speed position park switch 104 is opened and run switch 102 remains closed sawtooth oscillator 112 send signals to the negative input of oscillator 110 and potentiometers 106 108 send pulsed signals to the positive input of oscillator 110 the output of oscillator 110 is a corresponding pulsed signal to run valve 70 through fet transistor 116 the pulsed signal energizes and deenergizes run valve 70 the park valve 72 is closed during 34 low 34 and 34 high 34 speed operations at regular intervals to allow air flow into the motor at a constant volume and produce continuous fluid motion of piston 24 and shaft 36 as the knob 78 is advanced towards the 34 high 34 speed position the signals sent through potentiometers 106 108 and oscillator 110 decrease the interval between pulses sent to the run valve 70 and increase the volume of air delivered to chambers 28 30 this increase the speed of reciprocation of piston 24 and correspondingly the speed of oscillation of shaft 36 finally when the knob 78 is advanced to the 34 high 34 speed position the signals sent to run valve 70 are constant and the run valve is always open fluid pressure through line 74 determines the top speed of reciprocation of piston 24 and shaft 36 when controller 64 is switched to 34 off 34 from any of the active duty cycles described above an electric signal is delivered to park valve 72 to 34 park 34 the motor prior.