tfe 731 chap 79 (1)

Garret TFE 731 Turbofan Engine (CAT C)

CHAPTER 79

of 24 FOR TRAINING PURPOSES ONLY © TFE 731 - ISSUE 2, 2010


CHAPTER 79


INTRODUCTION

0 TABLE OF CONTENTS

1 Description and Operation 3 2 Oil Tank 4 3 Lube Oil Pump 5 4 Oil Pressure Regulator 6 5 Pressure Regulator Adjustment 7 6 Oil Filter 8 7 Bypass Valve 9 8 Filter Bypass Switch Operation 10 9 Fuel Heater 11 10 Air/Oil Cooler 12 11 Oil Temperature Control Valve 13 12 Fuel/Oil Cooler 14 13 Bearing Sump 15 14 Breather Pressurisation Valve 16 15 Magnetic Chip Detector 17 16 Lubrication System - Schematic 19 17 TFE731 Lubrication Plumbing 21 18 Lubrication System Pressure Problems 21 19 Lubrication System Temperature Problems 22 20 Oil Loss Causes 23


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LUBRICATION SYSTEM

1 DESCRIPTION AND OPERATION The TFE731 lubrication system is similar to lubrication systems found on other engines. The engine lubricant is drawn from the oil tank by the oil-pressure pump and is passed through the filter, the pressure-regulating valve, and the fuel heater, and then to the oil-to-air heat exchanger, commonly called air/oil coolers. This exchanger is a three-segment, finned cooler that forms the inner surface of the engine fan duct. From the air/oil coolers, the oil flow is divided so that part of the flow is directed to the accessory and transfer gearboxes and the engine bearings. The remaining oil passes through the fuel/oil cooler and is then delivered to the fan gearbox. Both exchangers are equipped with thermostatic bypass valves to maintain the oil at the desired temperature during cold weather operation. All pumps are in the engine oil pump package, which contains four scavenge pumps and the oil-pressure pump. These pumps scavenge: (1) The fan gearbox and forward-engine

bearings, (2) The aft-engine bearing, (3) The transfer gearbox and the mid-engine

bearings (through the tower shaft housing), and

(4) The accessory gearbox. The discharge side of all scavenge pumps connects to a common line that is routed to the oil tank.


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The capacity of the scavenge pumps is greater than that of the pressure pump to ensure good scavenge performance. Air is separated from the oil by the de-aerator in the optional oil tank and is vented to the accessory gearbox. Suspended oil droplets are centrifugally removed from the air before the air is vented overboard through the breather pressurising valve. This valve maintains a minimum pressure in the lubrication system compartments to ensure proper oil-pump operation at all altitudes within the engine operating envelope. A magnetic chip detector that is capable of attracting magnetically permeable materials is provided on the engine oil pump. Provisions for electrical connection of the magnetic chip detector to an airframe-furnished indicator are optional on the TFE731 engines. A more detailed discussion of the lubrication system begins next with an in-depth look at each component.

2 OIL TANK The oil tank is mounted on the forward right side of the engine and includes service ports, sight gauge, and drain plug. Oil capacity of the tank for all engines except the -5 is 6 quarts. The -5 engine has a 6.6 quart capacity due to a slightly different system configuration. The total engine lubrication system capacity is 12-13 quarts depending upon the specific engine. Engine servicing/oil level checking is accomplished by using the tank service port and sight gauge. An alternate service port with an integral dipstick or sight gauge to check oil level is provided when access to the tank is restricted.

Oil servicing is required when the oil level is more than one quart low. If oil quantity is not checked within one hour of engine shutdown, an inaccurate indication may result. Check the engine maintenance manual for specific oil servicing procedures.


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3 LUBE OIL PUMP The oil pump is a positive displacement, seven-element gerotor type pump flange mounted to the aft right side of the accessory gearbox. The pressure lube system employs two elements, while five elements are used to scavenge the following areas: (1) Fan gearbox, #1, #2 and #3 bearing sump scavenge

utilises two elements. (2) Accessory gearbox utilises one element. (3) The numbers 4 and 5 bearing sump, tower shaft and

transfer gearbox utilises one element. (4) The number 6 bearing sump utilises one element. The volume of oil developed by the pressure lube elements exits the pump through a port in the accessory gearbox. This port is shown on the upper left of the pump illustration. Scavenge oil enters the pump at the four ports shown and is discharged through a common outlet. Also located at this outlet is the magnetic chip detector. All oil flowing through the engine passes across the chip detector. The oil pump pressure element capacity is 12 GPM at 125 psig whereas the scavenge elements total capacity exceeds 24 GPM to ensure good scavenge performance. The air-to-oil ratio from the scavenge pumps to the tank is approximately 80% air by volume. Air is separated from the scavenge oil by the de-aerator in the oil tank and is vented to the accessory gearbox.


