Product Specifications
Series 174A, 374, 740
ASME Water Pressure Relief Valves
For Pressure Protection of Hot
Water Heating Boilers
Sizes:
3
⁄4" – 2" (20 - 50mm)
Series 174A
Bronze body safety relief valves for pressure protection only of all
types of hot water heating boiler equipment. Pressure range 30 to
150psi (2 - 10 bar) with corresponding high ratings from 650,000
to 14,370,000 BTU/hr. Female inlet and outlet connections. Sizes
3
⁄4" - 2" (20 - 50mm).
Series 374A
Iron body with forged bronze inlet, 550,000 BTU/hr rating.
3
⁄4" (20mm) only.
Series 740
Iron body with expanded outlets for hot water space heating boil-
ers. Pressure range 30 to 75psi (2 to 5 bar) with corresponding
high ratings from 925,000 to 10,700,000 BTU/hr.
Features
• 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.
Specifications
Boiler Relief Valves
An ASME Section IV certified pressure relief valve shall be installed
on each boiler as noted. The valve shall have a BTU rating in
excess of the BTU rating of the boiler's heating output. Each hot
water space heating boiler shall be equipped with a pressure relief
valve set to relieve below the maximum boiler working pressure.
The valve shall feature a raised seat and non-mechanical disc align-
ment. Working parts and spring shall be isolated from any dis-
charge by a high temperature resistant material. Valve shall be a
Watts Regulator Company Series 174A, 374A or 740.
Operation
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.
For Hot Water Boiler Applications
ES-174A-740
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Watts product specifications in U.S. customary units and metric are approximate and are provided for reference only. For precise measurements,
please contact Watts Technical Service. Watts reserves the right to change or modify product design, construction, specifications, or materials with-
out prior notice and without incurring any obligation to make such changes and modifications on Watts products previously or subsequently sold.
Series 174A
Series 740