Pressure differential

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Phil Clemence, Mar 14, 2009.

  1. Phil Clemence

    Phil Clemence New Member

    Jul 12, 2008
    I have a friend .... no ... really!
    She has a Delta pressure balanced valve about 3 years old.
    She has galvanized supply lines and quite low hot water pressure.. but her cold water pressure is VERY good (near a river).
    She told me that things have gotten pregressively worse over the last couple of years, and it takes up to about 40 minutes to fill her tub enough for a bath!
    I went there and replaced her hot side supply from the main T to her valve but that did not help. I used a dielectric on a 4" long iron stub from the "T" and made a flushout pipe from another. I reamed out the 4" pipe and screwed on the flushout to the "T" line dielectric and got a lot of crud out and checked the section of copper that led to her valve.
    I screwed on the supply to the valve and checked to see if there was any improvement, but ... it was worse. I could only get a few drops of water from the tub spout.
    With the cartridge removed i turned on the main a bit. I held my finger on the cold port and saw there was very little water from the hot side port. I opened the sink (within reach) and saw the hot port could flow very well with the mixing of the pressure via the sink.
    So, i figure there must be so much pressure difference that the pressure balance cartridge is preventing any water flow. I have never seen this before. I have seen the same thing if one supply line is totally closed, but never checked it with a partialy closed supply.
    I figure the temporary solution is to put in a shut-off for the cold side to limit the pressure there and the cartridge should allow some flow again. I guess she needs to have the whole house repiped as soon as she can afford it :(

    My biggest question is: Has anyone seen this effect? (I thought they operated at the lowest pressure available at either side, so this seems strange)

  2. nhmaster

    nhmaster Master Plumber

    Jul 30, 2008
    Tech. Instructor
    S. Maine
    You either still have a restriction in the hot line or the balance spool is sticking or full of crud.
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  4. Phil Clemence

    Phil Clemence New Member

    Jul 12, 2008
    thanks - I did replace the catridge, ran a wire through the port, and blew through the copper pipe leading to the valve. That part *seems* clear ... at least enough so the mixed pressure through the sink faucet being opened lets a fair pressure through the hot port while i have my finger over the cold port. With the sink faucet closed and my finger over the cold port, the hot port IS VERY slow (although i don't have the main opened much when i do this, the cold side shoots to the back of the tub, while the water arc from the hot side just clears the valve body). With the sink faucet opened the stream from the hot side makes it about 2/3 of the way to the back of the tub and the cold stream still reaches the back.
    Last edited by a moderator: Mar 15, 2009
  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    IT does operate at the lower pressure of the two sides which is why it takes so long to fill the tub. If you put a valve on the cold side and shut it off, that will completely stop the hot flow. The hot improves when the sink is turned on because then some of the cold water from the sink faucet is flowing into the hot side and giving the impression of greater hot flow. The blockage is ahead of the point where the sink and tub lines are joined. IT could be a single point in the vicinity of the water heater, but you would have to do some investigation to find out where.
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