compressor wont start under load

by Joe

7.5 hp 80 gal speedaire

Dayton motor kept blowing breaker - took motor off and was told it was bad and replaced with Baldor motor of same specs
Now when any load on motor breaker blows
What we have done so far:
removed belts - motor starts fine and pulls correct load
Installed belts, drained tank, motor starts fine
removed and cleaned check valve - reinstalled - filled tank and removed line to see if there was back pressure - everything was fine
removed safety valve from top of head - compressor starts fine
removed unloader valve line - compressor starts fine
-- in both of these previous situations there was air in tank but obviously not full load with air leaking at startup
reattached unloader valve line while compressor running and unloader valve worked fine when tank was full
removed and cleaned unloader valve - reinstalled - same problem; no start under load
Motor spins several revolutions and then when pressure builds slightly the breaker blows
Installed new breaker - same problem
Nothing else on that line - dedicated to compressor
Any suggestions?
Sorry I don't have a picture - vertical style compressor
________________
Joe, two things that come to mind.

Empty the tank and the compressor starts fine? Is that correct? Do that, let the compressor run up to normal cut out, and monitor the unloader valve to be sure that it is opening and dumping the air over the piston when the compressor shuts off. If the unloader doesn't work, the trapped air is adding too much load to the motor and it pops the breaker.

Make sure there is no change in the power supply, no extension cord, and that nothing else is pulling power from the same circuit at the same time the compressor is trying to run.

Still no joy? See the electrical troubleshooting section on the site map to find how to test your capacitors.

Cheers,

Bill


Comments for compressor wont start under load

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Oct 22, 2013
testing unloader valve?
by: Anonymous

Hi Bill, May seem like a silly question, but how do you "test" an unloader valve? Issues:

1) can it be an intermittent problem ("sticks" sometimes but not others?)

2) motor "blown" - can it be tested "manually", or do I need to order yet another motor to test it?
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As to testing the unloader, run the compressor up to cut out, and watch and listen to see if the unloader valve actually does. Yup, it could be intermittent, but usually not.

If you suspect a blown motor, I'd be taking the motor to a an electric motor repair shop and ask them to do a load test on it. I have no idea how to test an electric motor in my shop. It goes on or does not. If not, I take it to an electrical shop.

B.

Jan 20, 2012
Follow up
by: Joe

Unloader works fine
check valve is okay
Compressor is hard wired with new breaker - no extension cords
Just finished taking multiple voltage and amp readings and talking to a service rep at speedaire; seems like there might be an internal issue in pump at this point in time.

_______________

It would be good to know what "internal issue" in the compressor pump is causing this issue.


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Value of an speedaire air compressor

by Ty
(Mobile ,al)

I have a speedaire air compressor that is model # 5z185b 1. I acquired it in a buy/sell transaction and have no idea what something like this is worth. It is a 5 hp 1 phase compressor. Can you tell me a roudabout figure of what this thing is worth?






b>Bill says...

Howdy Ty. Sorry, no I can't.

If you do an online search for your compressor, I suspect you'll find a number of sites that have yours, or similar units for sale, and this will give you an idea of value.

Good luck,

Bill

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What kind of fluid goes into the hydraulic side of my compressor?

by Steve steffey
(Fenton mi)

My compressor won't hold pressure and the fluid check stick is low what type do I put in that?
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Don't know many compressors that have a hydraulic side, Steve, and since you don't indicate a model number, I can't even try to find an image to have a look.

Add more details here about what your compressor complaint is, as a comment, and we'll work with you.

Do you mean, for example, that the oil level in the sump is low?

Bill

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How much oil and what type for my Speedaire air compressor

Just freed rusted pistons, all is together, need to know how much oil and what type should be put in this rather old speedaire..
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Without model and manual, no absolute knowledge or recommendations.

To help out folks in your compressor circumstances this issue though has been addressed many times under the Oil Issue link from the troubleshooting section on the sitemap page.

Bill

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