Open or closed system? Confused!

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by acer925, May 21, 2020 at 8:28 AM.

  1. acer925

    acer925 New Member

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    Hi, I just have a question..I’m trying to figure out if my plumbing is a closed or open system..how would I know? I didn’t see any type of check valve near the main water shut off, and my 2012 water heater doesn’t have an expansion tank so I’m thinking it’s open (meaning the water can back up into the municipal water system). The water department told me everyone has a closed system but I’m not sure he knew what I was asking. I had a very loud water hammer the other day after flushing toilet and tried turning main water valve off, openings all faucets to allow air in, then turning back on, but it hammered again. Installed water arrestor on toilet and it went away. Any info I’d greatly appreciate. Thank you!!

    Anthony
     
  2. fitter30

    fitter30 Active Member

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    To get rid of water hammer have to turn off main water supply, open all faucets, tub and shower. Drain down entire system and leave valves open for hour or more.
     
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  4. acer925

    acer925 New Member

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    yes I got rid of it thank you for extra info I didn’t realize leave it for an hour!..but was wondering if my system was opened or closed System..that was my main concern in the OP.
     
  5. Terry

    Terry Administrator Staff Member

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    If the water department told you that you had a closed system, then they must have checks at the water meters. A lot of them have been changed out with new meters that have that. It's not a question they haven't heard like a million times before.
     
  6. acer925

    acer925 New Member

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    Thanks for reply. Why wouldn’t they install an expansion tank when they put my water heater in in 2012 then? From what I read it seems like a requirement that started around 2003-2005. And everything I read online says I should get one, but they haven’t had any issues at all since the water heater was installed 8 years ago.
     
  7. Reach4

    Reach4 Well-Known Member

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    They might have put in a gadget that releases excess pressure outdoors.

    Get a pressure gauge. See what happens to the pressure after you use a lot of hot water, such as a shower, followed by not using any water. No toilet flush after the shower, for example. Watch the pressure gauge as the WH heats.
     
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  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Where I live, local code addendums have required an ET since the mid-80's, so this is not new. To protect the municipal water system, all utilities are or have installed check valves. So, even if you don't currently need one, it may be time to consider adding one. If you have any plumbing work done, you might just consider having the person include that task in the job list.

    Having a closed system would not make a water hammer more or less prevalent if it was properly controlled. The higher the pressure, the faster water can flow, and just like walking or running into a wall, when you try to stop the water flow, the faster you go, the more energy it has, and the more likely you are to get a hammer effect. Notice, though, that that tends to only happen with a valve that closes abruptly (like some toilet fill valves, dishwashers, icemakers, and some other valves and devices).

    Without knowing what your water pressure is and what it is doing, it's hard to tell if you might also need a pressure reduction valve in addition to an expansion tank. FWIW, a pressure reduction valve makes it a closed system as well as any check valve that the utility may have installed.

    Unless there's a leak somewhere in your system, once you use hot water in a closed system and the tank starts to reheat, the pressure WILL go up if you don't have an ET or there's a leak. Basically, the pipes are not elastic, so any volume increase rapidly raises the pressure...think pushing against a wall...the wall doesn't move, but the pressure rises...same as the water pressure.
     
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  9. acer925

    acer925 New Member

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    the t&p pipe goes to the outside of my house so maybe it releases some pressure there? I’ll have to check when the shower is on. I got a gauge and tested the pressure right after the shower was run hot and it was 67 psi. I retested it like 10 mins later and was still same. Maybe like 65. I don’t think it had any impact really. Next time I’ll read the gauge while the shower is running mid cycle. And also when nothing is running, to get a better idea.
     
  10. Reach4

    Reach4 Well-Known Member

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    You are not supposed to have the T+P valve doing that.

    Sounds like they intend to put a check valve on your meter some day, but so far they have not done so.
     
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  11. acer925

    acer925 New Member

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    the t&p pipe goes to the outside of my house so maybe it releases some pressure there? I got a gauge and tested pressure as dishwasher was on it was 65. I retested it like 10 mins after it finished and was still same. I don’t think it had any impact..
     
  12. acer925

    acer925 New Member

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    I’ve read some people have the pipe leading outside also so I didn’t think it was wrong, is there anything problematic about that? It’s not threaded and it’s about 8” off ground.
     
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    It depends on where you live and whether it could freeze up or get otherwise obstructed. There cannot be any obstructions to the outlet of the T&P valve.

    You won't see any pressure rise WHILE using hot water, since any expansion would be minimal since you're dumping in cold water and the system is open at that time by virtue of the water running. It's after you've used a bunch of hot water, and then stopped using any while the WH is heating the water that, if you have a closed system, the pressure will rise.

    If you DO have a closed system and the T&P valve is not opening, it's either bad, or something else in the house is leaking to relieve that pressure. A common item is a toilet fill valve...that can leak without any damage or obvious problem, but even a slow drip from a faucet could do it. Only when the system is really tight will the pressure rise in a closed system.
     
  14. JerryR

    JerryR Member

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    Typical T&P is routed to the outside in Florida. Every house I’ve owned in Florida did.

    Use a water pressure gauge like this on any hose Spicket, even outdoors. https://www.amazon.com/Watts-0950200-Water-Pressure-Gauge/dp/B000YMU8JC/

    it can be purchased at Amazon or local Home Depot. Connect it to hose spicket, turn on the Spicket and note the reading and leave it on. Set the red indicator to the current reading. After taking a shower wait about an hour and look at the pressure. If pressure goes up significantly then you have a closed system.

    Adding a expansion tank is easy.
     
  15. Reach4

    Reach4 Well-Known Member

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    I was referring to using the T+P valve as your thermal expansion solution.
     
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  16. JerryR

    JerryR Member

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  17. Jeff H Young

    Jeff H Young Active Member

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    1 water hammer has nothing to do with check valve toilet fill valves often do. 2 water company says it has a check valve You should have expansion tank. 3 plenty to read on expansion tanks with out us repeating all the reasons why , if you drove a car 8 years with out a seat belt and survived why wear one today. Im guilty myself I should put an expansion tank on my house but havent gotten around to it but it needs one
     
  18. Terry

    Terry Administrator Staff Member

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    With a closed system, the expansion tank is to prevent wear and tear on the tube going through the center of the gas water heater. Changing pressure can flex that tube. When my water meter was changed out without warning, my water heater failed in the next month. Granted, it was old, but the check in the line was the last straw. That replacement water heater lasted 15 years for the next owner of the home.
     
  19. acer925

    acer925 New Member

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    So it seems like my water pressure stays at 65 regardless of what appliance is on..I tested is after the appliance was on. How would I know if I had a leak?
     
  20. Reach4

    Reach4 Well-Known Member

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    Water meter would indicate water usage. Some have an indicator that makes it easy to detect low flows.
     
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  21. acer925

    acer925 New Member

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    One last question, if a water heater can go to 150 psi how do we know how close it gets to that? Is there any way of knowing? If my water pressure to house is 65.? Just curios as to what it’s actually doing on the inside as far as pressure goes.
     
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