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4 OIL PRESSURE REGULATOR The oil pressure regulator, housed in the oil pump, regulates oil pressure to maintain a desired pressure at the fan gearbox bearings. In operation, a sensing line from the fan gearbox oil manifold to the regulator detects variations from the set pressure. When oil manifold pressure exceeds set pressure, the increase is detected by the sense piston that compresses the adjusting spring and causes the bypass port to be opened to reduce oil delivery to the engine. As the sense piston moves the pilot valve follow it. When the pilot valve follows the sense piston, a modulating hole in the pilot valve is covered by a metering edge on the slave piston and pump discharge pressure is allowed to build up behind the slave piston providing more positive valve action. When sense pressure decreases, the pistons and valves move in the opposite direction and close the bypass port to provide increased engine oil delivery. During steady-state operation, the slave piston and sense piston assume positions dependent upon pump output, engine demand, and sense line pressure. The radial pilot valve ports expose the required area to cause the slave piston to assume the position required to bypass lube pump output in excess of engine requirements. On some pump models, a diagonal case passageway provides a pressure reference from pump inlet to the backside of the sense piston. Other models utilise the orifice in the sense piston to sense inlet pressure from the lube inlet return port portion of the regulator. During an engine start under conditions of extreme cold, the output lines may be unable to flow oil rapidly enough to prevent pressure from exceeding design limits. Under these conditions, the slave piston check valve opens and admits

lube output pressure to the slave piston assembly. This high pressure drives the slave piston into contact with the sense piston and both pistons move until the lube inlet return ports are fully open providing maximum oil bypassing action. There will be no flow in the sense line under extreme cold start conditions. As the engine runs and the oil warms, the control valve assumes normal operation.


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5 PRESSURE REGULATOR ADJUSTMENT Adjustment of the oil pressure regulator is accomplished using the procedures in the maintenance manual. Remember that the pump is a positive displacement type and oil output will be a function of pump RPM. With the engine running, loosen the oil pressure regulator adjusting stud locknut and adjust the regulator to obtain 40 to 45 PSIG oil pressure indication. One full turn of the adjusting stud changes regulator setting approximately two PSIG. Turn clockwise to increase or counter clockwise to decrease. The adjusting stud depth in the pump body does not change when adjusted. Torque and lock wire the adjusting stud locknut after adjustment.


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6 OIL FILTER A 25-micron paper cellulose filter housed on the aft side of the accessory gearbox filters engine oil. The filter assembly is a bypass type that opens if the differential pressure across the filter exceeds 30-40 PSID. Oil filter content is analysed as part of the routine periodic inspection program. Condition of wetted area parts are evaluated with the filter content inspection. Kits are provided for filter changes. The oil filter bypass indicator valve (with integral delta pressure indicator) is located on the outside right hand side of the accessory drive gearbox and is connected in parallel with the oil filter. Should an accumulation of impurities clog the oil filter to the extent that the pressure drop across the filter exceeds 30-40 PSID, the normally closed bypass valve will open, allowing oil to bypass the filter to avoid possible bearing starvation. A pop up red button (pin) on the bypass valve actuates before the bypass valve opens.


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7 BYPASS VALVE The operation of the filter bypass valve is shown here. Note that the indicator assembly and bypass piston housed within the valve are magnetic, and an iron disc is mounted on either side of the indicator assembly. During normal operation, oil pressure is sensed on both sides of the bypass piston. The indicator assembly is magnetically held in the normal position. If the differential pressure between the inlet (upstream of filter) and discharge (downstream of filter) exceeds 25-35 PSID, the bypass piston will move sufficiently to cause the magnets to repel the indicator. The indicator will be held magnetically in the extended position. This indicates an impending bypass condition. As differential pressure increases to 30-40 PSID, the bypass piston uncovers the discharge port and allows oil to bypass the filter. The bypass valve also incorporates a thermal lockout device that prevents activation of the indicator assembly under cold conditions even though oil may be bypassed by the valve. The thermal lockout consists of a bimetallic lock that contracts and prevents the indicator from extending. As the oil temperature increases to normal, the indicator is released.


