Unloader Valve continously venting

[buckers]

My Clarke Ranger 25 compressor was fine until the other day. Apart from the odd bit of baked oil sitting on the NRV and causing a slight leak, which was easily fixed, it was great.



Now when I switch it on, the unloader valve is continuously venting out the pressurised air. It's coming out of the hole in the centre of the pic below. The air pressure does build up, but very slowly



I have taken apart the NRV and cleaned it thoroughly. The spring seems ok, the rubber washer is as flat as it can be on the mating surface, in fact I think it's a new one. This is what I mean by the NRV (hopefully its the right name)



I'm convinced the NRV is ok, so that makes me think the pressure/unloader valve at the other end are suspect.
This is the pressure switch



Any ideas? Help !

 

[brightspark]

strip and clean the safety valve. make sure the spring isnt weak and coroded if its adjustable nip it up a bit and fill the tank looking at the pressure gauge to make sure it doesnt go past its maximum cut out pressure it might need slight adjustment if the springs a bit tired

 

[rtbcomp]

Confusion here, I think we are talking about the unloader valve on the pressure switch, not the safety valve?

 

[buckers]

strip and clean the safety valve. make sure the spring isnt weak and coroded if its adjustable nip it up a bit and fill the tank looking at the pressure gauge to make sure it doesnt go past its maximum cut out pressure it might need slight adjustment if the springs a bit tired

Is the safety valve contained within the plastic housing that has the on/off switch on the top?

 

[buckers]

Confusion here, I think we are talking about the unloader valve on the pressure switch, not the safety valve?

By "unloader valve" I think you mean (and me too), the "valve" under the plastic box that houses the on/off switch.


Apologies if my terms are mixed up

 

[rtbcomp]

The safety valve is the one sticking out sideways on the last picture.

The unloader (relief) valve is the one connected to the thin pipe, fitted on the bottom of the pressure switch.

 

[buckers]

Yup, unloader/relief valve is where the air is coming from..............

 

[rtbcomp]

Does it carry on leaking when the pump stops, or does it only leak while the pump is running?

 

[buckers]

Does it carry on leaking when the pump stops, or does it only leak while the pump is running?

Thanks for your help.........

If I switch it off manually at say 50 psi using the on/off switch (obviously), prior to it getting to max air pressure (and switching itself off automatically), then there is no air leakage from the valve. ie only leaks when the pump is running

I am reluctant to keep the compressor running too long to see if it actually gets to its shut off pressure and shuts off. It took a long time to get to 50-60 psi, much longer than normal (obviously with a leak it would do).

 

[rtbcomp]

That means the NRV is OK.

The relief valve could have failed, or some debris may have found its way in there.

Check that the operating lever in the pressure switch isn't holding it open.

 

[buckers]

Took off the relief valve and cleaned it out. There was a small brass needle with a rather limp looking rubber gaiter around it. The needle can be pushed in against a spring within the housing of the relief valve. There was muck within the valve assembly. Re-assembled and tried again. This time it worked with no obvious leak, for a short spell, then the leak started again. I'm sure I'm in the right area here, since it briefly worked. I just don't know exactly how the relief valve should work, and if the lateral play of the needle within the rubber gaiter within the housing is causing this fault.

 

[rtbcomp]

Basically the spring holds it open and when pressure builds upto about 20 psi (on most types) the valve closes. When the pressure switch is turned off (either via the knob or when cut-off pressure is reached) a the valve is forced open to relieve the pressure in the delivery tube so that the motor doesn't restart under load. This gives the characteristic hiss.

 

[buckers]

Basically the spring holds it open and when pressure builds upto about 20 psi (on most types) the valve closes. When the pressure switch is turned off (either via the knob or when cut-off pressure is reached) a the valve is forced open to relieve the pressure in the delivery tube so that the motor doesn't restart under load. This gives the characteristic hiss.

So it sounds like the valve is being kept open, hence the resultant loss of air.
Could it be the grotty rubber seal, NOT sealing properly.
I can't get any further into the relief valve to check the spring below, but since that appears to be offering resistance, I'm putting my money on the rubber seal not doing its job. Yes/No?

 

[rtbcomp]

That sounds possible, it may be worth giving it another clean just in case there is more debris in the thin pipe. If you're getting oil in the air that could cause the O-ring to deteriorate.

It's difficult to give a definitive answer without actually being there. You may end up replacign the pressure switch, they're around £15.00, you may be able to get a new valve, but there are a lot of different types, but you must get the delayed type.

 

[buckers]

Sorry about not updating you, and thanks for your help.

Managed to get the unloader/bleed valve apart, and thoroughly clean the inside of it. That appeared to be the problem, I suspect muck on the seal within the switch. Compreesor works fine now.
Cheers
Phil

 

[rtbcomp]

Great, thanks for letting us know.