"Tim Downie" wrote in message
...
Gale Pearce wrote:
You can restrict the outflow side of the pump, but not the intake or
you will burn out your pump prematurely - I use a "ball valve" to
reduce the waterflow on my submersible pump on the line to my filter
Gale :~)

I've already got a restrictor and T-piece on the pump outlet so I can
control the output at present. Somehow it doesn't feel "right" to reduce
the flow this way. I can't help feeling that it's putting extra load on
the
pump. As I have a reasonably hefty lamp dimmer kicking around, I was
just
wondering if using a device like this would be more mechanically
"sympathetic" IYKWIM. (Probably complete nonsense I know).

Since these are just turbine pumps, there is no difference as far as the
pump is concerned as to the location of the restriction on either the input
or output. I would not use a lamp dimmer since these are typically just
triacs and have a spiky output waveform which will cause motor heating,
however a variable speed control for a ceiling fan should work fine. One
other aspect to be aware of is that many pumps use either a fan or in the
case of submersibles, water to cool the motor. In this case any restriction
of flow, either by speed control, or by restriction may result in some
heating and should be watched.

Jeff Lowe