Buying 2nd hand compressor - what to look for? checks to do?

[visor_down]

Hi looking at a secondhand belt drive compressor, other than aesthetically are there any checks you can do on a compressor when viewing it to ensure its OK? Other than the obvious one of checking it works! any way to tell the wear on the internals or any signs that point to imminent failure? (aside from dismantling it!)

Lastly anyone have any knowledge or experience of the ERP brand good, bad, weak points etc.

Cheers

 

[the snooper]

ive got an erp and has always worked perfectly over 20 odd years, make sure oil is clean no knocking, it doesn't take ages to fill and that there is not tones of back pressure coming from crankcase

 

[mfletch]

Open the drain plug and look to see if red rust comes out this indicates the tank is rusty

 

[rtbcomp]

Check for oil leaks. Take your own know good pressure gauge with you. I once bought a compressor that showed 120psi on its gauge, when I got it home it wouldn't go beyond 50psi!

Run it up to pressure and it should give a short hiss when it stops, if it carries on hissing you'll need a new non-return valve.

 

[Bill Edwards]

Yep, working pressure gauge is a good idea, check it starts properly, doesn't knock and doesn't breath.

Use the condition of the oil and the air cleaner to get some idea of what maintenance has (or hasn't) been done.

If you can't get anything out of the drain then it might be blocked and has never been drained. Few people bother, and tanks can rust and become dangerous.

 

[brightspark]

look at the pulleys and belt for wear its a good indicator if it has done a lot

 

[visor_down]

cheers all, very helpful pointers there.
It appears the air line is coming straight out the end of the tank is this the norm? From what i can see in the pics this bypasses the reg? would this indicate a fault of any kind to bypass it?

 

[Bill Edwards]

Unlikely, it's not uncommon (in fact, it's often recommended on this forum) as it allows large diameter air fittings/hose to come out of the receiver without being hindered by a regulator.
For running some tools this is best, regulators and small fittings can impede the air flow quite a lot.

 

[visor_down]

The seller has apparently "tightened up a small bolt that regulates how long it goes on for and how much it fills up. Only because it went on too long for my needs"

I am guessing something isn't right somewhere with it then, or is this a usual adjustment!?

 

[Bill Edwards]

Under the (normally black) cover on the pressure switch there should be a screw.
You can alter it and make the compressor cut in and out at higher or lower pressures (of course, when increasing the pressure you need to be careful not to exceed what the compressor is safe to handle).

I've never had cause to turn one down, perhaps some can think of reasons why you might. If you only needed say 50 psi then you could set it to shut off and come at say 75 and 60 psi, rather than 120 and 100 I suppose.