Plumbing Question

[Richard in Smithville]

"Buddy" comes into work today( knowing that I'm usually the guy to ask) with questions about his run-on toilet. I walked him through a rebuild of the tank hardware to make his old toilet new again.

Now here is the puzzler. The toilet tank would continue to fill ( bad float?) until someone turned on the tap in the bathroom sink. Then the float would jump that extra hair width and shut the fill valve. I have some guesses as to the cause but still at a loss. Any ideas?

[Cochese]

I know almost nothing about plumbing. But any chance it's related to a pressure equalization in the vent?

[pelligrini]

It might be a bad valve. My upstairs toilet would about do the opposite, if I turned on the sink the thing would start leaking. I've had pretty poor luck with the cheap plastic kits from HD.

[herb fellows]

If that's a direct effect every time, it would seem as if the sink is taking water pressure away from the toilet fill valve, which is allowing the float to complete it's ascension. So I guess the question is why would 'excess' water pressure in the fill valve prevent the float from seating properly in the first place.
Bugger all if I know the mechanics of this though!

[jdon]

Does the toilet valve shut off when the lavatory tap is opened, or, after flowing, when it is shut off? If the latter is the case, assuming the two are on the same run, shutting off the lav faucet could create a localized water hammer (a short spike in water pressure) which might be enough to "nudge" a balky toilet valve closed.

[JimD]

If he doesn't have a fluidmaster valve he should get one. The float goes straight up and down the shaft. They work much better and are less than $10. If he has a fluidmaster, he can try replacing the seat for about $3. It is fluidmaster part 242 and should be available at the local home center. If the fluidmaster is really old, it might need replaced. That shouldn't happen for at least 5 years. I've tried other types and brands but I don't mess around any more. I replace the valve in new toilets with a fluidmaster. They are better and are not expensive. They are also simple to install. The hardest thing is draining the tank.

The valve cannot seat until the pressure is reduced by the sink opening. Soon, it won't shut off then either.

Jim

[Richard in Smithville]

A lot of what everyone has said is alone what I was thinking too. I just told him to get a kit from the hardware store and rebuild it. He's a big computer "geek" so I figure he will look up how it's done.

[4estgump]

Just a thought. Maybe it's a reminder to wash your hands.
4est Ha Ha

[LCHIEN]

I like 4-ests answer that its a sign from god to wash you hands after u know what.

JDons probably on the right track, the shut off valve and float being old, sticky or weak and marginal just can't muster the force to shut off the water flow against the pressure.

The drop in pressure when turned on or perhaps the water hammer from turning it off may be just enough to nudge the valve and/or overcome the pressure and to do its thing and close. I'll bet that replacing the valve and float parts fixes it.

[JimD]

I told a couple who are both engineers (nuclear I think) to get fluidmaster parts and rebuild their toilet. They bought the kit with everything. The wife read the instructions to the husband and they used all the part in the kit. Including the bolts that hold the tank to the base. They commented that was a hard part. I felt bad. I had no idea they would replace those bolts. I guess no harm done but I counted on them having a little common sense... Their toilet worked when they were done.

Jim