View Full Version : Pressure relief valve questions

10-02-2007, 01:08 PM
Hi all!!
This is my first post as I am a new member.
While I have read many closely related posts on this site, none seems to quite answer my questions. So here goes...........

I just had a shallow well installed (40' with submersible 1 hp Goulds pump) for irrigation only, and recently completed the irrigation installation.
I understand the need for a pressure relief valve (water hammer issues and deadheading the pump) but my question is how to plumb it in?? I have a large valve box at the well/pump outlet, so I believe it should be installed there.

Do I get a 1" (that's the mainline size) or step it down to a 3/4"?
Suppliers?? Plastic, Brass other??

Where/how do you plumb the water discharge for the relief side? to the ground??

I believe that it will most likely be set for 75 psi as the discharge side is approximately 60 psi. Correct?

Any help on this is GREATLY appreciated, and I look forward to any and ALL responses!!


Bob NH
10-02-2007, 01:26 PM
You need to plumb it off the a tee in the line from the pump to the tank. There must be no shutoff valves that could ever be closed to isolate the relief valve from the tank or the pump.

The valve must be sized to protect the tank. Most tanks will handle more than 100 psi and many pumps will exceed that at shutoff (low flow).

Determine the flow of the pump at the rated tank pressure. The valve must be large enough to discharge the flow of the pump at the safe pressure of the tank. A preset 75 psi, 3/4" valve will discharge a lot of water. If you need to pipe it anywhere the pipe should not have any thread on the end. A 3/4" Watts 530C costs about $20 at Grainger. I couldn't find the flow rating right now but I'm sure it's available.

10-02-2007, 04:05 PM
Thanks so much for responding!!
Let me clarify a little, there is no tank going in this system. I have the pump feeding the irrigation system directly, and is actuated by a pump start relay that is turned on by the irrgation controller.
I feel I need the pressure relief valve installed (as you pointed out), in the main line after the shutoff valve from the well/pump.
Does this information change the requirement, or your advice??

Bob NH
10-02-2007, 04:19 PM
The relief valve should be teed off a line where it will protect the pump and the pipes directly connected to the pump. The pump is the source of the pressure and it must be relieved if the pump is turned on while the valves to the irrigation system are closed. The relief pressure should be something less than the pressure that the pump will deliver at zero flow. That will ensure that the pump never pumps against a completely closed system.

Since you never expect to operate the pump at that point you can just let the relief valve dump out on the ground.

10-03-2007, 08:16 AM
I understand the need for a pressure relief valve (water hammer issues and deadheading the pump)

A pressure relief valve really doesn't have anything to do with water hammer. But it can save your pump in the event a valve doesn't open.


10-03-2007, 01:10 PM
Thanks so much for the excellent advice and clarification!!!