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OT-Why does solenoid valve hammer?

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  • OT-Why does solenoid valve hammer?

    The solenoid-operated fill valve on our dishwasher suddenly decided to start jack-hammering, continuously, while open. Nothing else has changed in the plumbing, water pressure, or whatever. Anybody have any ideas?

    It lessens, somewhat, if I throttle the water supply, but then the dishwasher may not fill with enough water.

    It is a built-in unit so it is a PITA to work on. I will replace the valve if I can understand what is going on and have some confidence that a new one will be the cure.

    Orrin
    So many projects. So little time.

  • #2
    There is a good chance it is full of crud, or it is just going bad.

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    • #3
      solenoid/servo valve
      the solenoid is quite small and only opens a passage via needle valve, sorta like the float needle in a carby

      whip 'er out and check, crack the valve body by 3-4 screws
      usually a clean of the plastic "needle" and seat sorts it

      you may have a split in the diaphragm of the main valve though
      either way it's no big deal to fix/replace

      if you are not confident, or don't have the time, a replacement valve should not cause too much pain in the $$$nerve
      Just got my head together
      now my body's falling apart

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      • #4
        Filling solenoids often give rise to water hammer .
        It can arise from pipe clips failing allowing the pipe to move.
        Some solenoids are soft close type but the "soft close" function wears out.
        It may be the water company has increased the mains head without telling you if other customers down the line have complained about inadequate pressure.
        A small vessel teed onto the line should act as a shock absorber

        This sort is commonly used in UK http://cgi.ebay.co.uk/Worcester-24-2...item4aaae7feca

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        • #5
          I too thought of water hammer from air in the system sounds like it might be correct to me. Alistair
          Please excuse my typing as I have a form of parkinsons disease

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          • #6
            Originally posted by Orrin
            The solenoid-operated fill valve on our dishwasher suddenly decided to start jack-hammering, continuously, while open. Nothing else has changed in the plumbing, water pressure, or whatever. Anybody have any ideas?
            There are generally arrestors for water hammer somewhere in the system. Older houses just used a vertical stub that's supposed to remain empty and just have air in it. Acts as a shock absorber for water hammer. Used to be a pair at every sink but I'm not sure what they do these days. Usually buried in the wall and you can't see them. Supposed to be an arrestor within 20 feet of each fixture. Over time, the air can get absorbed by the water, the stub fills up and it doesn't work anymore. Drain the system down. Let the supply pipes sit empty for a while. Fill it up again and the arrestors start working again. Might not work because there's a vacuum that keeps the water from draining out of the stubs. New houses use arrestors with a rubber balloon inside or a piston that can't get waterlogged and work in any position. Sediment could restrict things just enough to make it hammer when it didn't before. Try leaving the sink faucet open a little when you run the dishwasher.

            I'd stick one right at the dishwasher. They cost about 20 bucks. You can even get them with screw-on fittings you could adapt so there's no soldering involved. Make sure to get one rated for hot water. They come in both flavors.

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            • #7
              maybe missing something here but didn't the OP state nothing had changed in the supply?
              I'd still be looking for a servo valve fault
              Just got my head together
              now my body's falling apart

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              • #8
                Originally posted by Swarf&Sparks
                maybe missing something here but didn't the OP state nothing had changed in the supply?
                I'd still be looking for a servo valve fault
                It's either water hammer or a dishwasher problem. Water hammer can start for no apparent visible reason; i.e. sediment or a waterlogged arrestor. If the problem can be changed by changing the water pressure, likely not an electrical problem. Dishwasher fill valves are either on or off. They fill until the float switch in the sump says its full. If the valve isn't flapping on and off, it's a water supply problem. If the valve is rapidly going open and closed then you have to diagnose that with a voltmeter and etc.

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                • #9
                  "It lessens, somewhat, if I throttle the water supply..."

                  We have a valve that's just the opposite. It starts hammering if you partially CLOSE the shutoff valve.
                  Any products mentioned in my posts have been endorsed by their manufacturer.

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