OT- Where to position water hammer arrestor? - Page 2
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  1. #21
    Join Date
    Apr 2005
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    Quote Originally Posted by deltap View Post
    Try it with the top check valve removed. Two check valves may be your problem.
    Quote Originally Posted by UncleFrank View Post
    Is this a new house, or a new plumbing job?
    If my memory serves me correctly, you just upgraded your system recently. If so, did you have a water hammer problem before the upgrade? If the answer is No, then what's changed?

    Your pipe size sounds about right for a 1-1/4 pipe if you are pumping about 20 gpm, that gives a flow rate of about 5 fps, a safe value for PVC pipe.

    I think deltap is on to something. Check Vales can be the bane-of-existence, one extra Check Valve can be one-to-many!

    When you change the check valve, if it still has the hammer then the worst case for you would be a leak between the well head check valve and the down hole check valve. This would give you the water hammer on startup.

    This can be checked relatively easy. If you have a valve that will turn off the water to your building after the pressure tank, will make it easier.

    First test: When leaving for the day make sure that no water will be used overnight then turn your pump off. Write down how much pressure that the system has. Check it the next morning before turning the pump back on. If all is good, then you know everything up to the well head check valve is good.

    Next test: Remove the well head check valve and cycle your pump a few times by turning on a faucet and see if the hammering has stopped. If it has, you may want to do a happy dance and go about business as usual! Of course you could repeat the the first test without the well head check valve. If there is a pressure drop, well you at least know in which direction to look!

    No leak on either test: Run outside, throw your hands up in the air while dancing wildly about, yelling and screaming (and don't kick the dog) - NOT THE happy dance! The problem is not solved and I wish you the best of luck!

  2. #22
    Join Date
    Sep 2004
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    UNITED STATES
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    Wisconsin
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    Many states do not allow a second check valve in supply line because it can lead to negative pressure in the pipe and allow contaminants to enter. Two checks can also lead to water hammer. I worked in a building that had pumps on ground level and cooling towers on 10th floor roof. When you shut off a pump with a 12" swing check on the discharge it was scarry. The check valve would slam with a horrendous bang and the pipes would jump in the hangers. Made you want to run for the door.


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