Choking down pump output

[sdboers]

G'day,
  Really simple question...  Is it hard on a pump to choke down the flow with a control valve?

  Assuming I need a 500gph flow, and I buy a 900gph pump and choke down the flow, does the pump really care?  Will it last as long as the same pump allowed to free flow at a full 900gph?

  My assumption is - it makes no difference to the pump. It's not like the impeller is directly connected to the load and will have to strain to move it.

Sean.

[Carl]

I have cut flow on many pumps over the years, whether for an aquarium or pond.

In general, I never noted an issue with about 1 1/3 cut back whether by a valve or simply via head pressure.
With larger cut backs in flow, I did note that the pump ran hotter (depending somewhat on the pump and size of the magnet, not impeller). Since I never made a controlled head to head test of whether this shortened the life, I cannot say for sure if this shortened the life of the pump, but anecdotal observations seemed to say yes with some light duty pumps.

What I can say for sure is that adding the control valve on the inlet side of the pump will cause premature failure of the pump
So any control valves should be on the outlet.

You can also bleed off some of the excess water with a T valve

Resource:
www.americanaquariumproducts.com/PlumbingParts.html

Carl