Chapter 9 Lubrication Systems

Introduction to Lubrication Systems

• Lubrication systems provide lubrication and cooling for gears, bearings, and splines.
• Lubrication systems collect foreign matter from the oil tank, bearing housing, or gearbox.
• Lubrication systems protect lubricated components made of non-corrosion resistant materials.
• Oil must maintain integrity without significant deterioration.

Purpose of Turbine Engine Lubrication

• Lubricating mating parts reduces friction and wear.
• Cleaning moving parts removes metal particles formed during wear and tear, preventing further damage.
• Cooling hot parts prevents heat-induced degradation of material properties and potential seizure of parts.
• Oil damping reduces vibration.

Requirements of Aviation Lubricants

• Low volatility reduces evaporation at high altitudes.
• Anti-forming characteristics ensure positive lubrication.
• High flash point is required.
• Wide temperature range capability.
• Excellent film strength qualities of cohesion and adhesion.
• High viscosity index indicates that the viscosity of the oil is retained when heated.

Types of Oil Systems

• Wet Sump Lubrication System
  • This is the oldest design and is rarely seen in modern engines.
  • The oil is contained integrally in an engine sump.
  • The parts to be lubricated are immersed partially or fully in a bath of oil.
• Dry Sump Lubrication System
  • Most modern turbine engines of the axial flow configuration use a Dry Sump Lubrication System.
  • A Dry Sump Lubrication Subsystem contains a Pressure, Scavenge, and Breather vent.
  • Oil is supplied to the lubricating parts by pressure pumps and is returned to the tank by Scavenge pumps.
• Full Flow Type Oil System (Dry Sump)
  • This system achieves desired oil flow rates by dispensing oil based on maximum RPM.
  • Excess oil returns through the Pressure Relief Valve to the feeding point of the Supply Pump.
  • The pressure pump size is determined by the flow required at maximum engine speed.

Operation of a Full Flow Lubricating System (Supply)

• Oil flows from the tank to the pressure stage in the lubrication and scavenge oil pump.
• The oil pump pressurizes the oil and sends it to the main oil filter.
• If oil pressure before the filter exceeds the set pressure, some oil goes through a pressure relief valve and back to the oil tank.
• From the main oil filter, the oil is sent to the engine air/oil heat exchanger.
• The oil then goes to the fuel oil cooler.
• At the top of the fuel oil cooler, a manifold distributes oil.
• The manifold sends oil through the last chance strainers/filters, and to the bearing compartments and gearboxes.

Operation of a Full Flow Lubricating System (Scavenge Line)

• Oil is removed from the bearing compartments and gearboxes by the scavenge oil pumps.
• A Magnetic Chip Detector helps remove ferrous metal chips or powder from the bearings before the oil reaches the scavenge pump.
• After the scavenge pump, oil travels to the Electric Magnetic Chip Detector and Oil Temperature Sensor before returning to the Oil Tank.

Operation of a Full Flow Lubricating System (Breather Line)

• Oil mist is removed from the breather air by the deoiler (centrifugal breather).
• From the deoiler, oil goes to the Tank, and breather air is vented overboard.
• any left over Oil mist at the LP Turbine will be flushed out from the exhaust.

Components of Oil System

• Oil Tank
• Pressure & Scavenge Pumps
• Pressure Relief Valves
• Fuel Oil Heat Exchanger/Oil Cooler
• Air Oil Heat Exchanger
• Deoiler/Centrifugal Breather
• Magnetic Chip Detectors
• Filters

Oil Tank

• The oil tank is usually mounted and is normally a separate unit but may be part of the external gearbox.
• It has a provision to allow the lubrication system to be drained and replenished.
• A sight glass or dipstick is used to check the oil level.

Oil Pump

• Oil pumps are vital to the efficient operation of the engine.
• Failure of the pumps will necessitate a rapid shutdown.
  • The oil pump drive-shafts do not have a weak shear neck.
  • They continue to supple oil regardless of damage.
• The Supply pump integrated together with the Scavenge pump is in an Oil Pump Assembly.

Gear Type Pump

• Gear pumps: intermeshing steel gears in a close-fitting aluminum casing.
• When the steel gears are rotating, the oil is between the teeth and casing.
• Gear pumps pressure (feed) pumps and/or scavenge (return) pumps.
• The Accessory drive system drives the oil pumps pack.

Other Types of Pump - Vane type pump

• Refer to FIG 4 for illustration on SLIDING-VANE-TYPE OIL PUMP

Pressure Relief Valve System

• The Pressure Relief Valve system in the oil flow is controlled by pressure in the feed line.
• The spring-loaded valve allows oil to be returned to the oil tank or pressure pump inlet when the design value is exceeded.

Fuel-Cooled Oil Cooler

• A large number of tubes convey the fuel through the matrix.
• The baffle plates direct the oil in series, across the tubes.
• Heat transfers from the oil to the fuel, lowering the oil temperature.

Air-Cooled Oil Cooler

• The air-cooled oil cooler is similar to the fuel-cooled type.
• The main difference is that atmospheric/ram air is used as the cooling medium.

Centrifugal Breather

• Refer to CENTRIFUGAL BREATHER illustration

Magnetic Chip Detector

• Plugs or chip detectors fit on the scavenge (return) side to collect ferrite debris in the bearing chamber.
• They are permanent magnets retained in self-sealing valve housings.
• Testing detectors warns of failing bearings and splines.
• Maintenance inspections are designed to be removed to monitor the purposes without oil loss.

Filters

• Filters and strainers prevent foreign matter from circulating.
• Coarse strainers fit at the oil tank outlet or before the pumps to prevent them from damaging.
• A fine pressure filter after the pressure pump keeps particles from blocking the oil feed jets.
• A "pop up indicator" on the filter housing gives a visual warning of a blocked filter.

Filter Types

• Thread-type Oil Filter (fine):
  • These filters are 'last chance' and immediately upstream of the oil jets.
• Electronic Cleaning Of A Cleanable Filter
  • Hand cleaning with solvent is accepted.
  • Ultrasounds are needed to clean the systems.
  • Metals on the filter are normal.
  • A high contamination level could mean failure.
  • Draining will be rerunning the engine to inspect.

Important Facts on Oil System

• Modern gas turbine engines use synthetic oil for lubrication:
  • Mobil jet type II oil, exxon 2380.
• The Oil tank in inspected within 10 minutes after shutdown.
• The oil tank is usually filled to the neck, and a change in oil height means expansion.
• Oil quantity is read via a sight glass or on a gauge from the LED screen engine page.
• Low oil pressure (red warning light) indicates engine shutdown.
• High oil temperature drives an engine shutdown too.

Recap

• What is a lubricating systems?
• What are the 4 principles of engine lubrication?
• What is the Wet sump vs Dry Sump engine difference?
• Draw the Hot Oil Tank Full Flow Lubrication System
• What is the functionality of all major components in the diagram
• Name an important fact of an oil system relating to shutdown

Explore the essentials of lubrication systems, crucial for cooling and lubricating vital engine components like gears and bearings. Discover how these systems maintain oil integrity by collecting foreign matter and protecting against corrosion. Learn about the specific requirements for aviation lubricants, including low volatility, anti-forming properties, and high flash points.