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Thread: Sudden Drop in Water Pressure

  1. #1
    DIY Member Phillbo's Avatar
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    Default Sudden Drop in Water Pressure

    A couple days ago I notice a significant drop in my water pressure. I've tested for a leak and don't appear to have one. I don't believe I have a pressure reducing valve that could be failing either.

    Looking for advice on what else to look for?

    I plan to ask a neighbor if they have the same problem next time i see them.. We are on City Water, should I call the city ? Will they charge me to come diagnose?

  2. #2
    Master Plumber-Gas Fitter shacko's Avatar
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    Quote Originally Posted by Phillbo View Post
    A couple days ago I notice a significant drop in my water pressure. I've tested for a leak and don't appear to have one. I don't believe I have a pressure reducing valve that could be failing either.

    Looking for advice on what else to look for?

    I plan to ask a neighbor if they have the same problem next time i see them.. We are on City Water, should I call the city ? Will they charge me to come diagnose?
    I think you have to make sure you don't have a PRV in your system.

    Whether the city will charge you depends on where you live, they are all different

    Get yourself a screw on pressure gage and check the pressure on the nearest hose bit to your meter or supply line, if you are getting over 50lb it's not the cities fault.

  3. #3
    DIY Member Phillbo's Avatar
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    The valve to turn the water off to the house (other than at the meter) is on the front hose bib, there is no other valve located there.

    I'll get a pressure gauge and see what i have at the hose bib at the front of the house.

    Thanks for the advice.

  4. #4
    DIY Member Phillbo's Avatar
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    Must have been a city issue since the pressure returned to normal yesterday. I bought a gauge anyway and am getting 60 psi at the front hose bib.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Water pressure can change consisderably throughout a 24-hour period. In the morning, when everyone is taking showers, and again in the evening. At night, the pressure often goes up while they may be trying to replenish any water towers, plus few people are using water. So, a single check often can be misleading.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    IT would have to be a "horrendous" leak to create a pressure drop that you would notice. You would have a easy time seeing or hearing it.

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    DIY Member Phillbo's Avatar
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    OK, this is strange. Again this morning (saturday morning same as last weekend ) the pressure inside the house is so low you can barely get the shower to turn on and my washing machine took forever to fill up for a load.

    I just checked the pressure at the front hose bib and it's still 60psi.

    Any advice on what to look at ? Why would it only appear to drop on the weekends?

  8. #8
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Phillbo View Post
    is so low you can barely get the shower to turn on and my washing machine took forever to fill up for a load.
    I just checked the pressure at the front hose bib and it's still 60psi.
    Your GPM is low. High GPM would drop the pressure somewhat.
    Look for an obstruction upstream of both the shower and the washing machine. The pressure difference across the obstruction tells the story. The GPM on either side of the obstruction should be unchanged since water is incompressible.

    It's a long shot, but if you have a micrometer, the pipe under high pressure will have a slightly larger diameter than the downstream pipe, other things being equal. As to how much larger, I'm waiting on an e-mail answer from some copper people.

    And, in principle, since pipe under pressure is stretched it will "ring" with a higher frequency if struck with a chunk of metal, if it rings at all. I'll have to try this sometime.

    To figure out the weekend connection you'd have to be S. Holmes.
    Last edited by Thatguy; 11-20-2010 at 04:55 PM.

  9. #9
    DIY Member Phillbo's Avatar
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    I have a GE Smartwater water softener and I noticed that I can get an increase in pressure buy switching the bypass value. I have no way of measuring the pressure at the tub for instance but I'd guess the flow increases by about 25-30% with the softener bypassed.

    Is this typical or a sign of a clogged or failing water softener?

  10. #10
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Thatguy View Post
    I'm waiting on an e-mail answer from some copper people.
    And they respond:

    "The mechanical properties of C12200, the alloy used for copper plumbing tube, are 55 ksi tensile and 50 ksi yield and 8% elongation in 2 inches, for hard drawn tube.

    At an hydronic pressure of 60 psi you would not see any yielding, at such a low strain, at least one that you could measure with a micrometer. "

    Too bad.

  11. #11
    Nuclear Engineer nukeman's Avatar
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    Try putting the pressure tester on either another hose bib (if you have another) or connect it to your washer hookups. The front hose bib is before your problem area, so the pressure is not changing. Checking the pressure at the washer will help you figure out what the pressure inside of the house is.

    Flow (GPM) depends on pressure difference and resistance. If your flow is dropping, either the pressure at the street has changed (and you have verified that it has not) or something in the house is causing a very high pressure drop. With nothing flowing, everything in the house should be at street pressure (60 psi). There can be a variation it this pressure +/- a few psi due to elevation change (2nd floor vs. basement), but it should be pretty close to the street pressure. Even if your pipes were nearly completely blocked, you should still see 60 psi everywhere when everything is off. If that checks out, turn on a sink to the tub and look at the pressure again (at the washer). If everything is normal, the pressure should only drop a bit when something else is flowing.

    If the pressure drops a bunch when you turn something on, something is causing a large resistance. Start by checking mechanical things (verify valves fully open, PRV is good (if you had one), check the softener, etc.). What type of pipes do you have and how old is the house? Galvanized pipes can close up on you over the years, but it is normally a slow progression.

    Another thing you could do is to measure GPM. Take a 5 gallon (or whatever) size bucket and see how long it takes to fill. Try to start where the water enters the house (hose bib) and then check tub, washer, sinks, etc. Some things will natually flow more water than others (tub spout vs. bath lav), but if you record what you are getting and report back, we can help to tell you if it is "normal" or not. Have someone look at the pressure tester when you do this and see when you see a big pressure drop.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    It is possible that the water softener is partially clogged and thus you see a lower flow through it. The pressure would be the same without flow, but if the softener is partially plugged, it would act sort of like a partially closed valve. If you get the 'normal' flow with it bypassed, I'd just look there. The people on the water softener section of the forum could probably help since they deal with those more often.
    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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