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Safety Relief Valves in Commercial and Industrial Potable Water Heaters

• Safety relief valves are installed on commercial and industrial potable water heaters and hot water storage tanks, designed according to ASME BPVC IV, Part HLW.
• These heaters and tanks operate at pressures not exceeding 1100 kPa and temperatures not exceeding 99°C.
• Safety relief valves protect against explosion dangers associated with super-saturated hot water.

Temperature and Pressure Safety Relief Valves

• Most potable water heaters and hot water storage tanks use temperature and pressure safety relief valves.
• These valves protect against both over-pressurization and high water temperatures.
• ASME BPVC Section IV, Part HLW-800 refers to safety relief valve requirements for industrial and commercial potable water heaters.

Installation Requirements

• Safety relief valves must be installed not lower than 100 mm from the top of the shell.
• Valves must be directly connected to the water heater or a fitting connected to the water heater.
• Spindles must be upright and vertical, with no horizontal connecting pipe.
• No piping or fitting used to mount the safety relief valve can be smaller than the valve inlet.
• Safety relief valves shall not be connected to an internal pipe or a cold water feed line.

Combination Temperature and Pressure Relief Valves

• These valves provide protection for both over-pressurization and high water temperatures.
• The pressure element opens to relieve excess pressure, usually caused by thermal expansion.
• The temperature element opens when the water temperature rises to about 99°C.
• Unlike safety relief valves, T&P valves do not operate with a pop action when over-pressurization occurs.

Temperature-Sensitive Element

• The temperature-sensitive element consists of a wax-filled thermostatic sensor probe that extends into the water storage tank.
• When exposed to high temperature, the wax expands, lifts the valve disc off its seat, and discharges the overheated water.
• When the temperature returns to a safe level, the wax contracts, and allows the spring to reseat the valve.

Testing and Maintenance

• It is recommended that T&P valves receive annual try lever tests.
• Various types of temperature relief devices can be used, but they must always have additional pressure relief.