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Thread: Tap - knocking?

  1. #1
    Senile Member sarel's Avatar
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    Default Tap - knocking?

    When I open a certain outside tap, and the tap stays open, if you use any other tap in the house - hot or cold water tap - this outside tap seems to "knock". Sounds like the pipe hitting something (typical water hammer scenario I thought). I've replaced all the washers on all the taps in my house, no change. I somehow got this nagging feeling that it all may be due to a sticky valve in the hot water cylinder?

    Any-one got better ideas?

    sarel
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    IT Consultant johcar's Avatar
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    Default Re: Tap - knocking?

    Maybe it wants to come in?

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    Debiant Myth's Avatar
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    Default Re: Tap - knocking?

    I had this problem with an outside tap. The neiighbour reckoned there was air in the pipes, and to get rid of it, run all taps in the house at once. I havent done it yet, so not sure if that really is the case
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  4. #4
    Senile Member sarel's Avatar
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    Default Re: Tap - knocking?

    Did that after I changed all the washers in all the taps in the house but I could probably do it again, no harm in doing it again.

    Sarel
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  5. #5
    Smiling Down On Youse SurferJoe46's Avatar
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    Default Re: Tap - knocking?

    It isn't air in the lines, it's lack of an anti-hammer in the system that you need to remedy. You may have one installed already, but it may also be malfunctioning.

    Let me find a reference to it - it's easy to install if you want to do it yourself.

    We use them here in the US all of the time to eliminate this very problem. It isn't metric or in the King's measure and it can be readily adapted to foreign water supplies too.

    Here's the link.
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  6. #6
    Senile Member sarel's Avatar
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    Default Re: Tap - knocking?

    But then somebody mentioned somewhere something about a sticky valve on a HW cylinder?

    sarel
    Fishing is not a matter of life or death, it's more serious than that.

  7. #7
    Smiling Down On Youse SurferJoe46's Avatar
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    Default Re: Tap - knocking?

    I don't know what youse guys use to heat water - I've heard the term "wet-backs" and others, so I may be a little off curve here for you.

    Our water heaters have no valves at all unless you count the cold-feed shut off in case the heater tank starts to leak and a "T&P" valve to relieve water pressure if the pressure gets too high or the unit fires on an empty tank and makes real steam under pressure.

    They can create a crater where the house used to be - but most people don't know that.

    No moving parts usually equals no noise either unless it's low water boiling and slugging the lines - but you'd KNOW that sound I'm sure!

    I bet your anti-hammers (if you even have or use them) are full of water and cannot operate as an accumulator to keep the "slamming" to a minimum.

    Read the article a little further down the page and see how easy it is to make one or more for yourself.

    Build NH's Do-It-Yourself Air Chamber!!

    Sometimes, draining down the pipes just doesn't work. Perhaps the air chambers are blocked so they don't drain... or they don't exist! And you're not in the mood to open up the walls and investigate.

    If that's the case, you can assemble our do-it-yourself air chamber that does not require much plumbing skill AND doesn't require making any holes in the walls!

    These two graphics really say it all! This sample air chamber (left) is designed to fit behind the toilet tank... a typical water hammer culprit. Basically, the chamber consists of a vertical piece of 3/8" copper tubing sealed at the upper end. In this case, I used a 3/8" compression tubing connector, replacing one of the compression rings and nuts with a compression cap. (Be sure to wrap the threads with at least five or six turns of Teflon tape before installing the cap to prevent air leakage.)

    A compression "T" is installed above the shutoff valve using a short length of tubing. The air chamber is connected to the second connection and the toilet inlet tube (or, in this case, no-burst hose) to the third.
    (check the link for pixs!) the air chamber tubing has been bent to neatly "hide" behind the toilet tank. Use as long a length of tubing as you can for the chamber. The longer the air chamber is, the better it will work. In fact, you can coil it or zig-zag it across the back of the tank for added length... as long as it is above the shutoff and inlet tubes so water can't leak into it (and air leak out of it).

    For an even neater and more professional job, use all chrome parts. It will look positively spiffy and work just as well. If you can't get chrome tubing, purchase an extra long 3/8" faucet supply tube and cut off as much as you need.

    If you have soldering skills, this entire assembly can be soldered into a single piece, needing compression connections only at the shutoff and at the toilet inlet tube!

    One caveat. Because your plumbing is probably 1/2" copper pipe and our DIY air chamber is 3/8" tubing, it will not absorb severe shocks as well as a 1/2" chamber... but it will sure help in most cases!

    If that just isn't good enough for you, you can design a similar air chamber by adding a soldered 1/2" T between the shutoff and the wall, or other variation depending on the type of shutoff you have and the amount of visible pipe. Seriously, if you have the plumbing skills to understand this, you undoubtedly have the creativity to design one of your very own!!
    Last edited by SurferJoe46; 19-03-2009 at 01:47 PM.
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  8. #8
    Smiling Down On Youse SurferJoe46's Avatar
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    Default Re: Tap - knocking?

    I usually make my own - but there are commercially available ones if you prefer with springs and nitrogen-charged cylinders and bladders etc. .

    Here's a link to what I generally make during a remodel or even a fresh-new construction.

    I try to put them in the walls of every post where water is used and controllable there by the customer. (sinks, toilets, water faucets and bibs, etc).

    They are there for the life of the system and if they don't leak at first, they prolly never will. You might want to make one larger version outside near your water supply inlet line. That way it's sky'd-out and available for inspections and service - but that should be never.
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  9. #9
    Zippity Fan Club Member prefect's Avatar
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    Default Re: Tap - knocking?

    Its called fluid hammer or shot gunning only way to fix is to to fit an accumulator.
    An accumulator is a cylinder with a sealed piston or diaphragm in it. One side is filled with air or nitrogen to about 40% of the water pressure. Some have a spring. If you could score a pressure tank of something like a Masport Onga pump it will do the same thing just tee it into the effected line.
    Either fit one or live with noise.
    Last edited by prefect; 19-03-2009 at 03:02 PM.
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  10. #10
    Awaiting Enlightenment R2x1's Avatar
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    Default Re: Tap - knocking?

    Or alternatively, try putting a little silicon grease, or even margarine, around the stem of the outside tap jumper. (The stalk on the bit that holds the washer.) The idea is to get the jumper to stay stuck to the tap spindle and not dance up and down in the water turbulence at certain flow rates. If you vary the opening of the outside tap, does this stop / otherwise affect the water hammer?
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