/.4=111. Lubrication Systems 6-23

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Jonah Miller
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Lubrication Systems 6-23 The transducer is designed so that it sends a corrected oil pressure (fluid pressure minus vent "air" pressure) to the cockpit gauge.

The vent system is explained in detail later in this chapter. The oil pressure indicating system is explained in detail in Chapter XII.

1 Lubrication Systems 6-23 The transducer is designed so that it sends a corrected oil pressure (fluid pressure minus vent "air" pressure) to the cockpit gauge. This design is used because vent pressure opposes oil flow at the oil jets, and the operator needs to know the flow condition in terms of corrected oil pressure. The vent system is explained in detail later in this chapter. The oil pressure indicating system is explained in detail in Chapter XII. Note that in this system, the entire oil supply circulates approximately three times per minute. This is typical of most gas turbine engines. The CJ61 lubrication system is considered a hot tank system because the oil cooler is located in the pressure subsystem and the oil is scavenged (hot) back to the oil tank. b. System Components 1) Oil Cooler The oil cooler's main function is to maintain a specific oil temperature under differing oil heat conditions which occur at varying engine speeds. The oil cooler shown in Figure 6-28 is a liquid-to-liquid heat exchanger. It contains numerous soda-straw type passageways for fuel flow on its way to the combustor while the oil circulates around the straws. This allows an exchange of heat to occur between the fuel and the oil. This fuel-cooled oil cooler contains a combination differential pressure bypass valve and thermostatic bypass valve at the cooler inlet. When the oil is cold, the valve is open, allowing oil to take the path of least POPPET /.4=111 SPRING SYSTEM RELIEF VALVE TO ENGINE ANTI-STATIC LEAK CHECK VALVE (2-3 PSID) #9'.'" Mrli, An> or#m14 wire. FROM RESERVOIR PUMP Fig. 6-26A In-line type antistatic-leak check valve. Fig. 6-26B In oil-filter type antistatic-leak check valve.

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If a restriction occurs from cooler clogging, pressure buildup off-seats the bypass valve and oil flows uncooled, at a slightly reduced pressure, to the system.

3 Lubrication Systems 6-25 resistance, bypassing the cooling chamber and flowing directly to the system (Figure 6-28B). When the oil heats up, the thermo-valve expands to close, forcing the oil to flow through the cooler. If a restriction occurs from cooler clogging, pressure buildup off-seats the bypass valve and oil flows uncooled, at a slightly reduced pressure, to the system. The thermostatic valve contains a bi-metallic spring, typically constructed of iron/nickel alloy and brass, which, because of the different coefficient of expansion, produces movement with loss or gain of heat (Figure 6-28C). A typical oil cooler operational schedule might be as follows: Oil cooler thermostatic valve starts to close at 165 F, and is fully closed at 185 F, with normal engine oil temperature stabiliing at 21 F. From this point, the cooler capacity for fuel flow and oil flow regulate the operational oil temperature rather than the thermo-valve. As the throttle is advanced for the engine to create more power, and therefore more heat for the oil to absorb, the fuel flow through the cooler increases and absorbs this heat. The maximum continuous oil temperature in this system would be 21 F. If the temperature reached a value over 21 Fbut under 23 F, the red line, the engine would have to be operated at reduced power at the (A) THERMOSTAT TEMPERATURE DIFFERENTIAL PRESSURE AND THERMOSTATIC BY-PASS VALVE (SHOWN I? COLD MODE) (C) TEMPERATURE THERMOSTAT (IN HOT MODE) BY-PASS SPRING L PRESSURE BY-PASS VALVE Fig. 6-28A Oil cooler exterior. Fig 6-28B Thermo-valve in transit with oil both cooling and bypassing. Fig. 6-28C Thermo-valve closed when oil is hot.

