Given a specific set of characteristics for a fluid and the flow requirements of the system, pumps and fittings can easily be selected. Each pump is designed for a specific flow rate and head pressure, and fittings are built for specific applications. These optimized points are called best efficiency points, BEPs.
Common practice is to select a pump with a BEP slightly higher on a system pump curve than the situation calls for. While this practice is conservative, and avoids pumps stresses from impacting longevity, systems can use pumps slightly underrated for the application without worry. If the operating requirements are too far away from the pump BEP, vibrations can cause early failure.
“Selecting a pump that will operate near the minimum flow limits is just as risky as choosing one that will operate at the end of the curve.” –Pumps&Systems
Click here for the full article by Jim Elsey.