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Overdriving A Belt Driven Compressor

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Forum topic by uMinded posted 07-16-2017 04:00 AM 240 views 0 times favorited 7 replies Add to Favorites Watch
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uMinded

110 posts in 1546 days


07-16-2017 04:00 AM

I recently rescued a belt driven 3/4HP compressor. It has a cast iron single 3” piston for compression.

I need to get a new motor for it and was wondering which would get the maximum CFM out of it, a higher HP motor or faster rotation?

The compressor is this style from the 80’s I am thinking by the layers of paint.

I took the head off and it’s just a flapper valve inlet/outlet design, no rods or anything. I imagine a pneumatic check valve would take the load off the old flapper valves and help out.


7 replies so far

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RichTaylor

1151 posts in 283 days


#1 posted 07-16-2017 04:37 AM

Horsepower won’t change a thing, as long as it’s adequate. I’d match the specs on the motor you’re replacing.

-- No matter how much you push the envelope, it'll still be stationery.

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JoshNZ

82 posts in 763 days


#2 posted 07-16-2017 04:59 AM

Faster rotation – to answer your question.

Extra horsepower above what is required to run it at full pressure will be wasted. More RPM will fill it faster, but I imagine you would run into the limitations of the valves or bearings eventually so as suggested, matching the specs of the original, or close to it would be the go.

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uMinded

110 posts in 1546 days


#3 posted 07-16-2017 05:09 AM

I may get a variable diameter pulley so I can tweak it a bit. The goal is to run a HVLP gun for 30min spray jobs. I’m thinking on my 20gal tank if I set it to 60psi cut in I should be able to spray no problem. My current compressor takes 15min to fill the 20gal tank to 120psi.

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RichTaylor

1151 posts in 283 days


#4 posted 07-16-2017 05:17 AM


I may get a variable diameter pulley so I can tweak it a bit. The goal is to run a HVLP gun for 30min spray jobs. I m thinking on my 20gal tank if I set it to 60psi cut in I should be able to spray no problem. My current compressor takes 15min to fill the 20gal tank to 120psi.

- uMinded

Be safe out there. They design them to those specs for a reason. Compressed air is not to be trifled with. It fails catastrophically. That’s why they do pressure tests on vessels using liquid instead of air.

-- No matter how much you push the envelope, it'll still be stationery.

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dhazelton

2571 posts in 1990 days


#5 posted 07-16-2017 12:52 PM

Old compressor and ‘layers of paint’ say rust. If outside was rusty what about the inside?

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uMinded

110 posts in 1546 days


#6 posted 07-16-2017 03:44 PM


Old compressor and layers of paint say rust. If outside was rusty what about the inside?

- dhazelton

No sign of rust anywhere, I plan on sandblasting the housing after a compression test. I took the head off and looked at the bore and it’s clean and smooth, no scrapes or build up. Likely sat for so long the oil coagulated in the bottom end. A trip through the varsol bath will solve that.

I plan on taking the front plate off today and checking the bearings. I have bulk gasket material so will to a poor mans rebuild and then test.

I have a new 20gal air tank as I don’t trust 30+ year old vessels at 150psi.

P.S – I will try to remember to take pictures.

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uMinded

110 posts in 1546 days


#7 posted 07-19-2017 03:39 AM

I sand blasted the heck out of the unit to get all that paint off of it and found a few reasons why it wasn’t working so great anymore. #1 is that the reed valves are in rough shape, shouldn’t be hard to replace but I have no idea what make/model this compressor is. (Shim stock or putty knife may be my fix option) #2 The head gasket was a sandwitch of old cork and rubber gaskets. Looks like the previous repairer never cleaned the old ones off.

So cleaned everything up and polished the mating surfaces with 600grit then 2000 grit until they shine. Need to make new gaskets but that’s an easy job.


Anybody know what make/model this may be? I am thinking the 80’s Sears style unit as the cylinder and base are cast iron but the head pieces are cast aluminum.

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