4 6-26 Aircraft Gas Turbine Pow rplants discretion of the pilot. Once an oil temperature of 23 F is reached, the engine would have to be shut down. The purpose of the thermostatic valve is to quickly bypass oil to the lube points on a cold start. It is not uncommon, however, to see an oil cooler without a thermostatic device if oil can be distributed rapidly enough for quick lubrication when the oil is cold. One of the checks on an oil cooler is to see a momentary oil temperature rise on engine deceleration, and drop on acceleration as a function of fuel flow. From this, the operator can conclude that the thermo-valve is not stuck in a transient position and is not bypassing. The fuel-oil cooler is used on most engines and often on larger engines, in combination with an air-oil cooler. The air-oil cooler is also in popular use. The air-oil cooler and thermostatic valve arrangement is quite similar in principle and design to the fuel-oil coolers shown, but the heat exchanger section looks similar to the small radiator type cooler used on reciprocating engines (Figure 6-33). 2) Oil Jets (Figure 6-29A) Oil jets, or noles, as they are sometimes called, are located at the various places within the engine that need to be lubricated. Oil jets are the terminating point of the pressure subsystem. They deliver either an atomied spray or a fluid stream of oil to bearings, oil seals, gears, and other parts. The fluid stream method is the most common, especially when high loads are present. In most cases this stream of oil is directed onto the bearing surfaces from what is termed a Direct Lubrication Oil Jet (Figure 6-29B). Another less common method is called a Mist and Vapor Lubrication Oil Jet, where the oil stream (sometimes an air-oil stream) is aimed at a splash pan and slinger ring device. This allows for a wider area of lubrication from a single oil jet and is utilied in some larger engines (Figure 6-29C). A newer type of oil jet coming into use is called "under-race lubrication", in which oil is routed through rotor shafts and bearing journals, then fed through slots acting as oil jets in the bearing inner races. Manufacturer's information indicates that they are achieving superior cooling when comparing traditional spray-jet lubrication with this method. Over time, a restriction to flow may occur at the calibrated orifice of the oil jet. An accumulation of carbon (called coking) takes place due to residual engine heat acting on oil coated metal parts. This condition results faster if the prescribed cooling down period prior to engine shutdown is ignored. Oil jets can be checked for sie and cleanliness with a drill pin or the shank end of a new numbered drill bit. It is very important that the drill shank be free from any nicks or burrs. Another method of checking for restrictions to flow is the smoke check. Smoke or shop air is directe oil nole inlet port and a check is made of the rate through the orifice. A comparison is usually known good or new oil jet. A flow tester is also available in most larg facilities. This device can measure rate accurately, in gallons per minute, with the oil jet in the engine. On some engines, bearing flow c part of the 1-hour inspection, or similar i requirements. 3) Last Chance Filters Quite often, last chance filters are installed i to prevent plugging of the oil jets. Observe 6-29A the last chance filters. Because of thei location within the engine, last chance fi accessible for cleaning only during engine ove prevent engine damage from clogged last chanc or plugged oil jets, the main filters are ins frequent intervals by ground personnel. Flow detect early signs of filter blockage is also acco at periodic intervals. into the ischarge ade to a r repair f flow installed ecks are spection oil lines 1 Figure remote ters are haul. To screens ected at sting to plished 2. Scavenge Subsystem (C161) (Figure 6-27) The scavenge subsystem removes oil from th- bearing compartments and gearboxes by suction rom the lubrication pump scavenge return elements (1 o 5). All five scavenge elements route oil to one return li e, which enters the dwell chamber in the oil tank. T e dwell chamber acts as an air--oil separator. The total eturn oil capacity is nine gallons per minute. The entrain4d air that accumulates in the oil increases oil vol me and necessitates the use of a much higher capacity scavenge subsystem than the pressure subsystem. a. Chip Detectors Many scavenge systems contain permane magnet chip detectors which attract and hold ferr s metal particles (Figure 6-3) which would otherwise circulate back to the oil tank and the engine pressure subsystem, possibly causing wear or damage. Chip detectors are a point of frequent inspection to detect early signs of main bearing failure. As a general rule, the presence of small fuy particles or gray metallic paste is considered satisfactory and the result of normal wear. Metallic chips or flakbs are an indication of serious internal wear or malfunction. Refer to Figures 6-3A and 6-3B. Figure 6-33 (insert) shows an indicting-type magnetic chip detector. It has a warning circuit feature. When debris bridges the gap between the magnetic positive electrode in the center and the ground electrode (shell), a warning light is activated in the cockpit. When the light illuminates, the flight crew will take whatever action is warranted, such as in-flight shutdown, continued operation at flight idle, or continued operation at normal cruise, depending on the other engine in truments readings.

5 Lubrication Systems 6-27 b. Pulsed Chip Detector System A newer type of chip detector is the Electric Pulsed Chip Detector, which can discriminate between small wear-metal particles, both ferrous and non-ferrous, considered non-failure related, and larger particles, which can be an indication of bearing failure, gearbox failure, or other potentially serious engine malfunction (Figure 6-3C). The Pulsed Chip Detector looks like the Indicating Chip Detector at the gap-end, but its electrical circuit contains a pulsing mechanism which is powered by the aircraft 28 VDC bus. The pulsed detector is designed with either one or two operating modes: Manual only or manual and automatic. In the manual mode, each time the gap is sufficiently bridged, regardless of the particle sie, the warning light will illuminate in the cockpit. The operator will then initiate the pulse; electrical energy will discharge across the gap-end in an attempt to separate the debris from the hot center electrode. This procedure is called burn-off. If the light goes out and stays out, the operator will consider the bridging a result of a non-failure related cause. If the light does not go out, or repeatedly comes on after being cleared, the operator will take appropriate action, such as reducing engine power or shutting down the engine. In the automatic mode, if the gap is bridged by small debris, a pulse of electrical energy discharges across the gap. The resulting burn-off prevents a cockpit warning light from illuminating by opening the circuit before a time-delay relay in the circuit activates to complete the current path to ground. If the debris is a large particle, it will remain in place after the burn-off cycle is completed and a warning light will illuminate in the cockpit when the time delay relay closes. LAST CHANCE FILTER IN LAST CHANCE FILTER CARBON SEAL JETS LABYRINTH AIR- SEAL,:iCOMPRESSOR SHAFT CARBON SEALS GEARBOX DRIVE SHAFT DRAIN DETAIL OF NOZZLE OPERATION 7SSMSS:ZZT JET Fig. 6-29A Location of main bearing oil jets and filters. Fig. 6-29B Direct lubrication oil jet. Fig. 6-29C Mist and vapor oil jet.

LUBRICATION SYSTEM B-17 Technical Session for Flight Engineers 10/14/2017

LUBRICATION SYSTEM B-17 Technical Session for Flight Engineers 10/14/2017 The Lubrication System, and most everything else, is described in B-17 MANUALS published by the Army. Note that these Manuals were