DE LA PRUEBA DE LA FILIACION DE LOS HIJOS DE LOS CONYUGES

INTRODUCTION

When two surfaces are in contact and moving there is always friction because, even apparently smooth surfaces, have minute imperfections.

In order to overcome the potential for development of intense heat, lubricating of the affected parts is essential.

The primary method of cooling would be oil lubrication. There are two basic phases of lubrication – film lubrication where the surfaces are separated by a substantial quantity of oil and boundary lubrication where the oil film may be only a few molecules thick.

In general, the parts to be lubricated and cooled include the main bearings and accessory drive gears and the propeller gearing in the turboprop.

OIL SYSTEM COMPONENTS

The oil system components used on gas turbine engines are: ! Tanks. ! Pressure pumps. ! Scavenger pumps. ! Filters. ! Oil coolers. ! Relief valves.

! Breathers and pressurizing components. ! Pressure and temperature gages lights. ! Temperature-regulating valves.

! Oil-jet nozzle.

! Fittings, valves, and plumbing. ! Chip detectors.

Not all of the units will be found in the oil system of any one engine. But a majority of the parts listed will be found in most engines.

The major difference between a wet-sump system and a dry-sump system is the location of the oil reservoir.

TURBINE ENGINE DRY-SUMP LUBRICATION

In a turbine dry-sump lubrication system, the oil supply is carried in a tank mounted externally on or near the engine.

With this type of system a larger oil supply can be carried and the oil temperature can be controlled.

An oil cooler is usually included in a dry-sump oil system. It is designed to furnish a

constant supply of oil to the engine. This is done by a swivel outlet assembly mounted inside the tank, a horizontal baffle mounted in the centre of the tank, two flapper check valves

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All oil tanks have expansion space. This allows for oil expansion after heat is absorbed from the bearings and gears and after the oil foams after circulating through the system. Some tanks also incorporate a de-aerator tray. The tray separates air from the oil returned to the top of the tank by the scavenger system. Usually these de-aerators are the "can" type in which oil enters a tangent. The air released is carried out through the vent system in the top of the tank.

In most oil tanks a pressure build-up is desired within the tank. This assures a positive flow of oil to the oil pump inlet. This pressure build-up is made possible by running the vent line through an adjustable check-relief valve.

A dipstick is usually used to measure the quantity of oil or, in some aircraft; electric quantity indicators give direct readings on a gauge in the cockpit.

TURBINE ENGINE WET-SUMP LUBRICATION

In some engines the lubrication system is the wet-sump type. Because only a few models of centrifugal-flow engines are in operation, there are few engines using a wet-sump type of oil system.

The reservoir for the wet-sump oil system is the sump mounted on the bottom of the accessory case or lower crankcase.

A bayonet-type gage indicates the oil level in the sump.

Two or more finger strainers (filters) are inserted in the accessory case for straining pressure and scavenged oil before it leaves or enters the sump. These strainers aid the main oil strainer.

A vent or breather equalizes pressure within the accessory casing.

Pump Relief Valve

Oil Tank

System Relief Valve Feed Oil

Return Oil

A magnetic drain plug may be provided to drain the oil and to trap any ferrous metal particles in the oil. This plug should always be examined closely during inspections. The presence of metal particles may indicate gear or bearing failure.

A temperature bulb and an oil pressure fitting may be provided.

LUBRICATION METHODS 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

! Although pressure lubrication is the principle method of lubrication on all aircraft engines, some engines use splash lubrication also

Splash Lubrication and Combination Systems

! Splash lubrication is never used by itself. It is so called due to the moving parts picking up oil and ‘splashing’ it around.

! All lubrication systems are pressure systems or combination pressure/splash systems

Mist or Spray Lubrication

! High pressure oil is fed to the main bearings by pipes and ducts and then into the hollow crankshaft via holes drilled into the journals.

! Oil passes through holes in the crankpins to the big end bearings and then escapes in the form of a mist or spray due to the centrifugal forces of the rotating crankshaft.

PRESSURE PUMPS

! Oil pressure pumps may be 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

The gear-type pump consists of a driving and a driven gear. The engine-accessory section drives the rotation of the pump. Rotation causes the oil to pass around the outside of the gears in pockets formed by the gear teeth and the pump casing. The pressure developed is proportional to engine RPM up to the time the relief valve opens. After that any further increase in engine speed will not result in an oil pressure increase. The relief valve may be located in the pump housing or elsewhere in the pressure system for both types of pumps.

SCAVENGER PUMPS

These pumps are similar to the pressure pumps but have a much larger total capacity. An engine is generally provided with several scavenger pumps to drain oil from various parts of the engine. Often one or two of the scavenger elements are incorporated in the same housing as the pressure pump.

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OIL PRESSURE RELIEF VALVE

To allow for oil flow in the event of filter blockage, all filters incorporate a bypass or relief valve as part of the filter or in the oil passages. When the pressure differential reaches a specified value (about 15 to 20 psi), the valve opens and allows oil to bypass the filter. Some filters incorporate a check valve. This prevents reverse flow or flow through the system when the engine is stopped

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 pressure is registered from that point where oil enters the engine. Oil, under pressure, flowing into a semi bent tube, attempts to straighten the tube. This straightening force is amplified through a system of gears and levers and positions a needle on a calibrated dial in p.s.i.

VISCOSITY

! Viscosity is technically defined as the fluid friction of an oil or: ! More simply, it is the resistance an oil offers to flowing

! Heavy-bodied oil is high in viscosity and pours or flows slowly ! At high temperatures oil becomes thin (low viscosity)

CHARACTERISTICS OF AIRCRAFT 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 anti-wear properties

! Maximum cooling abilities

! Maximum resistance to oxidation ! Non-corrosive

FUNCTIONS OF ENGINE OIL

! Lubrication, thus reducing friction ! Cools various engine parts ! Seals the combustion chamber ! Cleans the engine

! Aids in preventing corrosion