Oil flow. Oil from the tank flows from the bottom of the engine inlet housing through
an external line to the pressure side of the main oil pump. The oil flow may be followed by referring to
the schematic shown in figure 5.19.
The main oil pump is located on the aft face of the accessory gearbox. I contains both
pressure and scavenge elements. An adjustable relief valve in the pump maintains nearly constant oil
pressure during engine operation. Oil goes from the pump and through a filter located in the accessory
gearbox. A bypass valve will open if the filter becomes clogged. On the outlet side of the filter, oil
temperature is measured by a temperature bulb. Then the oil is routed through the oil cooler into two
external low paths. One flow path directs the oil to the rear of the engine. At that location it lubricates
number 2, 4, and 5 bearings. The second flow path directs oil to the front bearings and accessory drive
gear trains. Oil from the rear bearings is force-scavenged into an external oil-return line by paddle
pumps mounted on the power turbine shaft. This scavenge oil is directed back to the accessory gearbox.
A scavenge impeller in the accessory gearbox picks up the scavenge oil and pumps it to
the scavenge element of the main oil pump. The oil is then returned to the inlet housing where it is
discharged into the oil tank.
Chip detectors. On the T55-L-7,
the engine magnetic chip detector is located in
the scavenge-pump housing on the lower left face
of the accessory gearbox. The detector attracts
ferrous material, which builds up until it bridges a
gap, as shown in the accompanying sketch. This
makes it possible to check for the presence of
foreign material by checking continuity across the
contacts. The detectors are electrically connected
to caution lights in the cockpit.
The T55-L-11 engine is equipped with three chip detectors. Each bearing scavenge line
dual chip detector is mounted externally. Each detects ferrous and nonferrous metal chips originating in
the No. 2, 4, and 5 bearing areas of the engine. Another is located near the gearbox scavenge impeller.