Filter pump height?

[Dave Smith]

I have a 50 gallon tank and am using a Fluval404 canister filter to
filter and circulate the water through a reverse undergravel setup. I
have the Fluval mounted in the cabinet that the tank sits on, so the
rotor for the pump is about three feet below the surface of the water.
I've always thought that since it is a closed system, the height of
the water above the pump is not an issue. A friend insists that if I
raise the pump to reduce the "head" that it will pump more
efficiently.

What's the truth?

Thanks very much.

[Billy]

"pausto" > wrote in message
...
>
> You are correct, lift isn't an issue with a closed system. Only
> loss due to friction (line length and diameter) and fittings.
>
> Paul

Yup. With canister filters, siphon is the primary force at work once
it's primed.:)

[Bart van Herk]

>>I've always thought that since it is a closed system, the height of
the water above the pump is not an issue. A friend insists that if I
raise the pump to reduce the "head" that it will pump more
efficiently.
<<

1) it isn't closed, the aquarium is presumably open on the top.
2) But the inlet to the pump has the same hydrostatic pressure as the outlet
so the pump doesnt have to pump against gravity. you are still right.