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Inspection and Maintenance Procedures
from that given on the valve nameplate, the valve sensing element may have been improperly assembled
into its well or have an improper charge of sensing fluid.
The element could be defective, or there may be too much friction in the valve mechanism. Sensing bulbs
are marked "TOP" or "UP" and must be assembled properly. If it is noted that the valve proportional
band increases with time, the sensing element probably has a small pinhole leak and should be replaced.
If the temperature sensing system must be replaced, the valve can be cranked open mechanically and
the temperature sensing probe, capillary tube, and diaphragm in the valve bonnet can be replaced without
having to shut off the cooling water or shut down the turbine.
Note: If sensor bulb is removed for any reason make sure that the tempera-
ture well is filled with heat transfer compound prior to replacement
of the sensing bulb. Refer to Standard Practices, Solvents, Sealers and
Cleaners for proper compound.
Valve stem packing nuts should be tightened just enough to stop water leaks. The valve manufacturer
generally states that if the packing nut is hand tightened, enough force is applied to stop water leakage.
Use of excessive force causes friction between the valve stem and packing. This results in erratic
operation.
It is recommended that the valve stem packing be replaced every five years unless operating experience
indicates the advisability of more frequent replacement.
HYDRAULIC/MECHANICAL EQUIPMENT
Relief Valves
Spring-loaded relief valves protect the system component, or pumps from overpressure. Adjustment of
the valve setting is accomplished by an adjusting screw. Turning the screw into the valve body increases
the spring force (raises opening pressure). The relief valve is set to open at the pressure specified on the
Device Summary Schematic Piping Diagram.
Annually, all the relief valves listed should be removed and bench-tested against the settings listed on
the Device Summary.
Solenoid Valves
If any oil leakage is observed, replace the "O" ring seals. Energize the solenoid and check valve opera-
tion (a metallic click should be heard and in some cases, the valve travel can be seen).
Sluggish valve operation, or excessive leakage can result from dirt. Therefore, periodic disassembly and
cleaning of all solenoid valves is desirable when improper operation or leakage is evident.
Servovalves
If any oil leakage is observed, replace O-ring seals.
Verify that lock washer, required by assembly drawings but not provided with new replacement servo-
valves, are in place on all servovalve mounting screws.
IMP–4
Inspection and Maintenance
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