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I have an application that is drawing fluid from a reservoir via a standard dip tube. This application has a special requirement that once the fluid is depleted from the reservoir, the pump pulling liquid from the reservoir needs to shut off before drawing air into the system.

The function of this type of valve would be more or less the opposite of a floating shutoff valve used in toilet tanks where the floating mechanism closes the valve once the tank is filled. My application would do the opposite, where the float closes a valve on the dip tube or shuts of the pump once the tank is empty (or close to it).

Does anyone know if this type of valve exists on the market, or is it something I need to design on my own? Thanks!

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  • $\begingroup$ If you are ok with an electronic setup, you could use a float switch with a solenoid valve. It may need a relay to work opposite to the normal application. $\endgroup$ – morristtu Jul 18 '16 at 18:43
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    $\begingroup$ Just to clarify, are you looking for a non-electronic solution? $\endgroup$ – GisMofx Jul 18 '16 at 22:28
  • $\begingroup$ Yes, a purely mechanical solution would be preferable. $\endgroup$ – bgmaster Jul 19 '16 at 0:00
  • $\begingroup$ Do you want it to electrically shut off the pump, or just close off the pump inlet? $\endgroup$ – Ethan48 Jul 19 '16 at 0:42
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    $\begingroup$ And your pump is OK running indefinitely with a blocked inlet? $\endgroup$ – Ethan48 Jul 19 '16 at 13:34
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As I understand your problem, you have a pump mounted outside the tank that draws fluid via a dip tube, and you want to protect this pump from running dry.

You need to turn off the pump anyway once the tank is empty, so I would use a level switch (float, conductive, swing ... any will do) to shut off the pump and have a check valve on the line somewhere.

Many switches can be mounted above the tank so that you can service them without getting your hands wet. The valve should also be mounted dry. Make sure the pipe always ends under the water level, I would always leave 1,5 time the pipe diameter water in the tank and have 1x pipe diameter space between pipe end and floor.

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  • $\begingroup$ I am going to start trying this solution. Can you explain the purpose of the check valve further? What backflow would I want to prevent? I'll have to research level switches a bit further. Are those what are typically used in vehicle gas tanks to provide a reading on fuel levels? $\endgroup$ – bgmaster Jul 21 '16 at 15:53
  • $\begingroup$ The check valve prevents that water flows back into the tank when you shut of the pump, which also ensures that you don't get air into the suction pipe. A level switch gives a binary (on/off) signal only. $\endgroup$ – mart Jul 22 '16 at 5:47
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I'm running into a similar issue at the original poster. It seems like a workable mechanical solution would be to mount your float valve upside down, so as the water level drops, the valve would close. In my setup, I have several source tanks for irrigation. Because of the different height of the tanks, I need to automate the shutoff of the two higher tanks as the water is pumped out so the pump will start to draw from a lower level tank as flow is shut off from the higher level tank.

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