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  1. #1
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    Perhaps this would be a good thread to summarize the various methods of diagnosing faile suction or discharge valves.

    I know there are temperature methods, amperage methods, and pumpdown methods. Let's complicate it a bit and diagnose failed valves on parallel racks. Often, I find it like looking for the leak on a roof. It begins over here, but shows up over there.

    Dan



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    I apologize for the typo. "Failed" would be the word. The most common practice for checking for bad valves is closing the suction service valve and seeking a level of vacuum. Then also seeing how the vacuum holds. I see some flaws in this practice, but it is common practice.

    Other things come to mind. What is more common, discharge valve failure or suction valve failure? What causes one as opposed to the other?

    Dan

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    Talking

    Diagnosis

    Good old MK 1 ear typically sounds like marbles being chewed. Set of good manifold gauges assuming you have a good system profile to compare and there are no unloaders or similar to complex the profile.


    To date all Suction valve failures and I estimate all caused by slugging.

    Causes include poor design e.g. having single gas bypass on close control equipment, over charging and you are going to love this Dan……'Messing' with them TEV's (any control valves) without putting the system under full load and checking all the p and t's first. But them my kit is a bit special….

    I also had a few theories on hydrocarbon systems that chewed inlet valves after long off cycles where the lubricant migrated but the PhD never got finished.

    Other thoughts copper plating?
    Contamination (oil)
    Heavy Temperature/stress profiles
    Derek

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    I thought copper plating was simply the result of acidic conditions mostly resultant from high moisture content and exacerbated by high compression ratios. I have never heard of a "copper plating" related failure, however.

    Back to the valve failures.... can anything be observed by closing the discharge valve slowly and observing pressures?

    I knew a tech who would put a line with a sight glass on the diptube of the crankcase and the suction service valve to observe oil flow and diagnose valve plate problems. I have used IR thermometers to find which head is suspect of valve plate problems, as well as running a compressor amperage curve to confirm suspected valve plate damage.

    I have seen Copeland discus discharge valves just not wear in properly and cause overloaded conditions on compressor startup. Even with reed valves, I suspect there are subtle seating problems that cause difficult to diagnose loss of capacity problems.

    Also, with the discus compressors, 404A applications resulted in massive suction valve failures. Compound refrigeration also exhibited inordinate valve failures. Something to do with valve fluttering and wearing at the pins in both instances. Carlyle compressors have high valve plate failures on compound refrigeration applications as well. Something about the reduced compression ratio. All of which were suction reed failures.

    But for simple diagnostic purposes, is there a way to determine whether one has a discharge valve gone bad, versus a suction valve gone bad?

    Dan

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    Valves

    No just seems a lot of concern about copper deposition especially with HFC conversions, its a corrosion mode so perhaps a failure mode? just the ratings of a madman.

    No real inlet or outlet diagnosis as without local instrumentation your are working blind so to speak (manufacturers take note interstage tapping please). Just seems inlets go first on my kit. If you could drop a PRT and a micro transducer into the inlet and outlet line that might work. At college we used to use a mechanacal inicator that gave a p 'v' t output on engine test beds so good trace and overlay might work.

    I have to say once a vave is suspect off comes the head anyway. I have an R22 Copeland semi thats just sucked a few litres of seconadary PFC and popped another inlet on Thursday night so I could try the line and valve idea.
    Derek

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    An old Prestcold hand once told me that if, on vac, the suction pressure rises fast, it's probably the discharge reeds. If the pressure rises slowly, and stops at suctin pressure, then it's the suction valves.
    I know some old engineers who use a stethoscope to listen to the pots, in oreder to isolate the problem head. They also listen elsewhere in the system for other diagnosis.
    Sadly, I doubt anyone of my generation has that sort of knowlege / experience. I know I don't.

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    Hey FreezerGeezer!!!Not so much of the old Thanks!!I have always found that a big screwdriver tip against the suspect head with the handle against your ear will indicate right away whats going on.I also found the same as you with the speed of rise in pressure has always been a good indicator of which valves.At the end of the day the head comes off but knowing which valves let go helps with the trouble shooting.As to your generation,I agree,,we saw equipment that is not even around anymore thanks to package kit and no more training for the guys wanting to make a go of the trade.Hang in there though it's worth it. Cheers Rick

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    If the
    pressure rises slowly, and stops at suctin pressure, then it's the
    suction valves.
    How so? What would cause the suction pressure to rise? I hope that's about as dumb a question as I will ever ask. The discharge part makes sense, though.

