what is this called?

[Emo113]

Hello,

my water heater started spewing out water from the pipe that is connected from the T&P relieve valve so I thought it needed to be changed. I did change it but the water kept going. (By going I mean it will fill up a 8oz glass in less than a minute). I went back to my W/H and I noticed that the HOT water pipe going back to the house has a samller 1/2 inch pipe connected to that pipe that is going outside the house.

so at this point I think I have to replace that brass part that is in the middle of the connections but I have no idea what's it called or where to get it... Lowes or HomeDepot do not carry this.

I noticed I can turn a knob on the top of it left and right but that did not help the water flow to go down.

At this point I dont know what else to do! Please help!

Thank you!

[Emo113]

To give you a better view of the whole setup that I was talking about here is another pic that might help

thanks!

[phishfood]

HATE, HATE, HATE! I hate my internet connection!

I had a nice reply all typed up, with a big explanation of what a thermal expansion valve is, how it works, why it is needed, etc. And then, as I clicked the post reply button, my connection died. Aaaarrrgggghhhhh!

Anyway, a thermal expansion valve relieves excess pressure that is built up when cold water is added to the water heater and expands when it is heated. It is a valve that is held closed by a strong spring. When the pressure gets high enough to push back on the spring, the pressure is relieved. Normally, you can adjust the pressure setting by turning the knob on top. Since you can't, your best bet is to replace the valve. Any plumbing supply house should stock them. If none in your area will sell to you, I found one on Grainger's website, here

[Mr_David]

Must be an east coast thing. I have never seen one of those used here in southern Calif. We are required to use expansion tanks to deal with thermal expansion.

[phishfood]

An expansion tank is the best option, no argument there. I even had something about that in my original post that got eaten by the big mean web monster.

[CHRISM]

As it is IMPOSSIBLE to heat water to a temperature suitable for `Household Use` WITHOUT EXPANSION - is it being suggested here that the Hot Water Cylinder / Tank is just `Holding` the pressure of the Expanded Water because it is `Strong Enough` - ?? - AND that the resulting increase in Pressure is always BELOW the Pressure that would normally `activate` the `spring loaded` Pressure Relief Valve ??

I am assuming that THIS Hot Water Cylinder / Tank is `Mains Fed` [Water] - So has to `withstand` the Pressure of the `Incoming Water Main` [regulated ?] - AND `Thermal Expansion`[?]
These are called `Unvented Cylinders`- in the U.K. - and have `Expansion Vessels` - often built into the Unit - within the casing.
Because of the `Dangers` of the incorrect installation of this type of Hot Water Cylinder - especially when heated by connection to a `Gas [or other] `Boiler` [Furnace] - by Flow and Return Pipework - We have to pass assessments [exams] on these appliances - AND be `registered` to be able to LEGALLY install - maintain or service them.
This is to ENSURE knowlege of the `Safety Controls`- Thermostatically controlled Zone [2 Port] Valve - Pressure AND Temperature Relief Valves - plus a `safely run` and `correctly sized` Discharge Pipework [can be `Scalding Hot Water] - etc.


I have `come across` Hot Water Cylinders in the Mediterranean Countries of Europe where the Water is primarily heated by a Solar Panel connected to the Hot water Cylinder - where the Thermal Expansion is `Allowed` to just `run off` - discharging via a spring loaded valve - Wasting water every time the Cylinder is heated - EVERY DAY.
This also applies when an Immersion Heater is used - Autumn / Winter / Early Spring.

BUT - I KNOW that is NOT allowed in the U.S.A. - !!! - OR even the `possibility` of that happening [as a norm.] ??

In the U.K. and most of `Mainland Europe` - There are Hot Water Cylinders which are Insulated and `Clad` [Casing] - as in the Photo for this original `Post` - which HAVE an Expansion Vessel - Built into the Unit - WITHIN THE `CASING`. [ Unvented Cylinders ]

This MUST be the case HERE [?] - IF it is - then the Expansion Vessel has `lost` its `charge` - cannot take up the Thermal Expansion - and the `Pressure Valve` is doing `its job`.
If there is an Expansion Vessel that EITHER needs `Recharging` or Replacing [?] - replacing the spring loaded `Pressure Valve` would do NO GOOD AT ALL !! - although IF I were `Recharging` [ pumping-up] or Replacing the Expansion Vessel [ there must be one ?] - I would replace the `Pressure Relief Valve` [inexpensive].

