Troubleshooting; Replacing Gauges; Replacing The Pilot Valve - Fisher 4070 Instruction Manual

Type 4060 & 4070
Use bypass valves or completely
shut off the process to isolate the valve
from process pressure. Relieve process
pressure on both sides of the valve.
Drain the process media from both
sides of the valve.
Vent actuator loading pressure and
relieve any actuator spring precompres-
sion.
Use lock-out procedures to be sure
that the above measures stay in effect
while you work on the equipment.
For Type 4070 electro-pneumatic
positioners in intrinsically safe areas,
current monitoring during operation
must be with an approved meter for haz-
ardous areas in order to avoid personal
injury or property damage caused by an
explosion or fire.

Troubleshooting

Signal change has no effect on the actuator posi-
tion.
—Check indicator and screw.
—Check air supply to positioner and tubing to the ac-
tuator.
—Check input signal to positioner.
—Check diaphragm for damage or leakage.
—Check pilot valve function.
—Check cam for correct setting.
—Check I/P output
Signal change results in actuator running to end
positions.
—Check coupling between positioner and actuator.
—Check cam position and locking screw.
—Check input signal.
Inaccurate positioning.
—Dirty or worn pilot valve.
—Defective or leaking diaphragm.
10
A7232 / IL
Figure 13. Pilot Valve Assembly
—Input signal fluctuates.
—Incorrect sizing of actuator.
—Valve/actuator "stiction".
—High valve/actuator breakaway torque.
—Loose cam.

Replacing Gauges

1. Shut off supply pressure and process lines to the
positioner.
2. Remove the defective gauge.
3. Coat the threads of the replacement gauge with a
sealant (Zink plate No. 770 or equivalent).
4. Screw the replacement gauge into the gauge port.
5. Apply supply pressure to the positioner. Using a
soap solution, check around the ports and connections
for leaks.

Replacing the Pilot Valve

Refer to figure 13 to remove the pilot valve for clean-
ing or inspection.
1. Remove the screw and carefully lift out the com-
plete pilot valve assembly.
2. Gently remove the spool from the block and clean
the parts, using mentholated cleaner or similar. Blow
the parts dry with compressed air. If the parts show
signs of wear, replace the assembly.
Mixing spool valves and valve bodies
may result in very high bleed rates and
poor performance.
BALANCE ARM
SPOOL SPOOL GROVE
PILOT VALVE
ASSEMBLY
SCREW
LEAF SPRING
Note