Patent ID: 6901841

Claim:
In an air motor of the expansible chamber type comprising an air cylinder, a piston reciprocable therein, a valve mechanism shiftable alternately to effect supply of air to and venting of air from opposite sides of the piston to reciprocate the piston, and a runaway control operable on increase in speed of the air motor above a speed limit to stop the motor, said control comprising a pressure-responsive mechanism comprising an air chamber for air under pressure, a movable mechanism movable away from a first position in response to increase in air pressure in said chamber above a predetermined pressure limit to a second position, and movable back to said first position on reduction of pressure in said chamber below said pressure limit, said movable mechanism when in its first position enabling operation of the air motor and when in its second position cutting off the operation of the motor, an air pump interconnected with the motor for operation simultaneously with the motor for delivering air under pressure to the chamber at a rate related to the speed of the motor, wherein the improvement comprises: a bleed mechanism for bleeding air from the chamber at a controlled rate, the pressure in the chamber being controlled by the rate of delivery of air under pressure to the chamber and the bleed of air from the chamber, whereby on increase in speed of the motor above said speed limit, the pump, operating at increased speed, delivers air under pressure at an increased rate to said chamber over and above the capability of the bleed to bleed off the increase, and on ensuing increase in air pressure in the chamber above said pressure limit, said movable mechanism moves to its said second position to cut off the motor; said bleed mechanism comprising a plurality of bleed flow paths of different lengths providing varying resistance to the flow of air, each bleed flow path having an inlet communicating with the chamber and an outlet, and a bleed path selector mechanism movable between a plurality of different settings corresponding to said plurality of different flow paths, said bleed path selector mechanism communicating in each of said settings with the outlet of one of said bleed flow paths and allowing said bleed flow path to vent for bleeding air from the chamber while sealing the outlets of the other bleed flow paths, whereby the speed limit at which motor cuts off can be adjusted by moving the selector mechanism to the desired setting.