Can my `American Colleagues`inform me IF it is possible that THIS / OTHER Hot Water Cylinders are installed WITHOUT any `Expansion Vessel` ??
IF that were the case - The Cylinders / Tanks would have to be of a `Very Strong` Construction - to `Hold` the Pressure of the Water Main and EXPANDED WATER - Also a spring loaded `Pressure Relief Valve` would be `Suspect` as a design - because of the Substantial difference in the VOLUME of EXPANSION depending on the `SET TEMPERATURE`.
Although stored water should always be `Set` at a minimum of 60 Degrees Centigrade - [140 Fahrenheit] - to prevent `Legionella`- People `set` their Hot Water at `all sorts` of Temperatures - AND therefor - `all sorts` of `Thermal Expansion` has to be `allowed for` in the Design / Safety parameters of Hot Water Cylinders / Tanks.

I cannot imagine that a `Primitive Design` such as is being suggested - is `ALLOWED` - in ANY State of the U.S.A. ?? - For `SAFETY REASONS - IF nothing else !!

ANY idea of allowing Expansion of Heated / Stored Water to be `taken-up` within the Water MAIN - should not be `applicable` in this `Day and Age` - regarding `protecting` the `Potable`[Drinking Quality] Water to the Building, and also the `configuration` of Pressure Reducing Valves - `Non-Return` [check] Valves and `Isolating Valves` - that are installed at `most` properties - would stop that being an `option`.

I look forward to reading responses on this, Your `Fellow Professional` from the U.K. [ England].

"Regards", CHRISM.

[phishfood]

In my experience, it is not the norm for water heaters to have a built in expansion tank. Expansion is relieved either through a relief valve, or through means of an externally mounted expansion tank.

In all new construction cases that I see, check valve arrangments HAVE to be installed between the dwelling and the water main, so obviously, the water main cannot be counted upon to absorb the expansion.

The thermal expansion valve that is at issue in this thread is meant to be the primary expansion relief system. If it were to fail, the backup would be the Temperature and Pressure Relief valve that is also required. It is designed to discharge at a much higher pressure than the thermal expansion valve, and is also designed to release in cases of excessive temperature.

As I noted above, expansion tanks are the best option, but in some areas expansion valves are allowable by code.

[CHRISM]

As it is IMPOSSIBLE to COMPRESS WATER - regarding the pressures found in Domestic Hot Water supply - where are you saying that the Increased VOLUME of the Stored Water is `Accommodated` ??

The example in the Photo`s is a `Mains Fed`[Water] Hot Water `Cylinder`[Tank] - `UNVENTED` - WHERE are you suggesting that the `Expanded Volume` is `Taken - up`/ `Accommodated` ??

In my `extremely long` original Post I was suggesting that an `Expansion Vessel` might be Built - into the Hot Water Unit - IF that is NOT the case - I ask the `QUESTIONER` IF there IS such a `VESSEL` perhaps adjacent to the Unit - OR elsewhere [not recommended] on the Hot Water System ??

Thermal Expansion of Water HAS TO be `Accommodated` [extra VOLUME] somewhere - OR `Discharged`- note my comments in my original `Post` on this matter - regarding - IF no expansion vessel exists - parts of Europe ALLOW the Expanded Water to be `Discharged`- via a PIPE - usually not required to go to Drainage - just onto a Roof or onto the Ground ! !

I `fully understand` the operation of the `Pressure Relief Valve` AND the `Temperature Relief Valve` - As WE KNOW that - NO U.S. State would allow the Expanded Water to be `Discharged` / Wasted.

Without an `Open Vent` Pipe :
- The `Increased Volume` - even though small in percentage terms [of `cool` volume] - HAS TO be accommodated.

