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Old 05-25-2022, 09:02 AM   #1
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Pressure switch, not RV related

This is not RV related but I think someone here on iRV2 can help.

My irrigation system is powered by a rather expensive 220 volt pump with water from a lake. I'm concerned that if for some reason the water to the pump is stopped, (broken pipe, lake level low) and the pump continues to run, the pump would be ruined. So I would like to install a pressure switch on the output side that would disconnect electrical power to the pump if there is no flow to the pump when it is running. The pump output pressure is normally 50-60 psi. When the pump stops, the output side does not retain pressure and pressure on the output side drops to 0.


So does anyone know of such a pressure switch? The only thing I can come with is a pressure sensing relay, but it would have to include a timer to give the pump enough time to build pressure after it started before shutting the pump down if it did not build pressure.
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Old 05-25-2022, 09:10 AM   #2
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You use the NC contacts in a “time delay on” relay that allows the pump to run for a second or two before it opens the contacts, and a pressure switch on the output of the pump whose connections are across that set of contacts.
Those contacts then power the contactor coil for the pump.
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Old 05-25-2022, 09:41 AM   #3
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Every well pump I have ever been around had a pressure switch on pump discharge with delay relay

Just Goggle 'Well Pump Pressure Switch'
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Old 05-25-2022, 10:00 AM   #4
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Thanks Mark, let me see if I've got this right. When power is supplied to the NC time delay relay, the pump contacts which are closed and the pump starts. Lets say for 10 seconds. During that 10 seconds the pump pressure builds and the pressure switch closes. After 10 sec this relay opens. At this point I'm a little foggy.

Are you suggesting a 2nd NO relay is added wired in parallel to the NC time relay where the closed pressure switch allows power to the coil of this second relay thus closing the relay and allowing the pump to continue running after the 10 sec relay has opened?
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Old 05-25-2022, 10:02 AM   #5
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Originally Posted by Old-Biscuit View Post
Every well pump I have ever been around had a pressure switch on pump discharge with delay relay

Just Goggle 'Well Pump Pressure Switch'

I think most of those switches turn off power to the pump when the pressure reaches the cut off point. I want the opposite, power removed from the pump if it drops to 0.
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Old 05-25-2022, 10:19 AM   #6
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.

My house is on a pump. I installed a Square D control for exactly this event. On/off at "you" set limit. AND it also shuts off if the pressure falls below a "you set" level.

If your system is asking for pressure and it runs dry the pump shuts down.

It is a Class: 9013 Type: FSG 2 Form: M4 Ser: B

Sorry it doesn't show a part number. Just ask a pump supplier and they can provide that number.

regards Glenn
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Old 05-25-2022, 10:33 AM   #7
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Thanks Mark, let me see if I've got this right. When power is supplied to the NC time delay relay, the pump contacts are closed and the pump starts. Lets say for 10 seconds. During that 10 seconds the pump pressure builds and the pressure switch closes. After 10 sec this relay opens. At this point I'm a little foggy.

Are you suggesting a 2nd NO relay is added wired in parallel to the NC time relay where the closed pressure switch allows power to the coil of this second relay thus closing the relay and allowing the pump to continue running after the 10 sec relay has opened?
You got the first part right.

Your pump should have a contactor or relay that is driven by the output from your irrigation controller.

You take that signal off of the existing pump relay and feed it to an NC terminal of a time delay relay (tdr) and to the coil of the tdr.
You then take the wires from the pressure switch and parallel with the above NC and C contacts.

And you take a wire from the C contact of the tdr back to the pump relay where the wire was previously removed.

Operation -

Pressure switch is open
NC contacts of tdr are of course, closed.

1) Irrigation controller calls for pump
2) Pump starts as NC contacts are closed, but pressure switch contacts are open.
3) Pressure builds and satisfies pressure switch - they are now closed.
4) tdr times out, NC contacts open
5a) if pressure switch is satisfied, pump continues to run
5b) if pressure switch is not satisfied, pump stops
6) tdr remains latched (NC contacts are open) until power is removed from circuit - but at this point the tdr is out of the circuit

Let me know if you need a sketch
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Old 05-25-2022, 10:36 AM   #8
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.

My house is on a pump. I installed a Square D control for exactly this event. On/off at "you" set limit. AND it also shuts off if the pressure falls below a "you set" level.

If your system is asking for pressure and it runs dry the pump shuts down.

It is a Class: 9013 Type: FSG 2 Form: M4 Ser: B

Sorry it doesn't show a part number. Just ask a pump supplier and they can provide that number.

regards Glenn
YEP^^^^^^^^^
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Old 05-25-2022, 11:32 AM   #9
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With all due respect - depending on the design of the irrigation system, there may not be any pressure in the pump discharge line when the controller tells the pump to run.

The Square D Pumptroller requires there to be pressure in the discharge pipe such as for a fresh water or fire safety system. The delta between the settings allows for pressure fluctuations. But that control will not allow the pump to run if there is no initial pressure at the pump discharge.

Many irrigation controllers provide for pump control. And when the last station is finished, it simultaneously cuts the signal to the pump and to the valve that is currently open.
But irrigation valves don’t slam shut, and close even more slowly the lower the pressure differential across the valve is. Hence, the pumps discharge line pressure could very well fall below that of the low pressure setting of the Pumptrol, if not 0 psi.

Either stated methodology would work - it’s just that one would likely be a little more problematic than the other.
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Old 05-25-2022, 12:35 PM   #10
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YEP^^^^^^^^^
When I googled that part it came up with a well pump controller. It did have a low pressure cutoff circuit but you have to manually start the pump each time. After you manually started the pump then if pressure dropped below 5 psi the pump would shut off. At least that's how I understand it. Am I wrong??
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Old 05-25-2022, 12:40 PM   #11
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Mark, I know the diagram below is not how you described the circuitry. I think in my diagram voltage would back feed back to the circuit breakers during the time between the low pressure switch closed and the time delay ended. Could you please correct the diagram?
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Old 05-25-2022, 02:24 PM   #12
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Easier for me to just draw by hand (I’ve lost all my chair licenses to AutoCAD).

Let me know if you need it drawn as a wiring diagram.
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Old 05-25-2022, 02:30 PM   #13
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Thanks Mark. Hate to ask but I think I need it as a wiring diagram. Also do you know where to get a flow sensor and time delay relay. I can't believe how hard to find these items has been. I haven't been able to find a time delay relay that is 30 amps and flow switches are just not made for this. I guess I could use an automotive oil pressure switch.
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Old 05-25-2022, 02:47 PM   #14
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You need a low pressure cut off switch. I got one from a reverse osmosis water system that I use to control the electric element in my RV water heater. The pump in the RO system pressurizes the plumbing, if the filter hasn't made enough water for the pump to do that the low pressure switch won't close and the pump won't run, or quits running.


Use that to control a relay capable of the power your pump draws.
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