Figure 6-42.  Air oil cooler.  Figure 6-41.  Typical thermostatic bypass valve.  means that more heat is transferred to the oil. Consequently,  the oil coolers are the only means of dissipating the oil heat. The fuel-cooled oil cooler acts as a fuel oil heat exchanger  in that the fuel cools the hot oil and the oil heats the fuel  for combustion.  [Figure 6-43]  Fuel flowing to the engine  must pass through the heat exchanger; however, there is a  thermostatic valve that controls the oil flow, and the oil may  bypass the cooler if no cooling is needed. The fuel/oil heat  exchanger consists of a series of joined tubes with an inlet  and outlet port. The oil enters the inlet port, moves around  the fuel tubes, and goes out the oil outlet port. The deoiler removes the oil from the breather air. The  breather air goes into an impeller that turns in the deoiler  housing. Centrifugal force drives the oil towards the outer  wall of the impeller. Then, the oil drains from the deoiler into  a sump or oil tank. Because the air is much lighter than the  oil, it goes through the center of the impeller and is vented  overboard. valve. The valve is spring loaded because the pressure drop  through the oil cooler could become too great due to denting  or clogging of the cooler tubing. In such a case, the valve  opens, bypassing the oil around the cooler. Two basic types of oil coolers in general use are the air-cooled  and the fuel-cooled. Air oil coolers are used in the lubricating  systems of some turbine engines to reduce the temperature  of the oil to a degree suitable for recirculation through the  system. The air-cooled oil cooler is normally installed at  the forward end of the engine. It is similar in construction  and operation to the air-cooled cooler used on reciprocating  engines. An air oil cooler is usually included in a dry-sump  oil system.  [Figure 6-42]  This cooler may be air-cooled or  fuel-cooled and many engines use both. Dry-sump lubrication  systems require coolers for several reasons. First, air cooling  of bearings by using compressor bleed-air is not sufficient to  cool the turbine bearing cavities because of the heat present  in area of the turbine bearings. Second, the large turbofan  engines normally require a greater number of bearings, which  Magnetic chip detectors are used in the oil system to detect  and catch ferrous (magnetic) particles present in the oil.  [Figure 6-44]  Scavenge oil generally flows past chip detectors  so any magnetic particles are attracted and stick to the chip  detector. Chip detectors are placed in several locations but  generally are in the scavenge lines for each scavenge pump,  oil tank, and in the oil sumps. Some engines have several  detectors to one detector. During maintenance, the chip  detectors are removed from the engine and inspected for  metal; if none is found, the detector is cleaned, replaced,  and safety wired. If metal is found on a chip detector, an  investigation should be made to find the source of the metal  on the chip.  The turbine lubrication system is representative of turbine  engines using a dry-sump system.  [Figure 6-45]  The  lubrication system is a pressure regulated, high-pressure  design. It consists of the pressure, scavenge, and breather  subsystems. The pressure system supplies oil to the main engine bearings  and to the accessory drives. The scavenger system returns  the oil to the engine oil tank that is usually mounted on  the compressor case. It is connected to the inlet side of the  pressure oil pump and completes the oil flow cycle. A breather  system connecting the individual bearing compartments and  the oil tank with the breather pressurizing valve completes  Air Oil Coolers Fuel Oil Coolers  Deoiler Magnetic Chip Detectors $^{ }$Typical Dry-Sump Pressure Regulated  Turbine Lubrication System  6-28