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I am in an old home without any fixtures like PRV, backflow prevention etc.

I've never experienced issues with water pressure, but during the home inspection, the pressure was measured 65psi. I called my water company and pressure in my town is between 30 and 70 psi. My understanding is that a PRV is only necessary for much higher pressures (at least >80psi). So it seems, I really don’t need one.

I am planning to install a check valve and ball valve on the cold water line in the crawl space (via Sharkbite fittings). I am doing this in the crawl space because I have a copper line there and it’s somewhat accessible. The proper location would be outside of the house but this would involve digging, adding underground boxes and the pipes are steel. My target location in the crawl space is after the (outside) main shutoff valve and after one tee, but all major fixtures/appliances will be downstream.

I am only thinking adding a PRV since I am working on the line anyway. But PRV is expensive and it seems I don’t really need it.

Is there any reason to add a PRV to my plumbing project?

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  • Aside: Does your old home have an expansion tank at the water heater? If not then installing a check valve in the main line may have unintended consequences.
    – HABO
    Commented Sep 24 at 9:59
  • A typical crawl space is a terrible place to add a shutoff valve. There's evidently already an outside shutoff valve; if you need to shut things off in a hurry you'd be better served by valves you can get to easily and quickly without crawling under the house, even if that means you need 3 or 4 valves to cover various branches. And with 3 or 4 valves you can just shut off the part that's got the leak.
    – Ecnerwal
    Commented Sep 24 at 10:59
  • @HABO Yes, there’s a thermal expansion thank at the water heater (cold supply line)
    – divB
    Commented Sep 24 at 14:41
  • @Ecnerwal Right, im not replacing the main shutoff valve but I’m planning to install an automated actuator on it. The one outside is too old for this
    – divB
    Commented Sep 24 at 14:41

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Only reason would be that you have too much money and want to give some to the poor starving folks at the plumbing supply.

PRVs are complex devices that fail not infrequently, and are only needed where your incoming pressure is too high. Your incoming pressure is not too high, so why would you want to add needless complexity and expense?

If you are adding a check valve you can enrich the plumbing supply folks (more usefully to you) by getting an expansion tank for the water heater, which you need when you add a check valve or PRV (that acts as a check valve) to a system that does not have an expansion tank (or well pressure tank, but you are on municipal water, evidently.) You might have one depending on local codes, but you don't really NEED one until you have something that prevents excess in-house pressure from just feeding back to the supply system.

You could also add a permanently mounted pressure gauge, in some convenient location, which virtually all of us well owners have but surprisingly few water system customers have, even those with PRVs, who should really have two, one on each side of the PRV, so they can tell if it's working or not...

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  • Possibly reasons could have been safety, redundancy, code requirements (but none for existing homes) etc. But great to hear I can leave it out. I have a thermal expansion tank at the water heater. So will just proceed with the check valve
    – divB
    Commented Sep 24 at 16:23
  • Code (both IPC&UPC) does not require a PRV when the system supplying the water is not at pressures above 80 PSI. Safety tends to go with code.
    – Ecnerwal
    Commented Sep 25 at 12:05

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