- First, since water expands when heated, the water pressure in the tank will increase as the water is superheated. If the pressure exceeds the maximum pressure threshold (approximately 300 psi) the tank could rupture or even explode. I have seen pictures where a house has been severely damaged or destroyed by exploding pressure vessels.
- Second, the release of superheated water (now significantly above 212°F) would immediately return to atmospheric pressure and flash into steam, causing a sudden increase in volume and release of energy. The force of the flash steam would exceed the explosion of one pound of (TNT)!
How TPR Valves Work:
If the water reaches a temperature of 210°F (before superheating occurs) or the water pressure exceeds 150 PSI, the valve will open and release the overheated water. This will allow cold water to enter, lowering the temperature of the water in the tank and consequently the water pressure. The valve will remain open as long as the temperature or pressure exceeds the preset limit. The valve must be located on the tank at the top or on the side near the top, where the water is generally the hottest. TPR valves are not included with the water heater, so be sure that the TPR valve matches the BTU (heat rating) rating of the water heater. A discharge tube must be attached to all TPR valves. A word about discharge tubes:
- The pipe itself must be made of a material that is rated for both high temperature and pressure, which includes most rigid wall copper or iron.
- The size of the pipe must match the opening size of the TPR valve discharge (usually ¾ inch).
- The tube must terminate no more than 6 inches from the floor or be directed to the exterior of the home.
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Our buyer's inspector caused the flood of our water heater. He must have flipped the TPR valve when inspecting and the next night when we came to fix the "fix list" and took a bath that night the entire basement flooded. This is a new water heater, never a single problem and here the inspector has been there and it goes crazy. My husband flipped the switch several times and it apparently seated itself and they had no problem with it after that. BUT...we had to face the flood damage.
Susan, are you saying that the TPR valve did not have any pipes that would run the water to the outside of the home?
Just recently saw the same thing in a friend house and I am suprised that they have not had any problems after so many years. How often do T and P valves disperse?
I would like to share a code inconsistany with you.
The plumbing code relys on the manufacturers instructions. The plumbing instructors hand out CO's with out verifying the instructions are at teh job site.
Owners are charged with the duty to maintain the T &P Safety valve. Owners can hire a professional to do this work!
The standard of care isw the manufacturers instructions.
We hve a report card tht sticks on the side of the water tank to inform any and all concerned tht eh maintenance has been completed.
Surveys of public schools hvae been conducted-The criteria included were:
Instructions from OEM are available.
Test for flow conducted
Valve removed and inspected for internal restrictions
Tampoer proofing methods employed to protect against external restrictions.
The survey documentation has proven 100% of the systems 3 years and more old are not in compliance.
More on this if you hve any interest.
Sorry for typo's the screen here provided is so small I can't even read what I type, and am not able to spell check.
Ned