Is there a requirement in a particular code or recommended practices document that requires a certain length of straight piping on centrifugal pump suction lines? I didn’t see anything in API 610, but I’ve always used 5 nominal diameters. I’ve also been told that 10 nominal diameters may be required for certain vertical, in-line pumps.

This requirement, I believe, is so that flow turbulence may be calmed before a liquid enters the pump cavity. Often, there is a reducer located just ahead of the pump suction nozzle… doesn’t this add to the turbulence prior to a liquid entering the pump?

Is this straight run requirement (or recommendation) listed in a specification somewhere or is this merely a manufacturer’s recommendation?

Best wishes,
Bob