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Thread: Drop in Water Pressure?

  1. #1
    DIY Junior Member bperillo's Avatar
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    Default Drop in Water Pressure?

    Hi all,

    I am new to the forum. Over the last couple of weeks, I am noticing a dramatic decrease in my water pressure when another source is used. If someone turns on a faucet or flushes the toilet while the shower is running, I get a dramatic decrease in the flow. It slows to almost a trickle. This will last for several minutes even after the other source is turned off.

    This same pressure happens to the sinks. If the dishwasher is on, the kitchen sink pressure goes.

    This is a new development and I am not sure what it could be. Can anyone help with some suggestions?

    Thanks!

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by bperillo View Post
    It slows to almost a trickle. This will last for several minutes even after the other source is turned off.
    Are you on a well?
    Is there a recall on your water heater for diptube problems?
    Copper pipes or iron?

  3. #3
    Moderator & Master Plumber hj's Avatar
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    The most likely problem, unless it is an old, old house with galvanized steel piping, is that you have a pressure reducing valve on your incoming line and it is failing.

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    Homeowner Thatguy's Avatar
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    And the PRV service life seems to depend on the "cavitation index"; if you have one how old is it?
    http://www.google.com/images?client=...w=1474&bih=805
    Last edited by Thatguy; 09-18-2010 at 09:50 AM.

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    DIY Junior Member bperillo's Avatar
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    Thanks, all.

    House was built in 1986. Copper pipes. No well.

    Where would I find that PRV? How do I tell if it needs to be replaced?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    IF you have a PRV, it is likely near where the water comes into the house. Many companies make them, but they all look similar. You might check www.watts.com for an example.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    DIY Junior Member bperillo's Avatar
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    Thanks for the images, I don't see one, though I guess its possible I'm missing it as it seems they would blend into the copper pipes. Is there anything else that could cause this problem?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Has there been any construction nearby? Did any heavy equipment happen to drive through your yard? The supply pipe could have gotten crimped, but that normally would be hard to do. Had you recently turned the main water supply valve off? Gate valves are known to break off from the handle, and then they (nearly) shut off the water. If you turn the knob on the shutoff handle, does it stop, or just keep turning? Have you checked the water meter to see if it is registering water when you don't have anything open in the house? There could be a leak inside, hidden (maybe under the slab?). Are there any soggy, wet areas outside? The pipe could be broken. If there was some construction, you might have gotten a big chunk of crud that is now blocking the pipe. Have the flushed the mains recently (they usually notify you in advance, but if you don't read th epaper, you may not have seen it)? If so, the crud could have now plugged most (all?) of your aerators in the faucets, and maybe inlet screens.

    Do you have a hose bib that is close to where the water comes into the house? Do you get good flow there?

    You might want to pick up a water pressure gauge. One with the fitting to screw it onto a hose bib is about $10. While you can have great pressure with things off, if there is a restriction somewhere, the pressure would drop a lot as you open things up. This would be telling. If the pressure is really low with no use, then you might want to check with the water company and check with neighbors, to see if they're having similar problems.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    George the Plumber Gsalet's Avatar
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    My bet is the Pressure reducing valve is bad or the gate valve is not open all the way. It could also have to do with a bad water meter but that's rare

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    Homeowner Thatguy's Avatar
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    To be thorough I guess you should ask your neighbors if they are having a similar problem.

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    DIY Junior Member rick52768's Avatar
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    I have pressure drop issue as well and your reply Thatguy made me think this would be the best place to start. New neighborhood and 3 year old house. Pressure is 65 PSI the meter and at one spigot and 62 PSI at the other. My dishwasher has never been able to clean all of soap or food completely out. Every repair tech, while it was under warranty said this is a flow issue and changed the hose and everything else they could around water flow. I can use only low, low psi water sprinklers and even at the I cannot cover my small, new neighborhood type yard, without moving the sprinkler twice. Both my neighbor and I have a 20 PSI drop when both hose spigots turned on either of our houses. The water company tech said that was a flow problem. We are on different meters. Very short run of copper then 3/4" CPVC the rest of the way. Unless I am crazy, is this amount of pressure drop normal? When to start, where to look, what to test. Thanks

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    CPVC OD is the same as copper, but if you ever look at a section, you'll see that the ID is a lot smaller...it needs to be because the copper is much stronger. Depending on the length, you might find that just replacing the pipe with a larger one is all it takes.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by rick52768 View Post
    Both my neighbor and I have a 20 PSI drop when both hose spigots turned on either of our houses.
    I've never seen a "pump curve" for city water as seen at a home. The WaCo refused to tell me.
    Ideally at the pumping station I guess it's 50 PSI at tens of thousands of GPM.

    Assuming it's supposed to be 50 PSI for 0 GPM, what are the resi. pass/fail specs for the allowable range of PSI at 12 GPM and at 6 GPM at the input to a house? Somebody must have these numbers.
    Last edited by Thatguy; 10-10-2010 at 07:47 AM.

  14. #14
    DIY Junior Member rick52768's Avatar
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    I did some more testing as I do not have any sound answers. My GPM at my best hose spigot without anything else on was 6.74 GPM. It dropped to 5.31 GPM with the other hose spigot on.

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    Homeowner Thatguy's Avatar
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    Upstream obstruction?
    A plumber told me that whatever debris is left in water lines by anyone who worked on them will migrate downstream until it can no longer pass, just like a blood clot in an artery.

    Ask your WaCo to check this and give you the readings upstream of both you and your neighbor. If they have ultrasonic flowmeters they don't even have to cut any pipes.
    If they balk write to your attorney general. This might even be a health and safety issue.

    http://www.jensign.com/science/fluid...ent/index.html
    A liter is 0.264 gallons.
    Last edited by Thatguy; 10-25-2010 at 01:53 PM.

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