Do I need a Pressure Releif Valve

I am setting up a newly designed system that uses an existing Goulds 1/2 HP jet pump on a shallow (dug) well (15 ft). My new tank T has room for either a drain OR a PRV, but I want the drain. I was told that this pump might not create the 100 PSI needed to blow the PRV, so just put in the drain and forget the PRV. Does this sound like a good idea? My new Well Mate fiberglass tank doesn't want to ever see 100 psi. Pump must push 150 ft horizontal and 30 ft vertical to the tank.

thanks,
Rick

I don't know what the codes are, but I think I'd be somewhat appreshensive about not having that safety device installed. A fiberglass tank, well, any tank, that exceeds the design pressure can explode. Now, they usually have a pretty big safety margin, but I'd want to keep things in check (pun intended).

I'm trying to avoid adding more T's, to keep the system as clean as possible.

Find the pressure rating of your tank. Then, find the shutoff pressure rating or your pump; considering the lift that is required.

If the shutoff head for the pump exceeds the pressure rating of the tank by more than maybe 5 psi, then you should have a relief valve.

That ½ HP jet pump will build a maximum of 63 PSI. It is not going to blow anything up. However, you still need a pressure relief valve. It needs to be adjustable and set at about 60 PSI. The pressure relief is just as important to prevent the pump from dead heading as it is to keep from blowing something up. When the pressure switch sticks closed from the pump cycling on and off too much, the pressure relief must discharge water before the dead head pressure of the pump. This keeps the pump from melting down, not just protects the system from high pressure.

It only takes about 5 or 10 minutes to melt down a pump when dead headed. A T&P valve is installed too far away from the pump to ever pop off on temperature. Even though a ½ HP is smaller than the rating of the switch, excessive cycling will still cause the switch to melt together. Most relief valves, even though already set at 75 PSI, are still adjustable. Most people do not set a pressure relief valve to protect the pump because it takes someone with knowledge about pumps to understand this.

When I have a problem with an overheat it's usually because of someone installing a pressure switch on a self priming centrifugal. The water table drops a few feet, the pump can't shut off and the pumps impeller, diffuser and PVC piping usually nuke. When this happens, I install a Hot Stop Thermostat. When it senses 110° it shuts off the motor then restarts it at 90°. I have one on my shallow well at home. I installed a two stage centrifugal which has a bad habit of doing the exact thing I mentioned above.

I think Valvemans has a good idea also, I have never tried it or even thought of it, but that shows how things differ from place to place. I do have PRV's here in 1/2 and 3/4" that are adjustable and inexpensive.

bob...

OK, if I want to protect the PUMP with the PRV, I assume that I need to know fairly accurately what pressure it craps out at. I would much rather measure this than attempt to calculate it. Should I simply hold the contacts down on the switch and watch the gauge till the pump stops (I assume it has a high heat cut-out switch) or should I just watch for the pressure increase to stop and use this as Max pump pressure then set the PRV to be just UNDER that setting?

OR, since my switch settings are 30/50 why can't I just set the PRV for 55 and just forget about the rest?

Wait until your pump shuts off at 50 PSI. Back off on the pressure relief adjustment until the PRV starts leaking, then tighten it back until it stops leaking. If the pressure drops too low while you are doing this, restart the pump, let it shut off at 50, and try again. Just tighten the PRV adjustment a little if it is still leaking.

Thanks Valveman. This sounds like the easiest and best way to set it.