VANE-TYPE MOTORSA typical vane-type air motor is shown infigure 10-13. This particular motor providesrotation in only one direction. The rotatingelement is a slotted rotor which is mounted ona drive shaft. Each slot of the rotor is fitted witha freely sliding rectangular vane. The rotor andvanes are enclosed in the housing, the innersurface of which is offset from the drive shaft axis.When the rotor is in motion, the vanes tend toslide outward due to centrifugal force. Thedistance the vanes slide is limited by the shape ofthe rotor housing.This motor operates on the principle ofdifferential areas. When compressed air is directedinto the inlet port, its pressure is exerted equallyin all directions. Since area A (fig. 10-13) is greaterthan area B, the rotor will turn counterclockwise.Each vane, in turn, assumes the No. 1 and No.2 positions and the rotor turns continuously. Thepotential energy of the compressed air is thusconverted into kinetic energy in the form of rotarymotion and force. The air at reduced pressure isexhausted to the atmosphere. The shaft of themotor is connected to the unit to be actuated.Many vane-type motors are capable ofproviding rotation in either direction. A motorof this design is shown in figure 10-14. This motoroperates on the same principle as the vane motorshown in figure 10-13. The two ports may bealternately used as inlet and outlet, thus providingrotation in either direction. Note the springs inthe slots of the rotor. Their purpose is to hold thevanes against the housing during the initialFigure 10-13.—Vane-type air motor.Figure 10-14.—Vane-type motor.starting of the motor, since centrifugal force doesnot exist until the rotor begins to rotate.PISTON-TYPE MOTORSPiston-type motors are the most commonlyused in hydraulic systems. They are basically thesame as hydraulic pumps except they are used toconvert hydraulic energy into mechanical (rotary)energy.The most commonly used hydraulic motor isthe fixed-displacement piston type. Someequipment uses a variable-displacement pistonmotor where very wide speed ranges are desired.Although some piston-type motors arecontrolled by directional control valves, theyare often used in combination with variable-displacement pumps. This pump-motor combina-tion is used to provide a transfer of power betweena driving element and a driven element. Someapplications for which hydraulic transmissionsmay be used are speed reducers, variable speeddrives, constant speed or constant torque drives,and torque converters. Some advantages ofhydraulic transmission of power over mechanicaltransmission of power are as follows:1.2.3.4.Quick, easy speed adjustment over a widerange while the power source is operatingat 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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