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8 FILTER BYPASS SWITCH OPERATION On some installations, a filter bypass switch is used in place of the pin-pop bypass valve. The switch will operate a remotely located indicator when an impending bypass condition is being sensed. During normal operation, oil pressure is sensed on both sides of the piston. If the differential pressure between the filter inlet port and filter outlet port exceeds 25-35 PSID, the piston as illustrated here will move to the right forcing the magnet in close proximity with the reed switch. The magnetic field will cause the reed switch to close, completing an electrical circuit between pins #2 and #4. A further increase in differential pressures (30-40 PSID) will cause the piston to move far enough to open the bypass port. Notice that with oil temperatures below 29°C, the temperature sensor is open. This temperature sensor prevents indicator actuation under cold conditions even though oil may be bypassed. As the oil temperature increases to 46°C, the temperature sensor will close completing an electrical circuit between pins #2 and #3 and allowing actuation of the indicator. Referring to the wiring diagram, note that a five pin connector is provided but only two pins are used. For functional check of the switch, at room temperature, continuity between pins #2 and #3 should not exist. Stroke the piston with a brass rod and check continuity between pins #3 and #4. Again, an open should be indicated. With the switch heated to above 46°C, and the piston stroked, continuity should exist between pins #3 and #4.


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9 FUEL HEATER Oil flows from the filter assembly to the fuel heater (if installed) located on the left side of the engine above the fuel module. The fuel heater provides oil-to-fuel heat exchanging to prevent ice formation in the fuel pump. The heater consists of a core assembly with welded oil and fuel pans and oil relief valve housing. The core assembly contains oil and fuel fins that are separated by plates to form fuel and oil passages running perpendicular to each other through the heater. Hot oil enters the heater through the OIL IN port, flows through connecting layers of fins in the core assembly and exits through the OIL OUT port. Cold fuel enters the heater through the FUEL IN port, flows through the perpendicular layers in fins and makes four passes through the core assembly, and exits through the FUEL OUT port. Heat from the oil is conducted through the fins and is transferred to the fuel flowing through the alternate layers of fins. A pressure relief valve in the oil inlet will open the relief valve poppet if a 40 PSI differential exists between the OIL "IN" and OIL "OUT" port. Hot oil will flow through the poppet opening and exit through the OIL OUT port, bypassing the core assembly.


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10 AIR/OIL COOLER Engine oil cooling is accomplished with the air/oil cooler. This is a three-segment, finned cooler that forms the inner surface of the engine fan duct. Oil enters the coolers and flows through the upper and lower segments, exiting through the oil temperature control valve located on the right side of the fan duct as shown. The oil temperature control valve maintains engine oil at the desired temperature. A more detailed discussion of the valve operation follows later.


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11 OIL TEMPERATURE CONTROL VALVE Oil enters the valve through the two core inlet ports and through the bypass inlet port. If the temperature of the oil is below 65°C, oil will pass through the unseated thermostat to the two outlet ports. In this condition, most of the oil will flow through the core bypass tube of the upper cooler. As oil temperature increases to the actuation temperature of the thermostat (approx. 65°C), the thermostat seats, blocking the supply of bypass oil and allowing only core oil to flow through the valve. All flowing oil passes across the sensing element of the thermostat. In the event of blockage in the cooler cores, the spring-loaded thermostat seat will be opened by oil pressure (30 PSID) allowing oil to flow to the bearing sumps and to the fuel/oil cooler.


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12 FUEL/OIL COOLER From the air/oil coolers the oil flow is divided so that part of the flow is directed to the accessory and transfer gearboxes and the engine bearings. The remaining oil flows through the fuel/oil cooler. This heat exchanger provides additional cooling of the oil flowing to the high speed gears and bearings in the fan gearbox. The fuel/oil cooler consists of a cooler assembly and a temperature control and pressure bypass valve. Oil enters through the "oil in" line and flows across the temperature control valve. If the temperature of the oil exceeds 99°C, the temperature valve opens directing the oil through the cooler. If oil is less than 99°C, the valve remains closed and oil bypasses the fuel/oil cooler and flows direct to the fan gearbox. Heat is transferred from the hot oil to the fuel through the walls of the tubes thus reducing the temperature of the oil. In the event the cooler oil passages become blocked, the bypass valve will open when a 30 PSI differential pressure is sensed. This allows oil to flow to the fan gearbox. A boss is provided on the fan gearbox supply line immediately downstream of the fuel/oil cooler for connecting the airframe oil pressure indicating system and for the installation of an oil temperature-sensing element.


