DIMENSIONS - WEIGHTS
MATERIALS
Series 174A
• Bronze body construction
• Nonmetallic disc-to-m etal seating
Series 740
• Iron body construction
• Nonmetallic disc-to-m etal seating
PRESSURE - TEMPERATURE
Series 174A
Pressure range: 30 psi to 150 psi (2 to 10 bars) with
corresponding high BTU/hr ratings from 650,000
to 14,370,000 BTU/hr.
Maximum Temperature: 250°F (121°C).
No. 374A
Pressure range: rated up to 550,000 BTU/hr at a 30
psi (2 bars) setting only.
Series 740
Pressure range: 30 PSI to 75 psi (2 to 5 bars) with cor-
responding hi gh ratings from 925,000 to 10,700,000
BTU/hr.
Maximum Temperature: 250°F (121°C).
STANDARDS
Tested and rated by A.S.M.E. National Board of Boiler
and Pressure Vessel Inspectors.
Meets Military Spec. MIL-V-18634B, Type I, Class 3A,
Style A (Bronze Body), Style B (Iron Body).
CAPACITY
ES-174A-740 0026 © Watts Regulator Co., 1998 Printed in U.S.A.
USA: 815 Chestnut St., No. Andover, MA 01845-6098; www.wattsreg.com
Canada: 5435 North Service Rd., Burlington, ONT. L7L 5H7; www.wattscda.com
HV
NB
ASME
Size (Dn) Height Length Weight
No. in. mm Model in. mm in . mm lbs. kg.
374A
3
⁄4 x
3
⁄4 20 x 20 – 3
5
⁄8 92 2
1
⁄2 64 1.13 .5
174A
3
⁄4 x
3
⁄4 20 x 20 M3 5
1
⁄8 130 2
1
⁄2 64 1.50 .7
174A 1 x 1 25 x 25 M1 5
3
⁄4 146 3 76 3.13 1.4
174A 1
1
⁄4 x 1
1
⁄4 32 x 32 M1 8
3
⁄8 213 4
3
⁄4 121 6.25 2.8
174A 1
1
⁄2 x 1
1
⁄2 40 x 40 M 9 229 4
7
⁄8 124 7.25 3.3
174A 2 x 2 50 x 50 M 11
5
⁄8 295 6
1
⁄4 159 13.75 6.2
Series 740
740
3
⁄4 x 1 20 x 25 M1 5
5
⁄8 143 3 76 1.88 .9
740 1 x 1
1
⁄4 25 x 32 M 7
1
⁄4 184 3
1
⁄2 89 3.13 1.4
740 1
1
⁄4 x 1
1
⁄2 32 x 40 M 8
3
⁄4 222 4
5
⁄8 117 6.13 2.8
740 1
1
⁄2 x 2 40 x 50 M 9
1
⁄4 235 5
1
⁄4 133 7.50 3.4
740 2 x 2
1
⁄2 50 x 65 M 11
5
⁄8 295 6
3
⁄4 171 16.50 7.5
Series 174A
BTU/hr Steam Pressure Discharge Capacities
As tested and rated by the National Board of Boiler and Pressure Vessel Inspectors
Set
3
⁄4" x
3
⁄4" 1" x 1" 1
1
⁄4" x 1
1
⁄4"1
1
⁄2" x 1
1
⁄2" 2" x 2"
Pressure 20 x 20mm 25 x 25mm 32 x 32mm 40 x 40mm 50 x 50mm
psi bars Model M3 Model M1 Model M1 Model M Model M
30 2.07 650,000 1,005,000 1,682,000 2,020,000 3,815,000
33 2.27 695,000 1,075,000 1,788,000 2,150,000 4,080,000
35 2.41 725,000 1,125,000 1,877,000 2,250,000 4,250,000
36 2.48 740,000 1,145,000 1,916,000 2,310,000 4,344,000
40 2.76 800,000 1,240,000 2,071,000 2,490,000 4,690,000
45 3.10 875,000 1,355,000 2,265,000 2,720,000 5,130,000
50 3.45 950,000 1,470,000 2,459,000 2,950,000 5,575,000
55 3.79 1,025,000 1,590,000 2,653,000 3,190,000 6,010,000
60 4.13 1,100,000 1,702,000 2,847,000 3,425,000 6,450,000
65 4.58 1,170,000 1,820,000 3,041,000 3,660,000 6,890,000
70 4.82 1,245,000 1,935,000 3,235,000 3,890,000 7,330,000
75 5.17 1,320,000 2,055,000 3,429,000 4,125,000 7,770,000
80 5.51 1,400,000 2,166,000 3,605,000 4,360,000 8,215,000
85 5.86 1,470,000 2,285,000 3,817,000 4,590,000 8,650,000
90 6.60 1,545,000 2,400,000 4,011,000 4,825,000 9,090,000
95 6.55 1,620,000 2,520,000 4,205,000 5,060,000 9,530,000
100 6.89 1,695,000 2,635,000 4,399,000 5,290,000 9,970,000
105 7.23 1,770,000 2,750,000 4,593,000 5,525,000 10,410,000
110 7.58 1,845,000 2,865,000 4,787,000 5,760,000 10,850,000
115 7.92 1,920,000 2,980,000 4,981,000 5,990,000 11,290,000
120 8.27 1,995,000 3,100,000 5,175,000 6,225,000 11,730,000
125 8.61 2,070,000 3,215,000 5,370,000 6,460,000 12,170,000
130 8.96 2,145,000 3,330,000 5,564,000 6,690,000 12,610,000
