The bathtub has two separate valves for hot and cold water, not a mixer. When I turn on the hot water valve, the cold one starts leaking from the stem.
Any ideas how that works? It’s not really a problem, because it only leaks when the water is running, and it leaks into the tub. So it’s not worth fixing in and of itself. I just think it’s very strange.
If both valves are mounted on a common bracket, and the bracket conducts heat to the cold water valve and heats the gland around the stem, it could conceivable expand enough to leak slightly. If they’re not so mounted, or if they are and the leak begins immediately, that wouldn’t be an explanation. We need more data…
Disclaimer: I haven’t been a licensed plumber in over 25 years. However, here’s my theory: I’m assuming that there’s one spout, but two separate valves. Therefore, there’s a mixing chamber at the spout. If you turn on the hot water only, then hot water could back up to the closed cold water valve and cause it to expand, causing a slight leak.
You might be able to just tighten the gland on the cold water faucet a bit. I doubt that it’s the valve cartridge.
There is a single spout, but it starts to leak immediately, even before the water gets hot, so it has nothing to do with heat. I repacked both valves several years ago. Maybe it’s time to do it again. They’re not easy to get at, being buried behind the tile. But as I said, it’s not a problem worth spending much time and effort on.
Perhaps turning on the hot water reduces the pressure in the entire system, unseating the valve. Does opening a faucet elsewhere in the house cause the cold water to leak?
[checking]
Nope. I opened all four faucets on the two sinks in the same bathroom, and don’t see anything.
Then I would guess that since turning on the hot water pressurizes everything downstream of the valves (if you completely blocked the nozzle then the whole system would be at 60 psi), the slight backpressure generated behind the nozzle might be unseating the cold water valve. Perhaps this could be tested by removing the shower head.
More liberal theories of the problem would include:
The cold water valve leaks in sympathy for the exploited hot water valve.
It’s a conspiracy by the water, gas, and electric utilities.
It’s a good thing, because you’ll hire a plumber or buy a new water heater, spurring the economy and generating jobs.
It’s your fault for not using a solar water heater and low pressure environmentally friendly plumbing made of bamboo, like on Gilligan’s Island.
Your inability to find a private-sector valve that doesn’t leak shows the futility of a new space rocket engine, full of valves required to handle much larger pressures and temperature extremes. If you want a bathtub that works, you need to hire a government plumber on a cost plus basis.
Since the two valves are connected via the spout, I’m going to guess that the hot water reverse pressurizes the cold water valve.
These old non-mixer tub valves may be prone to weird problems. My brother had one that wouldn’t hold a constant temperature; the hot water valve would slowly close itself over the course of a shower. We replaced everything we could get replacement parts for ( all the seals and the seat) without a fix.
2 gaskets for each valve. Low pressure cold seal is not.
For those who think it’s backpressure from the shower nozzle, note that I said it was a bathtub (no shower, which is separate). I wouldn’t think there’s much back pressure from an unvalved tub spout, but maybe that’s it. I may be completely replacing the tub and redoing the bath at some point soon, in which case it will be moot because I’ll probably replace the plumbing as well.
Rand said:
So an aerospace engineer from Rockwell has a mysterious, intermittent leak, cites the difficulty and labor of investigating it further because it’s buried behind the tiles, exchanges a few notes with other engineers, and concludes the leak isn’t really a problem, just something to be noted and monitored.
Who could’ve predicted that?
I don’t know whether you used the high temperature black tiles or the white tiles for the bathroom, but in retrospect it was a mistake. And sure, the leak may seem like a minor anoyance, but the cold water valve is in an off-nominal condition, operating way out of design specifications, and you shouldn’t stick your head in the sand, create some minor documentation about it (which will scroll off, forgotten, by Wednesday), and then treat the anomaly as normal.
This will not end well. One day you’ll be taking a shower, the entire valve stem will blow off and smack into your chest, the gushing stream will knock you down, you’ll hit your head, and your tub will suffer a loss of vessel and crew.
Then the accident investigation board, months later, will find this blog post, make recommendations, change procedures, and every freakin’ one of us will have to spend more time certifying our shower before each mission than actually showering. All because you built a shower with tiles (which probably seemed like a good long-term cost-saving measure at the time), making it too difficult to maintain.
Do you even read your own blog?
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Sorry, just had to go there! ^_^
your tub will suffer a loss of vessel and crew.
And after his tub overflows, Congress will force Rand to sit through weeks of hearings, then give him a billion dollars to fix the problem.
At that point, Tom Matula will say Rand was “punished” by Congress and needs to get out of human bathing and just wash robots.
He will also blame the Tea Party and Sarah Palin.
I *HATE* the way tubs and showers are piped with no thought to maintenance. In one of my houses there are no isolation valves, so I have to drain the entire house to work on a shower faucet. And don’t get me started on the lack of labelling on electrical wires.
For the last time, it’s a bath, not a shower. If it were a human-rated shower, obviously we would have repaired it long since, but the behavior for the tub is obviously in family.
In one of my houses there are no isolation valves, so I have to drain the entire house to work on a shower faucet.
I don’t think that’s unusual. There are shut-off valves for sink faucets, but I’ve never had a house with one for the bath faucets, other than the main. Though I could shut off the water heater to make it possible to work on the hot side.
