What Motor Pulley size for Quincy 325 with 3 HP Motor? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-15-2013, 07:41 PM
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What Motor Pulley size for Quincy 325 with 3 HP Motor?

I have a very old(I think it was manufactured in 1957) Quincy 325 ROC 4 Compressor. Mine is a Splash Lube Pump. It currently has a 3 HP, 220 Volt, Single Phase, 1725 RPM, 17 Amp Motor. The Pump has a 16" OD Pulley and the Motor has a 4.75" Pulley. The pump is obviously much older than the motor, so the motor was apparently replaced at some time. I assume the pump pulley is the original, but I have no idea if the motor pulley has been replaced and I do not know what the HP of the original motor was.

Quincy charts say that these pumps have a Minimum RPM of 400 and a Maximum RPM of 900, but I have not found anything that indicates what RPM a 3 HP Motor should run the pump at. I calculate that I am currently running the pump at about 512 RPM and some have suggested it should be running at a higher RPM with a 3 HP Motor.

What RPM/Pulley Size would you suggest for the compressor with the motor I have?

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Old 06-15-2013, 08:03 PM
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Check the current draw loaded with a clamp on ammeter. If its at nameplate current or less, don't mess with it.Its an old compressor. If it ain't broke, don't fix it. IMHO, Nolan
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Old 06-17-2013, 06:34 PM
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"If it ain't broke, don't fix it." may be an option, but I would like to know what my other options may be. A 3 HP Motor, even with optimum pulley sizes for maximum output does not put out a lot of CFM, so I would like to determine how far my current setup is from optimum.

When I can borrow a clamp on Amp Meter I will check to see how many Amps it is drawing. If it is somewhere close to a 17 Amps I will leave it as it is. If is drawing a lot less Amps I will want to put a larger Motor Pulley on it. How much larger is what I am trying to determine.

Anyone have an Quincy 325 with an OEM 3 HP Motor? Assuming it is a 1725 RPM Motor, what is the pulley size on it?

I would also like to know the OEM Motor Pulley size for of Quincy 325 with an OEM 5 HP, 1725 RPM Motor, as I may install a 5 HP Motor at some point.
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Old 06-17-2013, 09:19 PM
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I can see you wanting to get more CFM's out of it, but its real old. Good luck with it, check the current with an clamp on AMMETER and make your call. It gonna be hit & miss to find the perfect pulley to go 5 hp. Just when you get it pumping alot of CFM at a higher compressor speed, the old lung is likely to fail. Depending on what size wire and breaker you have now, you're likely going to need bigger wire and main breaker for the 5 hp. I'm just giving my opinion based on experience. olnolan
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Old 06-18-2013, 06:12 AM
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It may be old, but these compressors are "built like a tank", and many seem to think they are "the best" compressor ever made in the 5 HP range. I have just "rebuilt it" with rings/bearings/valve discs/springs/seals and it had very little no wear on the rings/rod bearings/valves. I and am hopeful that the pump is good for another 50 years or more.

I think MOST 325s came with a 5 HP motor, so I am no concerned with overworking the pump with a 3 HP motor, but I am concerned with how fast I can run a 3 HP motor when driving this pump.

The wiring to the compressor is 8 Gauge(I was expecting that I might someday install a larger motor, or compressor) so the wiring should easily be able to handle a 5 HP motor.
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Old 06-18-2013, 07:00 PM
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Well it does not look like I will be putting a larger pulley on the 3 HP Motor that I currently have. I was able to borrow an Amp Meter and it is pulling about 20 Amps.

I guess my plan is to continue to use it, as is, and if this motor fails I will then install a 5 HP Motor.

I would still like to know what the OEM Motor Pulley Sizes are for a 3 HP and for a 5 HP motor on the Quincy 325s.
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