Jack_Russells4ever

You can also run the drain to the exterior of the house if the WH is on or close to an exterior wall.

ddsrph

The walls on my house are 18 inches thick. I looked at the Tennessee plumbing codes as suggested and will replace the clear pipe from safety valve to drain pan with a length of galvanized 3/4 inch water pipe. A expansion tank is also required and I already have that. When we go away for more than a day I always cut off water at street and shut off power to water heater.

Pulaski

The problem with a "heat and pressure" failure is that if, as you inferred, you have water under pressure at over 100ºC, and anything happens to release the pressure, whether a valve failure (a valve working properly should never allow this situation to develop), or any other part of the tank failing/ rupturing, then the sudden drop in pressure while the water is above boiling point at normal atmospheric pressure, causes all the water in the tank to instantly turn to steam. This is what happened in the Mythbusters video linked above (I believe in that case the excess pressure caused the concave base of the tank to "pop" outwards, reducing the pressure in the tank), also in the house near me that had its water heater launched through the roof, and is also what happens in the class of volcanic eruptions called "steam explosions" - such as the disaster in December 2019 at New Zealand's White Island volcano, which killed 22 people, and injured 25 more, mostly with severe burns from the steam.

ddsrph

So I should have a pipe connecting the pressure/temp safety valve to discharge outside house or possibly in my case into the internal French drain via a pre-placed 3 inch pvc pipe.

Mic1

Yes, exactly right. And i knew that the volume of water under pressure when it turns to steam increased dramatically but had to look up what was. It's mind blowing, it increases in volume by 1600 times!! That's a big bang!!!

There was a school in the US where this happened as well, i'll try and find the link.

Mic1

Here's a link to the tank that exploded in a school
https://www.upi.com/Archives/1982/01...2579380264400/

As i say, don't play around with safety devices on hot water storage tanks, They are there for a reason and must be fitted and terminated correctly.

ddsrph

Tennessee is on international
plumbing codes and both PEX and CPVC would be ok. I can make a hole thru wall for a pipe. It would be fairly easy with the large hammer drill I have. I have 4 inch brick, 8 inch concrete filled block, 5 1/2 inches foam board insulation and 1/2 inch sheet rock for 18 inches total. I had to cut a four inch hole for dryer vent so a one inch hole will be easy. I will try to do it in near future.

ddsrph

Would this be ok to connect pressure valve to a thru wall galvanized water pipe for outside routing of pressure/temp overflow valve. According to IPC codes PEX is ok as a material for this purpose.

SpoogleDrummer

That doesn't have the right connection to connect to the outlet, you need a male thread. Honestly your original plan to just go to your drip pan would be fine especially as you already have your pan hooked up to drain.
https://www.lowes.com/pd/EASTMAN-Sid...ube/5001255387 would do the job

ddsrph

You are right. I thought that brass end was a 3/4 pipe thread.

Pulaski

That is true however you hook up a water heater, you need either a 3/4" iron nipple or a 3/4" male-[something] copper fitting. It's one of those mysteries of living in America, that somethings are unnecessarily complicated, you need extra "bits" every single time you install some very standard device/ appliance.
Agreed. I am not averse to a bit of over-engineering myself, but even I don't think I would take the time to add a dedicated drain line just for the PR valve when the drain pan is already connect to a drain line.

ddsrph

I am going to talk with some local plumbers just to see what they do on installations. Many dont install the expansion tank which I did. The female 3/4 inlet on water heaters is done to allow a variety of connection options based on plumbing pipe used. It’s a big No No to connect copper to galvanized steel and a dielectric connector is required in those cases. I used CPVC which I was most familiar with and has worked well for me in the past.

newadventure

You'd have thought someone would have tried to capture this by now and use it to perform some useful work

Pulaski

They did, sort of, and still do to this day in almost all electricity power stations that turn fuel into electricity.

The designs and resulting publicity are better known in the realm of steam locomotives. In the later years of largescale manufacture of steam locomotives the operating pressure of the boilers was 200-250psi (14-17 bar), but there were a number of experimental designs that ran at "high pressure" which meant above 350psi, and as high as 1,500psi! (100 bar) .... Note, the Mythbusters water heater failed at just over 300psi.

Even steam engines running at "normal" pressures were extremely dangerous when the boiler failed, and it was ultimately determined that is simply wasn't worth the effort and risk of trying to run steam locomotives at significantly higher pressures. This is a typical result of a failure of a steam locomotive boiler!



Steam engine explosions were invariably catastrophic, killing the crew (driver and fireman) in almost all cases. As previously discussed the failures were usually linked to over heating and/or failure to contain the pressure, with resulting explosion either going "KABLOOEY!" through the roof, often breaking the locomotive in two despite the steel chassis on which the entire locomitive was built, enveloping the area in superheated steam and throwing the contents of the fire box in all directions. There were several ways that the crew could be killed, none of them attractive. I did learn from the Mythbusters video (linked previously above) that in reality is likely that the pure explosive shock wave would kill them, which is probably a blessing when the alternatives are to be scalded by steam, burned by coals, and/or shredded by flying steel shrapnel.

The "or" to the previous "either" is for the boiler to fail internally, with water and superheated steam escaping into the firebox when one of the tubes ruptures. The immediate result of this is for the entire contents of the firebox, burning coals and superheated steam, to be blasted out through the firebox door onto the footplate where the crew are located. Needless to say, the result is no better for the crew than a bigger "through the roof" explosion, but in the case of the internal failure, the locomotive may be repairable, which is what happened to the experimental British high pressure locomotive 6399 Fury which, after a tube failure forced the contents of the firebox out of the firebox door, was later rebuilt with a new boiler as a more conventional locomotive.

Mic1

Interesting post, terrifying but interesting!