Drop in Water Pressure?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by bperillo, Sep 18, 2010.

  1. bperillo

    bperillo New Member

    Messages:
    3
    Location:
    New Jersey
    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. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Are you on a well?
    Is there a recall on your water heater for diptube problems?
    Copper pipes or iron?
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,815
    Location:
    Cave Creek, Arizona
    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.
  4. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Last edited: Sep 18, 2010
  5. bperillo

    bperillo New Member

    Messages:
    3
    Location:
    New Jersey
    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?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    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.
  7. bperillo

    bperillo New Member

    Messages:
    3
    Location:
    New Jersey
    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?
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    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.
  9. Gsalet

    Gsalet George the Plumber

    Messages:
    83
    Location:
    San Francisco
    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
  10. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    To be thorough I guess you should ask your neighbors if they are having a similar problem.
  11. rick52768

    rick52768 New Member

    Messages:
    8
    Location:
    Horse Capital of the World
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    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.
  13. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    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: Oct 10, 2010
  14. rick52768

    rick52768 New Member

    Messages:
    8
    Location:
    Horse Capital of the World
    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.
  15. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    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/fluidmechanics/hosemeasurement/index.html
    A liter is 0.264 gallons.
    Last edited: Oct 25, 2010
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    An elevation change can easily account for a couple of pounds of static water pressure. 3/4" cpvc pipe is about the same ID as 1/2" copper, and that is generally too small for a normal house with today's codes. How long is that 3/4" cpvc section?
  17. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    FWIW,
    if 5 psi [12' of head] @ 4.5 GPM is bad
    and
    40 PSI [92' of head] @ 16 GPM is good
    then a single number figure of merit for resi. water supplies would be how much hp is available at a sillcock with nothing else running.

    12 x 4.5/3956 = 0.014 hp
    and
    92 x 16/3956 = 0.37 hp

    I don't know what WaCo's benchmarks are except for this 40 PSI and 16 GPM.

    If anyone out there has pressure & GPM gauges I'd like to hear your values along with how satisfied you are with your city water supply. This will sharpen the line between a good resi. supply and a bad resi. supply.
    Last edited: Oct 25, 2010
  18. rick52768

    rick52768 New Member

    Messages:
    8
    Location:
    Horse Capital of the World
    A lot of science going through Thatguy's brain. I wish I could get to my old house as I used four sprinklers in the back yard (almost 1/3 acre) using a bunch of 5/8 water hoses all up hill supplied by 40+ yrs old copper pipe with not a lot of problems. Run-on sentence of the week.

    Jadnashua are you asking how long the 3/4" line is until it splits off to 1/2" to feed the hose spigots or dishwasher?

    Here is another possible issue. My water line comes in the house in the basement and shoots straight up 6'. I bet that does not help the issue.
  19. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    You said "very short run of copper, then cpvc the rest of the way"....how long is 'the rest of the way'? The house I grew up in had a 1/2" copper supply line (don't think it ever got changed), but we only had 1.5 bathrooms. Today, that would not pass code. 3/4" cpvc is much closer to 1/2" copper than 3/4". So, if that run is more than a few feet, it is restricting the water flow, or could be, depending on how many taps you have opened. Static pressure (no flow) would be the same with a 1/4" line verses a 3" line, but once you add flow, the smaller one would realy mess with the volume or flow.
  20. rick52768

    rick52768 New Member

    Messages:
    8
    Location:
    Horse Capital of the World
    Foot of copper, feet of CPVC

    The switch to CPVC is quick, water meter to a foot of copper to 30' of 3/4" CPVC. Then the 3/4" shoots up 6', over 35', then switches to one hose spigot with 15' of 1/2" CPVC. That was all from memory so the distance is not 100%, but close. Going to try the bucket GPM test again with a bigger bucket to decrease my error rate. Rain bird sprinklers states that if you have less than 7 GPM to call them? I was wanting to try the in ground sprinkler system as they are much more effective.
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