Air compressor won’t pressurise up - help?

[SVB]

Hi

My sip air compressor won’t pressurise. The motor runs and air hisses out of the pressure switch assembly. The over pressure relief valve is seated but I think there is another valve in the pressure switch box that is not seating to allow it to build any pressure.

is this a new pressure switch job (are they universal- sip want £50 for one but they are on eBay for £10 as a generic part) or is the valve inside mal operating and individually replaceable? Or should I be looking elsewhere?

thanks
Simon

 

[julianf]

There's an unloader in that box that unloads the cylinders and pipework when the motor turns off, so as, when it start up again, it's not initially trying to push against pressure.


So, you have the main connection which is what the over pressure valve is hanging off, but you will also have a small bit of nylon airline running to somwhere else on the pipework between the pump and the tank.

You can buy another one of the black lumps, but, before you do, maybe worth just taking the top off and seeing if you can find the leak - it may be somthing as simple as the nylon pipe and it's olive comming unseated, so worth minor investigation before you spend money.

Obviously there is 240v under the black cover, so don't lick any of the wires....

 

[Misterdog]

Soapy water applied to joints will show bubbles if there are leaks.

You have closed the drain plug on the receiver tank

 

[clogs]

It sounds like the diaphram in the on/off switch.....
they are very cheap from china...a small one is around £9-15squids...depending on size and if there are extra gauges.......
I always buy the next size (amps) up and actually have a spare for each size of comp.....I think even the 3phase/5hp one I have was less than 25 squids.........
they dont last long.....often the vibe's get em......
just buy new they aint worth the worry.....

 

[Sandyn]

I had an identical problem a couple of weeks ago. It was the diaphragm in the on/off switch as clogs says. I was really lucky I had kept the switch off an old failed compressor and was able to replace it and get the compressor going again.

 

[Misterdog]

they dont last long.....often the vibe's get em.....

The control switch on my DeVilbiss 3 phase compressor has not been changed in over 15 years....
The pump piston rings and valves have failed during that time though causing the same problem.

 

[julianf]

I have two 3hp units. One I've had for about a decade, bought used. The other is older, but I've only had it about 3 years.

I've had to make repairs to both, but never the diaphragm mentioned above.

I'm only mentioning this to assist - it's not a sure fire thing that the issue is the afore mentioned diaphragm. It may well be, just don't count on it, as I've never had to repair it on any of my units either.

 

[SVB]

Thanks all. I’ve ordered a new pressure switch assy - as above it’s only a tenner so I hope that will sort it.

 

[julianf]

It may be too late now, and I should have said before, but a lot of the cheap from China stuff is npt thread, and you may need BSP.

Somthing to check if it's not too late?

 

[SVB]

It may be too late now, and I should have said before, but a lot of the cheap from China stuff is npt thread, and you may need BSP.

Thanks and good prompt - the one I’ve gone for is BSP so hopefully all on. was only a tenner too so looks a bargain (provided it works and is reliable - time will tell!)

here for info: AIR COMPRESSOR PRESSURE SWITCH SINGLE PHASE SUITABLE FOR COMPRESSORS 1 - 3 HP | eBay

 

[Chris_Pallet]

How did you get on with your repairs? I'm having dramas with mine very similar.

 

[SVB]

I replaced the pressure switch with the one I linked in my last message and all sorted.

(as an aside, I also checked the air fittings round the workshop as I have ’plumbed it round’ - I did find one elbow with a Q/R fitting leaking due to perished o-ring so changed that too).

good luck
simon