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Help With Waterhammer

Discussion in 'Irrigation' started by Mach1, Apr 19, 2007.

  1. Mach1

    Mach1 LawnSite Member
    Messages: 16

    Hello all,

    I have a residential sprinkler system that I installed myself last year. From browsing the forums here, I can see that I will take some flak for using Rainbird parts from HD. I will claim ignorance, I thought they were all the same quality parts.:confused: I didn't know any better. Despite that, the system works well and has good coverage on my 1/4 acre lot.

    I am having trouble with waterhammer when switching zones. I have 1" PVC feeding the valve boxes, and some of the runs are pretty long from the source to the valve boxes. My zones use 12 to 14 GPM depending on which one is running, static water pressure is 62 PSI.

    I did not install a master valve on the system, and I'm wondering if that might help? The pipe runs basically the length of the house before exiting outside, so I wonder if a master valve would be a good idea even if it dosen't help with waterhammer?

    Just wondering if anything can be done to get the hammer:hammerhead: under control before something bad happens!
    Joe M.
  2. Let-it-mow!

    Let-it-mow! LawnSite Member
    Messages: 91

    You probably already know but water hammer is caused by the water in your pipes slamming into the valve when it snaps closed. The moving water acts like a heavy, fast moving solid and it really hits hard when it's forced to stop almost instantly.

    If you install a "Water hammer arrestor" you will solve the problem. This is installed on the supply side of the offending valve. It has a cushion of air inside. When the valve closes, some of the water will enter the chamber and this cushions the blow.

  3. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,158

    The arrestor is a good idea.....Rain-Bird valves are usually slow closing, but you may have "a made elsewhere" valve..the gpm seems fine for class 200
    pipe, but not for sch 40..remember the 5' a second rule.Master valves cool.
    Let-it-mow....great quote....I've been guilty of doing that to to our "bottom
    feeders" too; didn't take them too long to catch on!
  4. Mach1

    Mach1 LawnSite Member
    Messages: 16

    The valves I used are Rainbird JTV-100's. It says "Assembled in Mexico by Rainbird" on the box.:cry: They close slow but still cause hammer.:hammerhead:

    Thank-you much for the tip on the hammer-arrestor. Where's the best place to install it? Close to where my system connects to the main, close to the valve boxes or somewhere in between, or does it matter? Is there any certain size of arrestor I should be looking at?

    Thanks again,
    Joe M.
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,578

    What's the static water pressure? If the water hammer is resonating throughout the house, it might be possible to fit a pressure reducer in the house supply, and confine the hammer to the sprinkler system.
  6. Mach1

    Mach1 LawnSite Member
    Messages: 16

    Static water pressure is 62 PSI. I don't have any issues with waterhammer in the house's plumbing, it's isolated to the supply for the sprinkler system. That pipe does run through the basement for quite a ways, so the hammer can be heard in the house.

    Joe M.
  7. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,578

    Since water hammer is a function of water velocity and pipe length, it pays to up-size the pipe in long runs. Those hammer arrestors go as close to the zone valves as possible, so the moving water can 'run into' the arrestor.
  8. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Let me guess, the line inside the house is 1/2" copper?
  9. Mach1

    Mach1 LawnSite Member
    Messages: 16

    DW, The entire system is 1" pipe. It's copper where it taps in right after the watermeter for 3 feet in to a double-check backflow preventer. It's all 1" PVC after the backflow preventer as well.

    Joe M.
  10. Flow Control

    Flow Control LawnSite Bronze Member
    Messages: 1,267

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