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Instruction Manual
D200319X012
Figure 8. Fisher 377L Trip Valve Shown in Tripped Condition
SPRING
VALVE PLUG
UPPER DIAPHRAGM
EXHAUST
PORT
SUPPLY
PRESSURE
LOWER
DIAPHRAGM
PORT D
PORT E
LOWER PORTS
PORT F
SUPPLY PRESSURE
CONTROL PRESSURE TO TOP OF CYLINDER (BLOCKED)
CONTROL PRESSURE TO TOP BOTTOM OF CYLINDER (BLOCKED)
GE08414‐A
A6906-1
377U Trip Valve
Figure 9 illustrates trip valve operation in the fail‐up mode. The fail‐up mode of operation is similar to the fail‐down
mode of operation except that the connections to port C and F are reversed. When supply pressure falls below the trip
point, the top of the actuator cylinder vents, and volume tank pressure loads the bottom of the actuator cylinder. The
pressure imbalance created forces the actuator piston up.
MAIN SPRING
VENT
PORT A
PORT B
UPPER PORTS
PLUG
ASSEMBLIES
PORT C
ACTUATOR
PRESSURE TO TOP OF CYLINDER (STATIC)
PRESSURE FROM BOTTOM OF CYLINDER (STATIC)
LOWER DIAPHRAGM LOADING PRESSURE (BEING VENTED)
377 Trip Valve
June 2017
DVC6200
CONTROL
DEVICE
11
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