Dripping thermal expansion relief value

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MACPLUMB

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that is a thermal expansion relief valve and is in place of an expansion tank, so absolutely remove it if you install the tank. It is doing the job it was designed for but it is a waste of water.
you are all missing the point !
This is the correct answer that is a ball valve to shut the water off and a combination thermal expansion relief valve that opens at 80 psi
to relief excess water pressure and yes it is doing exactly what it is designed for ! ! And it also wastes water !
 

Jadnashua

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you are all missing the point !
This is the correct answer that is a ball valve to shut the water off and a combination thermal expansion relief valve that opens at 80 psi
to relief excess water pressure and yes it is doing exactly what it is designed for ! ! And it also wastes water !

No, I don't think we all are missing the point...this was already discussed. But, the better solution is an expansion tank - and maybe a PRV, if the supply pressure is also high, then the thing, if you left it there, should never open except if the other things fail.
 

Jerome2877

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Jerome, you're still mixing terms. Every water heater come equipment with a temperature/pressure safety valve, commonly referred to as a T/P valve. It will trip if the temperate or pressure reaches the danger points. Water heaters can and do explode, and I mean big time explode if this valve does not open. If your incoming water pressure is excessive, that's 80 psi or more, you need a pressure regulating valve, commonly called PRV. This will lower the pressure to a safe level. The PRV does have a slight downside. Most of them contain a back flow feature. I'll come back to that feature in a minute. We all know that heated water expands and it does not compress. This means when you water heater starts to heat, temperature builds up quite rapidly. If you do not have a PRV, the expansion can be absorbed by the city water main and you have no problem. However, with the PRV, the expansion has to find somewhere to go, and the back flow feature prevents it from get to the city main. It might find a weak toilet valve, but often it will trip the T/P safety valve. The cure for this is with a Thermal Expansion Tank that is installed in the incoming cold water line between the PRV and water heater. This tank provides a temporary escape route for the expansion. It is air charged to match the PRV setting. Hope this clears things a bit for you.

:) Thanks Gary but I think your the one that needs things cleared up. Like I said the valve is designed for thermal expansion relief and instead of a bladder tank it just drains off to accomplish this. While I agree that an expansion tank is a better solution, the valve (like Macplumb agreed) is doing its job!
 

Jerome2877

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That extra pressure relief valve that was leaking was an indication that the house pressure was too high OR there was no accommodation for expansion when the WH ran. Once you have an expansion tank in there, you do not need that relief valve (do NOT confuse this with the T&P valve on the WH - that MUST stay). Most people find that the pressure relief valves tend to start leaking as they age, even if the pressure isn't too high, so they're kind of a nuisance. You CAN keep it if you want, and it would be another level of protection. The vast majority of houses do not have one, and work just fine. FWIW, the T&P valve can also start to leak as it ages, especially if you have hard water and it gets tripped because of no expansion tank. You should test the thing annually, but as it ages, that may cause it to not seal after the test. One way to look at that, is it probably should have been changed anyways. Sometimes, the tank fails before the valve does.

Nope, the point your missing is the fact that thermal expansion accommodation was provided and the leaking valve you say starts to leak with age is designed to leak and is doing its job.
 

Reach4

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Nope, the point your missing is the fact that thermal expansion accommodation was provided and the leaking valve you say starts to leak with age is designed to leak and is doing its job.
You seem to have missed the "even if the pressure isn't too high" bit.
 

Jerome2877

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You seem to have missed the "even if the pressure isn't too high" bit.


No, he was stating that the leaking valve was "an indication that the house pressure was too high OR there was no accommodation for expansion". I am saying that in fact that valve is the "accommodation for expansion"

The valve like anything mechanical could fail and start to leak when its not supposed to but I don't see where I am missing anything here?
 

DonL

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Most of the safety valves I have played with are not made for Cyclic operation. Some do not even auto-reset.

You can build a old school expansion / hammer Protector - Tester with a dead ended piece of pipe.


A Expansion tank is the best solution, If the problem is do to heating water.
 
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psyq

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Home Depot was actual sold out on all their pressure gauges. I'll see if I can find one today somewhere else.

I did consider a DIY gauge from assorted fittings... but, nah
 

Terry

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Ballvalve loved those pressure releasing valves that needed drains.
He didn't like the expansion tanks. I would rather install an expansion tank, and not worry about where to drain the "pop off" water.

But if the vavle is releasing too often, I would look at house pressure first. It may be too high.
 

WJcandee

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The T&P Valve?
Not unless you want that water heater to launch itself through the roof and land on your neighbors home.

Like this (and other photos and videos out there show that this is no joke): [video=youtube;bVf6naulS1s]http://www.youtube.com/watch?v=bVf6naulS1s[/video]
 

Wrenched

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To meet code in Vancouver, auxillary thermal expansion relief valves have to dump at 80psi or less. The tag on the valve will tell you what the factory set point is.

When a residential tank is heating from cold a valve can dump as much as a cup of water, but usually it's less than that.

A steady drip or stream when the tank is not heating can be a sign of valve failure -if- the system pressure is below relief point.

Typically plumbers here will set house pressure at 60psi - a system pressure above that means either someone cranked the PRV, or the PRV isn't regulating properly.
 

Wet_Boots

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Most descriptions of the PRV's I've had mentioned a bypass feature that was designed to allow excess downstream pressure to bleed back through the device. Since expansion tanks are de rigueur in a system with a PRV, does that mean that the bypass feature of PRV isn't really being counted on to accomplish anything?
 

Jadnashua

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The bypass, if it exists, can only open if the house pressure exceeds the incoming pressure. The goal is to keep the house pressure fairly constant, which is typically the reason a PRV is installed in the first place. That entails an expansion tank unless you want to deal with dumping water periodically along with the periodic rise in pressure.

One poster here recently said his incoming water pressure was peaking at something like 190. At that pressure, before the PRV would ever open the bypass, the WH's T&P would have relieved the pressure or something else would have leaked or busted.

Certainly, a pressure relief valve can keep the pressure from maxing out, but if anything, I think the preference is to keep it steadier, and not have to deal with periodic dumping of water. With a PRV and no expansion tank, it is not uncommon at all to have a weeping T&P valve.
 

psyq

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The thermal expansion relief valve is made by Apollo and has a rating of 80psi. Since my pressure is WAY below that I should probably look at either replacing that valve, or buying an expansion tank. Thanks everyone, huge help!
 

Jadnashua

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A closed system can easily get high enough to cause the T&P valve to open (at 150psi) unless there's some other path to relieve the pressure from thermal expansion. Fluids like water do not compress to any significant amount like a gas does...expansion correlates directly with raising the pressure in a closed, primarily rigid system. The expansion tank, containing air, provides an easy place for that water to be accommodated. To keep from dripping through that valve, install an expansion tank. You can keep that valve or take it out if you want...if you did keep it, it would act as a secondary backup. Some people like the redundancy, but it is not required. Without it or an expansion tank, your T&P valve would be weeping each time the WH ran after you shut the hot water tap off. How much would depend on the aquastat setting and how much and at what temperature the incoming cold water was. Say you were to raise 1 gallon of water from 12C to 60C, you'd have about 1.32oz or almost 40ml of expansion http://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html Dealing with that is typically a nuisance, especially when an expansion tank takes care of it nicely with no leaks.
 
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