Home workshop compressor "hunting"

[Pantera2075]

Hi all, I could do with a bit of help if you would be so kind?

150 litre compressor, twin piston 2.2kW single phase. Motor is almost new.

It runs fine when getting up to pressure.

When it approaches shut off pressure it slows down a little - as would be expected - then shuts off, but immediately turns back on. Then cycles on and off every second or so till the breaker trips.

I've fitted a new pressure switch and a beefier power cable but no change.

Any ideas?

 

[Seadog]

It can only switch on if power is there, which sounds like a faulty switch or an air leak causing rapid pressure loss.

 

[Erie Fred]

What is the differential setting ?

 

[m_c]

Has the pressure switch been plumbed in correctly?
It should be connected in on the tank side of the one way valve, but it sounds like somebody has connected it on the compressor side.

 

[brightspark]

probably be the pressure switch. u can check the voltage at the motor when it happens it should be ether on or off

 

[voipio]

It could be a faulty motor. Try running it off load i.e. with the belt disconnected, for about 20 to 30 minutes. The motor casing might get warm, but shouldn't be any more than that. If it gets hot, the motor might be at fault, or the capacitor.

 

[dave h 2]

None of the above replies deals with the question asked.

When it approaches shut off pressure it slows down a little - as would be expected - then shuts off, but immediately turns back on. Then cycles on and off every second or so till the breaker trips.

I've fitted a new pressure switch and a beefier power cable but no change.

The new pressure switch should have dealt with the issue.

Unless the new switch is not brand new or as badly adjusted as the original?? (I'm assuming the OP would notice a massive air leak.)

 

[AVI_8]

I presume this is a 3 hp compressor, I can’t say with mine I notice it slow down before shutting off, what’s the pressure when it shuts off? And when it shuts off is there a loud hiss from the unloader valve?
Then after that is there any noticeable air leaking from anywhere, there shouldn’t be.

 

[m_c]

None of the above replies deals with the question asked.

If the pressure switch has been plumbed in before the one way valve, it would cause the compressor to cut in/out continually.
Compressor reaches pressure, pressure switch cuts motor and vents pressure before one way valve, pressure switch cuts in again because the pressure it's seeing has just been vented, and the cycle repeats.

 

[Pantera2075]

I think we are onto something here - there's no hiss from the unloader valve when it shuts off.
I doubt it's plumbed in wrong but there's a chance it is gummed up.
I'll take a look tomorrow and report back.
Thanks for the help so far.

 

[Erie Fred]

If the pressure switch has been plumbed in before the one way valve, it would cause the compressor to cut in/out continually.
Compressor reaches pressure, pressure switch cuts motor and vents pressure before one way valve, pressure switch cuts in again because the pressure it's seeing has just been vented, and the cycle repeats.

Yup ^^^ and the bleed down doesn't make it down to zero, so the motor is
starting under load, hence the tripping.

 

[AVI_8]

I think we are onto something here - there's no hiss from the unloader valve when it shuts off.
I doubt it's plumbed in wrong but there's a chance it is gummed up.
I'll take a look tomorrow and report back.
Thanks for the help so far.

Also check what the pressure is when it shuts off compared to the pressure it should be, I’m presuming it’s 10 bar if it’s a belt driven compressor, if it’s direct drive probably 8 bar.
Your earlier comment on it slowing down before shutting off which is unusual in my experience makes me think it’s not getting fully up to pressure before shutting down if so a possible issue with the motor, something else to check.
If that was the case it’s a reason why there’s no unloader valve activation.

 

[Pantera2075]

I don't know exactly what it was, but it's fixed - or at least, it now performs as it should.

I cleaned out the unloader - no change.

Then I cleaned out the check valve even though there was no muck in it. I did flip over the rubber "pastille" as I've seen elsewhere that this can be a thing.

When all reassembled, it worked.

So thanks for your help, you definitely pointed me in the right direction.