"Ian Stirling" wrote in message
...
In uk.d-i-y Jeff Lowe wrote:

"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

Cavitation is a real concern if you put it on the input.
This does cause RAPID wear on the impeller.

Since we were talking about lamp dimmers I guess I assumed we were talking
fractional horsepower. I didn't think these capable of enough suction get
below water's vapor pressure at pond temperature. I mean that's 29" Hg. Of
course some ponds and pumps are bigger than others ;-)

Jeff