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Thread: Water Pressure is too High

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    LazyPup's Avatar
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    Water Pressure is too High

    I have just replaced the expansion tank on the cold water line to the water heater. I have followed the recommended size and capacity, but I still measure as high as 120 psi on the house pipes. It should be 80psi or lower! Am I missing something here?


    NOTE: This question was originally posted by "Ramoncb" under the heading "Do I need an expansion Tank" but i thought this question was important enough that it deserved a separate thread so it doesn't get lost in the shuffle.
    Last edited by LazyPup; 10-03-2007 at 09:18 AM.

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    The plumbing codes require that when the water supply "static head pressure" (line pressure when no flow is occurring) exceeds 85psig or in situations where the pressure may occasionally spike above 85psig we are required to install both a PVR (Pressure Reducing Valve) on the main water supply line at the service entrance point and an expansion tank on the water heater cold water supply line.

    Although there are other reasons for installing an expansion tank, the presence of an expansion tank on your system and the excessive pressure that you recorded may be indicating that you already have a PRV which may be malfunctioning.

    I am posting a photo of a water meter location that has a PRV so you will know what to look for.
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    Last edited by LazyPup; 10-03-2007 at 10:04 AM.

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    An expansion tank is just that....it is intended to provide a small expansion chamber to absorb TEMPORARY excursions of pressure, such as the expansion of water that occurs when it is heated. Without an expansion chamber, or tank, this can result in a fairly large pressure excursion. It is a temporary excrsion, because faucets are run, water cools off in pipes, etc. to return the pressure in the closed loop to input supply pressure.


    In short, if your supplied pressure is 120, and expansion tank cannot reduce that. You need to install, or repair, a pressure regulator valve.

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    Yes, I have a PRV. Before I replace the PRV, is there an easy way to test it if it is malfunctioning? Once I replace the PRV, do I have to replace the expansion tank again?
    Last edited by LazyPup; 10-04-2007 at 08:21 AM.

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    To answer your second question first, the "Expansion Tank" works totally independent of the PRV so once you have the expansion tank installed you will not need to worry about that.

    Normally when a PRV is as far out of range as yours it is time to replace it, but just to be sure, you might try adjusting it.

    If you will look at the attached illustration you will see there is an adjustment screw sticking out of the top of the diaphragm housing. Turning that screw clockwise would increase the pressure while turning it "Counter clockwise" (Unscrewing the screw) will decrease the pressure.

    Try turning it one turn, then run a faucet to relieve the static pressure in your system, then take a new pressure reading. If the pressure has come down you may try again until you reach a maximum of 85psig. Remember that you must run some water between each test to relieve the standing pressure in the system and allow it to come to the new pressure before taking your new reading.

    If the pressure will not come down to 85psig you will need to replace the PRV valve.

    If you discover you need to replace the valve copy the manufacturers make & model number and any other pertinent data off the MFG data plate attached to the top of the diaphragm housing and take that information to your dealer to get a properly matched replacement.
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    Last edited by LazyPup; 10-04-2007 at 09:14 AM.

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    There is usually a tag with some specs on it, attached to the PRV. A typical residential unit has an output pressure range of 45to 75 PSI, so when you see full street pressure ( 120 PSI) on the house side, it usually means a failed seat or diaphragm, or both.

    While the major brands (Zurn/Wilkins, Watts, Cash-Acme) have rebuild kits available, in a household water situation the success rate of rebuilds is low. It costs not a lot more to buy a whole new valve.

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    Quote Originally Posted by LazyPup View Post
    To answer your second question first, the "Expansion Tank" works totally independent of the PRV so once you have the expansion tank installed you will not need to worry about that.

    Normally when a PRV is as far out of range as yours it is time to replace it, but just to be sure, you might try adjusting it.

    If you will look at the attached illustration you will see there is an adjustment screw sticking out of the top of the diaphragm housing. Turning that screw clockwise would increase the pressure while turning it "Counter clockwise" (Unscrewing the screw) will decrease the pressure.

    Try turning it one turn, then run a faucet to relieve the static pressure in your system, then take a new pressure reading. If the pressure has come down you may try again until you reach a maximum of 85psig. Remember that you must run some water between each test to relieve the standing pressure in the system and allow it to come to the new pressure before taking your new reading.

    If the pressure will not come down to 85psig you will need to replace the PRV valve.

    If you discover you need to replace the valve copy the manufacturers make & model number and any other pertinent data off the MFG data plate attached to the top of the diaphragm housing and take that information to your dealer to get a properly matched replacement.
    I have replaced the PRV successfully! The pressure is now about 50 psi. Big difference from 120! Thank you very much for your advise.

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