Instruction Manual
D200138X012
3582, 582i, and 3583
January 2013
25
for example, the stem will travel 50 percent with cam A, 68 percent with cam B, and 32 percent with cam C. Figure 13
shows how the flow characteristics change when using the cams with a valve that has equal percentage
characteristics. Figure 14 shows how the flow characteristics change when using the cams with a valve that has linear
characteristics.
Figure 12. Cam Characteristic Curves
CK4832‐A
PERCENT VALVE STEM TRAVEL
0 PERCENT CORRESPONDS TO
MINIMUM DIAPHRAGM PRESSURE
CAM
C
CAM
A
CAM
B
PERCENT INSTRUMENT PRESSURE SPAN
REVERSE
ACTING
POSITIONER
DIRECT
ACTING
POSITIONER
Figure 13. Flow Characteristics with Different Cams
and Equal Percentage Valve Plug
CK4835‐A
PERCENT
INSTRUMENT PRESSURE SPAN
INSTRUMENT PRESSURE ‐ FLOW
CHARACTERISTIC WITH EQUAL PERCENTAGE
VALVE PLUG AT CONSTANT PRESSURE DROP
PERCENT FLOW
NORMALLY
CLOSED
VALVE
NORMALLY
OPEN
VALVE
REVERSE
ACTING
POSITIONER
DIRECT
ACTING
POSITIONER
CAM
A
CAM
B
CAM
C
CAM
C
CAM
A
CAM
B
Figure 14. Flow Characteristics with Different Cams
and Linear Valve Plug
CK4833‐A
INSTRUMENT PRESSURE ‐ FLOW
CHARACTERISTIC WITH LINEAR VALVE
PLUG AT CONSTANT PRESSURE DROP
CAM
A
CAM
B
CAM
C CAM
A
CAM
B
PERCENT INSTRUMENT PRESSURE SPAN
PERCENT FLOW
REVERSE
ACTING
POSITIONER
DIRECT
ACTING
POSITIONER
CAM
C
NORMALLY
CLOSED
VALVE
NORMALLY
OPEN
VALVE