Maintenance: March drive motor size to pump size

The motor horsepower and speed will be determined by your application. Their are many variables to consider, the head needed, the specific gravity of the fluid, the GPM required by the process, etc. The first place to start is to asertain your requirments, then contact a manufacurers rep. to select an pump or check with the various manufacturers on line. Many of them will provide their pump curves free of charge. From the pump curve you can determine the horsepower and motor size needed for your application

I have found one curious fact when working with pumps. at each step in the selection process the engineer or rep seems to add a fudge factor to cover any discrepencies. I've seen pumps way oversized because of everyone involved covering his rear.

From the pump curves determine the maximum hp and input rpm.

Select the drive and the drive ratio with a 1.75 safety margin

For a reciprocating engine use 75% of the conitnuous power.

For an Electric motor use 88% of the rated power

Allow an extra 20% for electrical wiring, switches, starters ..........

Make sure you can keep everything cool

Use a "tinker toy" approach to design so that it is easy to service and replace.

Determining the motor size is a function of many factors. First you have to determine the system head. The additional safety factor mentioned is added to compensate for friction losses that were not considered or estimated, and for aging pipe systems. You then use the manfacturer's pump curves and select the appropriate pump and impeller for your pumping application. Many manufacturers produce a pump selection manual which is predominantly incorporated into their catalog. Your best bet is to consult a civil engineer as this is what we do.