Air compressor repower options?

I am considering a repower on my 5hp single phase 2 stage air compressor.
Would a 3hp 3phase motor ran off a VFD workout ok?

Also if I were to stay with the 5hp single phase could the compressor be setup with a unloader valve so the motor could run in continuous for large air loads and intermittent for normal loads by switching?

Thanks

jeff77indy said:

Also if I were to stay with the 5hp single phase could the compressor be setup with a unloader valve so the motor could run in continuous for large air loads and intermittent for normal loads by switching?

Thanks

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That unloader function is often controlled by air operated valves in the head of the compressor itself. I suppose it could be done by some sort of high flow solenoid valve to close off the intake. I would suggest looking at MAC valves for that function. My Quincy compressor with valves in the head is set up to operate either continuous run or intermittent by throwing a switch.

Would a 3hp 3phase motor run off a VFD workout ok?

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Maybe. The ratio of the motor sheave to the pump sheave is sized for the hp & the torque of a 5 hp motor. You'll need to install either a smaller motor sheave, or more likely a larger pump sheave, so that the smaller motor will be able to turn the pump. After the sheave change, you'll have 60% of the air capacity that you had with the 5 hp motor -- probably 11 cfm vs 18 cfm. I can't imagine why you'd want to do this, as you can buy a new compressor (3 hp, 60 gallon vertical, single stage) for the cost of a sensorless vector drive + a motor.

could the compressor be setup with a unloader valve

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That's easy to do, and not expensive. CDI (Control Devices Inc) makes the Load Genie line of unloaders. The one you want is either the Load Genie Mark 2, Mark 3, or Mark 4. Here's a description of all three:

http://www.rossbrownsales.com.au/files/continuous_run_vent_unloaders.pdf

Also some info from CDI: http://www.cdivalve.com/products/continuous/continuous.htm

FWIW, there's a new Mark 3 currently on eBay:
http://cgi.ebay.com/ebaymotors/Mark...emQQimsxZ20090105?IMSfp=TL0901051210008r11497

Also sold by Grainger & other industrial suppliers.