In my original `Post` about this - I suggested that the Expansion Vessel [must be one ?] `Charge` had dissipated - and the vessel was no longer `accepting` the Expanded VOLUME - of Heated Water - SO - the `Pressure Relief Valve` was `doing its job` and relieving the Pressure when the Expanded Water PRESSURISED THE UNIT, So - NOT ALLOWING THE UNIT TO `BECOME` `PRESSURISED` ! !

A Point to `note` is that the Hot Water `Cylinder`/ `Tank` is already `under pressure` from the `Incoming Water Main` - and although these `Units` are manufactured to be able to withstand fairly `high pressures`- `STATIC` and `WORKING`- they are NOT made to withstand the INCREASE in VOLUME - when `Thermal Expansion` occurs - in a `SEALED SYSTEM`.

When reading the paragraph above - you might think - WHAT is the `difference` between the Unit being pressurised by the Water Main - at various pressures - differing in various `States` and `Areas`- eg. 55psi in one State/Area and perhaps 70psi in another.
AND the Unit pressure on the Water Main [incoming pressure] here being perhaps 55psi - and INCREASING to 70psi when the Water is Heated ???

The DIFFERENCE is THIS: We can FILL the Unit / Hot Water System to EITHER of the `example pressures`- and the VOLUME of the Unit and System is the SAME on either `Incoming Main Pressure` - BUT when that Water is HEATED - the VOLUME INCREASES - THERE is the `DIFFERENCE` ! !
THAT increased VOLUME has to have `somewhere` to be `Accommodated`- `EXPAND TO`.

I THOUGHT that my Original `Post` FULLY EXPLAINED this - BUT as I have had to `REITTERATE` it - "Perhaps not" ???

I MUST `explain better` - perhaps `GOING INTO MORE DETAIL` - in future `Posts` - what do my `Professional Colleagues` think ???

As usual - I am `delighted` to be able to explain this to my `colleagues` - `Hydrodynamics` is a subject which very few people - including `Plumbers` understand - THAT is one of the `reasons` that some `seemingly` simple problems are `misdiagnosed` [not necessarily this post subject]

When systems are `Sealed` - by Design OR `inadvertently` by incorrect use of Valves etc. - the `Dynamics` of the system are COMPLETELY CHANGED - including for One example - the Boiling Point of Water - within a sealed system.

In a Sealed - `Unvented` Hot Water Cylinder - IF the Pressure Relief Valve and the Temperature Relief Valve were NOT fitted - NOT completely `unheard of` [in U.K. - by Unskilled Idiots] - AND the Thermostat of the Unit `FAILED` to turn off at Temperature setting - THAT UNIT would keep heating the Water - UNTIL the Unit OR another part of the Hot Water System Failed - under pressure.
IF the Water Temperature had risen to above boiling point - remembering the Water is NOT at `Atmospheric pressure` - which could happen - when the Unit `Failed` - BURST - the Contents / Water - NOW released at OVER BOILING POINT - would IMMEDIATLY EXPAND to approximately 1600 TIMES the Unit original Volume - of SCALDING STEAM ! !
Imagine for example even 50 GALLONS of Water X 1600 = 80.000 Gallons [Volume] of `INSTANTLY EXPANDING` VAPOUR = An `EXPLOSION` ! !

My Example assumes that the Pipework in the Hot Water System is Copper or Iron - Stronger than the Hot Water Unit itself.

That `DANGER` of `Incorrect Installation` is WHY we - in the U.K. have to pass EXAMS on this kind of `Installation` AND be `Registered` and `Licenced` to Install - Maintain or Service these `UnVented` Hot Water Units.
AND WHY `knowledge` is required to comment `on all aspects` about them,
- MORE KNOWLEDGE than - JUST `Installation techniques`! !

"Regards` to all my U.S. Colleagues - I would `welcome` ANY `informed` comments about ANY of my `Posts` - I don`t get any - WHY would that be ???

CHRISM.

