Pump start relay/ pressure switch

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JLC

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Ok, I see this topic all over the place but I can never find a definitive answer to my confusion. I am pulling water from a lake and have a 2 valve manifold operated by a controller. Why exactly is a pump start relay needed when there is a pressure switch with a low pressure shut off? I understand the whole controller turning the pump on but isnt that the same thing the pressure switch does? Thanks in advance.
 

WorthFlorida

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I think in your situation it is used as a fail save measure. Should you lose prime, etc, it will save the pump so you are not running dry. Usually the low pressure switch is used to turn on a pump. It sounds from your description some smartly wired it to shut the pump off.
 

Reach4

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Irrigation controllers and systems are often used where there is no pressure switch or pressure tank.
 
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JLC

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I think in your situation it is used as a fail save measure. Should you lose prime, etc, it will save the pump so you are not running dry. Usually the low pressure switch is used to turn on a pump. It sounds from your description some smartly wired it to shut the pump off.

Correct me if Im wrong. A low pressure shut off pressure switch is to shut the pump off if pressure drops too far below the kick in pressure.
 

WorthFlorida

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JLC

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Not to sound rude but this is exactly what I was saying. Except I called it a low pressure shut off instead of cutoff.
My confusion is why is a pump start relay needed if the pressure switch pretty much does the same thing. All I can find is that when pulling from a lake, the relay is imminent. Thanks
 

Reach4

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I still find your situation confusing. What controls your pump start relay? Is this part of an irrigation controller?
Is this water being used for both irrigation and house use?
 

JLC

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I still find your situation confusing. What controls your pump start relay? Is this part of an irrigation controller?
Is this water being used for both irrigation and house use?

Im working on installing a sprinkler system and pumping water out of a lake. I want to operate it with a controller ( timer/programmer) so I can program it to run some days during the week when Im not there. Its irrigation only. I am only asking for a definitive answer as to why the pump start relay is needed if there is already a pressure switch with low pressure cut off. Its mainly because I dont fully understand and I would like to know the reasoning.
 

Reach4

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I am only asking for a definitive answer as to why the pump start relay is needed if there is already a pressure switch with low pressure cut off.
Why is there a pressure switch? The answer to that would normally be that you want a spigot with water available at the turn of a knob.

If only sprinkling, then no pressure tank and no pressure switch would be needed.

I suspect you are looking at an existing system. Somebody else put in a separate relay, OR the relay is part of an irrigation controller. You are asking why that original person put in that relay, I guess. And the answer could be that the system evolved.

It could also be that the pressure switch and pump start relay are wired in parallel, so that running the sprinklers or the pressure switch calling for pressure could start the pump.
 
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