Lubrication Systems D.Chamundeswari

Classification of Lubricants Animal Vegetable Mineral Synthetic

Animal Lubricants Lubricants with animal origin: Tallow Tallow oil Lard oil Neat’s foot oil Sperm oil Porpoise oil These are highly stable at normal temperatures Animal lubricants may not be used for internal combustion because they produce fatty acids

Vegetable Lubricants Examples of vegetable lubricants are: Castor oil Olive oil Cottonseed oil Animal and vegetable oils have a lower coefficient of friction than most mineral oils but they rapidly wear away steel

Mineral Lubricants These lubricants are used to a large extent in the lubrication of aircraft internal combustion engines There are three classifications of mineral lubricants: Solid Semisolid Fluid

Synthetic Lubricants Because of the high operating temperatures of gas-turbine engines, it became necessary to develop lubricants which would retain their characteristics at temperatures that cause petroleum lubricants to evaporate and break down Synthetic lubricants do not break down easily and do not produce coke or other deposits

Lubricating Oil Properties Gravity Flash Point Viscosity Cloud Point Pour Point Carbon-Residue Test Ash Test Precipitation Number Corrosion and Neutralization Number Oiliness Extreme-Pressure (Hypoid) Lubricants Chemical and Physical Stability

Gravity The gravity of petroleum oil is a numerical value which serves as an index of the weight of a measured volume of this product There are two scales generally used by petroleum engineers: Specific-gravity scale American Petroleum Institute gravity scale

Flash Point The flash point of an oil is the temperature to which the oil must be heated in order to give off enough vapor to form a combustible mixture above the surface that will momentarily flash or burn when the vapor is brought into contact with a very small flame

Viscosity Viscosity is technically defined as the fluid friction of an oil To put it more simply, it is the resistance an oil offers to flowing Heavy-bodied oil is high in viscosity and pours or flows slowly

Cloud Point The cloud point is the temperature at which the separation of wax becomes visible in certain oils under prescribed testing conditions When such oils are tested, the cloud point is slightly above the solidification point

Pour Point The pour point of an oil is the temperature at which the oil will just flow without disturbance when chilled

Carbon-Residue Test The purpose of the carbon-residue test is to study the carbon-forming properties of a lubricating oil There are two methods: The Ramsbottom carbon-residue test The Conradson test

Ash Test The ash test is an extension of the carbon-residue test If an unused oil leaves almost no ash, it is regarded as pure The ash content is a percentage (by weight) of the residue after all carbon and all carbonaceous matter have been evaporated and burned

Precipitation Number The precipitation number recommended by the ASTM is the number of milliliters of precipitate formed when 10 mL of lubricating oil is mixed with 90 mL of petroleum naphtha under specific conditions and then centrifuged

Lubricant Requirements and Functions Characteristics of Aircraft Lubricating Oil Functions of Engine Oil Straight Mineral Oil Ash-less Dispersant Oil Multi-viscosity Oil

Characteristics of Aircraft Lubricating Oil It should have the proper body (viscosity) High antifriction characteristics Maximum fluidity at low temperatures Minimum changes in viscosity with changes in temperature High antiwear properties Maximum cooling abilities Maximum resistance to oxidation Noncorrosive

Functions of Engine Oil Lubrication, thus reducing friction Cools various engine parts Seals the combustion chamber Cleans the engine Aids in preventing corrosion Serves as a cushion between impacting parts

Straight Mineral Oil Straight mineral oil is one of many types of oil used in aircraft reciprocating engines It is blended from selected high-viscosity-index base stocks These oils do not contain additives, except for a small amount of pour-point depressant for improved fluidity at cold temperatures

Ashless Dispersant Oil Most aircraft oils other than straight mineral oils contain a dispersant that suspends contamination such as carbon, lead compound and dirt The dispersant helps prevent these contaminants from gathering into clumps and forming sludge or plugging oil passageways

Multiviscosity Oil In certain circumstances, all single-grade oils have short comings In cold-weather starts, single grade oil generally flows slowly to the upper reaches and vital parts of the engine Multigrade oils have viscosity characteristics that allow for better flow characteristics at engine start

Characteristics of Lubrication Systems Pressure Lubrication Splash Lubrication and Combination Systems Principal Components of a Lubrication System Oil Capacity

Pressure Lubrication In a pressure lubrication system, a mechanical pump supplies oil under pressure to the bearings Oil flows into the inlet of the pump through the pump and into an oil manifold which distributes it to the crankshaft bearings

Splash Lubrication and Combination Systems Although pressure lubrication is the principle method of lubrication on all aircraft engines, some engines use splash lubrication also Splash lubrication is never used by itself All lubrication systems are pressure systems or combination pressure/splash systems

Components of Lubrication Systems Plumbing for Lubrication Systems Temperature Regulator (Oil Cooler) Oil Viscosity Valve Oil Pressure Relief Valves Oil Separator Oil Pressure Guage Oil Temperature Guage Oil Pressure Pumps Scavenge Pumps Oil Dilution System

Plumbing for Lubrication Systems Oil plumbing is essentially the same as is used in oil and hydraulic systems When the lines will not be subject to bending, aluminum tubing is used Synthetic hose is often used near the engine and other places on the aircraft that are subject to vibration or other movement

Temperature Regulator (Oil Cooler) An oil temperature regulator is designed to maintain the temperature of the oil for an operating engine at the correct level These regulators are often called oil coolers since cooling of engine oil is one of their main functions

Oil Viscosity Valve The oil viscosity valve is generally considered a part of the oil temperature regulator unit and is employed in some oil systems The viscosity valve consists essentially of an aluminum alloy housing and a thermostatic control element The oil viscosity valve works with the oil cooler valve to maintain a desired temperature and keep the viscosity within required limits

Oil Pressure Relief Valves The purpose of the oil pressure relief valve is to control and limit the lubricating pressure in the oil system This is necessary to prevent damage caused by excessive system pressure and to ensure that engine parts are not deprived of fuel due to a system failure

Oil Separator Air systems where oil of oil mist is present may require the use of an oil separator These are often used on vacuum pump outlets The oil separator contains baffle plates which cause the air to swirl and it deposits on the baffles

Oil Pressure Gauge An oil pressure gauge is an essential component of any engine oil system These gauges generally use a bourdon tube to measure the pressure They are designed to measure a wide range of pressures

Oil Temperature Gauge The temperature probe for the oil temperature gauge in the oil inlet line or passage between the pressure pump and the engine system On some installations the temperature probe is located in the oil filter housing These are normally electric or electronic

Oil Pressure Pumps Oil pressure pumps may either be of the gear type or vane type The gear type pump is used in the majority of reciprocating engines and uses close fitting gears that rotate and push the oil through the system

Scavenge Pumps Scavenge pumps are driven in the same manner as the pressure pumps but have a greater capacity This higher capacity is because the oil in the sump is foamy which means it has a much greater volume than air-free oil

Oil Dilution System The purpose of the oil dilution system is to provide thinner oil during engine start This allows faster lubrication of engine components Oil dilution is accomplished by pumping a small amount of fuel into the oil

Sludge Chambers Some reciprocating engines have sludge chambers which are in the hollowed out connecting-rod journals These journals accumulate carbon sludge and dirt particles as they are designed to During engine overhaul these must be replaced

Typical Lubrication Systems Oil System for Wet-Sump Engine Oil System for Dry-Sump Engine Oil Tanks

Oil Tanks Dry sump engine lubrication systems require a separate tank for each engine system These tanks can be constructed in three different ways: Welded sheet aluminum Riveted aluminum Stainless steel Some aircraft are equipped synthetic rubber tanks