S S S S C C C C C C S No. 3 Bearing compartment No. 1, 1.5 and 2 Bearing compartment No. 4 Bearing compartment Angle gearbox C S Check valve No. 4  bearing  damper oil Oil quantity transmitter Pressure dampener Filler neck and  flapper valve Deaerator Breather air overboard Lubrication and  scavenge oil  pump Oil tank Baffle Pressure stage Main gearbox Layshaft Deoiler Oil temperature ports No. 3 bearing breather  restrictor valve No. 2 bearing damper oil shutoff valve No. 1, 1.5 and  2 breather pre- ssure tap Breather restrictor Oil pressure metering nipple Fuel oil cooler outlet manifold Oil pressure port IDGS oil to IDG Pressure fuel return Bypass fuel from pump Fuel from pump  boost stage IDGS oil from IDGs air/oil heat exchanger Engine air/oil heat  exchanger and valve Fan air or 2.5 air Tower shaft Fuel to fuel pump filter Servo return to oil tank Fuel oil cooler and valve Secondary filter Primary filter Oil filter switch Primary  filter  bypass  valve Pressure relief valve Supply oil Pressure oil Return oil Scavenge oil Last-chance oil filter Chip detector provision Breather air Scavenge and breather IDGS oil Interstage fuel Figure 6-46.  Typical turbine dry-sump variable pressure lubrication system.  Scavenger Subsystem Pressure Subsystem The scavenger oil pump has several stages that pull oil from  the bearing compartments and gear boxes and sends the oil  to the tank. At the tank, the oil enters the deaerator, which  separates the air from the scavenge oil. The oil returns to the  tank and the air is vented through a check valve overboard.  Each stage of the scavenge pump has a magnetic chip detector  that can be removed for inspection. Breather Subsystems The oil flows from the oil tank down to the pressure stage of  the oil pump. A slight pressure in the tank assures that the  flow of oil into the pressure pump is continuous. After being  pressurized, it moves on to the oil filter where it is filtered.  If the filter is clogged, the bypass valve sends the oil around  the filter. There is no regulating valve but there is a relief  valve to prevent the system pressure from exceeding the  maximum limits. This valve is usually set to open well above  the systems operating pressure. The oil flows from the filter  housing to the engine air/oil cooler. The oil either bypasses  the cooler (cold) or passes through the cooler (hot) and then  on to the fuel oil cooler. Through the use of the coolers, the  fuel temperature is adjusted to meet the requirements needed  for the engine. Some of the oil passes through the classified  oil pressure trim orifice that helps adjust oil pressure at low  speeds. The oil now flows through the last-chance oil filters  (strainers) that remove particles from the oil if the oil filter has  been bypassed. The engine oil passes through the nozzles to  lubricate the bearings, gearboxes, seals, and accessory drive  splines. After performing its functions of lubricating, cleaning,  and cooling the bearings, the oil needs to be returned to the  old tank by the scavenge system.  The purpose of the breather system is to remove air from the  bearing compartments, separate breather air from oil, and  vent the air overboard. The breather air from the bearing  compartments is drawn to the gearbox by the deoiler.  The deoiler is turned at high speed and causes the oil to  separate from the air. The air is then vented with air from  the deaerator overboard. By referring to  Figure 6-46 , notice  that the deaerator is in the oil tank and the deoiler is in the  main gear box. 6-31