Principle Of Operation; 3582 Valve Positioners - Emerson Fisher 3582i Instruction Manual

3582, 582i, and 3583
January 2013
Note
The positioner will fully vent or pressurize the actuator to supply pressure at the ends of actuator travel when the positioner is
calibrated correctly. Failure to properly calibrate the positioner may result in reduced seat loading.
Table 11. Minimum Travel with Given Pin Position
TRAVEL PIN POSITION ALONG ROTARY SHAFT ARM
1‐1/8
1‐1/2
2‐1/2

Principle of Operation

3582 Valve Positioners

The 3582 (3582, 3582NS and 3582A, C, D, and G pneumatic valve positioners) accepts a pneumatic input signal from
a control device. Figure 17 is an operational schematic for a direct‐acting pneumatic valve positioner.
As shown in figure 17, in a diaphragm‐actuated, sliding stem control valve package with a 3582 valve positioner,
supply pressure is connected to the 83L relay. A fixed restriction in the relay limits flow to the nozzle so that when the
flapper is not restricting the nozzle, air can bleed out faster than it is being supplied.
The input signal from the control device is connected to the bellows. When the input signal increases, the bellows
expands and moves the beam. The beam pivots about the input axis moving the flapper closer to the nozzle. The
nozzle pressure increases and, through relay action, increases the output pressure to the actuator. The increased
output pressure to the actuator causes the actuator stem to move downward. Stem movement is fed back to the
beam by means of a cam. As the cam rotates, the beam pivots about the feedback axis to move the flapper slightly
away from the nozzle. The nozzle pressure decreases and reduces the output pressure to the actuator. Stem
movement continues, backing the flapper away from the nozzle, until equilibrium is reached.
When the input signal decreases, the bellows contracts (aided by an internal range spring) and the beam pivots about
the input axis to move the flapper away from the nozzle. Nozzle pressure decreases and the relay permits the release
of diaphragm casing pressure to atmosphere. The actuator stem moves upward. Through the cam, stem movement is
fed back to the beam to reposition the flapper closer to the nozzle. When equilibrium conditions are obtained, stem
movement stops and the flapper is positioned to prevent any further decrease in diaphragm case pressure.
The principle of operation for reverse acting units is similar except that as the input signal increases, the diaphragm
casing pressure is decreased. Conversely, a decreasing input signal causes an increase in the pressure to the
diaphragm casing.
32
2
3
4
MINIMUM TRAVEL AVAILABLE
mm
6
8
11
13
16
22
Instruction Manual
D200138X012
Inch
0.25
0.3125
0.4375
0.5
0.625
0.875