[havasu]

I'll give a shot on answering some questions from Chrism. You advised in England, your water heaters heat water to a minimum of 140 degrees, but the recommended temperature setting for the US is between 120 and 140 degrees, and if children are present, 120 degrees should be the maximum. Much of this is due to the stringent water standards and lack of bacteria in city water supplies.

The steel tanks sold in the US are capable of handling 300 PSI, and there is space built into the tops of these tanks for thermal expansion. In addition to the fail safe thermostats, the water heaters must be supplied with a temperature and pressure relief (TPR) valve, and per code, must not be connected to a drain line, because this is an early warning sign of a failure.

Also, with normal boiling point being 212 degrees farenheit (give or take with altitude variances) or 100 degrees celcius, these water heaters fall way short of vaporizing, which reduces the dangers substantially. There are expansion tanks used sometimes, but for the most part, in normal residential usage, and normal temperatures, are deemed unnecessary.

Every hardware store in the United States sell water heaters, primarily for installation by homeowners themselves. I myself have installed in excess of 100 water heaters, and using only common sense, have yet to have a failure or defective installation.

[CHRISM]

"Thank You Havasu" - Good answers - Just a few `comments` on what you said - Regarding the Hot Water Temperature - ANY Temperature below 60 degrees Centigrade - 140 f - WILL allow bacterial growth - and U.K. Drinking Water - `Mains` is recognised as the `Purest` in Europe - by a `long way` - I would also expect that U.S. Drinking Water - `Mains` - would be `on a par` with ours - So the U.S. being able to heat water to a lower temperature BECAUSE of your `Water Quality` - is not a `Scientific` reason.

Regarding the Temperature of the Hot Water - To protect Children, the Blind or `Infirm` - We heat the Water to 60c - approx. 140f - THEN a Thermostatic Mixing Valve is installed to prevent the Hot Water being above between 40c and 44c - depending upon what Sanitary Fixture is being supplied.

I can `make sense` of your explanation regarding the Steel Water Heaters having a Design `Maximum Pressure` of 300 psi - AND the `Space` inside to accommodate `Thermal Expansion` - Acting like an Expansion Vessel - although I have `come across` this kind of design in the U.K. - they were `short lived` - I am intrigued as to WHY that Design would prevail in the U.S. - yet be consigned to `Obsolete` here in the U.K. ??

I would think that as our `Average` Water Mains Pressure in the U.K. is probably no more than 40psi - the Manufacturers have decided that `Medium Pressure` Unvented Hot Water Cylinders - WITH a `Built On` Expansion Vessel - is the `Best` Design ??
These Units have a MAXIMUM inlet pressure of 3 Bar - approx. = 44 psi.
and the `Thermal Expansion` is `Accommodated` by the Expansion Vessel - which has a `Membrane`inside - behind which the Vessel is Pressurised - when the Expansion of Water occurs - the Membrane `dilates` - to `take - up the extra VOLUME of water.

That explanation is Not directed at Havasu - who I am sure knows those details about an `Expansion Vessel`.


On your point about the `Boiling Point` of the Hot Water - What I stated in my example IS Correct for the `Extreme Scenario` that I described.
It is obviously RARE that an `Unvented Hot Water Heater` is installed in the way that I described - BUT - NOT `impossible`- I have been told of examples where this has been done - No Disaster occurred because the Hot Water Thermostat DID NOT FAIL to `ON`!

I would like to ask you - is it `Normal` for a Hot Water Heater to be `supplied` with heat from a Gas Boiler / Furnace - via `Flow and Return` primary pipework - HEATING a COIL/ ELEMENT within the Hot Water Heater ??

Obviously THIS type of Hot Water heater is MUCH more Dangerous if installed incorrectly - than a `DIRECT`- Electrically Heated Unit, because of the Control of the Heat Source when the Water Heater has `reached temperature`, We have `a lot` of this type of `Unvented Hot Water` Installation.

"Thank you" for responding - please have a look at some of my other `Posts`
I am particularly interested in `informed comments` on a Post the I did about the `SAFETY` of a Water Heater [Gas] Installation.

"Regards", CHRISM.