GEK 116862 Inspection and Maintenance Instructions for 7FA.05 Gas Only and Dual Fuel Gas Turbines
F. Panel Meters
Unless a competent instrument mechanic is available, it is recommended that the instrument be
returned to the manufacturer, or a laboratory, for calibration and for repairs.
In general, instruments should be on “zero” when the unit is shutdown. Whenever possible,
corrections should be made with the “zero” adjustment. If a pointer cannot be zeroed, it is probably
bent, or the “zero” adjuster crank arm is out of the regular slot.
Inspect for sticking, or jerky pointers. The most common causes of erratic operation are dirt on the
scale, pointer touching glass, dirt in a gap of moving element or damping magnet, or damaged
bearing. Correct as necessary.
III. CONTROL DEVICES
A. Temperature Switches
Temperature switches are pretested, set, and locked in the factory. If trouble is experienced in the
field, new pretested and set switches should be ordered. Faulty switches should be returned to the
equipment manufacturer or appropriate service representative for evaluation. These switches should
not be tested, adjusted, or reset in the field.
B. Thermostats
To check the accuracy of the space heater thermostats in the turbine, fuel, and control compartments,
compare the setting of the thermostat with the temperature shown on an accurate thermometer.
Sufficient hold time should be allowed when calibrating temperature instrumentation. If there is a
discrepancy of more than five degrees, the thermostat should be adjusted, or replaced.
C. Pressure Regulating Valves (VPRs)
Pressure regulating valves are of two types — pressure reducing and backpressure regulated. Except
in a few instances, a line-mounted pressure gauge is available very close to the valve to check and/or
set the control pressure required for that particular valve. Backpressure-regulated valves are preset at
the factory and should require no adjustment for normal operation. In most applications, the valve
stem is exposed to view, so valve movement can be checked visually or with a dial indicator. For
valves that do not have an exposed stem, the valve setting is best accomplished with the valve
removed from the stem. On some valves, it is possible to use an external pressure source, preferably
dry air, to check the valve setting while the machine is shutdown. Valve travel is checked with a dial
indicator inserted through a removable cover on the valve opposite the side where the valve yoke
(top-works) is located.
If the valve is not operating properly, remove it and bench-check it for:
1. Sensing line restrictions
2. Ruptured diaphragm
3. Valve body obstruction
4. Bent or binding valve stem
5. Broken spring
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