1

I have a water tank that is on a higher elevation that needs to be filled with water from the bottom tank. Would it be possible for the the pump to be on the top? This will greatly save me some money on the wiring cost and basically the safety of my control system equipment and pump as it wont be in a public area.

One of the most obvious problem is water from the top tank will go back to the lower tank, but placing a check valve solves that problem.

My second problem is a portion of the piping has to go above by 50cm above the tank, the issue with this I will be losing the "prime" of my pump, as water inside the higher elevation pipe will go to the tank. My solution to this is maybe to put a secondary check valve before the motor and rely on the minimum pressure for the check valve not to open.

Is there a better way of doing this?

I measured the height and lowest to highest point is 8m. Single pipe 3/4 inch inner diameter. The motor is a 1HP unfortunately the brand is unreadable, but it looks like a centrifugal pump (inlet in the middle and outlet on the top).

enter image description here

7
  • @isherwood Theoretically there will always be water above the pump as the tank is on a bit of higher elevation than the pump, its the air on the elevated pipe is what im concerned of. If possible i would like to reuse my old pump( i will follow up on the exact model) but what type of pump should i look out for if i can use it?
    – DrakeJest
    Apr 5, 2023 at 15:52
  • You didn't mention the total height of lift. Using a single pipe, the greatest possible lift with the pump at the top is just about 10 meters. For that height, the pump would quickly fail due to cavitation. The practical limit is more like 7-8 meters. So if the lift is greater and you have only a single pipe, the pump needs to be down below. (With 2 pipes you could use a jet pump at the top and lift about 25 meters, but I don't think anyone here would recommend it -- losing prime is a big hassle.)
    – MTA
    Apr 5, 2023 at 17:14
  • What is the tank you're pumping into feeding? Plumbing fixtures? Irrigation? Some sort of process? Fire sprinklers? Apr 6, 2023 at 2:08
  • @ThreePhaseEel water tank, non pottable water, the sort you wash your dishes with, take a bath with, etc. They are your typical non pressurized stainless tanks that holds water.
    – DrakeJest
    Apr 7, 2023 at 15:56
  • 1
    @isherwood i doubt the maker of this motor makes manual that detailed, so im out of luck there. Might be a cultural difference but the water is clear and generally clean. we just dont drink it, at the bare minimum is boiling it, normally we have it filtered and placed in water dispenser containers.
    – DrakeJest
    Apr 7, 2023 at 16:12

1 Answer 1

3

In your comments you mention that this is a centrifugal pump. This will not self-prime by sucking air until water reaches the pump. For that, you need a positive displacement pump such as a gear pump or a diaphragm pump.

In addition, ordinary centrifugal pumps are not known for having great suction to lift the water the 8 meters that you mentioned in your comments. For that, again, you would need a positive displacement pump.

Unless you have or can get specifications for the existing pump, I think an 8 meter lift from an ordinary centrifugal pump is a big challenge even if you find a way to prime the pump and the entire line by eliminating all air. And the slightest air leak on the suction side will make the system lose prime between pump cycles.

The best long-term solution for trouble-free operation is to run power to the lower tank and use a submersible cistern pump. These work just like a submersible well pump with excellent pressure and flow rate, and will easily pump against an 8 meter head.

For the lowest cost, but at greatly reduced flow, install a new diaphragm pump where the existing pump is located, but be sure to check specifications to confirm that it can manage 8 meters of suction.

2
  • Im planning to try it anyway as the additional components are not that expensive less than 20$ and will take me less than an hour to do. But atleast i now have the expectation that it will not work, i will not be scratching my head why it is not working. Makes me wonder though if assuming the pipe is airtight and primed why cant a centrifugal pump have not same suuction as its ouput.
    – DrakeJest
    Apr 8, 2023 at 11:14
  • @DrakeJest A positive displacement pump at the top will create a partial vacuum that allows the atmosphere over the lower tank to push the water up the pipe. With a perfect vacuum at the top, the atmosphere can push the water no higher than 10.3 meters. At that point, any further mechanical suction only serves to pull the water apart to create water vapor. The cold water literally boils vapor from the top of the water column but the liquid will rise no higher. An ordinary centrifugal pump can not make such low pressure, so all such pumps can pump much higher than they can draw.
    – MTA
    Apr 8, 2023 at 14:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.