24v control circuit

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  #1  
Old 06-16-14, 12:49 PM
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24v control circuit

Hi,

I have a 24vdc control circuit I am using in an irrigation system. I have a pressure switch which stops the pump at high pressure . There is a slight weep somewhere in the pipework which drops the pressure and the switch starts the pump again for a few seconds and then stops again. I would like to include a remote reset button so when the pressure switch operates for high pressure it would not start again until the reset button is pressed. Anyone recommend what I should use here please?

Jim
 
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Old 06-16-14, 01:21 PM
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More commonly I have seen systems wired so the pump can only run when an irrigation zone is activated. This prevents the pump from cycling on/off if there is a slight leak when the system is not being used.
 
  #3  
Old 06-16-14, 01:57 PM
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You will need a "MO" ( motor-on" ) relay with two Normally-Open (NO) contacts and one Normally-Closed (NC ) contact---- a "MS" relay ( motor-started) with two Normally-Open (NO) contacts- -- a "LO" ( lock-out ) relay with one Normally-Closed (NC) contact.

With the pressure-switch contact-action viewed as "Normally-Closed", the contacts opening on a pressure-rise as a high-limit opens on a temperature-rise, the operate-circuit for the "MO" relay is the NC pressure-switch contacts in series with the NC contacts of the "LO" relay.

One NO contact of the "MO" relay completes a circuit to the operating coil of a contactor that connects the pump to the line-circuit. The other "MO" NO contact closes a circuit to the "MS" relay thru the NC contacts of a "Reset" button. A "MS" NO contact "shunts" the NO contact of the "MS" relay so the "MS" relay remains operated thru the NC contacts of the "Reset" button.

When the NC contacts of the pressure-switch open , the "MO" relay is released , and the "LO" relay operates thru the NO contacts of the "MS" relay , the NC contacts of the "MO" relay , and the NC contacts of the "Reset button. The NC contacts of the "LO" relay opens the operate-circuit of
the "MO" relay.

The "MS" and "LO" relays remain operated until the NC contacts of the "Reset" button opens when the button is pushed.
 
  #4  
Old 06-16-14, 02:47 PM
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I think a latching relay would be a simple solution.

High pressure switch latches the relay and holds it till the reset coil is energized.
 
  #5  
Old 06-17-14, 04:10 AM
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Originally Posted by Pilot Dane
More commonly I have seen systems wired so the pump can only run when an irrigation zone is activated. This prevents the pump from cycling on/off if there is a slight leak when the system is not being used.
Agreed. A simple on/off switch on the +24VDC relay coil wire will disable the system when it's not in use.
 
  #6  
Old 06-23-14, 01:21 PM
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Hi,

I am struggling to create the latch relay circuit here! I have 2 switches in the circuit , one float switch which is effectively the start stop for the pump ( tank full pump on, tank empty pump off, and the high pressure switch which I would like too be the overall cutout. No sure how to wire this correctly, any help would be gratefully received.

In answer to Rick, the irrigation system may pressurize in the middle of the night as it is a travel sprinkler so unable to put a on/off switch in, although I would prob include one as a safety measure I think??

Jim
 
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