Compressor loses pressure

[Tony Fearn]

I just wonder if anyone can help me sort my compressor. It's a 'Top Gear' from Charnwood type and it has 'c15ell' on the side. It's a large compressor (perhaps 100-150 litre size) which I bought off a friend and it hasn't an instruction book.

I've had it two or three years and it has always held pressure until a couple of months ago.

Recently, after turning on and up to pressure, when turned off it loses air through a little hole in the filler cap for the oil bath:-

The hole is manufactured, not due to misuse.

Does anyone know why??

Tony.

P.S. I'm sorry it only has one cylinder!

[Keith Andrews]

Is this loosing pressure from the holding tanks thu there, or is there just pressure coming out of that what seems to be the crankcase vent.
Like an engine, as compressors wear..rings bores, pressure escapes around them into the crankcase and either is vented or 'recirculated' thru a PVC valve on modern engines.

So does the holding tank still hold pressure ?

[Tony Fearn]

Hi Keith.

Prior to the problem, the large holding tank didn't lose pressure, it maintained 100psi for days on end. Pressure loss just happened over one or two nights/days when I didn't go to the garage, and the gauge was at zero when I looked.

The next time I used the compressor I let it run up from 0 to 100psi again and blew tyres up etc. When I'd finished, there was still around 70psi in the tank, but I heard a slight sound of air escaping and traced it to the little hole in the oil filler cap.

I don't want just to seal-up the hole as it must be there for a purpose, but wondered if there's anything else in the oil filler/level fitment that might have perished.

Regards, Tony.

[Chris Spencer]

Tony - Most compressors have a one way valve fitted to them between the compressor motor and the tank in order to prevent air under pressure leaking back through the compressor motor from the tank - it sounds like the valve has stuck open hence the air is leaking back and pressurising the crankcase of the compressor. This not unusual - you need to locate the valve and see if you can dissemble it - clean it - and reassemble - obviously ensure that the tank is fully drained of air and that the compressor is switched off before attempting this. Some times these valves are within the external pipework from the compressor motor to the tank / air reciever but more often than not are located within the head of the compressor motor - they are normally a simple ball and spring type valve, if debris builds up on the ball it holds it off the seat and air leaks past. If you are still unsure try looking online through one of the search engines like google to see if you can find a handbook or manual for it in a printable format. Needless to say I have spent many a hurried moment attempting to fix a compressor whilst halfway through the final coats of spraying a car !!

Good luck

Chris

[Forumadmin]

If air is coming back out of the oil air vent I think I would suspect the non return valve in the line to the tank.
You beat me to it Chris!

[Keith Andrews]

Prior to the problem, the large holding tank didn't lose pressure, it maintained 100psi for days on end. Pressure loss just happened over one or two nights/days when I didn't go to the garage, and the gauge was at zero when I looked.

The next time I used the compressor I let it run up from 0 to 100psi again and blew tyres up etc. When I'd finished, there was still around 70psi in the tank, but I heard a slight sound of air escaping and traced it to the little hole in the oil filler cap.

That basically confirms what the guys above have said..
If the rings..it would only be when the compressor is running...And generally one has to really abuse a compressor to stuff or even wear rings.....or in hertate from ones great grandfather
Its not a good idea to leave compressors charged up
They should always be drained at the end of the day by cracking the tank drain valve....my home compressor since its not used every day, and even then usually for 10 minutes or so, I have the tank drain tap just cracked all the time and at such a level and humidity that does condese runs to the tap.

[Forumadmin]

Just another thought, the drain valve may have worked loose; but not with the symptoms you had.

[Tony Fearn]

I'm sorted now thanks to your replies. There is a sort of 'ball and spring non-return valve directly on top of the tank. I took it apart and there was a lot of oily gunge in the unit. When cleaned out, re-assembled and pressurised - Bingo!

Tony.

[Keith Andrews]

Due for an oil change at the same time?