CSP−900RMM−2 MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 2
Original
79-00-00
Calibrated Dipstick - the calibrated dipstick
is located on the reduction gearbox above the
fuel pump drive pad. The dipstick provides
visual oil level indication and a servicing point
to add engine oil.
Drain Plug - the drain plug is located at the
bottom of the reduction gearbox next to the oil
filter bypass indicator. The drain permits
engine oil to be drained from the reduction
gearbox sump.
Oil Temperature Sensor - the oil tempera
ture sensor is a resistive temperature probe
that is mounted on each engine reduction
gearbox. The sensing point is after the inlet
from the oil cooler, oil filter and pressure
adjustment valve.
The sensor sends a signal to the engine oil
temperature indicator on the IIDS display. The
temperature readout on the IIDS display is a
numeric value in degrees centigrade.
Oil Pressure Sensor - the oil pressure sensor
is a pressure transducer type sensing element
mounted to the bottom of the accessory
gearbox. The sensing point is located after the
pressure adjustment valve.
The sensor sends a signal to the engine oil
pressure indicator on the IIDS display. The
pressure readout on the IIDS display is a
numeric value in percent of psi under normal
operation.
B. Scavenge Oil Subsystem
The scavenge oil subsystem returns oil from
the engine accessory gearbox to the oil tank.
Scavenge oil from No. 1, 2 and 3 bearings is
gravity drained directly to the reduction
gearbox sump. All drained oil is collected into
a sump at the bottom of the reduction gearbox
housing. From the sump, the reduction
gearbox scavenge pump returns the oil to the
integral oil tank.
P3 Actuated Shutoff Valve - the P3 shutoff
valve is located above the accessory drive pad.
The shutoff valve is activated by P3 air to
reduce the flow restriction created by the
scavenge pump during shutdown.
When the shutoff valve is open, the second
scavenge pump (No. 5 bearing scavenge) is
assisted by P3 air entering the bearing cavity
and returns scavenge oil from No. 5 bearing to
the reduction gearbox sump. This pump is also
protected with an in-line screen. P3 supplied
air from the air seals at the No. 4 bearing
cavity force No. 4 bearing scavenge oil out to
the reduction gearbox sump.
Magnetic Chip Detector - a magnetic chip
detector, installed adjacent to the filter
assembly, collects any ferrous metal particles
in the oil. A screen located upstream of the
scavenge pump prevents foreign matter from
entering the oil tank.
C. Breather Subsystem
The breather subsystem provides a route for
air and oil vapors to evacuate the pressure oil
and scavenge oil subsystems. Air from the
bearing compartments is routed to the
reduction gearbox via the oil scavenge system.
A centrifugal breather impeller, mounted on
the starter/generator gearshaft within each
engine reduction gearbox, separates oil from
the air on each engine.
The centrifugal breather consists of a shrouded
aluminum alloy impeller indexed by three pins
on the face of the starter generator gear, and is
secured on the shaft by a retaining ring. Oil
vapor in the gearbox is picked up by vanes on
the rotating impeller face and thrown outward
by centrifugal force. The oil drains back to the
bottom of the reduction gearbox sump and the
air vents overboard through a passage in the
reduction gearbox housing.
Air exits the passage in the reduction gearbox
through flexible hoses and aluminum tubes
and is routed from the engine through the
engine firewall to the secondary exhaust
ejector that vents the oil vapors overboard.
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