Azbil FloWing VFR User Manual

Valve Positioner Azbil Corporation
4-6 Model VFR - FloWing Eccentric Rotary type Control Valves
4-2-4 : Selecting cam characteristics
To change valve characteristics Select a proper cam and install it. (For installation
and adjustment procedures, refer to the respective sections.)
Cam characteristics
A single sheet of cam for the positioner can satisfy either linear characteristics or
equal-percent characteristics.
100
90
80
70
60
50
40
30
20
10
0
0
10
20
30
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50
60
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80
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0102030405060708090
100
Valve opening (%)
Valve opening (%)
Input air pressure
Input air pressure
Direct action (Air-to-close)
Reverse action (Air-to-open)
Equal
percent
Linear
Figure 4-11 Cam characteristics
Using the equal-percent cam
When the inherent characteristics of the valve is linear but equal-percent
characteristics are required by the process, control characteristics of the valve can be
converted into the equal-percent type simply by using an equal-percent cam.
Selecting a cam
Select a proper cam as follows:
(1) Conrm whether the valve is a direct action (air-to close) or reverse action (air-to-
open) type.
(2) Refer to Figure 4-12, and then select a cam which will provide the required ow
characteristics for the process.
Valve opening (%)Valve opening (%)
Valve ow (%)Valve ow (%)
0
0
100
100
Input air pressure (%)
Input air pressure (%)
Valve opening (%)Valve opening (%)
0
0
100
100
Input air pressure (%)
Input air pressure (%)
Valve ow (%)Valve ow (%)
0
0
100
100
Valve ow characteristics + Cam (Equal-percent characteristics) g Final ow characteristics
Figure 4-12 Example of use of a cam - for FloWing valve (full port, reverse action)

Azbil FloWing VFR Specifications

General

Brand	Azbil
Model	FloWing VFR
Category	Control Unit
Language	English