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Backflow preventers

Dave Belisle
Dave Belisle Member Posts: 68
Anywhere you have a water hammer issue, even a small one that doesn't cause any problems in your water system , you may get a RPZ or even a 9D spitting a little water out the air gap.

After a while this problem can cause them to start leaking all the time.

What we have been doing when installing a small RPZ is install a simple non testable spring check before the RPZ ball valve . we end up with a third check but the spitting RPZ problem is gone, the water is flowing only in one direction so the check valves don't close and the intermediate valve doesn't open. Hense , No water coming out only when we test them.........

I have seen more of this problem since we have been using PEX. It cost us under ten bucks to make this problem go away.




  • Ron Root_2
    Ron Root_2 Member Posts: 12
    Different aswers on backflow preveters

    I called the manufacturer of a backflow preventer I found dripping out of the discharge port. It was after the pressure reducing valve feeding a hydronic boiler. The manufacturer's rep said it was installed correctly. Many guys in the trade tell me they always put it before the pressure reducing valve because there's no or very little fluctuation in pressure across it. I put it in before the pressure reducing valve, hope my faith is in the right place! Anyone else have any thoughts on this?
  • Al Corelli
    Al Corelli Member Posts: 454

    We always put it on the higher pressure part of the system. Always before the PRV (feeder). Probably mostly out of habit, as on steam systems, it would be the first thing after the shutoff valve.
  • no matter

    No matter where u put it, they leaks, taken them out ... I asked for record of anybody get ill from hot water heating system (without anti freeze) that didint have prv on system... No answer from anybody.... Any wallies?
  • Al Corelli
    Al Corelli Member Posts: 454

    The leakers I've seen are mostly on the low pressure side of the PRV. So, based on that, I've always assumed that the design of the backflow preventer utilzed water pressure in some "magic" way to ..prevent backflow, so I put them where they see the higher pressure.
    I would never remove one from a system bacuse some hotshot lawyer would just love to get litigious on me, I'm sure.
  • Plumdog_2
    Plumdog_2 Member Posts: 873
    immediately if not sooner

    get to a school where you can take a course in backflow prevention. Part of the course will cover specific cases of backflow and you will be amazed at what can happen. You will not be inclined to remove these devices with better understanding of what they do.
  • Albert Huntermark
    Albert Huntermark Member Posts: 68

    Agreed, never remove any backflow prevention device. At times they can be a pain, however, there is always a reason why they do what they do, whether they are operating correctly due to conditions downstream of them, or "malfunctioning" due to dirt in the line, or pressure issues upstream. These things need to be addressed so that the device works properly. As with many added safety devices, the odds are in favor of never needing them, however, if you have the bad luck of needing one! I’m with Plumdog, take the course, get certified, you’ll be surprised at what you will learn!
  • Donny
    Donny Member Posts: 37
    R.P.Z. location

    they definetly belong right after the supply valve. if installed downstream of the prv they are subject to any variations in the boiler side water pressure, if they are working properly an increase in pressure on the downstream side of the R.P.Z. will cause the relief to dump until the downstream pressure is lower than the feed side. therefore with the R.P.Z. installed before the prv chances of a leak are much less.
  • David Efflandt_2
    David Efflandt_2 Member Posts: 24

    Downstream pressure changes should not affect them (unless #2 check is leaking, which should be repaired).

    Fluctuations in upstream pressure can affect them during no flow. The purpose of the relief is to keep the zone between the checks lower than inlet pressure, so if inlet pressure drops much, the relief may squirt to keep the zone between the checks lower. City pressures have been known to fluctuate enough to make them squirt intermittantly. Continuous dribbling is either debris in a check valve (most likely) or the relief.

    So theoretically they should work best downstream of a pressure reducing valve (where static inlet pressure is steady). But the soft rubber parts that seal well in cold water may harden if regularly exposed to too much heat. So avoid putting them too close to boiler water temperatures.
  • Donny
    Donny Member Posts: 37
    RPZ location

    the relief valve will open, if unit is working properly, when the 2 # differential between the checks is not maintained, whether it caused by a rise and fall in incomming water pressure or an increase in the downstream pressure. Always position the RPZ as far upstream as possible, on the supply line to be isolated from the potable water distribution system, as that will afford maximum protection to the potable water supply.
  • KAG
    KAG Member Posts: 82

    This is all well and good, but most of these produts do not function properly. THey go off when thier is NO need or they seal up when there is a need. Has anyone gone to a job where the pressure in the boiler is over the relief valve or you shut down the system to work on it only to find the back flow now leaks and you can not stop it? I know there is to be regular maintance on these devices, but residentially who is really doing it? Why not just install a low water cut off valve and turn the feed/ back flow off. After all the feed valve probaly will not work after 3 years any way. This is my belief only that most so called safty devices are "lobbist provisions" and not reality. These may work in a controlled enviroment, but in the real world, pressure differentials, water content, and other daily changes this is the best we have. Just to give you an example, I had to repipe a 2" RPZ from the vertical to the horizantal just because the "TOWN" water department did not want the discharge to hit the wall, they wanted the floor instead, the manufacture and the plumbing inspector were O.K. with the way it was installed. I could have fought it, but customer was opening in 2 days and it was easier to Tuck tail and make customer happy. After all he was signing checks.
  • rich pickering
    rich pickering Member Posts: 277

    Had a rpz installed after the prv, feeding a condensate tank. Tank was about 2 feet away from rpz. Add some cold water to the tank, tank feeder shuts off, pressure is same on both sides of rpz, all is well. Tank heats up, 1/2" copper line heats up, water trapped between tank feeder and rpz heats up and pressure increases, rpz leaks.
  • Donny
    Donny Member Posts: 37
    rpz function

    The only function of an RPZ is to protect the potable water supply. In NY it nmust be installed with its center line min 30", max 60" off floor, due to conditions downstream it may be necessary to install a check valve, expansion tank or both, after the unit, it's also required to be tested and certified yearly by a licensed tester.
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