TM 1-1520-238-T-4
6–19
6–7.
SYSTEM DESCRIPTION (cont)
6–7
(d) In the primary oil system, most of the oil drained is collected in the gallery. The gallery is a common
area which accepts oil from both oil subsystems and diverts the oil to lubricate the main transmission assembly
primary gear train. Two check valves are installed on the oil return line entry into the gallery which prevents oil
from escaping the main transmission after an external oil line or component suffers an oil leak. Two pressure relief
valves channel excess oil from the gallery back into the main transmission housing. Two floater diverter valves
control oil flow into the oil sump. In case of a ballistic impact to the oil sump, the floater diverter valves close off
the oil sump, preventing complete loss of oil. When the oil level in the oil sump drops, the floats drop, closing a 28
VDC switch. When the switch closes, a solenoid is energized forcing the valve up and closing off the oil sump. Oil
level sight plugs, located on the left and right side of the main transmission housing, are bull’s–eye type indicators
that provide visual inspection of the oil quantity. The two oil pumps pressurize the oil system during operation by
scavenging oil from internal oil passages that feed the accessory gear train. The pumps are rated at 6.25 to 6.75
gpm at 75 psi while running at 4391 rpm. The two oil filter assemblies have impending bypass indicators and oil
bypass valves which remove contaminants from the main transmission oil system. The impending bypass
indicator pops out when the pressure differential across the filter is greater than 21 to 25 psid. The oil bypass
valve bypasses oil around the filter when a valve cracking pressure of 34 to 42 psid is reached. Two chip
detector/temperature switches sense the presence of metal chips in the oil and monitor oil temperature. A
capacitor discharges to burn off (fuzz suppression) any accumulation of small metal particles (ferromagnetic
material) without turning on the caution indicators. Large metal particles attracted to the chip detector cause the
CHIPS MAIN XMSN indicators on the pilot and CPG caution/warning panels to light. The pilot OIL HOT MAIN
XMSN 1 or 2 indicators, and the CPG MAIN XMSN 1 or 2 indicators on caution/warning panels light when oil
temperature reaches 274 to 294 F (134 to 146 C). Two oil pressure switches monitor main transmission oil
pressure. The switches light the pilot caution/warning panel OIL PSI MAIN XMSN 1 or 2 indicator, and the CPG
caution/warning panel MAIN XMSN 1 or 2 indicator when oil pressure is less than 26–30 psi. The switches turn
the indicators off when oil pressure exceeds 45 psi. The oil temperature transducer monitors the operating
temperature of the main transmission assembly and sends updated temperature readings through FD/LS to the
CPG’s HOD. A cooling fan maintains the main transmission assembly temperature within the requirement for
normal operations. Cooling air from the rotor down wash and the engine NGBs flow around the main transmission
assembly to aid in cooling. Main transmission oil is cooled by the heat exchangers mounted on each side of the
catwalk on the center deck area. Cooling air flows around the core tubes, cooling the oil in the heat exchangers,
then vents with engine exhaust air through the IR system. Thermal relief valves allow oil to bypass the heat
exchanger’s cooling cores until the oil reaches operating temperature. The valves automatically open as the oil
cools after shut down.
(e) The accessory lubrication system provides oil for the accessory gear train and components during
APU ground operations. The system includes the accessory oil pump, an accessory oil pressure switch,
accessory oil pump and accessory oil filter assembly. The accessory oil pressure switch turns off the pilot
caution/warning panel OIL PSI ACC PUMP indicator when oil pressure is at 45 psi and increasing. It also lights
the pilot caution/warning panel OIL PSI ACC PUMP indicator when oil pressure is 30 to 26 psid and decreasing.
(f) The accessory oil pump pressurizes the system and lubricates the accessory housing assembly
components and wicking disk. The oil pump is driven by the right generator spur gear. It is rated at 1.5 0.3 gpm,
100 psig at 12,251 rpm. The system draws oil from the right oil sump.
(g) An accessory oil filter assembly, with impending bypass indicators and oil bypass valves, removes
contaminants from the transmission’s oil system. An impending bypass indicator pops out when the pressure
differential across the filter is greater than 21 to 25 psid. An oil bypass valve bypasses oil around the filter when it
becomes partially clogged and a valve cracking pressure of 34 to 42 psid is reached.
