External pump plumbing, Non flooded condition

[eross13]

Has anyone had any luck in using an external pump in a non-flooded situation. Put another way, the intake of the pump is above the water line. I was considering using a check valve with an oversize pipe to keep the intake side primed. The pump is a mak4 and the height is about 2 feet.

Thanxs for your input. Pun not intended.

[ButterfyBoy]

I've not tried the check valve approach; I'm not sure if it won't just be an additional source of restriction / turbulence on the intake. Ideally, you want to attach something like a strainer basket chamber that can hold a fair bit of water and act as a priming chamber as well.

That said, all centrifugal pumps suffer substantial losses in efficiency when not installed flooded-suction. I don't even know if a mak4 can handle a two foot lift; even if it can I doubt you'd get much head out of the other end of it.

HTH

[eross13]

Butterfy, you mentioned a strainer basket? Are you talking about a inline chamber to hold some water in the pipe? Also the intake is 3/4, I was thinking about running an 1 inch to maybe help out. Maybe this would help or hinder it because of suction. Any other ideas on how to make this work?

[ButterfyBoy]

Are you talking about a inline chamber to hold some water in the pipe?

Exactly. Specifically, this chamber (which needs to be sealed) should be attached directly to the intake of the pump and hold a water level above that of the impeller chamber. The end result is that the pump essentially "sees" a flooded suction for priming purposes. This doesn't solve the efficiency issues, there's nothing really that can be done about the fact that centrifugal pumps just aren't built for suction.

Basically, the problem is that the pump has to rely on suction to lift the weight of the water in the line below it. Centrifugal pumps rely on conservation of momentum to basically "throw" water out of the impeller chamber. The only way in which they produce any suction is the fact that there is a very small low pressure zone is created when the water within the impeller is flung clear, and this draws new water in. But that draw is relatively weak.

Having the pump "lift" water is not really any different from putting a partially closed valve on the pump inlet and thus "starving" the pump. If you starve it too much, the pressure in the chamber will drop enough that the water will fall below its vapor point, and the pump will simply cavitate.

[AZDesertRat]

Most aquarium pumps require a positive suction head and will not lift water vertically. You are asking for trouble if you ask me. Its not worth taking a cahnce and losing a bunch of hard earned and possibly rare corals.

[eross13]

Thanks for the advice!