Vane-Type Motor  

VANE-TYPE   MOTORS A  typical  vane-type  air  motor  is  shown  in figure  10-13.  This  particular  motor  provides rotation  in  only  one  direction.  The  rotating element  is  a  slotted  rotor  which  is  mounted  on a drive shaft. Each slot of the rotor is fitted with a freely sliding rectangular vane. The rotor and vanes  are  enclosed  in  the  housing,  the  inner surface of which is offset from the drive shaft axis. When  the  rotor  is  in  motion,  the  vanes  tend  to slide   outward   due   to   centrifugal   force.   The distance the vanes slide is limited by the shape of the  rotor  housing. This   motor   operates   on   the   principle   of differential  areas.  When  compressed  air  is  directed into the inlet port, its pressure is exerted equally in all directions. Since area A (fig. 10-13) is greater than area B, the rotor will turn counterclockwise. Each  vane,  in  turn,  assumes  the  No.  1  and  No. 2 positions and the rotor turns continuously. The potential  energy  of  the  compressed  air  is  thus converted  into  kinetic  energy  in  the  form  of  rotary motion and force. The air at reduced pressure is exhausted  to  the  atmosphere.  The  shaft  of  the motor  is  connected  to  the  unit  to  be  actuated. Many   vane-type   motors   are   capable   of providing  rotation  in  either  direction.  A  motor of this design is shown in figure 10-14. This motor operates on the same principle as the vane motor shown  in  figure  10-13.  The  two  ports  may  be alternately used as inlet and outlet, thus providing rotation  in  either  direction.  Note  the  springs  in the slots of the rotor. Their purpose is to hold the vanes   against   the   housing   during   the   initial Figure  10-13.—Vane-type  air  motor. Figure  10-14.—Vane-type  motor. starting of the motor, since centrifugal force does not  exist  until  the  rotor  begins  to  rotate. PISTON-TYPE  MOTORS Piston-type  motors  are  the  most  commonly used in hydraulic systems. They are basically the same as hydraulic pumps except they are used to convert hydraulic energy into mechanical (rotary) energy. The  most  commonly  used  hydraulic  motor  is the   fixed-displacement   piston   type.   Some equipment  uses  a  variable-displacement  piston motor where very wide speed ranges are desired. Although   some   piston-type   motors   are controlled   by   directional   control   valves,   they are   often   used   in   combination   with   variable- displacement pumps. This pump-motor combina- tion is used to provide a transfer of power between a  driving  element  and  a  driven  element.  Some applications  for  which  hydraulic  transmissions may be used are speed reducers, variable speed drives, constant speed or constant torque drives, and   torque   converters.   Some   advantages   of hydraulic transmission of power over mechanical transmission  of  power  are  as  follows: 1. 2. 3. 4. Quick, easy speed adjustment over a wide range while the power source is operating at a constant (most efficient) speed. Rapid, smooth  acceleration  or  deceleration. Control over maximum torque and power. Cushioning  effect  to  reduce  shock  loads. Smoother  reversal  of  motion. 10-9


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