2 hp air compressor.

[Geo-TH,In]

I have a cheapie $100 two Hp HF air compressor in garage to air up car tires.
I turned it on today and it just hummed.

Tank has about 100 psi. Haven't used compressor in months.

So I pulled out the pop off an bleed air out of tank.

Well it worked. Compressor fired up.

I'm guessing air pressure got on top of piston. Never happen before.

What's your guess?
George

 

[chuckinnc]

Its suppose to have a relief valve that lets air escape the line between pressure switch and compressor, thats so it can startup without a load

 

[Geo-TH,In]

I know about the pressure relief but it won't start without bleeding all air out.
George

 

[David G]

Unloader not working right.

 

[Steve@Advance]

Some have a check valve where the line goes into the tank. If it's bad the compressor will try to start loaded.

Unloader valve not working (if equipped).

If no check valve the outlet valve in the compressor can leak and pressure up the piston.

Could be the motor, weak start, bad cap or start switch, voltage drop on an under size extension cord.

 

[kencombs]

That pressure unloader probably leaked while setting for so long. What surprises me is that the piston rings didn't leak too, and held pressure for that long.

 

[TimV]

Not saying this definitely is your problem, but a lot of the one-way valves on the cheapie compressors are identical--understandable as the compressors are more than likely made by the same company in You Know Where and they're just a rubber flapper which tends to fail. I've been given a few compressors with the same problem. Haven't bothered fixing them--usually tore them down to use the components for various other projects, though I imagine you could replace the valve if you needed to. See if you can fill the tank, pull off the supply line going to the one-way valve, and soap-test the valve under the pressure of the tank to see if it's leaking back--the last time I did that I could hear the air coming back out of it and so it wasn't necessary to even soap it.

 

[Hobo,NC]

(quoted from post at 06:09:17 05/01/20) That pressure unloader probably leaked while setting for so long. What surprises me is that the piston rings didn't leak too, and held pressure for that long.

Those cheap not a real 2 HP compressor may have a one piece piston ring/seal it may not leak past it...

 

[Geo-TH,In]

One piston and oil in crank.
So air pressure had to be on the top of
the piston don't you think?

Couldn't have leaked too much, over 100
psi in tank that had sit there for
months.


George

 

[Hobo,NC]

On the inverted deal the compressor posted does not take much to turn a short stroke small displacement unit the only thing that impressed me was the inverted set up...

 

[Handsome Devil]

I do not know how to test a capacitor but would turn power off or unplug if not wired direct, pull cover off motor and look to see if one swelled up or is leaking or looks fubar. Friend has an upright 5 hp built in China with a name brand on it. Was a capacitor and it cost under $15 to buy a new one. Electronic repair shop had them or you can order on line.

I have a 3ph rotary phase convertor that I fused every line out so each machine is fused. Both my compressor and small lathe blew a fuse. Same hum as a bad capacitor. In my case the 3rd leg is not getting start up power so it hums. I think it is the same case when a cap blows. Not enough starting juice. Or like others have said your unloader is not working. Good luck. Regards, John.

 

[Stephen Newell]

The compressor switch is suppose to release the pressure at the piston when it shuts off. Somewhere there should be a one way valve that allows air to go to the tank but not back to the pump. This is so the compressor can get a running start before it starts putting air in the tank. If either one of these valves are malfunctioning it can cause the compressor to stall.

 

[Geo-TH,In]

Yes switch had a pressure relief valve which only works when switch is in the off position.
It was unplugged and over time air slowly leaked and switch was in the on position closing the relief valve. Air leaked passed the check valve and put pressure on the top of the piston.

It worked flawlessly today because the pressure switch was in the off position when I plugged it in.
George