135 9.30 2,220,000 3,445,000 5,758,000 6,925,000 13,050,000
140 9.65 2,295,000 3,565,000 5,952,000 7,160,000 13,490,000
145 9.99 2,370,000 3,680,000 6,146,000 7,390,000 13,930,000
150 10.34 2,445,000 3,795,000 6,340,000 7,630,000 14,370,000
Series 174A
Set
3
⁄4" x 1" 1" x 1
1
⁄4"1
1
⁄4" x 1
1
⁄2"1
1
⁄2" x 2" 2" x 2
1
⁄2"
Pressure 20 x 25mm 25 x 32mm 32 x 40mm 40 x 50mm 50 x 65mm
psi bars Model M3 Model M1 Model M1 Model M Model M
30 2.07 925,000 1,300,000 2,105,000 2,900,000 5,250,000
33 2.27 989,000 1,390,000 2,250,000 3,100,000 5,613,000
35 2.41 1,032,000 1,450,000 2,345,000 3,235,000 5,855,000
36 2.48 1,053,000 1,480,000 2,395,000 3,300,000 5,975,000
40 2.76 1,139,000 1,600,000 2,590,000 3,569,000 6,461,000
45 3.10 1,245,000 1,750,000 2,830,000 3,903,000 7,067,000
50 3.45 1,352,000 1,899,000 3,075,000 4,237,000 7,672,000
55 3.79 1,459,000 2,049,000 3,315,000 4,572,000 8,277,000
60 4.13 1,566,000 2,200,000 3,560,000 4,907,000 8,883,000
65 4.58 1,672,000 2,349,000 3,800,000 5,241,000 9,488,000
70 4.82 1,779,000 2,499,000 4,045,000 5,575,000 10,093,000
75 5.17 1,886,000 2,649,000 4,285,000 5,909,000 10,700,000
Series 740
Series 174A-740
ASME Water Pressure
Relief Valves
for Pressure Protection of
Hot Water Heating Boilers
Sizes:
3
⁄4" through 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 150 psi (2 - 10 bars) with corresponding high rat-
ings from 650,000 to 14,370,000 BTU/hr. Female inlet and
outlet connections. Sizes
3
⁄4" to 2" (20 to 50mm).
Series 374A
Iron body with forged bronze i nlet, 550,000 BTU/hr rating.
Size
3
⁄4" (20mm) only.
Series 740
Iron body with expanded outlets for hot water space heating
boilers. Pressure range 30 to 75 psi (2 to 5 bars) 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 boilers heat-
ing 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 fea-
ture a raised seat and non-mechanical disc alignment.
Working parts and spring shall be isolated from any dis-
charge by a high temperature resistant material. Valve shall
be a Watts 174A or 740 Series.
ES-174A-740
OPERATION
As thermal expansion conditions develop, pressure builds up
to the setting of the relief valve. This wi ll cause discharging of
small quantity of water.
Should operating controls fai l, permitting runaway firing, the
boiler water m ay reach steam temperatures. The valve will
then open to discharge steam at the rate or faster than the
boiler can generate i t, thus restoring system pressure to a
safer level.
Important: The discharge line must be the same size as the
valve outlet, and must pi tch downward from the valve to a
safe place for disposal.
Valve lever must be tr
ipped at least once a year to insure that
waterways are clear. This device is designed for emergency
safety relief and shall not be used as an operating control.
Series 174A Series 740
For Hot Water Boiler Applications
Job Name Contractor
Job Location Approval
Engineer Contractor’s P.O. No.
Approval Representative
Watts product specifications in U.S. customary units and metric
are approximate and are provided for reference only. Watts re-
serves the right to change or modify product design, construction,
specifications, or materials without prior notice and without incur-
ring any obligation to make such changes and modifications on
Watts products previously or subsequently sold.
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