is already of some age, I never recommend to replace parts.
I prefer some more on my bread then only butter.
Look to the computers. Why you think AMD and Intel always change there pin set-up? Because after a failure of a preocessor after some yeras, you also need a new motherboard.
Re: Diagnosing valve plate problems
hi peter,
as usuall, you are right, but its in every field of our lifenow.
I always hear the sentence: "they dont make them anymore like they used to....)
I have in one of the units that I look after, coplematic 40 HP under 5cm of dust, works from 1978, no problems.
chemi
Re: Diagnosing valve plate problems
Peter, I agree with you with regards to MTBF etc. In fact we are almost a throw away world. The need to make money and keep people employed is a top priority these days. I don't recommend we make products last too long and we should make sure that they are need of repair quite often, otherwise we would have no need of so many mechanics, technitions etc. lol :D :D
Roger
Re: Diagnosing valve plate problems
Quote:
Originally Posted by 750 Valve
Sorry to wake an old thread but what i've always been told (and observed too) is if you isolate the comp suction (and oil) while running and observe time comp takes to reach vacuum as well as whether or not it holds vac.
If it struggles to get a vac but holds vacuum (or rises to suction pressure), worn suction valves. If it pulls down quickly but leaks through - eventually to disch press then obviously its the disch valves
750 Valve, I think you said it best; but, of course, I still have questions....
Flawed suction reed - piston loses efficiency on the up-stroke because the suction valve is leaking... permitting gas to flow back through the suction valve instead of the discharge valve?
We could spot higher temperatures upstream. On the end bell for instance. If this happens over and over.
Re: Diagnosing valve plate problems
Perhaps this could be usefully for others.
Copeland compressors so also the oilpumps can run in both directions.
Therefore, in the oilpump, they have fitted a system which reverse the oil suction hole of the pump, whatever the rotation may be.
You can see this easily if you take off the cover plate.The second piece (after the cover plate) can swing 1/10 of a turn and is then blocked by a small pin of +/- 3 mm diameter.
So the first thing the oilpump performs when the compressors starts up is swinging the - I call it the oil suction plate - with the rotation to that blocking pin. Then is the suction hole correct located for that specific rotation.
But if that pin has broken, then the suction hole can be located on the wrong side resulting in no oil pressure.
You restart it again and by coincidence, it's then located on the correct position and the oil pump functions properly again.
It all depends on that swashing plate.
We had this failure once and each time we went to the client, everything was OK. Cleaned the oil filter, added some oil, installed a new oil pressures switch...till I found that broken pin.
Have a look at these oil pumps the next time you can open one.
Re: Diagnosing valve plate problems
Thanks Peter.
will keep it in mind. :)
Chemi
Re: Diagnosing valve plate problems
We diagnose valve plate fauls fairly easily with head temperature readings above each pot with surface temperature probe. Works fine as you get a significant difference.
Re: Diagnosing valve plate problems
Used a Co2 Fire exstinguisher Horn and hose as a stethoscope to listen to the head before.Thought that a doctors stethoscope would look a bit strange if sombody walked in on me.:p Also good for listening for hard to find leaks on coils as when the leak lines up with the end it's very loud.
Re: Diagnosing valve plate problems
Quote:
Used a Co2 Fire exstinguisher Horn and hose as a stethoscope to listen to the head before.Thought that a doctors stethoscope would look a bit strange if sombody walked in on me.Also good for listening for hard to find leaks on coils as when the leak lines up with the end it's very loud.
Edit/Delete Message
So, in your opinion, it is less embarrassing.. or perhaps more professional to be seen holding a fire-extinguisher cone to your ear than a stethoscope. You have made my day, smiling-wise. But I bet you found some leaks my doctor would have missed.:)
Re: Diagnosing valve plate problems
Quote:
Originally Posted by Dan
So, in your opinion, it is less embarrassing.. or perhaps more professional to be seen holding a fire-extinguisher cone to your ear than a stethoscope. You have made my day, smiling-wise. But I bet you found some leaks my doctor would have missed.:)
I prefer holding my ear to the head... hearing aids don't you know :D
Re: Diagnosing valve plate problems
One thing I have seen is to use an electronic stethoscope with some Bose noise canceling earphones. I have not tried it, but it seems like a good idea.
Myself, I will stick with using my trusty screwdriver and hands.
Re: Diagnosing valve plate problems
I place a screwdriver with the tip against the tubes or compressor and listen on the plastic end.
You must try this once.
Re: Diagnosing valve plate problems
Have used the Head temperature useing a surface probe on each cylinder and it works well. But 9 times out of 10 the good old screwdriver as it's always at hand. We have an Electronic stethoscope had the chance to use it once. With some adjustment to remove the back ground sounds a good tool to use.
Re: Diagnosing valve plate problems
Diagnosing faulty valve reeds seems to be a problem everyone has a different answer for.The "pulling 20inch vaccuum" worked on open compressors but can cause electrical failure on hermetic or semi hermetics. Also some high temp hemetics were not designed for "vaccuums" and will not pull down below a positive pressure. If the compressor pressure rises on the off cycle with the suction valve closed the mostly likely cause is faulty discharge reeds.If the compressor has trouble pulling low pressures with the suction valve "choked" or pulls down slowly with the suction valve closed then most likely the suction reeds are leaking.
Diagnosing valve plate problems
If you could provide more information, that would become useful. If you cant play a concert F, but you can sort of play around when you press valves down, it could be that something is clogged within a valve or valve slide. What is the make of your horn? Etc.
Re: Diagnosing valve plate problems
Quote:
Originally Posted by
setrite
Here we pump down the system to a vaccum below 20", if the compressor cannot a pull a vaccum below 20" it is cause of leaky suction valve reeds, if it pulls a vaccum and holds the vaccum it is determined the valve reeds are good. If the pressure in the low side rises above atmospheric it is cause of leaking valve reeds, if the pressure rises only to atmospheric pressure it is cause of leaking shaft seal or a low side leak. A broken discharge valve reed causes high Compressor head temperatures. And we still use the stethoscope to check on the valves. Valve reeds can get damaged because of liquid pumping and also because of the wrong head gaskets.
Regards.
I done this test for yrs. by closing the service valve but then I found that most of the service valves leak @ the stem and pull in air in the system and compressor cannot a pull a vaccum below 20" . this is
I use the Stethoscope with ir meeter
Re: Diagnosing valve plate problems
just because a reasonable vacumm cannot be obtained is not a reason to justify valve failure.blowpass has the same effect
Re: Diagnosing valve plate problems
Another reason of failure is the contamination wherein semi-hermetic compressor`s stator windings are victims . Particles rotate alongwith refrigerant and end up slashing fine filter mesh in suction line & eventually damage stators .
Re: Diagnosing valve plate problems
Valve reeds are usually checked for leak back .
Re: Diagnosing valve plate problems
I used a stethoscope for the first time yesterday, and it's sooo much easier to hear what you're looking for in noisy environments. One is now on my Chrissy wish list. :D