GEK 116862 Inspection and Maintenance Instructions for 7FA.05 Gas Only and Dual Fuel Gas Turbines
D. Check Valves, Orifices and Orifice Check Valves
During a shutdown period, the system has to be drained and the valves and orifices have to be
removed to check for evidence of erosion, corrosion, or component deterioration. Check the orifices
for plugging, size and sharpness of the hole. Check the valve seat for leakage. Check the condition of
the seals, “O” rings, or gaskets, and replace them if there is any indication of wear.
E. Lube Oil Filters
The lube oil system filters should be changed once a year, regardless of the pressure drop. The
pressure drops must be checked under turbine operating conditions, with the lubricant at normal
operating temperature, and at rated flow through the filter. In most gas turbine lube systems, the main
lube filter, which filters the lubricant to the main bearing header, can be checked for clogging by the
pressure drop indication. Here, the pressure downstream from the filter is maintained by a pressure
regulating valve, and the difference in the pressures shown on the gauges before and after the filter
will provide a reliable indication of the filter condition. The condition of other filters in the lube
system, such as the control fluid filter or hydraulic control pump filter, cannot be determined as
reliably by the pressure drop indication since the flow through these filters may be very low under
steady-state conditions. It is unlikely, however, that these low-flow filters will foul before the
recommended annual change out of the filter element.
Dual filter arrangements with transfer valve are incorporated into the lube oil system to facilitate
transfer between the filters without turbine shutdown. It is recommended that the turbine be shut
down and the system isolated before servicing the filters.
F. Hydraulic Supply Filters
The hydraulic supply system filter should be changed when the pressure drop across the filter is 60
psid (4.14 bars), or once a year, regardless of the pressure drop.
The pressure drop must be checked under turbine operating conditions, with the hydraulic fluid at
operating temperature and at rated flow through the filter. The rated flow can be assumed to be
realized during maximum transient conditions, such as at the instant of hydraulic trip of the gas
turbine. Under steady-state conditions, there will be only a small flow through the filter and any
differential pressure indicated on the system gauge will probably be small and not a true indication of
the condition of the filter. It is unlikely, however that these low-flow filters will foul before the
recommended annual change-out of the filter cartridge.
Dual filter arrangements are incorporated into the hydraulic supply system to extend the hydraulic
system run time before required maintenance. It is recommended that the turbine be shut down and
the system isolated before servicing the filters.
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