[APD] HOB as overflow?

[Mike Wickham <mewickham at compuserve_com>]

Candy,

 >> Has anyone tried to convert a hob power filter to a overflow for a
 >> sump?... The In theory using a hob would also be self priming if the
 >> power went out.

It won't work-- not if you run the filter motor. It would be okay to use
the filter box (filter turned off!) to convert into a hang-on-the-back
overflow. (It would be a lot cheaper to buy a Lee's specimen container for
conversion, though!)

One must never put two pumps into the overflow loop (in this case the
filter pump and the sump pump). There is no way to balance the flow between
the two. The flow in one will always be stronger than the flow in the
other, no matter how much you tweak valves. Inevitably, the pump from one
container will overflow the other. If your filter pump is stronger than the
sump return pump, then more water will flow down into the sump than the
filter can remove. Since the filter intake usually hangs 3/4 the way to the
tank bottom, that means 3/4 of the water in your tank can be overpumped to
the sump and flood your floor. Likewise, if the sump pump is stronger than
the overflow, it can empty nearly the entire sump into the tank-- and flood
the tank.

Pumps should always be in the sump. Gravity moves the water downhill and
the pump moves it back uphill. Any other design WILL fail.

Mike Wickham

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