Pressure Tank prevents Cut-off Switch when well runs dry

[MANaboutTOOLS]

I have a shallow irrigation well that runs dry in late summer. I have a 3/4hp pump with a 30/50 switch and low pressure cut-off. And I have a pressure tank. When the well runs dry the pump will continue to run, overheat, and melt my plastic fittings. Water will spray out and only then will the pressure drop enough to shut down. When it's in this dry run situation the pressure gauge reads approx 26psi even though it's not moving any water. I suspect the pressure tank is interfering here as it is set to just below the cut in pressure (also close to 26psi). Any advice would be helpful. Thanks!

 

[Valveman]

This is exactly the scenario I try to explain to people as to why a low pressure cut off switch is not reliable for protecting a pump from running dry. You have to be using water when the dry run happens or the pump will not shut off as you said.

Using low amps as an indicator of a pump running dry is much more dependable. Amps drop no matter the pressure. A Cycle Sensor looks for low amps and shuts the pump off before things start melting. With a Jet pump you set the Restart Delay for 000, which means manual reset.

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[MANaboutTOOLS]

Thanks! I have ordered one.

 

[Chris E]

This very close to my house situation, 1/2hp jet pump, well runs dry, doesn't trip the low pressure switch till the line has blown off. Currently have been carefully managing how long the pump can stay on, would really like to automate that!
With a Cycle Stop, does it need to be set to 000 and have to manually reset?

 

[Valveman]

To protect the pump from running dry you need a Cycle Sensor, not a Cycle Stop Valve. And yes, when working with a jet pump the restart delay needs to be set at 000 so it will not reset automatically. After pumping air a submersible does not need priming and can be set to come back on automatically after a certain amount of time. A jet pump will need to be primed, so the Cycle Sensor needs to be set for manual reset as well.

 

[Chris E]

My bad, I was thinking of the Cycle Sensor! How long before it shuts off when the amperage drops?

 

[Valveman]

10 seconds.

 

[Chris E]

I see, thank you! Is it the same with the Pumpsaver, or do you know?

 

[Valveman]

Not sure.

 

[Chucky_ott]

@Valveman , the Cycle Sensor only works with 230V, right ? No 115V model if I recall?

I had the exact same issue as the OP and considered a Cycle Sensor at the time. But I seem to remember that it only worked with 230V and I did not have 230V at my pump.

What I did was put a temperature relief valve on my pump.

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When the pump dead heads and the water overheats, the valve will release water until the low pressure cutoff powers off the pump.

 

[Valveman]

Hope it works for you. You are correct we no longer make a 115V version of the Cycle Sensor. But that motor should be dual voltage and able to run on 230V if you wanted. Never had much luck with heat sensors. By the time they get hot enough to pop off the pump can be damaged. If the temp set point is lowered, many times they would pop off just from the heat in the well house with our hot southern climate. I am also not sure that will pop off enough flow to get the pump to the low pressure cut off setting, but maybe.

 

[Chucky_ott]

It probably does. But I only have a two conductor cable to the pump house. If I want 240v, I'd need another (underground) wire. I know I could use the existing two wires for 240v but I'd have to give up the 120v, which I need for other stuff.

The temperature valve trips at 40C if I remember correctly. Fortunately (or unfortunately) I never had to test it. After my pipe melted the first time, I fixed the underlying issue and I haven't had a problem since. Unlike the OP, my well wasn't running dry. Rather, I had a suction leak and the pump was losing prime.

 

[Reach4]

With a Jet pump you set the Restart Delay for 000, which means manual reset.

Would having a "self priming" jet pump let you have auto-restart, or is that just too slow to reprime itself?

 

[Valveman]

Might work for you in cold country. 40C is 104F. I would have to air condition my well house to keep the ambient temperature from popping it off. Lol! Don't know if it would be code, but I think you could split off of the 240V at the well house and still have the 115V.