fixing an air compressor

[Lamont in NC]

I recently got a Westinghouse air compressor that stops building pressure at about 20psi. The pressure switch has been bypassed so the motor continues to run but pressure stops building. At the point it stops building pressure I makes a subtle but distinct change in the noise it's making as if the load has suddenly been lessened. The pump itself has model 1AVC-1 on the label. It had been sitting unused for years in a heavy truck repair facility. I'm kind looking for any ideas on how I can fairly quickly identify the problem.

 

[sms]

The pressure switch should have a relief valve to bleed the pressure in the line for start up. Maybe this valve is stuck or not working at the correct pressure?

 

[Tiger Joe]

I too have an old Westinghouse compressor. I believe most of them had Leroi pumps on them.

sounds like you have an issue with valves either stuck of broken.

if still hooked up like it was originally. the leroi pump does not use the pressure switch to bleed off pressure ( called the unloader) but rather the oil pressure of the pump.

 

[Tiger Joe]

replying to my own post since I cant edit.

I doubt its the unloader. like I said leroi pumps have the unloader built into them, not much to go wrong.

When I said valves, I was referring to the valves in the head of the pump.

 

[markiz41]

I second Joe's guess on the valves. The seats are probably rusted to heck after years of sitting and not closing properly. I believe you DON'T have to pull the head off these units to get to the valves, just remove the caps and take out the valve assembly. Squirt some solvent into the valve to see if it's leaking.

 

[Lamont in NC]

Sorry, I meant to include a picture but forgot and can't seem to edit it--this might help. Hope the pic uploaded correctly[/img]

 

[Tiger Joe]

yup looks just like my Westinghouse but with a smaller pump. same unloader valve style like I was talking about.

I'd pull the valves and try to clean them. a word of caution though, there does not seem to be much availability for parts with these old leroi pumps, so don't go sinking too much $$$ into it

 

[Steve A W]

I agree with Tiger Joe and Markiz41.
If your a mechanic you should be able to clean and dress
the valves.
The pump is a Leroi pump.
I have either the same compressor or the next bigger.
It sounds like a Harley Davidson at idle when it runs!
Get that pressure switch fixed and in line before you
run it too much. The valves might start working and it
will over pressure and it could be bad.

Steve A W

 

[Ted in NE-OH]

Verify that the pressure gauge is reading correctly

 

[old]

I have messed with a few old compressors and I have fired them up and then poured a small amount of ATF into the air intake and that has many times helped make them work better.

 

[Lamont in NC]

There doesn't seem to be any notation on the pump, tank or motor as to what PSI it should be set at and nothing to indicate CFMs. Any ideas?

 

[Steve A W]

What's the motor h/p?
That comp is old enough to figure 4cfm per horse.
I always set pressure switch to cut off at 120psi
and on at 95psi.
That is the range for most air tools. And the compressor
runs a lot cooler than if you go higher.

Steve A W

 

[Steve@Advance]

From looking at the picture, the small line from the end of the crankcase is the air to the unloader valves on top of the cylinders.

That compressor uses a pressure oil system (the gauge at the end of the crankcase). When the compressor is running and making oil pressure, the air to the unloader valves is dumped and the compressor pumps air. When the compressor stops, the oil pressure drops and the unloader is activated. That relieves the pressure for the compressor to start easier when it cycles back on, it gets a few unloaded strokes to get to speed before it gets oil pressure.

Where I'm going with this, could be there is no oil pressure! Therefore the unloader would kick in as soon as there is enough air pressure to activate it. Could be a problem with the oil pump, bearing clearances, or simply low on oil. Or, it may have oil pressure and there is a problem with the oil pressure activated valve.

Just something to check along with the valves. If it is turning, and not hammering, chances are it is repairable.

 

[Lamont in NC]

it's 1.5hp

 

[Lamont in NC]

Thanks, I'm honestly not sure what all the parts are on top the cylinders but I understand what your saying--I can check oil pressure easily and I'd suspect if I disconnect the little copper air lines from that small gauge area to the top of the cylinders that would prevent the unloader from activating thus if that's the problem it should continue to pump up. I'll try to do this tomorrow.

 

[Steve A W]

Check out these links;

Steve A W
How the unloader works.

Parts

 

[Tiger Joe]

I just put together an old Champion compressor over the weekend and it had leaking unloader valves. unless something is wrong with the pump it will easily overcome unloader valves up to and over 20 psi.

my unloader was literally wide open blowing air and my tank was chugging right up to 50 psi(that's where I killed power) t

also, what size air tank is that? that looks just like my 80 gallon and this is an incredibly small motor for an 80 gallon tank if it is.

 

[Mashbox]

Had the same thing happen last year. Found a stink bug had got into the contactor, so I only had 120V instead of 240V. Pulled the contactor out, blew it out with air, reassembled and the house was cool in a couple of hours.

 

[shaun wallace]

The square plate that has line going to center of tank has piston with either oring or ucup inside. We have one setup similar at work, every year or so has to be replaced.