Commode water "Knock"

[Tyme2fish]

I installed a new fill valve several months ago and have had a problem with "knocking" ever since.<br />My old unit was the arm with float ball on the end.The new unit has the "riser" on the fill valve. I also installed a new "flapper" <br />I put dye in the tank and there does not appear to be a leak from the tank to the commode.<br />About every hour or so, the water in the tank comes on for 2 or 3 seconds and then "knocks" off.<br />What have I done wrong and what is the solution?

 

[ob]

Re: Commode water "Knock"

Gotta be losing water from the tank to the bowl.Float drops and opens valve.A small leak that only refills every hour or so may not show a color change in bowl water on your dye test.As far as the water hammer when valve shuts off,I suspect the water supply riser may have a small leak and there is insufficient trapped air to damper.May try draining the line completely by removing the supply valve under toilet and reinstalling.

 

[Paul Moir]

Re: Commode water "Knock"

Is it overflowing into the overflow tube? If not, those 2-3 seconds of water have to be going somewhere right?<br />Those Fluidmaster valves shut off very suddenly and produce water hammers. There's not much you can do but install dampers; a long vertical run of pipe capped at the end to trap air. Other than that I like them very much.<br />At least I assume that's the valve we're talking about. Looks like this?<br />

 

[Tyme2fish]

Re: Commode water "Knock"

Originally posted by Paul Moir:<br /> Is it overflowing into the overflow tube? If not, those 2-3 seconds of water have to be going somewhere right?<br />Those Fluidmaster valves shut off very suddenly and produce water hammers. There's not much you can do but install dampers; a long vertical run of pipe capped at the end to trap air. Other than that I like them very much.<br />At least I assume that's the valve we're talking about. Looks like this?<br />

Yep, that's what I have. I'm confused as to where<br />I would connect a damper.

 

[ob]

Re: Commode water "Knock"

Your water suppky line (in the wall if you have thru slab plumbing)should have a riser that prevents this very thing.I've had both the old style and the style of tank valves that you have and haven't found them to cause water hammer unless you're plumbing wasn't up to par to begin with.

 

[KilroyJC]

Re: Commode water "Knock"

Dumb thing to check, but it just happened in my parents' bathroom:<br /><br />Check the chain from the lever to the flapper for a twisted ling - it may be putting just enough tension to cause a slow seep, which will make it refill every so often.<br /><br />If it is one with a platic chain, the links float, and sometimes they can get hung up and cause this as well. I lace a short piece of thin solder into the links for ballast so that does not happen.<br /><br />Hope this helps!

 

[Paul Moir]

Re: Commode water "Knock"

Sorry, in my last post I came across as a lot more absolute than I ment to be. A far simpler solution to the water hammer is simply to replace the valve with one that doesn't cause it. Fluidmaster makes one called Silent-something-or-rather. <br />Wether or not your house has dampers really depends on it's age. Around here where we're mostly dealing with houses built in the 70s or prior they're very uncommon. I would not call their plumbing sub-par though. Properly placed, they should be at the end of the line as far from the water meter as possible and on the end of each branch.<br />One of the benifits of those hysterisis type valves is they really show when you've got a slow leak. Triple check the flapper installation to make sure it's sitting freely nice and square. Check the overflow tube for cracks and even shine a flash light down it to make sure you see no drips.

 

[rottenray6402]

Re: Commode water "Knock"

I had the same problem with that type of valve and found by lowering the float level about 1/2" it eliminated the problem. The float was set to high and a small amount of water was going into the overflow very slowly. Didn't make sense but it worked. On the hammering problem try closing the supply valve at the toliet just a little so there isn't quite as much pressure going to the valve. The tank will fill a little slower but it should help with the hammering a little bit.

 

[Tyme2fish]

Re: Commode water "Knock"

Originally posted by rottenray6402:<br /> I had the same problem with that type of valve and found by lowering the float level about 1/2" it eliminated the problem. The float was set to high and a small amount of water was going into the overflow very slowly. Didn't make sense but it worked. On the hammering problem try closing the supply valve at the toliet just a little so there isn't quite as much pressure going to the valve. The tank will fill a little slower but it should help with the hammering a little bit.

Rottenray, I think that may have done the trick. At least I haven't heard it knock yet this morning. Thanks

 

[rottenray6402]

Re: Commode water "Knock"

I hope that does it for you, glad to help.