User Guide

TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
1-800-432-8373
Temperature And Pressure Relief Valves
Discharge of the T&P valve may indicate that an unsafe temperature or pressure condition exists.
Contact a licensed plumber immediately!
Technical Competence, Product Confidence
Page 1 of 3
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Temperature and Pressure Relief Valves, also called T&P valves,
are emergency safety limit devices that will prevent or relieve
overheated water and pressure. Without a relief valve during an unsafe
condition, the pressure inside the tank would rise to the point the tank
may rupture or explode. This would cause potential damage to both
people and property. Rheem water heaters are pressure tested to 300
pounds per square inch (PSI) and have a working pressure of 150 PSI.
The T&P valve is designed to open when the pressure inside the tank
exceeds 150 PSI, allowing pressure to vent safely. The T&P valve will
also open if the water temperature reaches 210
0
F. The valve will remain
open allowing cold water into the tank until the unsafe condition is over.
Why is hot water over 212° F dangerous? The containment
vessel or storage tank used to store the hot water causes the danger. This
tank is under pressure – the normal working pressure caused by the cold
water supply. As water is heated under pressure, the boiling point rises.
For example, with a nominal incoming supply pressure of 50 PSI, water
will not boil under pressure until the temperature reaches approximately
297° F. The energy potential in the superheated water is called latent
heat energy and will flash to steam when exposed to normal atmospheric
pressure. This flash to steam has the explosive potential of over two
million foot-pounds of energy.
The Temperature and Pressure Relief Valve is
the safety device that prevents these conditions from
happening. It is a 2-in-1 device that responds to both
pressure increases and temperature increases. When
actuating by pressure, the T&P valve will open and
allow the tanks internal pressure to drop below 150PSI.
Generally, when you see a T&P valve weeping or
dribbling, it is due to pressure (thermal expansion) or foreign material such
as calcium buildup in the valve seat. This material on the valve seat will
prevent the valve from closing tightly. If the valve is discharging large
quantities of water, them the release is due to temperature. Recall the T&P
is installed in the top six inches of the tank. If the temperature probe on the
T&P senses water temperatures of 210° F, it will open the valve. The valve
will stay open until the temperature probe cools. With cold water entering
the bottom area of the tank, you can see a large volume of water (gallons)
will be discharged before the temperature probe cools.