User Guide

F-24381-2 © Copyright 2008 TAC All Rights Reserved. 5
C
v
Equation
Where:
C
v
= Coefficient of flow
GPM = U.S. gallons per minute (60°F, 15.6°C)
ΔP = Differential pressure in psi (pressure drop)
Steam Two-position
Two-position zone valves and direct radiation valves are normally sized using a minimum of
10% of inlet pressure (psig).
Proportional
Proportional control valves are normally sized using:
• For low pressure (15 psig or less), use ΔP of 80% of gauge inlet pressure.
• For steam pressures greater than 15 psig, use ΔP of 42% of absolute (gauge plus 14.7)
inlet pressure.
• When the C
v
required is between two valve sizes, select the larger size. Do not size
steam valves using a pressure drop greater than 42% of the absolute inlet pressure.
Steam Capacity
See Table-6 for steam capacity of VB-7212 series valves.
Table-6 Steam Capacity in Pounds Per Hour for VB-7212 Series.
C
v
Equation
Where:
C
v
= Coefficient of flow
Q = Lbs. per hour of steam
ΔP = Differential pressure in psi (pressure drop)
P2 = Outlet pressure in psia (absolute) (P2 = Inlet pressure + 14.7 –
ΔP)
K = 1 + (0.0007 x °F superheat) (K = 1 for saturated steam)
C
v
=
GPM
ΔP=
GPM
C
v
()
GPM = C
v
ΔP
2
ΔP
Valve Body
Part Number
Cv
Rating
Differential Pressure (
ΔP in psi)
a
a
Values are for saturated steam (K = 1). Left column under each inlet pressure is for two-position control, and right column is for proportional control.
2 psig Inlet 5 psig Inlet
10 psig
Inlet
15 psig
Inlet
20 psig
Inlet
25 psig
Inlet
30 psig
Inlet
35 psig
Inlet
0.2 1.6 0.5 4 1 8 1.5 12 2 14 2.5 16 3 18 3.5 20
VB-7212-0-4-1 0.4 2.2 5.9 3.7 9.5 5.8 14 7.8 18 9.7 20 12 23 13 26 15 29
VB-7212-0-4-2 1.3 7.1 19 12 31 19 45 25 57 32 66 38 76 44 86 50 95
VB-7212-0-4-3 2.2 123220523276439653112641297414584161
VB-7212-0-4-4 4.4 24 65 41 105 64 153 86 192 107 225 127 257 148 289 168 322
C
v
=
QK
Q=
K
ΔP • P23
ΔP • P23C
v