Where to install a pressure regulator

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Mad Plumber, Jan 23, 2006.

  1. Mad Plumber

    Mad Plumber Mad Skills

    I am sorry, I did not register because of I just have one
    simple question where to install a pressure regulator.
    Recently I installed two stages whole house filter. This
    filter has two pressure gauges: inlet and outlet. This way I
    figured out that my city water pressure is too high 90+psi.
    So, I decided to install pressure regulator. My first thought
    was to install it right after the whole house shut off valve
    but now I am thinking about to install it right after whole
    house filter. I think, this way filter will be doing better job
    with higher input pressure, house pressure will be more
    stable (pressure regulator will compensate for pressure
    drop across the filter) plus regulator itself will get filtered
    water and diaphragm will be lasting longer.

    Are my assumptions correct?

    Thank you,

    - Vitaliy
  2. Gary Swart

    Gary Swart In the Trades

    Yakima WA
    You're right, 90 psi is too much. A PRV is installed in the cold water supply prior to reaching the water heater. I really don't know about the filter situtation, someone else will have to answer that. You might contact the manufacturer or the dealer that handles that brand. You need to realize that a PRV creates a closed system so an expansion tank will be needed. We've had several discussions about them quite recently, you can scroll back and find them.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Don't know the answer to your question, but note you will probably need to also install an expansion tank so that your water heater doesn't vent when the water expands when heated. A prv creates a closed system, and the expanding water needs somewhere to go. Also, was that pressure continous or after things sat for awhile? The water heater can cause high peak pressure, and a pressure reading may not represent normal operations.
  4. before the filter

    install it before the filter.....

    theirs less stress on the filter that way....
  5. That can work but remember that high pressure can climb at night when there are less people using the water in your area. Take this into consideration so that you know what kind of potential pressure that system will take before entering the PRV.
  6. Bob NH

    Bob NH In the Trades

    New Hampshire
    Regulator after the filter

    A good filter should be able to stand 100 psi with no problem. I use filter housings that are rated for 125 psi, but you should check yours for the pressure rating.

    I would put the filters after the inlet valve or water meter, then put the PRV after the filters. If you discover that you are getting short filter life or too much pressure drop, the solution is to replace them with larger filters. The small filters are often too small for "whole house" use.

    At maximum flow near end of life, two cartridge filters in series could have a pressure drop of 40 psi. That wouldn't work very well if they are after the regulator.

    You should have a pressure gauge between the two stages so you know which stage needs changing. They probably don't need changing at the same time.

    With the PRV you need an expansion tank or a relief valve after the regulator. The usual practice is to use an expansion tank but you can install one of the little 75 psi relief valves that are used with submersible pumps. That is far below the 150 psi that T&P valves are usually set at. The relief valve protects against regulator failure up to the capacity of the relief valve and will waste only a small amount of water when water expands in the water heater. The outlet of the relief valve must be piped to drain with an air gap.

    You should try to take your "outside" water off before the filters becuase that is often high flow and you don't want to filter it.
  7. finnegan

    finnegan New Member

    The pressure in my area is 125psi. No one has a pressure reducing valve. Water straight out of the hose hurts.
  8. http://img.photobucket.com/albums/v70/DUNBAR/PPV016.jpg

    Here is what 84 pounds will do with no one home and a daughter that is afraid to go downstairs to find out what is broke and spraying all over the place. I'm sure she didn't even know where the main shutoff was,,,,and it was hard for me to turn off as well. Did a ton of damage, it was a whole house filter with a turn top for bypass or filter. Insurance claim was $4900.

    Notice the discoloration of the plastic; that is what happens when plastic is subjected to various temperature changes over time, it gets hard and brittle and the result is property damage.

    A 75 psi pressure relief valve is ideal and would protect from over pressure....but if the above happens the pressure will reduce and the pressure relief valve will close. Mfg. specs are designed to be used in a normal function, not to it's potential maximum. You are dealing with disaster like the above pics indicate.
  9. ss3964spd

    ss3964spd New Member

    Uh oh.

    Expansion tank required with a PRV, 'eh?

    Then I've got a problem right now. Bought the house 6 years ago and it already had a PRV and no expansion tank (or pressure relief valve). Only the T&P on the WH, and that has never opened. WH temp is set around 100-105 I believe.

    The PRV that was installed when we purchased the house did spring a leak and I replaced it. New one has been installed for well over two years now, probably closer to three years.

    So, give it to me straight. How serious an issue am I looking at here? Is this a "take tomorrow off and fix it immediately" sort of concern?

  10. Bob NH

    Bob NH In the Trades

    New Hampshire
    Automatic Shutoff for Failure

    SS3964SPD - Lack of an expansion tank is not a "take tomorrow off and fix it" problem. Your low water heater temperature setting minimizes the problem.

    Regarding the flood problem for a broken filter housing:

    I recall seeing a valve that was like a spring loaded check valve installed backwards, except that the spring was strong enough to keep it open in normal flows. If there was a failure downstream, the very high flow was enough to close the valve against the spring.

    I have not seen one lately. Do they still exist and does anyone know where they can be found?
  11. ss3964spd

    ss3964spd New Member

    Many thanks Bob.

    Apologies for hi-jacking the thread.

  12. Plumbcatastrophe

    Plumbcatastrophe New Member

    expansion tank

    interesting info on the expansion tank. didn't know one was needed, either. does this still apply if the water heater is forty feet away? good info
  13. Cass

    Cass Plumber

    Pressure will be equal any where on the line, distance makes no difference.
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