User Guide

4 © Copyright 2006 TAC All Rights Reserved. F-24384-1
Rangeability
Rangeability is the ratio of rated flow to the minimum controllable flow through a valve.
Table-3 lists the rangeability for VB-7221 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-7221-0-4-P (Union End NPT 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
Figure-2 Temperature and Pressure Ratings for VB-7221 Series Valve Bodies.
VALVE SIZING AND SELECTION
Water Two-position
Two-position control valves are normally selected “line size” to keep pressure drop at a
minimum. If it is desirable to reduce the valve below line size, then 10% of “available
pressure” (that is, the pump pressure differential available between supply and return mains
with design flow at the valve location) is normally used to select the valve.
Proportional
Proportional control valves are usually selected to take a pressure drop equal to at least 50%
of the “available pressure.” As “available pressure” is often difficult to calculate, the normal
procedure is to select the valve using a pressure drop at least equal to the drop in the coil
or other load being controlled (except where small booster pumps are used) with a minimum
recommended pressure drop of 5 psi (34 kPa). When the design temperature drop is less
than 60°F (33°C) for conventional heating systems, higher pressure drops across the valve
are needed for good results (Table-4).
Valve Body
Part Number
Nominal
Rangeability
Valve Body
Part Number
Nominal
Rangeability
Valve Body
Part Number
Nominal
Rangeability
VB-7221-0-4-1 5:1 VB-7221-0-4-4 40:1 VB-7221-0-4-7 60:1
VB-7221-0-4-2 15:1 VB-7221-0-4-5 50:1 VB-7221-0-4-8 75:1
VB-7221-0-4-3 25:1 VB-7221-0-4-6 60:1 VB-7221-0-4-9 75:1
50
(345)
250 (121)
200 (93)
150 (65)
100 (38)
50 (10)
300 (149)
150
(1034)
250
(1724)
350
(2458)
100
(689)
Pressure — psig (kPa)
321 psig
(2218 kPa)
Temperature — °F (°C)
200
(1379)
300
(2068)
400
(2758)
Maximum Media
Temperature
281°F (138°C)
Minimum Fluid
Temperature
20°F (-7°C)
VB-7221-0-4-P