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    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.
    Last edited by setrite; 14-06-2002 at 02:54 PM.
    Setrite

    A group of Donkey's Led by a Lion can defeat a group of Lion's led by a Donkey

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    Curious about the stethescope, Setrite. I bought one with a metal rod for one of my techs but he has never given me any feedback on its worthiness. I have never used one myself.

  11. #11
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    Dan, the Stethoscope is very useful when we have to detect the source of the sound. It saves us time, I am a tech myself and I rarely give any feedback to my supervisor unless it is important or I wait till he asks me. Thats me I guess.

    Regards.
    Setrite

    A group of Donkey's Led by a Lion can defeat a group of Lion's led by a Donkey

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    As regard to lack of training for this generation of engineers, i myself have often tried to obtain compressor manuals for fault diagnosis and strip down but havent found any of worth. The only one close is a Trane publication from 1979. Anyone out there have any suggestions?

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    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

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    hi 750 valve,

    not a bad idea to wake it up. myself, I'm using this funny looking stethoscope and its doind good job.

    you can tell real good if something is wrong inside. I also keep in the van many kinds of valves, suction, discharge and seals.

    the way you mention is the way it works and its the fastest way to know if something is wrong with the valves.
    what is wrong is a different story .

    I always before taking compressor apart, let the oil out, check for suspicious objects, check the fiter magnet and then go for the head.

    valves are made from a special steel mot like the rest of the inparts so it give me an idea what to expect.

    as I'm not working much with thnew gases, I could not tell you much about their problems but with R-22 the only problems I saw was metal particals, acidic oil and gas that cosed tiny holes in the vave seat, liquid knoking which bends them or making holes in suction valves. or just fatigue of the metal. more then a few times it was the manufacturer fault but there is nobody to talk to there.

    what I always suggest is that every one find his best way to find the basic problem but fixing it is only with the manufacturer instructions.

    chemi

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    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
    I know it's an old thread, and that the answer above has been submitted in different words by others, more or less. The use of the stethescope still intrigues me.. I have one now.

    But for a short answer to the original question, 750's answer seems pretty good. There might be a 15-year-old fellow just getting curious about our trade, and I would hope he is exposed to this simple observation before confusion sets in.

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    We have an ultrasonic stethoscop for this from SDT. Also usefull for controlling bearings but we use it mostly to control the sealings of refrigerator and freezer doors.

    I fI haven't the SDT with me (most of the time ), I use same method, pulling vacuum with compressor itself.
    If it rises slowly and stops at 'ambient pressure' -->Low pressure reeds, if vacuuum breaks fast, mostly associated with very hot head temperatures --> high pressure reeds.

    If compressor is not older then 5 years, or we have one bigger then 10 HP (the more expensive sorts) , we then do the following: open up the compressor head and turn the reeds 180° (if they're not broken of course)
    Sometimes you see that the reeds are worn out a liitle bit with a little ring pressed in it (the circle of the valve plate itself).
    Then do the test again and if problem remains, replace mostly the whole compressor if below 5HP and not older then let's say 7 years.
    A new valve plate with gaskets is too expensive to take any risk.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  17. #17
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    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


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    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.
    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.
    Last edited by Peter_1; 05-04-2004 at 07:59 AM.

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    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

  20. #20
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    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
    Roger

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    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.

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    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.
    Last edited by Peter_1; 04-08-2004 at 08:44 PM.

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    Re: Diagnosing valve plate problems

    Thanks Peter.

    will keep it in mind.

    Chemi

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    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.

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    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. Also good for listening for hard to find leaks on coils as when the leak lines up with the end it's very loud.
    Last edited by Andy T; 06-05-2006 at 09:08 AM. Reason: just adding a smile so they know it was a joke.I Have a reputation to keep up you know.

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    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.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.

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    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

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    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.

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    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.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    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.

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    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.

  32. #32
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    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.

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    Re: Diagnosing valve plate problems

    Quote Originally Posted by setrite View Post
    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

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    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
    mmm to beer or not to beer...........lets drink breakfast

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    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 .

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    Re: Diagnosing valve plate problems

    Valve reeds are usually checked for leak back .

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    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.

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