GE Masoneilan 4700P, Maintenance Manual

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Maintenance
WARNING
Before commencing any calibration or maintenance procedure
on these positioners, ensure that the valves under control are
isolated from the controlled process and that the area is verified
as nonhazardous.
Pilot
See Figure 18 on page 62.
To clean or replace deteriorated parts, the valve must be isolated from process. Shut off air sup-
ply. To minimize maintenance time, it is recommended that the entire pilot subassembly (11) be
replaced by a new subassembly, so that the old unit can be worked on when time permits.
Disassembly
1. Unscrew the pilot subassembly (11) and disengage it from the body (1). Note: Turn
the pilot subassembly while removing it to prevent damage to the O-rings.
2. Remove end plug and withdraw the spring, plug and extension pin. If necessary,
use a penetrating oil to free parts.
CAUTION
Do not disassemble or adjust extension pin.
3. Wipe the parts with a clean soft lint free cloth and blow compressed air through
the orifices. Use isopropyl alcohol to clean. Do not use chloride based solvents.
Reassembly
1. Install three new O-rings on the pilot spool. Put a light coating of silicone grease
on each O-ring.
2. Replace the extension pin and the plug, countersunk end first into the pilot spool.
The plug should slide into the pilot spool by its own weight.
3. Install the spring in the pilot spool. The end having the smallest diameter must be
in contact with the plug. Screw the pilot end plug into the pilot spool.
4. Install the pilot subassembly (11) into the body (1).