Need help with air compressor

[KeithB]

Hoping some of you mechanic type guys can share your wisdom with me. I have a large air compressor V-twin type that I'm having trouble with. It surges and almost stalls out at times. Other times it runs just fine. We just took it off the tank and took the heads off. The pistons haven't even scuffed off the cross-hatching in the bores and the crank spins very easily. We cleaned off the butterfly valves in the head but again everything there was clean and seemed to be in good shape. We have drained the oil and will refill with new after reassembly.

The tank is drained of water, the compressor seems OK, but why is it surging and stalling? There is a pressure sensor line that Tee's off to a solenoid that shuts off the unit at a given pressure. Could this be defective? We just put a new electric motor on it a couple months ago.

Anybody care to share any insight?

 

[freebullet]

Well, I'm not a mechanic. I play one to keep my stuff working.

That includes a few compressors, one being a large 220v unit that sounds similar.

From the sounds of it your looking at a bad solenoid on the motor, the relay, or a bad air pressure cut off switch.

Ours was the solenoids early this spring. The bad solenoid took out the electric motor. Ours has 6 solenoid. We went ahead & replaced all solenoids the motor & the on/off switch with the relay & box. The pressure cutoff got replaced also.

Was surging at start up, then failing to start.

Was almost 1500 in parts alone.

 

[Ian]

Belts probably stretched since the motor install and are slipping on the motor sheaves. They slip and get hot and sticky, start to grab again, then get too slippery and slip again, rinse and repeat, causing the compressor to surge and stall.

 

[KeithB]

I've ordered a new in-tank check valve ($15) from Grainger, going to pick it up shortly. I reasoned that if it was sticking that might block the line and slow/stall the motor. It's a brand new motor of the proper rated HP. If this doesn't help I will replace the solenoid unit, it's the only thing left. The belts aren't slipping, its a logical thing to check but they were snug and there is no signs of scuffing, rubbing, or fraying.

 

[freebullet]

http://www.compressor-source.com/mobile/default.aspx

Extremely helpful folks there. Very attractive prices on some stuff. Got our 10hp baldor from them.

 

[Ian]

The main thing to determine is if it's bogging because of excess load on the motor or low power input. Got amprobe? Pull-in relays are famous for burning the contacts like FB mentioned and you can lose all or some power on one leg intermittently (not intended as a bad joke, Keith, that's what the power company calls them). You can also detect burned contacts with an AC voltmeter by checking voltage drop across the switch contacts while it's running...and malfunctioning. Pressure switches usually either work or don't work, very little in-between especially when they operate a solenoid.

 

[freebullet]

The motors have start & run capacitors. You have be careful testing around caps they can fry you instantly. Most can be drained to ground.

Be careful, & good luck!

 

[fiver]

it is definitely in the electronics.
electric motors really can't surge and stuff unless their power is being cut or partially cut then re-applied.
solenoids are the controls to that power source.

 

[freebullet]

In my og post I meant capacitor where I said solenoid. My apologies.

Mine works like this-


Power in to relay box with switch. Should have 110-120v on each leg incoming to the relay, otherwise bad wiring or breakers.

From relay to motor 2 power legs & neutral . The caps are in the rectangular grey box on the motor. Test the wires for 110- 120v on each leg before that point(before the caps) to determine if the relay is bad.

If the caps in that box are bad they are usually expanded or the contacts on the top are melted off.



Last is the air pressure cut off solenoid. This tells the relay to start or stop the motor based on pressure, it also relieves excess pressure when shutting down. We replaced them all at the same time. When swapping the motor you want it all new as the other parts can cause premature failure of the expensive motor.

 

[S Mac]

I think the check valve may be your problem.

 

[KeithB]

Put in new check valve, reassembled everything. It's building up pressure as I write this. We'll see if everything is tight with no leaks once it hit max P. So far no surging, etc. running real smooth.

 

[KeithB]

Well, so far so good, I've tapped the air to drop the pressure several times and the motor kicks on and runs smoothly each time. It has a small leak where the air sensor line connects to the solenoid and we will fix that but it is a very minor problem. I think the piston inside the in-tank shutoff valve was partially frozen in place, the new one cycled under thumb pressure, the old one wouldn't move from hand pressure alone.

Tank filled up very quickly from 0 to 120 psi. It used to take longer than that to bring it up from 90 to 120 psi.

The tool changer on my CNC mill has to have air pressure to operate. It's a very expensive statue without air!

Appreciate all the suggestions and help from you guys, having never fixed an air compressor before it was nice to have some support when diving into the unknown.

PS - Ian, I'm not the least bit sensitive about my leg, it is what it is. I wouldn't use the sig line I use if I was touchy about things.

 

[freebullet]

Glad to hear it's working.

Big pain when something you need for work breaks down.

 

[KeithB]

Just a follow up. The in-tank check valve must have been the problem, it's been working perfectly for the last 12 days. Appreciate all the help and advice on this one.

 

[Pistolero]

Good to learn about this.

Bill