First, best practive is to never throttle a pump from the suction side, always on the discharge side.  Starving the pump for water will damage the bearings, generate excessive heat inside the pump volute, and cause cavitation which destroys the impeller in time.  A pump running dry will actually generate steam and once this happens, it is time to look for a replacement.  

The next worst thing is to operate the pump fully shut on the discharge side for an extended period - like several hours or days.  The pump may be operated closed on the discharge side for a short period of time - this will cause no undue problem
as long as there is water supplying the pump.

On one of our installations, we used a globe valve (standard plumbing valves in USA) on the dischage of the pump for throttling/controlling the flow.  The valve can creep open over time and can foul shut.  I found it fouled almost shut at the 1 year anniversary visit and this was causing the pump to surge in a manner most disturbing to
the operator.  I simply exersized the valve and cleared the system. I suspect the condition may have existed for some time.  

(Contributed by Bruce Spaulding)

Last update: 06:26 PM Tuesday, July 7, 2009

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