Low Speed Compressor

[keelan]

I was wandering around Princess Auto recently, and spotted a big 4 cylinder air compressor head in their surplus section, and it got me thinking... Nothing quite drives me to crapping my pants more than my little oil-less compressor kicking in when I least expect it; would it be reasonable to belt up a big compressor head to a smaller motor to run at low rpm/high torque to create a low speed/high displacement compressor? Or is there a whole bunch of leakage in the rings and valves that is overcome by spinning the compressor at its proper design speed that will become a problem turning it at say 250 RPM?


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[manwithtools]

Compressors require motors that are capable of turning them at their design speed. It's necessary for proper lubrication and air output. You could conceivably turn certain units slower if the have positive lubrication systems and not splash lubrication like most lower end units, but you still need horsepower to turn them. It's not about leakage; it's about the opposite, displacement and compression. A compressor is a pump, it takes more hp to pump more air.

 

[keelan]

Good point on the lube. My goal isn't more air, it's less noise. I'm aiming for the same volumetric output as my little compressor, but lower speeds thanks to 4x the cylinders, larger displacement per cylinder, and much lower overall speed.


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[CNGsaves]

Post up PIC's of the 4 cyl compressor head along with diameter of the pulley.

GJ guru like Kam1973 or others can give you details on motor HP size & motor pulley needed.

 

[keelan]

Y'all are missing the point I don't want to run it to spec. In fact it has no pulley at all, probably part of the reason why it's in the surplus section. I don't need lots of air, I'm just wondering if I can use a big pump and run it slow to cut down on the noise.


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[keelan]

Thinking about this more, I think I am the knucklehead. 2" bore, 2.375" stroke, 4 cyl, single stage. If my math is any good, i'd need to get down to 30 rpm[edit: divided when I should have multiplied; make that 22 rpm] to run this thing off a half-horse motor @ 125 psi output.

 

[CNGsaves]

Compressors have intended RPM range . . . .sure anything that low is not possible.

 

[Zeke]

The only compressor to have IN the shop is a belt driven cast iron pump. Some of the oldies by goodies lumbered along making a 'pooka pooka pooka' sound that you could easily talk over.

I don't see a 1/2 HP motor doing much in this case.

 

[LS6 Tommy]

The only compressor to have IN the shop is a belt driven cast iron pump.

Or one of the expensive rotary screw units they have now. They're almost silent.

Tommy