Centrifugal  Supercharger The centrifugal supercharger (fig. 1-33, view A) has an impeller equipped with curved vanes. As the impeller is driven by the engine, it draws air into its center and throws it off at its rim. The air then is pushed along the inside  of  the  circular  housing.  The  diameter  of  the housing gradually increases to the outlet where the air is pushed out to the engine intake system. Roots  Supercharger The  Roots  supercharger  (fig.  1-33,  view  B)  is  a positive  displacement  type  of  supercharger  that  consists of two rotors inside a housing. As the rotors are driven by the engine, air is trapped between them and the housing. The air is then carried to the outlet where it is discharged. Because of the extremely narrow clearance between the rotors and the housing, this supercharger is very sensitive to dirt. Vane  Supercharger The  vane  supercharger  (fig.  1-33,  view  C)  is  a positive displacement supercharger that has a rotor that revolves in a body, the bore of which is eccentric to the rotor. Two sliding vanes are placed 180 degrees apart in slots in the rotor and are pressed against the body bore by springs in the slots. When the shaft is rotated, the vanes pick up air at the inlet port and carry it around the body to the outlet side where the air is discharged to the intake  system  of  the  engine. AIR CLEANERS Clean air is essential to the performance and life of an engine. The air cleaner must remove fine materials, such as sand, dust, or lint, from the air before it enters the  intake  system.  The  air  cleaner  normally  has  a reservoir large enough to hold material taken out of the air;  therefore,  operation  over  a  reasonable  time  is possible before cleaning and servicing are necessary. NOTE: A buildup of dust and dirt in the air cleaner passages  will  eventually  choke  off  the  air  supply, causing  poor  combustion. Multiple  air  cleaners  are  sometimes  used  in locations  where  engines  are  operated  under  extremely dusty air conditions or when two small air cleaners must be used in place of a single large cleaner. The  most  common  type  of  air  cleaners  are  the following: pre-cleaners, dry air cleaners, dry element air cleaners, and oil bath air cleaners. Pre-Cleaners Pre-cleaners are devices that remove large particles of dirt or other foreign matter from the air before it enters the main air cleaner. This relieves most of the load on the air cleaner. Pre-cleaners are normally installed at the end of an air cleaner inlet pipe that extends upward into the air (fig. 1-34). This locates them in an area relatively free of dust. NOTE:  Cleaning  out  the  collector  bowl  of  the pre-cleaner is part of operator’s maintenance and should be  performed  during  both  prestart  and  post-operation maintenance. Dry Air Cleaners Dry air cleaners (fig. 1-35) are attached directly to the intake system and are used on engines in which the Figure 1-34 .—Pre-cleaner. Figure  1-35.—Dry  air  cleaner. 1-25