Relief Valve 2 Port IPC
- The importance of installing the correct temperature and pressure relief valve on a water heater or hot-water storage tank cannot be overemphasized.
- It is important to note that when the valve is weeping or dripping, the cause is usually excessive pressure.
- Most valves are rated at 150 psi and 210° F, but their capacity ratings vary greatly.
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Relief Valve 2 Port IPC
The importance of installing the correct temperature and pressure relief valve on a water heater or hot-water storage tank cannot be overemphasized. This applies to new vessels as well as relief valve replacements. The importance of installing a valve with the correct pressure rating is common knowledge to many, but it also is crucial to install a valve with the appropriate relieving capacity rating. Many times the capacity factor is overlooked.
The code of construction of the vessel itself can play a key role in choosing the correct valve capacity. Unfortunately, the code of construction criteria is unknown to many and overlooked by others.
As the name indicates, T&P relief valves are designed to protect water heaters and hot-water storage vessels against excess temperature and excess pressure. Most valves are rated at 150 psi and 210° F, but their capacity ratings vary greatly. Sometimes, an additional T&P relief valve with a lower temperature and pressure rating (typically 180° and 100 psi) is installed in a plastic hot-water distribution system to protect the piping system itself. A T&P relief valve is, in essence, a dual device because it meets the code requirements of an individual temperature relief valve and an individual pressure relief valve.
The temperature function of the valve is controlled by an internal thermostatic element. At 210°, the internal expansion within the probe causes a piston to push against the valve’s disk. The spring is overpowered and compressed, and the water escapes between the disc and seat. The extremely hot water within the tank is forced out under pressure as cold water replenishes the discharge. The cold water rushing into the vessel lowers the water temperature, and when the temperature drops back below 210°, the valve is reseated.
The pressure function of the valve also is controlled by the spring, disc and seat. When the pressure exceeds the valve’s pressure rating, the water pressure overcomes the spring. The spring is compressed (just like a typical pressure-only relief valve) and the water escapes between the disc and seat.
It is important to note that when the valve is weeping or dripping, the cause is usually excessive pressure. Many times this is caused by thermal expansion. A T&P relief valve is not designed to nor should it be used to continuously control thermal expansion within a closed system. Thermal expansion of hot water within a closed system should be controlled with the installation of an approved expansion tank or by other means permitted by local code.
Dripping may continue because of debris within the valve, such as a build-up of calcium in the seat, and over time, large mineral deposits can make the valve ineffective. When a valve is discharging a large quantity of water, the cause is almost always excessive temperature.