3573 And 3577 Valve Positioners - Fisher 3570 Instruction Manual

Instruction Manual
D200137X012
In the 3576 positioner, the feedback is provided to the range spring by a wire that is connected to the actuator‐valve
stem connector.
As the input signal decreases, the reverse action takes place. The bellows contracts, and as the beam pivots, it
uncovers the relay nozzle. Through relay action, the pressure on top of the piston decreases, and the force of the
actuator spring moves the piston upward.

3573 and 3577 Valve Positioners

Refer to the schematic diagram in figure 8, which shows the 3573 positioner mounted on a 473 pneumatic piston
actuator. For the 3577 positioner, the principle of operation is identical to the 3573 positioner, but the actuator can be
direct or reverse acting.
Figure 8. Schematic Diagram of Fisher 3573 Positioner with 473 Pneumatic Piston Actuator
RANGE SPRING
BIAS
SPRING
CYLINDER
CR4007‐A
A1082‐1/IL
The pneumatic output signal from a control device is piped to the positioner bellows. For explanation purposes,
assume this signal has increased. The bellows expands and moves the beam, which pivots around a fixed point and
uncovers the relay nozzle. The nozzle pressure decreases due to the uncovering of the nozzle by the beam. Through
RELAY
R
INPUT
SIGNAL
SUPPLY
R = RESTRICTION
PISTON
YOKE
INPUT SIGNAL PRESSURE
SUPPLY PRESSURE
BOTTOM CYLINDER PRESSURE
NOZZLE PRESSURE
BELLOWS
REVERSED
POSITION
3570 Positioners
September 2015
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