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I have a pump connected to a water tank.
The city water fills the tank through a (mechanical) float valve (to prevent overfill).
And the pump's inlet is connected to both the tank's outlet, and also the city water pipe (through two check valves, so that the tank won't be over-filled through its outlet).

The problem is that, if the tank is empty, the pump will suck air through the tank (instead of just sucking water through the city water pipe).
The solution I thought of was to mount a float valve, albeit inverted, to the outlet of the tank, so that when the tank is empty, it would shut the outlet.

Would this solution work? would there be any problems with it?

Edit:
A Schematic of what I'm trying to setup: enter image description here

The reason I want the city water pipe to be connected directly to the pump is because of low city water pressure which could fail to keep up with the rate at which the water is getting depleted from the tank, especially if the consumption is high (and the tank could go dry).

The problem is that I think if the tank goes dry, even with the city water pipe connected to the pump's inlet, it will suck air through the empty tank.

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    Wait, isn't the city water line under considerable pressure (like municipal water systems typically are)? If so, how come water is even pulled from the tank instead of city water just flowing freely through the pump? And why is the pump even connected to city water when the same water is also used to fill the tank?
    – TooTea
    Mar 9, 2022 at 10:00
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    It might help to include a diagram of your setup, as this strikes me as a reasonably uncommon setup for those of us in the US (where many of your answerers are).
    – FreeMan
    Mar 9, 2022 at 13:12
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    Why not just always pump from the tank and put a float switch in the tank to prevent pumping when it's dry? If city water is available then it'll fill the tank as you pump from it.
    – brhans
    Mar 9, 2022 at 18:44
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    Do you need the city water to go through the pump? Would the city water pressure be enough?
    – Polypipe Wrangler
    Mar 9, 2022 at 22:36
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    If use is > supply from utilities then tank will empty. If it empties, it will suck air - no choice. Only way is to reduce use, so water supply can catch up. Pump shutoff on empty will do this, allowing tank to fill. If u really want more storage, add more and larger tanks.
    – Chris
    Mar 10, 2022 at 0:10

1 Answer 1

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Shutting the outlet will not protect the pump.

Fit a float switch to turn the pump off when the level is too low.

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2
  • But I want the pump to keep running (and getting fed directly from the city water pipe ...)
    – Microsoft Linux TM
    Mar 9, 2022 at 7:40
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    @MicrosoftLinuxTM then connect the pump to the city pipe.
    – Solar Mike
    Mar 9, 2022 at 8:40

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