3rd stage piston pressure valve blown, symptoms

[dougoh]

Hi Everyone,

First off, thanks for the wealth of information you have on here for compressor maintenance. one of the best sources of useful info I've found on the web

I'm in the process of restoring an old LMF compressor (V12 made in 1982), which has a nominal output on paper of 155 litres per min at 200bar. I'm seeing about 100 litres/min or less though at less than 100bar pressure, so it's way off target output.

I've stripped down the compressor to clean the valves, pistons etc (was also switching from mineral to synthetic oil) and noticed that the 3rd stage piston pressure valve has a broken spring. What type of symptoms would this broken 3rd stage pressure valve show ? Would it cause overheating of the 3rd stage, reduced output ? Just curious. I know I need to replace it but wanting to know if it's the likely significant cause of the reduced compressor output.

Thanks for any thoughts,

Doug

 

[veriqster]

do you have overpressure valves in between stages?
if you don't it might explain the reduced output, otherwise it should have little to do with it. if you have interstage overpressure valves are any of them "popping"?
a valve that does not close properly does not "isolate" the cylinder from the coiling before or after it. an intake valve on the 3rd would pop the 2 stage overpressure by increasing the pressure in between the stages beyond design, if there is no overpressure valve it would just get to the point where the 2nd stage exceeds its compression capabilities (get hot, increased ware as well). a broken exxhaust valve would leave the cylinder "connected" to the output and decrease / prevent output.
I would fix it and see if it fixes the problem, also, after you fix it check for leaks, blow-by and pump RPM, all of them can influence your output.

 

[dougoh]

Thanks Verigster,

yes there is an overpressure valve between the 1st and 2nd stages. The only time I have heard it pop was if I switch off the compressor pressurised. However, that was before I cleaned all the valves and generally cleaned up the compressor. It doesn't pop when the compressor is running and since cleaning the valves I'll bet it will pop less frequently. However, I'll check this.

There are two separate valves in the 3rd stage piston. LMF call one of them the 'suction valve' and the other the 'pressure valve'. From what you're saying I guess that translates to 'intake valve' and 'exhaust valve'. The intake valve is working fine, so I'm guessing this would isolate 3rd stage piston from previous coiling. I'm hoping that the semi-functional exhaust valve, once replaced will increase output, per your comment.

Thanks again and I'll report back. I'll also double check for leaks again etc.

 

[veriqster]

if the overpressure in between 1st and 2nd pops your valves are either dirty or toast, at least some of them. the overpressure should not pop even if you leave the unit pressurized.
while you are in the process of cleaning / dismantling clean the cooling coiling if you can (on mine I used a hot soap solution, rinse with lots of water and blow with compressed air), also have a look at other parts that can be cleaned (overpressure valves, etc, but make sure you don't break them, can reassemble / calibrate them as required)
the valve you say is broken would explain reduced output, change it and see how it works after.

 

[dougoh]

just ran the compressor and verified that the overpressure between 1st and 2nd stage isn't popping anymore even when left pressurised. you were right though, I do remember the valves on the 2nd stage being pretty grubby as I cleaned them, so no surprise they were likely leaking. All good now though. It's just the 3rd stage valve needing replacing at this stage. I've done the cleaning bit to death, including the cooling coils, which seem to be doing their job just fine.

At this point I'm just waiting for a quote from LMF for the 3rd stage valve. Will post results once I get/fit the valve. Thanks again!

 

[veriqster]

post some pics of the head / valve, broken part included

 

[dougoh]

will try to do that later today Verigster, family stuff is pulling me away from my labour of love on a 28 year old compressor

BTW, I got a quote back from LMF for the replacement valve. A little over EUR100, which considering the age of the compressor I think it's ok. I'm sure they'll have to make it specially.
They also offered the alternative of just replacing the spring and valve plate (cheaper) but the body of the valve is so small and so caked in carbon that it won't easily come apart without me destroying it! Anyway, photos to follow later.

 

[Graeme Tolton]

will try to do that later today Verigster, family stuff is pulling me away from my labour of love on a 28 year old compressor

BTW, I got a quote back from LMF for the replacement valve. A little over EUR100, which considering the age of the compressor I think it's ok. I'm sure they'll have to make it specially.
They also offered the alternative of just replacing the spring and valve plate (cheaper) but the body of the valve is so small and so caked in carbon that it won't easily come apart without me destroying it! Anyway, photos to follow later.

There are some very good automotive products for removing carbon from parts. Intake cleaners or combustion chamber cleaners can work wonders on badly fouled up parts.

 

[dougoh]

Thanks Graeme, pretty sure I tried Carb cleaner on it (evil stuff - especially if it spits back on your face :-( ) but I know I really shouldn't have, so was quite restrained and didn't leave it soak in it.

Anyway, as fate would have it I ended up slightly damaging the valve when trying to take apart, so needed to replace anyway. Hopefully I'll be getting it sometime next week from LMF

In the meantime, still owed pics of the Piston head, with valves going in either side of it. See attached. The small Cylinders with the copper(?) gaskets on them are the intake/exhaust valves. In the picture, the left is the exhaust/hi-pressure side and the right is the intake/low-pressure side.

 

[dougoh]

Just to update the thread:

I got the replacement valve from LMF in the week and just fitted it yesterday. Seems to be working like a charm The output of the compressor has gone up to spec, pretty much. Filling a 12litre from empty to 200 bar took 14-15 minutes. High pressure internals are about 0.75l(filter housing etc..), so that's about 170-180l/min on average I reckon.

BTW, I've also noticed that the 2nd stage pressure has also dropped from a peak of 60bar (with broken valve) to about 40 bar now, so I'm guessing there must have been some leak in the 3rd stage intake valve too but maybe this was a knock on to the extra pressure put on it as a result of the broken exhaust valve ? dunno, I'm guessing....

So, for the record, the stuff I've done to fix this & get up to spec:

- replaced the high pressure exhaust valve on the 3rd stage piston.
- refitted/replaced the 1st and 2nd stage gaskets, both aluminium and rubber/paper s.t. there was no additional leakage from them(slight leaks before).

Thanks for all the thoughts/guidance guys. I'm a happy camper now.

Doug