Submersible pump question

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Old 10-14-15, 10:01 PM
Z
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Submersible pump question

Does a submersible pump have to be fully submerged in order to function properly? Or is it model/design/manufacturer dependent?

If it need not be fully submerged, then will keeping it primed become an issue?

My intended application will sometimes only have a few inches of water.

Thank you very much for your insights.
 
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Old 10-14-15, 10:47 PM
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I use a submersible pump like in the picture for my pool cover. It pumps down to about 1/2".

Most submersible pumps have a slotted or screened area at the bottom where the water is drawn in. Usually as long as that part is underwater it will work...... around 2"-4". The exact amount of water is type dependent.

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Old 10-16-15, 12:03 AM
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Thank you for your reply, PJ. It is comforting to know that the pump need not be completely submerged in order to function -- It can't be, as you will understand below.

My application is to pump water from a river up some 40-50 feet to a holding tank. The electrical power for the pump will be controlled by a sensor switch inside that tank.

The pump will be installed on a raft that will float up and down with the water level of the river. My concern is that the water surface can become choppy, due to wind action, and the pump intake may rise above water level for short intervals. However, OTOH, if I lower the pump too far, or submerge it, then the intake will be damaged on the rocks.

Thus my questions:
1) Are submersible pumps designed to tolerate occasional "air pockets" while running, and to then resume pumping?
2) If the air voids occur when the pump is not running, will the pump lose it's prime?

Thank you very much for your thoughts,
 
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Old 10-16-15, 12:43 AM
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Submersible pumps are self priming. If it picks up a little air.... it will re-prime when under water again. You'd want the pump partially under water to stay cool too if you're talking about long pumping times.

Up 40'-50' is pretty high. Make sure the pump you get lists 50' of head in it's performance rating. The head is how high the pump needs to push the water up.
 
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Old 10-16-15, 11:02 AM
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Instead of dealing with a raft concept, why don't you create your own little sump pit in the river? Not quite the size river you're talking about, so you may need to scale up/down based on the flow, but the basics are the same:

Dig a 2'x2'x2' hole in the river and box it in with concrete blocks. Put one block in the center of the pit and the pump secured (somehow) on top of that block. Set it up so the lowest water level is always over your walled pit. What you've done is created a box of 'clean' water that will always be under water, perfect for the pump. No rocks or silt to compromise the pump.

It may need to cleaned out occasionally, but I think the concept would work.

-Mike
 
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Old 10-18-15, 04:49 AM
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Zorftd: Your concept is clean and satisfying -- thank you!

However it is the details here on the ground that you have no way to be familiar with. The river has a few rocky shoals, but mainly it is covered in deep sandy silt -- that rearranges itself every year during the high-water season.. So I'm afraid that the box, along with the pump, would find itself buried pretty quickly.

The second problem would be fishermen's boat anchors. (If they can't see it, it doesn't exist. ) With a raft however, at least they know that there is a cable there -- which can be a real nuisance for boat propellers to avoid.

But please accept my thanks for your idea -- I appreciate your taking the time!
 
 

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