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Thread: Water Pressure Problem

  1. #1

    Default Water Pressure Problem

    I've got an old home (galvanized water supply, originally on well). A few years back the well went dry and burnt out the pump. I opted to go on city water.

    The new water supply was a 3/4 inch pvc line (the utility says that is the standard in this area). When the plumber tied into the old system, he just connected in at the t leading up to the washing machine (about 15-20 feet from where the old well entered. This continued to the water heater, and all the other fixtures. Once past the kitchen sink, the galvanized pipe expands to 1 inch for some reason, (but this never caused any problem before), then t's to each bathroom. 4 hose bibs just branch off along the way.

    Recently, the pipes between the new service and the kitchen sink have been obviously rusting through, and need to be replaced. I decided to do this myself, and for the time being, replaced the old (3/4 galvanized) from the point of entry of the city water supply to the kitchen sink with a 3/4 inch cpvc line.

    The new pipe supplies the washer first, t's (3/4 cpvc) to the tankless heater, continues to the kitchen sink, then the old plumbing runs go from there to the bathroom fixtures.

    Since replacing the pipe, my pressure has dropped considerably, even when only 1 fixture is running. There is no sludge in the lines, the aerators are not showing any sediment, the only thing that appears to have changed is that I replaced the old, mostly blocked lines with new cpvc.

    I'm assuming that if anything, the inside diameter of these pipes is greater than what has been replaced. I'm wondering if anyone has got any idea for me.

    1)Would bringing the supply directly past the washer to the heater, then kitchen sink....then back to the washer have any effect? Seems this would only be a possibility if the washer was running, yet the pressure is always low.

    2) Can I alter the pressure significantly without a larger line from the municipal supply?

  2. #2
    In the Trades Gary Swart's Avatar
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    First, you must know the difference between pressure and flow. Pressure does not change with pipe size. A 1" pipe and a 1/4" pipe coming from the same source will have exactly the same pressure. Obviously there will be more flow from the 1" pipe than from the 1/4" pipe. Increasing the pressure will increase the flow to be sure, but that's not your problem. You can buy a pressure gauge at a hardware store for under $15 and check it. I believe your flow is restricted. It could be from a valve that is not completely open, it could be from a corroded galvanized pipe, but it is most likely the CPVC pipe. The inside of a 3/4" CPVC is close to the same size as a 1/2" copper. If you insist that you want CPVC in your home, you should size it larger than pipes of other material.

  3. #3

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    Quote Originally Posted by Gary Swart
    First, you must know the difference between pressure and flow. Pressure does not change with pipe size. A 1" pipe and a 1/4" pipe coming from the same source will have exactly the same pressure. Obviously there will be more flow from the 1" pipe than from the 1/4" pipe. Increasing the pressure will increase the flow to be sure, but that's not your problem. You can buy a pressure gauge at a hardware store for under $15 and check it. I believe your flow is restricted. It could be from a valve that is not completely open, it could be from a corroded galvanized pipe, but it is most likely the CPVC pipe. The inside of a 3/4" CPVC is close to the same size as a 1/2" copper. If you insist that you want CPVC in your home, you should size it larger than pipes of other material.
    I've already done the pressure test, though I'm not convinced the gauge from Lowe's was all that accurate. It read 80lbs at the hose bib, and after opening an inside valve, it momentarily dropped to mid 70's, then right back at 80. Does this seem right? I expected some drop.

    I guess I don't understand completely. At first I thought just as you say, but before I made any recent change, the supply line from the meter was 3/4 pvc, and the pressure was fine. I had been thinking that since this had not created a problem, then the new 3/4 inch CPVC I installed would not either.

    If I follow your advice and replace my recent cpvc with larger pipe, don't I also need to run a larger pipe from the meter to the house (presently 3/4 inch pvc)? If so, I need to get a new water meter installed?

  4. #4
    In the Trades Gary Swart's Avatar
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    Actually, your pressure is a bit higher than "normal" which is around 60 psi. That can be a problem, but it's a totally different discussion. Your 3/4" PVC supply line is large enough. You must understand that PVC and CPVC are different animals. It's the small inside diameter of the CPVC that is choking your flow. My advice is to forget the plastic pipe and use 3/4" copper.

  5. #5

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    Quote Originally Posted by Gary Swart
    Actually, your pressure is a bit higher than "normal" which is around 60 psi. That can be a problem, but it's a totally different discussion. Your 3/4" PVC supply line is large enough. You must understand that PVC and CPVC are different animals. It's the small inside diameter of the CPVC that is choking your flow. My advice is to forget the plastic pipe and use 3/4" copper.

    Gary:

    First, thanks for your advice, I appreciate it.

    I knew there was some ID difference, I just had no idea it would have so drastic an effect.

    So:

    1) The 3/4 PVC supply line is fine.
    2) I should see improvement if I replace the 20' or so of CPVC cold water line with 3/4 inch pvc (what would be the result if I went all the way up to 1"?).

    My house is over a crawl, the quarters are pretty tight, and run in close proximity to gas lines. I think, for the time being, I'll avoid flames. I'm confident in my ability to become adept at DIY stuff, but I'll probably pace myself.

    I'll try what you suggest, should only take about an hour.

    One more question. I've left in place the old galvanized tees leading to both the washer and kitchen sink (they seemed in good shape, and I wanted to avoid cutting into walls and such until I get to the remodel portion of each room). They look to be 1/2 inch. Are they adequate?

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Meter size and supply pipe size are two different animals, and one seldom affects the other as long as the meter flow is adequate. When you start mixing materials you have to check the size of the hole in the pipe to be sure IT is adequate.

  7. #7
    In the Trades Gary Swart's Avatar
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    PVC is not acceptable for interior use. Certainly using a torch around a gas line is cause for caution, but you should be able to protect the gas lines from flame. If there is a gas leak, then you need to fix that before anything else.

    1/2" feeds to fixtures is fine. If this was my home, I look to replacing everything with copper. You may want to do this yourself, but before you do, check to make sure what size pipe you need. Probably 3/4" with 1/2" to fixtures. You may also have a pressure regulator valve and expansion tank in you future.

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