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Engineering
G-7
Refer to Conversion Factors on page G-32.
Control Valves
Selection and Sizing
The temperature-pressure ratings for ANSI Classes 125 and 250 valve bodies made of bronze or cast iron are
shown below.
Description Temperature
Pressure
ANSI Class 125 ANSI Class 250
Bronze Screwed Bodies
Specication #B16.15-1978
ANSI Amer. Std.;
USA; ASME
-20 to + 150°F (-30 to + 66°C) 200 psi (1378 kPa) 400 psi (2758 kPa)
-20 to + 200°F (-30 to + 93°C) 190 psi (1310 kPa) 385 psi (2655 kPa)
-20 to + 250°F (-30 to + 121°C) 180 psi (1241 kPa) 365 psi (2586 kPa)
-20 to + 300°F (-30 to + 149°C) 165 psi (1138 kPa) 335 psi (2300 kPa)
-20 to + 350°F (-30 to + 177°C) 150 psi (1034 kPa) 300 psi (2068 kPa)
-20 to + 400°F (-30 to + 204°C) 125 psi (862 kPa) 250 psi (1724 kPa)
Cast Iron Flanged Bodies
Class B-sizes 1 to 12
Specication #B16.1 1975
ANSI Amer. Std.;
USA; ASME
-20 to + 150°F (-30 to + 66°C) 200 psi (1378 kPa) 500 psi (3445 kPa)
-20 to + 200°F (-30 to + 93°C) 190 psi (1310 kPa) 460 psi (3169 kPa)
-20 to + 225°F (-30 to + 106°C) 180 psi (1241 kPa) 440 psi (3032 kPa)
-20 to + 250°F (-30 to + 121°C) 175 psi (1206 kPa) 415 psi (2859 kPa)
-20 to + 275°F (-30 to + 135°C) 170 psi (1171 kPa) 395 psi (2722 kPa)
-20 to + 300°F (-30 to + 149°C) 165 psi (1138 kPa) 375 psi (2584 kPa)
-20 to + 325°F (-30 to + 163°C) 155 psi (1069 kPa) 355 psi (2448 kPa)
-20 to + 350°F (-30 to + 177°C) 150 psi (1034 kPa) 335 psi (2308 kPa)
-20 to + 375°F (-30 to + 191°C) 145 psi (1000 kPa) 315 psi (2170 kPa)
-20 to + 400°F (-30 to + 204°C) 140 psi (965 kPa) 290 psi (1998 kPa)
-20 to + 425°F (-30 to + 218°C) 130 psi (896 kPa) 270 psi (1860 kPa)
-20 to + 450°F (-30 to + 232°C) 125 psi (862 kPa) 250 psi (1734 kPa)
1. Flow characteristic — Modied Equal Percentage which
provides good control for a water coil.
2. Body rating and material — Suitable for water.
3. Valve type and action — A single seat NC valve with an
adjustable spring range which can be sequenced with a
NO valve used for heating.
4. Valve actuator — Actuator close-off rating is higher than
the system differential pressure.
5. Valve line size — Its Cv is close to and slightly larger
than the calculated Cv (15.6).
6. For Ball Valves — use the same selection criteria.
Valve Sizing and Selection Example
Valve Body Rating
Valve Selection Criteria
Sizing a Valve
Select a valve to control a chilled water coil that must have
a ow of 35 GPM with a valve differential pressure (∆P) of
5 psi.
Determine the valve Cv using the formula for liquids.
Cv = Q = 35 GPM = 15.6
Select a valve that is suitable for this application and has
a Cv as close as possible to the calculated value.
One choice is 277-03186: a 1-1/4" NC valve with a Cv of
16. Refer to Flowrite Valves Reference section.
S
P
√
1
5 psi
√