Brochure

VB-7XXX, VB-9XXX Globe Valve Flow Curves, Rangeability, and Close-off
170
© Copyright 2006 TAC. All Rights Reserved. F-27414-1
Flow Curves
Flow curves shown below are representative of all sizes.
All valve plugs have lower gain when nearly closed to
enhance control at low demand. Mixing and diverting valves
are nominally linear. Separate curves shown for “A” or “B”
ports are not directly additive. Total flow with both ports
contributing is rated C
v
.
Two-way valves with brass trim are nominally equal
percentage in the composition disc types and normally used
for water and low pressure steam.
Two-way valves with stainless trim are nominally linear in the
TFE and metal-to-metal disc types, and normally used for
higher temperature water and steam.
Rangeability
Rangeability is defined as the ratio of rated to minimum
controllable flow.
For mixing and diverting valves, control begins as soon as
plug displacement allows flow. Thus, Three-way valve
rangeability normally exceeds 500:1 which is the reciprocal of
0.2% nominal leakage.
For Two-way valves, modulation occurs when plug
displacement allows flow through the area between the plug
and the port. The rangeability value is achieved by accurately
machining the plug and port diameters for appropriate
clearance. The following are nominal values.
TABLE 9. Two-way Valve Rangeability.
Close-off Ratings (Unless Otherwise Specified)
Nominal actuator close-off ratings are based on ANSI IV
(0.01% leakage) with EPDM discs and PTFE discs in steam
applications. Metal-to-metal trim such as brass three-way and
high temperature stainless are designed for ANSI III (0.1%
leakage). Seat leakage for reduced port versions of metal-to-
metal seats may match the full port versions allowing up to
1% on the 0.4 C
v
plugs.
Consult factory for actuator requirements for ANSI VI,
virtually bubble tight for EPDM and PTFE applications.
Nominal
Two-Way Valve Characteristics
Flow
Stroke
0%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
100%
90% 80% 70% 60% 50% 40% 30% 20% 10%
316 Stainless Trim
Brass Trim
Closed
Open
Rated Flow
Stroke
Nominal
Three-Way Valve Characteristics
Stem In
Stem Out
0%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
80% 60%
40%
20%
100%
"A" Port
"B" Port
Nominal Size
Port Code (P) Nominal Ratio
Standard Metric
1/2” 15 mm
15:1
2 15:1
3 25:1
4 40:1
3/4” 20 mm
5 50:1
6 60:1
1” 25 mm
7 60:1
8 75:1
1-1/4” 32 mm 9 75:1
1-1/2” 40 mm 10 75:1
2” 50 mm 11 75:1
2-1/2” 65 mm 12 75:1
3” 80 mm 13 75:1
4” — 14 75:1
5” — 15 75:1
6” — 16 75:1
VB-
7XXX,
VB-
9XXX
Globe
Valve
Flow
Curves,
Rangeab
ility, and