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Thread: This is a PRV, right? Expansion Tank needed?

  1. #1

    Default This is a PRV, right? Expansion Tank needed?

    Hi all,

    I'm getting a new water heater and wanted to make sure that the install will be done correctly, so I've been doing some research and read up on here about the need for an expansion tank. I looked at my water supply line (in my garage) and noticed that I had a Wilkins "Model 70" Pressure Reducing Valve. I just wanted to confirm that this is what's referred to as a pressure regulating valve and that this means that I have a closed system...




    So this means that I definitely need an expansion tank, correct?

    My TPR valve did not leak before, but a week ago I tested it and since then has been leaking consistently. Don't know whether this is due to a faulty valve or a bigger presuure problem, but if it is a pressure problem, I want to ensure that I have the correct setup this time around. Below 80 psi is the number that I should shoot for, right?

  2. #2
    In the Trades Gary Swart's Avatar
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    That's a PRV pictured, and that makes a closed system which requires an expansion tank. The reason the TP valve is leaking is most like due to the increased pressure when the water heater is heating. That's why you need the expansion tank. The expansion tank has a Schrader valve like a tire and is charged with an air pump just like a tire. You pressurize the tank to the same pressure the PRV is set to. If you don't already have a water pressure gauge, get one. I actually installed one in my supply line between the PRV and expansion tank, but it's not necessary to install it, but you need to have one to set the PRV. The air pump recommended is just a bicycle tire pump or similar, but I used my big compressor with caution and it worked great.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    When a T&P valve gets old, opening it manually often ends up with it leaking for awhile. Deposits on the shaft, stiff seals, crud caught on the seals and probably other things all combine to not allow it to reseal well. I've had mine finally stop leaking after a week or so. Sometimes, you just have to replace them with a new one. An expansion tank would be a good addition to the new HWH install. Depending on your piping and fixtures, you may not have experienced leaks from the T&P valve, but they are common.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Senior Member SteveW's Avatar
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    Looks like you've got a hose bib in the picture. Just for kicks, go to your favorite plumbing supply house, hardware store, or HD and get a pressure gauge (screws on standard hose fittings) and see what happens to your pressure at night. See my separate thread-- under the "right" conditions, my house pressure goes up to 120 PSI when I isolate my expansion tank.

  5. #5

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    Hi guys,

    Thank you for your help. I got myself a gauge and the pressure was a little under 80. A guy from the water company came out and told me the pressure coming from the street was a little above 80. He also mentioned that most homeowners have their pressures at about 65 and said that 70 psi would be good for a house of my size.

    The question I have is, is it okay to install the expansion tank in the area I posted pictures of in the first post - and not above the water heater - as long as it is between the PRV and the water heater? This is due to space concerns.

    In other words, the setup would be like this in my garage:

    Main shuttoff ball valve --> PRV --> (expansion tank inserted here) --> T (and hose bib) --> Wall.....(about 15 feet away).....Wall --> stop valve --> water heater

    So the expansion tank would still be between the water heater and PRV, just about 15 feet away. That would work fine, right?

  6. #6
    DIY Senior Member SteveW's Avatar
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    Should be fine. Really, since static house pressure should theoretically be the same anywhere in the house, you could conceivably put the expansion tank at the other end of the house as the WH. Of course, it's usually most practical to put it near the WH.

  7. #7
    In the Trades Gary Swart's Avatar
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    Anywhere between the PRV and water heater. Be sure you support the expansion tank well. Best way is with straps from the ceiling to the pipes on both sides of the tank although the tank can be installed in different configurations if necessary. In any case support it.

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