Thread: Learned something about air compressors.

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Since most of us have air compressors I thought I might pass along something I learned yesterday. You might remember I was having trouble with the motor on my air compressor failing, and Eaton supplied a new one at no charge. We put the new motor on and after using it several times we started blowing fuses. ( My switchbox has two 30 amp fuses in it) Also, when it would come up to pressure and shut off the little check valve on the square D switch would keep hissing, releasing air until the pressure would drop and the compressor would kick on again.

Yesterday I decided to fix the problem so I took off the lid from the square D switch and headed to our local industrial supply company to see what I needed to fix the problem. Ran into a very knowledgeable guy there who told me what was going on. There is a check valve on the inlet to the tank, it's purpose is to let air into the tank, but once the compressor shuts off it traps the air in the tank. Right above that is a bleed off line that goes to the square D switch. It's purpose is to relieve the air pressure off of the cylinders so that the motor can more easily crank the compressor when it first fires up. The check valve isolates the tank air from the cylinder pressure so that only the cylinder pressure is released upon shut down.

He said the reason I was blowing fuses (and probably why my first two motors failed) was because the check valve had failed and the line that was supposed to relieve cylinder pressure was unable to do it's job, so when the motor kicked on it was having to work very hard to get the compressor to turn over that first few revolutions (too much cylinder pressure). That was overworking the motor and causing the fuses to blow too.

I replaced that check valve (when I pulled out the old one it was rusted from moist air going over it, and also the seat was crooked from corrosion) and now the compressor comes up to pressure, shuts down, and I can hear the bleeder momentary hiss until all the cylinder pressure bleeds off. My compressor also fills up faster now because the check valve being rusted was somewhat restricting air getting into the tank.

Like I said, I know most of us have air compressors and thought you might want to keep this in mind in case you ever start having similar problems.

Don

Thanks for the info, always nice to know about things like this.

Richard

It's called an "unloader" since it takes the load off
the compressor for easier starting.

Good to know these things. I have two compressors and would never
have given this a thought..Thanks for sharing

Thanks for the info Don.
Had a freind that had that problem too,
But never heard how he had fixed it.
Thats some, Good to know stuff!!!
Kurt

I hoped it would help someone else out. We have been chasing our tails on this one for a few weeks and couldn't figure out why all of a sudden fuses were blowing after only a little bit of running. We were buying them left and right. I also wonder if this problem hasn't been happening for a while and was the cause of the shortened motor life?

You are right, Robot, that is what he called it too, an unloader. I bet it isn't good for the compressor section of the air compressor too, trying to start it with that pressure in the cylinders. I now know a lot more about how compressors work thanks to the guy at the store who was willing to help me out.

Don

Speaking of compressors, Uncle Bob told me about Kaeser Compressors
a couple of years ago...we visted their booth at SEMA two years ago.
I was so impressed, I came home and bought one. It is far beyond any
compressor that I have seen....it is so quiet, ours is installed in the shop.
You can carry on a normal conversation standing next to it. It has a
water separator and filter built inside the cabinet.....and it spits out painting
quality air. We bought a 25 cfm unit as I remember.....I think it's a 10 hp
unit.

Thanks, Bob!

mike in tucson

I keep the compressors working on our boat (air start, air throttle, air brakes, etc)

Unloaders go out more often than you'd think.
Most Quincy units have an unloader valve, and also an oil pressure switch, so that the compressor will not take a load until oil pressure is up.
Without an unloader a compressor would be hitting a brick wall everytime the motor fired up.

Drew

Originally Posted by robot

Speaking of compressors, Uncle Bob told me about Kaeser Compressors
a couple of years ago...we visted their booth at SEMA two years ago.
I was so impressed, I came home and bought one. It is far beyond any
compressor that I have seen....it is so quiet, ours is installed in the shop.
You can carry on a normal conversation standing next to it. It has a
water separator and filter built inside the cabinet.....and it spits out painting
quality air. We bought a 25 cfm unit as I remember.....I think it's a 10 hp
unit.

Thanks, Bob!

mike in tucson

You're welcome Mike, and it was a special pleasure to spend YOUR money...

Don,

Also, thanks for the info. I have an old (50ish) Wayne compressor that I bought used a few years ago. Don't know if that problem will rear it's ugly head but if or when it does I will now be ready to deal with it. Thanks again.

Jack.

You're welcome. Ours has been running like a champ since I replaced that check valve, and it fills up quicker. No more blown fuses either.

Don

That's some awesome and helpful info...Thanks for sharing, Don!

Regards,
Shea

You're welcome. Last week we were trying to spray some primer on Dan's car again and the d*** compressor blew some fuses again. We packed it in for the night and the next day I decided to fix it once and for all. I found two problems. The fuse box I had installed specifically for the compressor was badly burned inside from all those fuses blowing. Also, when the compressor shut off it was not unloading the heads again, but was letting air from the tank escape too.

I bought a new fuse box, and removed the check valve to see what was going on there. The new check valve I had bought has a circlip on the bottom so you can remove the plastic disc that acts as the check valve. When I dismantled it I found a piece of black crud had become lodged under the corner of the plastic piece, keeping it from sealing. I cleaned it up and replaced it, and last weekend we got through the entire weekend of spraying with no more problems.

It looks like our tank (which is probably 8 years old) is rusting inside and that is where I think that piece of dirt came from. But the fuses stayed cool this time. No sin on this setup, when we are at the shop it gets a real work out.

Don