What's the valve with the flip-up handle on the water heater for?
Sunday, October 14, 2018
It’s called at TPR valve, which is an acronym for Temperature and Pressure Release, and also sometimes referred to as a T&P valve. TPRs are designed to automatically release water in the event that pressure or temperature in the water tank exceeds safe levels.
If a TPR valve malfunctions, water in the system may become superheated (exceed the boiling point). Once the tank ruptures and water is exposed to the atmosphere, it will expand into steam almost instantly with explosive force. This process can propel a heating tank like a rocket through multiple floors, causing personal injury and property damage.
Water heater explosions are rare, because they require a simultaneous combination of unusual conditions and failure of redundant safety components--usually the result of negligence or malfunctioning equipment.
The TPR valve will activate if either water temperature (measured in degrees Fahrenheit) or pressure (measured in pounds per square inch [PSI]) exceed safe levels. The valve should be connected to a discharge pipe (also called a drain line) that runs down the length of the water heater tank. This pipe is responsible for routing hot water released from the TPR to a proper discharge location.
The TPR valve should meet these requirements:
- Be constructed of a plumbing material rated for hot water, typically CPVC, copper, or galvanized steel. PVC and other non-approved plastics should not be used since they can easily melt.
- Be the same diameter, or larger, than the supply pipe serving the water heater.
- Be as short and as straight as possible so as to avoid undue stress on the valve and installed so that it drains by gravity (downward flow).
- Not be trapped, since standing water may become contaminated and backflow into the drinking water.
- Discharge to within 6-inches of the floor, or to a waste receptor with an air gap, or to visible exterior location. It should not be directly connected to the drainage system to prevent backflow, which potentially can contaminate the drinking water.
- Not have a valve, T-fitting, or threaded end, to avoid any scenario that might result in a restriction or capping of the discharge piping.
A properly functioning TPR valve will eject a powerful jet of hot water from the discharge pipe when fully activated, not a gentle leak. If a TPR valve is just leaking slowly, it is an indication that it needs to be replaced. In the rare case that the TPR valve does activate, you should immediately shut off the water and contact a qualified plumber for assistance and repair.
Although most TPR valves never become activated, it is an essential safety component on domestic water heaters. Guidelines concerning these valves and their discharge pipes reflect real hazards that every homeowner should take seriously.
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