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13 BEARING SUMP This illustrates the forward bearing sump housing the numbers 1, 2, and 3 bearings and the planetary gear assembly. Oil pressure enters the sump at the 6 o'clock service strut, through the planet carrier oil manifold and to each bearing assembly. Oil gravity flows to the bottom of the sump where it is scavenged. The sump is vented to the accessory gearbox. Due to the capacity of the scavenge pump, the sump is at a negative pressure during engine operation. That is to say that during operation, pressure outside the sump is slightly higher than inside the sump due to the amount of aerated oil being scavenged. A carbon face seal and rotor arrangement is used to prevent oil leaking from the sump during engine operation. Compressor discharge pressure enters the area, or chamber, behind the carbon seals creating a buffer pressure higher on the outside of the sump than on the inside. The knife edge seals are designed so that a controlled leak regulates the buffered air pressure within the chamber. Consequently, a leaking carbon seal would allow buffered air into the oil sump during operation instead of leaking oil out of the sump. If excessive amounts of compressor discharge air leaks through the carbon face seal into the oil sump, it would increase the pressure within the sump and consequently, increase the temperature of the oil returning to the tank. This increase in temperature and pressure would be indicated in the cockpit. Static leaks can also occur not only from the carbon seals, but also from various "O" ring seals within the bearing sumps. Leaking seals can allow small

amounts of oil to puddle in low areas of the compressor gas path. When the engine is started, the oil and resultant oil fumes can be introduced into the environmental systems and into the cabin. Small leaks caused by carbon face seals normally disappear soon after engine start because the buffer air pressure behind the carbon face seal would stop the oil leakage through the carbon face seal.


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14 BREATHER PRESSURISATION VALVE The breather pressurisation valve provides an ambient vent for the lubrication system at low altitudes and at high altitudes increases the vent and tank pressure to prevent oil foaming and to ensure proper oil pump operation. The valve is mounted on the aft side of the accessory gearbox. The forward bearing sump, 4 and 5 bearing sump, transfer gearbox and reservoir are vented to the accessory gearbox. This vent air containing atomised oil droplets passes over the gear driven air/oil separator to remove the oil. Oil removed returns to scavenge and air passes through the shaft and through the breather pressurisation valve, to atmosphere. An encapsulated bellows within the valve reacts to altitude and begins to modulate to the closed position at approximately 27,000 feet to maintain 3.5 ± 0.5 PSIA in the reservoir. Because of the positive pressure within the accessory gearbox, sealing of the drive shafts is required. In the case of the oil separator shaft a lip seal is mounted in the breather pressurisation valve. Leaks can develop due to wear of the lip seal or improper installation. The lip seal has been improved over the years. Refer to the LMM and appropriate service bulletins for the latest seal and replacement procedures.


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15 MAGNETIC CHIP DETECTOR The magnetic chip detector is mounted on the aft housing of the oil pump at the scavenge oil outlet. All scavenged oil returning to the tank flows across it. The chip detector consists of an insulated magnet centred within a grounded housing assembly. Accumulation of magnetically permeable materials provides an electrical ground circuit for an optional cockpit mounted warning indicator. This indicates to the operator that ferrous material is present in the lubrication system. Some installations utilise a chip collector (magnetic plug) in place of the electrical chip detector. Material accumulation on the chip detector is checked visually by removing and inspecting the magnetic plug. Specific inspection requirements for this condition are outlined in the maintenance manual.


