the following discussion on oil flow through the
sump. An indicating type of magnetic plug is
system.
located in the scavenge side of the pump.
The engine lube oil system is an LP, dry sump
system. It consists of a combination lube supply
Oil Filter
and scavenge pump (1), an external scavenge
pump (2), a turbine scavenge pump (3), pressure-
An oil filter is mounted on the front of the
regulating valves (4), an oil filter and check valve
AGB. It has a pleated-type element and
(5), a filter bypass valve (6), and a scavenge
incorporates a Teflon-seated, poppet-type check
pressure relief valve (7).
valve. This valve prevents oil from draining out
In operation, oil from the reduction gear sump
of the engine when the engine is shut down. A
(supply tank) is picked up by the reduction gear
bypass valve, located in the AGB front cover,
lube oil pump. It then flows through the supply
opens at a specific pressure differential. This
filter and the oil cooler. Oil from the cooler
bypasses the filter if it becomes clogged.
supplies both the reduction gear and engine lube
oil systems. Oil to the engine flows through a
pressure regulating valve and into the inlet of the
External Scavenge Pump
engine supply pump. From the engine supply
pump, the oil flows through a filter and check
The external scavenge pump is a three-gear,
dual-element pump. It is mounted on the aft side
valve. It then flows through drilled and cored
of the AGB. It scavenges the oil from the
passages and internal and external lines to areas
compressor rear bearing sump and from the
of the engine needing lubrication.
turbine forward bearing sump. The oil from the
Scavenge oil is collected by the scavenge
element of the main lube and scavenge pump, the
pump is combined with the scavenge oil from the
main scavenge pump. It is then returned to the
external scavenge pump, and the turbine scavenge
pump. Oil from the turbine scavenge pump flows
reduction gear sump.
through drilled passages and internal lines to the
AGB. There it is picked up by the scavenge
Turbine Scavenge Pump
element of the main pump. Flow from the external
scavenge pump joins the flow from the main
The turbine scavenge pump is a gear-type
scavenge pump (through external lines) and is
pump. It is mounted in the rear turbine bearing
returned to the reduction gear sump. The
support assembly. A splined coupling drives the
magnetic drain plugs (not shown) are on the
pump from the turbine-to-compressor tie bolt.
bottom of the AGB and the discharge of the main
The pump scavenges oil from the turbine rear
scavenge pump. These collect any steel particles
bearing and returns it to the accessory drive
in the oil.
housing. It is covered by a thermal insulation
blanket and the exhaust inner cone.
Main Pressure and Scavenge Oil
Pump
Vent System
The main pressure (supply) and scavenge oil
pump assembly is mounted on the front of the
The air inlet housing cavity and AGB are
vented. This is through an external line from the
AGB. It has two gear-type pumps, one for the
AGB to a breather mounted on top of the air inlet
supply system and one for the scavenge system.
housing. Air used to send the compressor rear
It also has a pressure-regulating valve. Oil is
bearing sump is vented through the two horizontal
pumped by the pressure (supply) element of the
struts of the compressor diffuser. The combustor
pump to the following components: the com-
pressor extension shaft bearing, the PTO shaft
inner casing is vented to atmosphere through two
mid-bearing, the AGB, the four main bearings of
horizontal struts in the turbine inlet casing. The
combustion inner casing liner provides a passage
the engine, and the EG actuator.
for venting along the shaft. This flows through
The scavenge element picks up scavenge oil in
holes in the turbine coupling shaft. From there
the AGB. The oil is gravity drained from the
it flows to and pressurizes the turbine rear bearing
compressor extension shaft bearing and the
labyrinth seal at the rear face of the turbine
compressor front bearing. The scavenge element
fourth-stage wheel, finally entering the exhaust
returns the scavenge oil, along with the oil from
gas stream.
other scavenge pumps, to the reduction gear
3-28
