🔵✈️ 268. Turbine Aircraft Engines: Typical Dry-Sump Pressure Regulated Turbine Lubrication System and Pressure System 🚁🎞️
Source: FAA-H-8083-32A, Aviation Maintenance Technician Handbook Powerplant, Volume 2, Pag: 6-28
The turbine lubrication system is representative of turbine engines using a dry-sump system. The lubrication system is a pressure regulated, high-pressure design. It consists of the pressure, scavenge, and breather subsystems.
The pressure system supplies oil to the main engine bearings and to the accessory drives. The scavenger system returns the oil to the engine oil tank that is usually mounted on the compressor case. It is connected to the inlet side of the pressure oil pump and completes the oil flow cycle.
A breather system connecting the individual bearing compartments and the oil tank with the breather pressurizing valve completes the engine lubrication system. In a turbine pressure relief dry-sump lubrication system, the oil supply is carried in a tank mounted on the engine. With this type of system, a larger oil supply can be carried, and the temperature of the oil can be readily controlled.
Pressure System
The oil pressure branch of the engine lubrication system is pressurized by a gear-type pressure pump located in the oil pump and accessory drive housing. The pressure pump receives engine oil at its lower (inlet) side and discharges pressurized oil to an oil filter located on the housing.
From the oil filter, which is equipped with a bypass valve for operation in case the filter clogs, the pressurized oil is transmitted to a cored passage running through to the pressure regulating (relief) valve that maintains system pressure. The pressure regulating (relief) valve is located downstream of the pump.
It is adjusted to maintain a proper pressure to the oil metering jets in the engine. The pressure regulating (relief) valve is usually easily accessible for adjustment. Then, the oil flows through the fuel oil cooler and on to the bearing cavities through last-chance filters and out spray nozzles to the bearings.
Pressurized oil distributed to the engine main bearings is sprayed on the bearings through fixed orifice nozzles providing a relatively constant oil flow at all engine operating speeds.
Scavenge System
The scavenge system scavenges the main bearing compartments and circulates the scavenged oil back to the tank. The scavenge oil system includes five gear-type pumps. The No.1 bearing oil scavenge pump scavenges accumulated oil from the front bearing case. It directs the oil through an external line to a central collecting point in the main accessory gearbox.
The oil return from No. 2 and 3 bearings is through internal passages to a central collecting point in the main accessory case. The accessory gearbox oil suction pump, located in the main accessory gearbox, scavenges oil from the gearbox housing to the oil tank. Oil from the No. 4, No. 4 1/2 and No. 5 bearing accumulates in the bearing cavity and is scavenged to the accessory gearbox.
The turbine rear bearing oil suction pump scavenges oil from the No. 6 bearing compartment and directs the scavenged oil through a passage in the turbine case strut. From there, it is directed to the bearing cavity for the 4, 4 1/2, and 5 bearing cavity where it joins this oil and is returned to the oil tank.
The scavenge oil passes through the deaerator as it enters the oil tank, which separates the air mixed in the return oil. The oil stays in the tank while the air flow into the accessory gearbox and enters the deoiler.
Breather Pressurizing System
The breather pressurizing system ensures a proper oil spray pattern from the main bearing oil jets and furnishes a pressure head to the scavenge system. Breather tubes in the compressor inlet case, the oil tank, the diffuser case, and the turbine exhaust case are connected to external tubing at the top of the engine.
By means of this tubing, the vapor-laden atmospheres of the various bearing compartments and the oil tank are brought together in the deoiler in the accessory gearbox. The deoiler separates out the oil from the air/oil mist and vents the air back to the atmosphere.
| Subsystem Name | Primary Function | Key Components | Oil Flow Path | Pressure Regulation Method | Scavenging Source (Inferred) |
| Pressure System | Supplies oil to the main engine bearings and to the accessory drives | Gear-type pressure pump, oil filter, bypass valve, pressure regulating (relief) valve, fuel oil cooler, last-chance filters, spray nozzles | Oil tank to pressure pump inlet; through oil filter to pressure regulating valve; then through fuel oil cooler to bearing cavities/nozzles | A pressure regulating (relief) valve located downstream of the pump maintains and adjusts pressure to the oil metering jets | Main engine bearings and accessory drives. |
| Scavenge System | Scavenges main bearing compartments and circulates oil back to the engine oil tank | Five gear-type pumps, No. 1 bearing scavenge pump, accessory gearbox oil suction pump, turbine rear bearing oil suction pump, deaerator | Bearing compartments to central collecting points in accessory gearbox/case; through deaerator into the oil tank | Maintains flow via gear-type suction pumps and a breather pressurizing valve for head pressure | No. 1 bearing (front case), No. 2, 3, 4, 4 1/2, 5, and 6 (rear) bearings, and accessory gearbox |
| Breather Pressurizing System | Ensures proper oil spray patterns and furnishes a pressure head to the scavenge system | Breather tubes (compressor inlet, oil tank, diffuser case, turbine exhaust), external tubing, breather pressurizing valve, deoiler | Vapor-laden atmospheres from bearing compartments and oil tank move through tubes to the deoiler, air is vented to atmosphere | Breather pressurizing valve controls the connection between bearing compartments and the atmosphere | Compressor inlet case, oil tank, diffuser case, and turbine exhaust case |