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Waterpump cutoff (for broken pipe)

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rustycarr

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I'm looking for a way to stop a 240vac pressure pump on a rainwater tank, if a pipe breaks. Pressure pumps normally turn on an off as you are using them . The pressure "bulb" (like on an air compressor tank) turns on and off as you are using them. The electric motor turns on an off to keep the pressure constant.

However when a pipe breaks the pump will run continuosly until all the water is gone and overheats the pump and destroys it.
I'm looking for something that will turn of the power supply if the pump runs continously
for half an hour, or hour.
I had ideas of a VOX (as thats how I know a pump is going) But if you are away from home thats no good. A mic on the pump, or a current sensing device.
 
Would pressure work?

A way that's used to protect motors is a thermal switch on the pump itself.

Vibration is probably too expensive and may not work.

Continuous run time is another?

A delay on make timer, used with a dual coil latching relay could possibly work. This would not reset with a power outage. A second switch would reset the system. I'm not sure if dual-coil latching relays are available in an AC coil.

As the contactor is engages, the delay on make relay would be started. If the delay on make completes, the reset coil on the latching relay would be engaged.

A separate button will be used to engage the set coil.

The contact/contacts could be used to disable the pump and light a trouble indicator.

You may need a DC supply.

Here https://www.electro-tech-online.com/custompdfs/2011/03/MY2K.pdf is an AC relay. The diagram is difficult to understand. 24 VDC is a typical industrial control voltage.

The hard part is picking parts.

What activates the coil on the relay that controls the pump? What's the voltage?

Take a look at SSAC Timers & Controls Home Page,


Level sensing in another option.
 
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You can use the fact that thare is line voltage across the presser switch when it is open (pump off) and 0 volts when it is closed (pump on) to trigger a timing relay. Andy
 
If the system is pressurized, a simple solution is a low-pressure cut-off pressure switch, which will shutdown the pump when the pressure falls below ~15-20PSI until manually reset. One manuf. of such common here in the US is Square D. Where are you located on our island in space? If not that type of system...

Years ago when I went back to school, I did a project on this very thing; detecting when a problem occurred when a pump broke suction. Without a load, the pump moving water, the motor current will drop. That is what you need to detect to shutdown the pump. Let me look through my archives and see if I have the info still on record somewhere.

In the meantime, please provide any info you have on the motor as to HP, load current, etc.
 
Does the run-time circuit description make any sense to you?
Sort of, seems pretty complicated to me. Thare has to be a easyer way. You know keep it simple.
Andy
 
Here: http://www.ssac.com/timerscat/Sect5DOM.pdf the TRM series on PDF page 4.

If the Coil is activated when the pump turns on, that's the activation signal. If the timer completes, it would turn on the RESET coil of the relay.

Each coil of a latching relay is held magnetically therefore a continuous energizing and a pulse will activate it.
DC latching relays are easier to understand because the polarity of the coil determines whether the contact bar is pushed toward or away from say the NO contacts. The single coil latching relay uses a change of polarity to latch and unlatch the contact.

So, once this relay is latched, if the system looses power, the relay stays in its previous position. Once it's latched, then the motor contactor coil would be unable to get power.

The SET coil would just be activated with a pushbutton.

The total # of components is possibly 3.

A small DC power supply might make sourceing the delay on break relay easier.

Power failures will not cause any issues with operation.

Additional options is the use of "alarm contacts" or "indicator lamps". 24 VDC is common for industrial controls.

To me a DPDT latching relay would make sense. One contact for "contactor disable" and the other for "Indicator or alarm".

Now does it make sense?
 
Here is a dual coil DPDT 24 VDC latching relay. Lots of info on this page: **broken link removed**

They are available with AC activation.

If this was industry, 24 VDC would be the way to go.
 
A cheap and reliable way is using a water level switch as mounted in laundry washers.

Many of them are adjustable.

Adjust the switch to be pressurized when water leaves the end of the pipe and activate it with the pump.

As soon as the pipe is interrupted the pressure drops to zero which makes the switch open, and hence make a usable signal to switch off the pump.

Boncuk
 
I would use a circuit around ronsimpson's suggestion or Boncuk's suggestion. I just see using line pressure as a problem. Float switches or the pressure type switch Boncuk suggest just seems a simple and more reliable solution. I would also keep my control voltages low around 12 or 24 VAC.

Just My Take
Ron
 

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can you monitor the other end of the system, to see if the water is arriving? if it isn't then there is a leak and shut off the pump
 
The 'no flow= pump off' and 'low pressure=pump off' is like the chicken & egg. If there is no flow, how do you start the pump or keep it on until water flows and the pressure gets up. I would use a manual over ride button where you force the pump on until it is up and running. A small hiccup or a small drop in power and this is off.
 
I think my design goal is similar - I want to cut the pump off if it runs too long (over 15 minutes in a 1 hour period) or if it runs hot, or if there's no water coming in.

I'm going to use a little PIC processor to be the smarts. The tough part for me is detecting when the inflow is happening. Best idea so far is to use a forward biased NPN transistor as a thermometer - with a little more current than normal to provide a minor heating effect. If water's flowing, it will cool the transistor.

Not simple, but I haven't heard of a simple solution that ticks all the boxes.
 
A typical way of doing this is to mount a thermal switch in the motor. A "roots blower" vacuum pump that I used did have the option and it was used to shut down the pump. This particular pump dropped out on a power failure.

You basically have to monitor the bearing temp and latch a shutdown, A magnetic latching relay would work fine here.
 
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