Specification Sheet

For Pressure Protection of Hot
Water Heating Boilers
Sizes:
3
⁄4" – 2"
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 (2.1 - 10 bar) with corresponding high rat-
ings 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 brass inlet, 550,000 BTU/hr rating.
3
⁄4" (20mm) only.
Series 740
Iron body with expanded outlets for hot water space heating
boilers. Pressure range 30 to 75psi (2 to 5 bar) with corre-
sponding 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 alignment. Working parts and spring shall
be isolated from any discharge by a high temperature resistant
material.* Valve shall be a Watts 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.
NOTICE
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.
ES-174A-740
Series 174A
Series 740
Series 174A, 374, 740
ASME Water Pressure Relief Valves
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Approval
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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.
It is illegal to use this product in any plumbing system providing
water for human consumption, such as drinking or dishwashing,
in the United States. Before installing standard material product,
consult your local water authority, building and plumbing codes.
WARNING
!
The information contained herein is not intended to replace the full
product installation and safety information available or the experience
of a trained product installer. You are required to thoroughly read all
installation instructions and product safety information before begin-
ning the installation of this product.
* Does not apply to 374A
NOTICE