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Lubrication Systems
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Table of Contents
1. Introduction
2. Wet Sump System
3. Dry Sump
4. Oil Tanks
5. Oil Pumps
6. Oil Filters
7. Bearing Chamber (may be deleted)
8. Oil System Valves
9. Other Oil Components
10.Spectrometric Oil Analysis Program (SOAP)
11.Trouble Shooting & Maintenance
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1- Introduction
The primary function of a lubricationsystem is to provide oil to the various partsof the engine which are subject to friction
loads from engine rotation and heat loadsfrom the gas path.
The lubrication system can be divided intotwo sections:
The Pressure side
The Scavenge side.
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There are two basic classifications of gas
turbine lubrication systems:
Wet Sump
Dry Sump
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2-Wet Sump System
A wet sump lubrication system was used on early gasturbine engines and is now more often found on smallerengines or APU's.
A wet sump system is a lubrication system where the oilsupply is carried within the engine itself or accessorygearbox.
Pressurized oil is used to lubricate the main enginebearings but the accessory gearbox is splash lubricatedby oil carried in the gearbox housing that also acts as aoil reservoir
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3-Dry Sump
A dry sump lubrication system carries its
oil supply in a tank separate from the
engine.
This now the most common type of
lubrication system in modern gas turbine
engines.
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Dry sump cont
Dry sump lubrication systems are divided
into two categories;
hot-tank system and
the cold-tank systems.
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-Hot-Tank Lubrication System
Has the oil cooler placed in the pressure
side of the system, and the oil is returned
'hot' to the oil tank.
An advantage of this type of system is that
a maximum heat exchange occurs
because the oil has less entrained air in
the pressure side of the system and thisallows a smaller oil-cooler to be used.
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Cold-Tank Lubrication System
A cold tank system is essentially the sameas the hot-tank system except that the oil
cooler is located in the scavenge sideofthe lubrication system and the oil is cooledbefore being returned to the oil tank.
In engines that have higher oiltemperatures this is an advantage, as highoil temperatures affect oil service life.
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5-Oil Tanks
A gas turbine engine oil reservoir is
usually mounted on the engine or nearby
airframe.
They are usually constructed of aluminum
or stainless steel and are designed to
provide a constant supply of oil to the
lubrication system.
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Oil tanks cont
Federal Aviation Regulations (FAR's) require that thetanks have an oil tight filler cap and an expansion spaceof 10%.
The expansion space is to make allowance for an
increase in oil volume due to thermal expansion andentrapped air when the engine is operating.
Most tanks are pressurized to approximately 4 psi, thishas two purposes:
Positive flow of oil
Suppresses foaming and pump cavitations.
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Oil tanks cont
The tanks can contain:
A venting system
Filler cap and strainer
De-aerator to remove air
Oil pick up
Dip stick
Sight gauge Oil quantity transmitter
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Oil Pumps
Vane Pump
Vane pumps are a constant displacement
pump more often found in the scavengeside of the lubrication system as they are
more tolerant of debris and have a high
volume and relatively low pressure.
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Gerotor Pump
Gerotor pumps are a constant
displacement pump and are used in boththe pressure side and the scavenge side
of the engine.
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Oil pumps cont
Gear Pump
Gear pumps are the most commonly used
constant displacement pump and can befound in the either the scavenge side or
the pressure side.
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6- Oil Filters
It is extremely important that the oil used in a gas turbineengine is free from foreign particles as these particlescan cause severe bearing damage.
To keep the oil clean filters are used as the oil leaves the
pressure pump and again in what are called the 'lastchance' filters just before the oil is sprayed from the oil
jet nozzle.
There are three common types of filter used in gas
turbine engines:
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Woven Wire Mesh Filter
Easy to clean, but can generally only
remove particles larger than 40 microns.
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Disk-type / Wafer Type Filter
Made up of a series of screen type filters
with spacers in between each screen to
form a chamber which is ported to the
central collection tube.
This type of filter is easily cleaned and
provides better filtration than a wire mesh
filter.
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Pleated Fiber Filter
Can remove particles as small as 15
microns. Can be cleanable or disposable
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Bearing Chambers
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8-Oil System Valves
Relief Valve
Relief valves are designed to maintain a constantpressure in the lubrication system and prevent over
pressurization and damage. The relief valves are situated on the discharge side of
the pump, when the oil pressure exceeds the valvesetting the valve opens and ports oil to the inlet side ofthe pump.
Some valve pressure settings can be adjusted by ascrew.
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Bypass valves
normally found in oil system components
and are designed to allow oil to bypass a
component should the component fail and
oil is prevented flowing through it.
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Check Valve
A one-way valve that ensures that oil flows
in one direction only
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9-Other Oil Components
Chip Detectors
Magnetic chip detectors are installed inscavenge side of the lubrication system
used to determine the level of metallic wearoccurring in the engine.
Some chip detectors are easily removed forvisual inspections while other may include an
electrical circuit that illuminates a warning light inthe flight deck when enough metal chips haveaccumulated to close the gap in the detector.
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Heat exchanger
The oil in a gas turbine engine gathers a
great deal of heat from the main bearings
and this heat maybe transferred to eitherfuel or air.
Most modern gas turbine engines transfer
the heat to the fuel to prevent theformation of ice crystals.
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Air-Oil Separator
The oil that is picked up by the scavenge pumpcontains a lot of air.
Oil tanks contain dwell chambers which allowthe air to separate and the air-free oil to enter
the tank. Some engines also utilize a gear driven
centrifugal air-oil separator.
As oil laden air enters the rotating slinger
chamber, centrifugal action throws the oiloutwards to collect on the walls and drain downinto the tank
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Breather system
The breather system is used to keep the
air in the oil tank at the same pressure as
the air in the bearing housing.
This ensures that there is a positive flow of
oil to the inlet of the main pump and
prevents cavitations.
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After lubricating the bearing the oil drains down into the sump and iscollected by the scavenge pump and returned to the oil tank.
The scavenge pump not only collects all the oil, but also collectssome air as well.
This air is transferred to the tank and is separated from the oil by thedeaerator and is used to pressurize the tank.
The bearing chamber is vented to the oil tank by the vent line and acheck valve.
The oil tank is also vented to ambient air through the pressurizingvalve which maintains the tank at approximately 3-4 psi.
If the scavenge pump lowers the pressure in the bearing chamber,the vacuum valve opens and allows air to enter the chamber
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10-Spectrometric Oil Analysis
Program (SOAP)
Oil sampling should be done at regular
intervals just after an engine has been run.
The contaminants in the oil provide an
indication of engine wear.
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Oil samples taken are passed through a
spectrometer which precisely burns the oil
and measures the wavelength of the
emitted light to determine the type andquantity of contaminates in the oil.
The spectrometer can detect contaminants
at 2-3 parts per million of oil
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The contents of the filters can be
examined for evidence of metal particles,
but by the time particles large enough to
be visible are discovered serious enginedamage has already occurred
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