User Guide

F-24381-2 © Copyright 2008 TAC All Rights Reserved. 3
Flow Characteristics
All valves have modified equal percentage flow characteristics. That is, for equal increments
of valve stem stroke, the change in flow rate with respect to valve stroke may be expressed
as a constant percent of the flow rate at the time of the change. The change of flow rate with
respect to valve stroke is relatively small when the valve plug is near the valve seat and
relatively high when the valve plug is nearly wide open. See Figure-1 for typical modified
equal percentage flow characteristics of VB-7212 series valve bodies.
Figure-1 Typical Modified Equal Percentage Flow Characteristics.
Rangeability
Rangeability is the ratio of rated flow to the minimum controllable flow through a valve.
Table-3 lists the rangeability for VB-7212 series valves.
Table-3 Rangeability.
Temperature/Pressure Ratings
See Figure-2 for temperature and pressure ratings. Consult the appropriate valve linkage
general instruction sheet for the effect of valve body ambient temperatures on specific
actuators. Ratings conform with published values and disclaimer.
VB-7212-0-4-P (45° SAE Flared Cast Bronze Body)
Standards: Pressure to ANSI B16.15 Class 250 with 400 psig up to 150°F decreasing to
321 psig at 281°F
Materials: Bronze, ASTM B584
Flow
Stroke
Closed
Open
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0%
10% 20% 30% 40% 50% 60% 70% 80% 90%
100%
Valve Body
Part Number
Nominal
Rangeability
Valve Body
Part Number
Nominal
Rangeability
VB-7212-0-4-1 5:1 VB-7212-0-4-3 25:1
VB-7212-0-4-2 15:1 VB-7212-0-4-4 40:1