Watts 374A Relief Valves

Watts Series 374A Boiler Pressure Relief Valves are used in hot water boiler applications to protect against excessive pressure on all types of hot water heating boiler equipment. It consists of an iron body construction with forged bronze inlet connections, non-metallic disc-to-metal seating, stainless steel spring, and test lever.

Series 374A resists corrosive water conditions, sticking and freezing, and prevents water and sediment from being trapped in the seat. It is designed for emergency safety relief and shall not be used as an operating control. Standard Pressure Setting: 30psi (206.9 kPa), Pressure range: rated up to 550,000 BTU/hr at a 30psi (2 bar) setting only.

Specification Sheet 

Pipe Size Part # Description Pressure Capacity Weight
3/4" x 3/4"  0274428 Series 374A, Model M3 30 PSI 550,000 btu/hr 1.5 lbs


As thermal expansion conditions develop, pressure builds up to the setting of the relief valve. This will cause discharging of small quantity of water.  Should operating controls fail, permitting runaway firing, the boiler water may reach steam temperatures. The valve will then open to discharge steam at the rate or faster than the boiler can generate it, thus restoring system pressure to a safer level.

Important: The discharge line must be the same size as the valve outlet, and must pitch downward from the valve to a safe place for disposal. Valve lever must be tripped at least once a year to ensure that waterways are clear. This device is designed for emergency safety relief and shall not be used as an operating control.


• Seat located above drain; water can’t be trapped and sediment can’t foul seat.
• Non-mechanical seat-to-disc alignment will not stick or freeze.
• Water seal of high temperature resisting material isolates spring working parts from water during relief.

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