while the engine is not operating. Piston ring-like oil seals are  used on the compressor wheel shaft to prevent the lubricating  oil from entering the turbine and compressor housings from  the center housing. The position of the waste gate is controlled by adjusting the  oil pressure in the waste gate actuator. Several different types  of controllers are used to provide the correct pressure in the  waste gate actuator. This is done either by restricting the oil  flow or by allowing the oil to return to the engine. The more  the oil is restricted, the more pressure is in the waste gate  actuator and the more closed the waste gate is. This causes  the exhaust gases to pass through the turbine, increasing  the speed of the compressor raising the inlet pressure. The  reverse happens if the oil is not restricted by the controllers  and boost is reduced. The pressure from the outlet of the  compressor of the turbocharger to the throttle is referred to  as deck pressure or upper deck pressure. By regulating the waste gate position and the “fully open”  and “closed” positions, a constant power output can be  maintained. When the waste gate is fully open, all the exhaust  gases are directed overboard to the atmosphere, and no air is  compressed and delivered to the engine air inlet. Conversely,  when the waste gate is fully closed, a maximum volume  of exhaust gases flows into the turbocharger turbine, and  maximum supercharging is accomplished. Between these  two extremes of waste gate position, constant power output  can be achieved below the maximum altitude at which the  system is designed to operate. An engine with a critical  altitude of 16,000 feet cannot produce 100 percent of its rated  manifold pressure above 16,000 feet. Critical altitude means  Figure 3-18  is a schematic of a sea level booster  turbosupercharger system. This system used widely is  automatically regulated by three components: A Typical Turbosupercharger System •  Exhaust bypass valve assembly •  Density controller •  Differential pressure controller Figure 3-18.  Sea level booster turbosupercharger system. 3-13 Fuel injector Density controller Oil return to  crankcase Differential pressure control Exhaust manifold Oil return  to crankcase Filter Air inlet Turbocharger Exhaust gas discharge Engine oil  pressure inlet Exhaust bypass  valve assembly Exhaust gases Compressor  discharge pressure Inlet manifold  pressure Oil Air Oil Exhaust gas