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16 LUBRICATION SYSTEM - SCHEMATIC The operations of the major lube system components as the oil flows from the tank through the engine and back to the tank have been discussed. Using the illustration on the previous page, follow the path the oil takes through this complete system and review the components involved. The oil can be traced from the tank, through the dual element pressure pump to the regulator. Note that reservoir pressure is referenced to both sides of the oil pressure regulator sense piston. From the regulator, oil regulated to the required system pressure flows to the filter, and through the fuel heater (if installed) to the air/oil coolers. Oil flows through the temperature control valve and follows two routes: one directly to the 4, 5, and 6 bearing sump and gearboxes, and one directly to the fuel/oil cooler. The fuel/oil cooler provides additional cooling of the oil that lubricates the high speed gears and bearings in the fan gearbox. Oil pressure and temperature sensing ports are located in the oil line at the outlet of the fuel/oil cooler. Note also that a pressure sense line is routed to the oil pressure regulator. This sense pressure plus the reservoir sense pressure and regulator adjustment determines system pressure. Oil is scavenged from the sumps and gearboxes by the five scavenge elements and returned to the reservoir through a common scavenge line. All scavenged oil passes across the chip detector on return to the reservoir. As scavenge oil returns to the reservoir, some is routed to an anti-siphon orifice. During pump operation, some of the scavenge oil enters the orifice within the pump supply line. On engine shutdown as the flow of oil stops, air enters the oil pump supply line thereby preventing a siphon action. Oil returning to the reservoir is directed to the topside of the tank. The aerated oil is sprayed against the side of the tank where the oil droplets drain to the fluid level. Air is vented to the accessory drive gearbox. The planetary gear case and transfer gearbox is vented to the accessory gearbox, through the air/oil separator and overboard through the breather pressurisation valve.


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17 TFE731 LUBRICATION PLUMBING The figure on the previous page gives a layout of the lubrication system plumbing.

18 LUBRICATION SYSTEM PRESSURE PROBLEMS This list summarises the possible causes for high and low pressure readings within the lubrication system. To review, three causes of high

oil pressure indications are:

restricted oil jets or nozzles,

a malfunctioning regulator, or

a breather pressurisation valve stuck in the closed position. Obviously, this is not an all-inclusive list of components that could cause problems. A leaking carbon/rotor element could allow compressor discharge air to enter the sump with a resulting increase in system pressure and temperature. Understanding the individual component operation will aid in troubleshooting system malfunctions. Some possible reasons for low oil pressure readings are:

broken or lost oil jets or nozzles,

a malfunctioning oil pressure pump or pressure regulator,

high oil temperature,

a low quantity of oil, or

a breather pressurisation valve remaining open at altitudes above 27,000 feet.


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19 LUBRICATION SYSTEM TEMPERATURE PROBLEMS This list reviews some possible causes for high oil temperatures within the lubrication system. These include a low quantity, a malfunctioning oil temperature control valve, blocked air/oil coolers and seal leaks. Depending upon engine type, 12 to 13 quarts of oil flow through the lube system at a rate of 12 GPM (48 qts. per minute). Any loss of quantity will cause the oil to flow at a higher rate, producing more heat in the system. A malfunctioning oil temperature control valve could allow oil to bypass the air/oil coolers, thereby losing the cooling capacity of the heat exchangers. A blockage of either the air/oil or the fuel/oil coolers would cause an increase of oil temperature. As discussed previously, hot buffer air leaks past the carbon face seal will raise the temperature of the scavenge oil with a resultant increase in system oil temperature.


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20 OIL LOSS CAUSES Loss of oil may occur within the lubrication system. This list emphasis four of the main causes. 1. Plumbing or component leaks: These losses can be detected normally

by noticing streaking of oil or oil leaks external of the engine. 2. Seals leaking into gas path: This is generally a difficult item to identify.

You may or may not be able to detect with a visual inspection in these areas. The maintenance manual provides step-by-step detection and correction procedures for troubleshooting seal leaks. Use the plumbing drawing at the end of this section to draw further conclusions concerning oil temperature, pressure problems and potential leak sources. As always, the light maintenance manual provides valuable troubleshooting procedures that will save you time and money in troubleshooting the lubrication system.

3. Venting of oil through the gearbox: If the breather pressurisation valve is not operating properly, oil could be escaping through the vent system.

4. Siphoning of oil to sumps and gearboxes: A false indication of loss of oil would be siphoning of oil from the tank. A clogged anti-siphon orifice would normally cause this.


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tfe 731 chap 79 (1)

Documents

oilpressure pump

oil filter

oil flow

oil loss

engine oil pump package

oil pressure regulator

lube oil pump

optional oil tank