Is a Pressure Relief Valve Necessary when using a Jet Pump?

[Dean Erger]

I’m installing a 1-½ HP Goulds J15S Jet Pump to pump water from a cistern. My pressure switch is set at 40/60 psi. Goulds says that the maximum shut off pressure for that pump is 80 psi (at five feet total suction lift).

Is it advisable that I install a pressure relief valve? If so, should I use a 75 psi or 100 psi valve?

 

[LLigetfa]

From the standpoint of protecting from over-pressure, the answer is no.

If you know for sure that the pump can go to 80 PSI, a 75 PSI PRV could save the pump from dead-heading and melting down. Problem is you cannot count on the PRV to be that accurate.

There is a temperature sensor marketed that supposedly will shut down a pump that gets too hot. I'm not talking about the motor, but rather the pump body.

 

[Sponsor]

 

[Dean Erger]

My cistern supplies water to the pump inlet at about 14 psi, so my uneducated guess is that if my pump can do a maximum of 80 psi at five feet total suction lift, it should easily be able to do 80 psi, maybe more, with water from my cistern.

 

[DonL]

You should install one if the pump or pressure tank manufacture recommends it, or local code requires it.

100 PSI would be a safe rating.


Good Luck.

 

[Valveman]

100 PSI will do no good if the pump can only build 80. Let the pump shut off at 60. Turn the pressure relief to the left until it starts leaking. Turn it to the right until it quits leaking, then another 1/4 turn. That is as close as you can get it.

 

[DonL]

100 PSI will do no good if the pump can only build 80. Let the pump shut off at 60. Turn the pressure relief to the left until it starts leaking. Turn it to the right until it quits leaking, then another 1/4 turn. That is as close as you can get it.

I agree.

It is a safety, and if the pump can only build 80, then it is not needed.


My guess is that, that pump will do more than 80, with the jet in it.

 

[Valveman]

I don't use a pressure relief valve to keep the pipe from exploding. I use it to keep the pump from melting down on a deadhead condition. I would use a pressure relief valve even if the pump could only build 30 PSI.

 

[DonL]

That sounds fair.

But why would a pump in that application Deadhead ?

 

[LLigetfa]

If the switch were to fuse shut, the pump would not shut off and could deadhead. A PRV set as valveman described would relieve and keep the pump from melting down.

If the OP had made mention right off of the +14 PSI head and not the 5 feet of suction, then it would have been obvious that the pump can exceed 80 PSI.

 

[Dean Erger]

Thanks for the very helpful advice. I’ll install a PRV, but I’d appreciate some basic plumbing advice.

What is the best way to join all the fittings shown in my diagram so that when I get them all sufficiently tightened the pressure switch and PRV are pointed in my desired directions? Should I just start at the bottom and tighten each fitting in turn, and then hold the PRV in place when I tighten the fittings above it - or is there a better method? (I realize that I wouldn't tighten the close nipples by themselves, but would tighten them by tightening the fittings above nipples.)

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