Direction Of Compressor Pump Sheave Rotation

Compressor Pump Sheave
(Last Updated On: September 19, 2020)

An owner of a small DIY type air compressor asked me about the rotation of the pump sheave, and whether or not I thought that the direction of compressor pump sheave rotation was important, and how would they find out the answer?

I responded to that visitor that as far as I was concerned since a reciprocating compressor pump piston only goes up and down, whether the crank was rotating one way or the other would make no difference to that compressor pump operation.

 Pump Sheave Rotation
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Another visitor strongly disagreed, pointing out that there were timing issues for valves, for this and for that, and direction of rotation very much made a difference.

Direction Of Compressor Pump Sheave Rotation

Yes, where there are ancillary functions dependent on the rotation of the crank… water pumps, oil pumps, fuel pumps, ignition sequences etc. etc., sure rotation matters. In fact, in these compressor types pump sheave rotation direction is critical.

However, a DIY $149 air compressor doesn’t have all of that stuff!

What it has is intake and pressure valves made of spring steel. When the piston cycles up or down (reciprocates) one or the other of the two valves opens and the other closes based on the air being pulled into the cylinder or being pushed out of the cylinder into the compressor tank as the piston cycles.

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Direction Of Compressor Pump Sheave Rotation

There are no other components that rely on the rotation of the compressor pump crankshaft to operate, and the intake and pressure valves couldn’t care less what the direction of the crank is, as long as the piston moves up and down!

Having said that, another visitor says that sometimes, if you look closely at the pump pulley, you might see a small arrow on the side of the sheave to show direction of travel. Or, check with the compressor manufacturer to be absolutely sure, if you can find them!

I have to add one more factor. If the pump sheave (pulley) is designed to provide air flow to the pump housing to aid in cooling, then yes, the direction of compressor pump sheave rotation becomes more important. If a compressor is being run to its maximum duty cycle, and the pump sheave drives air over the pump to cool it, not having the cooling effect of what is, essentially, a fan, could allow the compressor to overheat.

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This is my .02 cents worth. Other opinions, which can be added below, are welcome.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


  1. I ran into this problem when trying to put together a makeshift compressor 4 my woodshop. Instead of spending my .02 cents (which was about all I had at that time),I merely flipped the flywheel. This allowed the air to flow in the proper direction , thus cooling the compression chambers.


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