My valve stems in my bath tub do the exact same thing. My bathtub uses the Sayco brand valve stems. They have an adjustable stem (that screws in and out of a valve body) which turns with an inner nut. The larger outer nut tightens the valve body into the stand. The inner valve stem nut is adjustable so that you can adjust the lash between the valve seat and the gasket. But there is a sweet spot that you have to find that lets you fully close the valve but also doesn’t let water leak out the valve stem adjuster itself. I guess the adjuster has to be deep enough into the valve body to provide a proper seal around the stem. I think when you install a new valve stem, you are supposed to loosen the inner nut to back the valve stem adjustment nearly all the way out. If you don’t do this you can actually crack your brand new valve seat when you torque the valve’s body into the stand. Make sure the new valve seat is fully seated or it will throw off the lash adjustment later.
To adjust the valve stem: open the water valve completely and then start screwing in the valve stem adjustment occasionally checking the lash by closing and opening the valve. When it feels like it is fully butting against the seat yet opens barely wide enough to let full water pressure out then you are getting close. Only way to find out is to go and turn the water back on and run a wet test and then shut it back down and readjust from there.
I’ve found that getting a suitable sized spark plug socket and wrench to fit the lug on the end of the spark plug socket makes like easier for the fine tuning. You just have to remove the handle and slide the spark plug socket onto the stem. Use a wrench to grab the lug on the end of the spark plug socket. Move the stem adjustment in and out until you find that sweet spot. I have to say that it seems more art than science as to where that spot is. I have one cold water stand stem in one bathtub that for the life of me I can’t get it to stop leaking past the stem 🙁
His insistence that his bath is not a shower sounds like a psychological problem. He’s in denial. We need to send a team of healthcare workers to his location immediately.
All taxpayers will of course have to pay.
It sounds to me like the thing is broken.
I grew up with separate dials for hot and cold, therefore I still find those mixer dials stupid and annoying. I have two hands, I can operate two dials at the same time, why would I want some two dimensional interface to the hot-cold/pressure gradients.
Oh, and the way it remembers the hot-cold setting, I guess they never heard of heat acclimatization. The result being that some people fail to turn the hot-cold back down to cold before increasing the pressure.. or worse yet, moaning that other people need to always turn it down to cold for them.
Now get off my lawn.
The valves are very likely globe valves with the water supply connected to the side under the plug which leaves the valve stem seal side vented through the common spout. Therefore, the valve stem seal only sees water when the downstream side is flooded, i.e. when hot is flowing.
And after his tub overflows, Congress will force Rand to sit through weeks of hearings, then give him a billion dollars to fix the problem.
No they won’t. The EPA will step in and fine Rand a billion dollars for screwing around with a federally protected wetland.
So, it’s established that Rand has a tub, not a shower. Obviously the Senate needs to make him upgrade to an Olympic sized swimming pool, but what other suggestions do we have?
There’s a possibility that it’s not a valve leak but a leak between the outlet side of the valve and the downstream pipe, following along the exterior of the valve before appearing in the tub. Arguing against that diagnosis is that the water comes out in the tub instead of mostly somewhere down below, which should be obvious.
It’s possible the seal on outflow side of the valve is completely shot, and unless pushed in place by pressure from the inflow side of the valve, and water on the outflow side will just flow right out the valve stem.
Bathtubs need a maintenance access panel (possibly accessed through a Jeffries tube), with ball valves for hot and cold water shut off and servo-driven flow controls in a PID loop temperature control system.
Further federal funding should be allocated to figure out how to use the system to safely bathe a cat.
With the proper funding ($1b.) I’m prepared to develop a fully automated green energy cat washing machine.
I promise I will not go bankrupt although I will vanish so the FBI will not be able to raid my non existent offices.
I would of course, indirectly, employ thousands of people as I flee to various resorts throughout the world.
Don’t let the fact that my cat washing machine looks like a regular front loading clothes washing machine fool you… It really is a green, environmentally friendly exclusive design you can purchase at any Kmart.
All the plumbing values I’m familiar with have 2 seals, a primary operated by the handle, and a second for the shaft from the handle to the primary valve. If the second seal is bad on the cold valve, turning on the hot water to the common faucet could it to leak.
If the shaft seal is marginal it may leak at some handle positions but not others.
Rand:
Your tub is likely a pair of globe valves (most common in house plumbing). Globe valves have the stem packing connected to the outlet. When both valves are closed, neither stem is pressurized. hence no leaks to the outside world (as opposed to a leak downstream). This allows the valve to not leak to the outside world when shut off, even if the stem packing is faulty. On SOME globe valves, you can change or tighten the stem packing without shutting off the system. (remove the handle and use Josh’s comments)
This is a nice feature of globe valves, but their truly horrible insertion pressure drop prevents their use in weight critical applications.
It takes several turns to open them. I don’t thing that’s a characteristic of a globe valve. I suspect it’s a gate.
I’m not sure what that means in the context of the discussion…
“It takes several turns to open them.” That is a characteristic of globe valves, and are used as flow regulators. They are unlikely gate valves which are used as shutoff valves (open/close).
Globe and gate valves both take several turns to open, depending on the screw pitch. The stem both rotates and translates inside the packing, so the leak may only happen at one setting due to uneven wear. As rtsquard says, gate valves are usually used as shutoff, not throttling valves. One reason is that they tend to erode unevenly and leak through after a few years of throttling service. Gate valves are also not typically used for frequent service because they tend to stick in the closed position.
Of course, both types could show the same stem packing leak when the other valve is actuated on your tub.