Direction of compressor pump sheave rotation…

I was criticized recently by a visitor to my about-air-compressors.com information site. 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 travel 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.

My, 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.

I stand my ground.

Yes, where there are ancillary functions dependent on the rotation of the crank… water pumps, oil pumps, fuel pumps, ignition sequences etc, sure rotation matters.

A DIY $200 air compressor doesn’t have all of that stuff! It has intake and pressure valves made of spring steel, and 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 as the piston cycles.

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!

This is my .02 cents worth. Other opinions are welcome.

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4 Responses to Direction of compressor pump sheave rotation…

  1. THOMAS MCGUIRE says:

    YOU HAVE JUST ENOUGH KNOWLEDGE TO BE DANGEROUS.

    MOST AIR COMPRESSORS ARE AIR COOLED, AND MUST ROTATE IN THE PROPER DIRECTION: THE AIR FLOW FROM THE FLYWHEEL / FAN WILL COOL THE PUMP.. THIS IS WHY WE CALL IT AN AIR COOLED COMPRESSOR.

    NOTE: SOME AIR COMPRESSOR ARE PRESSURE LUBRICATED AND HAVE A DIRECTIONAL OIL PUMP AND WILL NOT PUMP ANY OIL TO LUBRICATE THE PUMP IF RUN BACKWARD. BUT WILL COMPRESS AIR.

    • Bill says:

      Please note… “Yes, where there are ancillary functions dependent on the rotation of the crank… water pumps, oil pumps, fuel pumps, ignition sequences etc, sure rotation matters.” If there are ancillary functions, then yes, rotation matters.

  2. Jw says:

    You may find most sheaves have fan blade design to blow air across compressor head for cooling

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