I am wondering what is the straight run minimum suction line for a centrifugal pump. i really more explanation about this requirement why do we need it. every single input from you guys would help

jawal, most pump manufacturers will recommend a maximum flow velocity at pump suction which is generally between 6ft/s and 10ft/s for liquid at vapour/liquid equilibrium. Exceeding these numbers will often lead to problems hammer, cavitation, etc.) during pump start up and shut down. The desire is to provide a smooth laminar flow into the impeller eye.

In any given pump you should of course go through the calculations for NPSH which will take into account the critical variables.

http://www.lightmypump.com/centrifugal-pump-tips.htm has a great deal of good information on pump installation, see specifically tip #24 for the suction piping guidelines.

John from PA