Pneumatic motor

A pneumatic motor comprising:

• a cylinder having a first end cover and a second end cover respectively mounted in opposite ends of the cylinder, an inlet port defined in the first end cover and an outlet port defined in the second end cover, a rod base mounted in the second end cover and having a through hole defined to communicate with an interior of the cylinder;
• a piston movably received in the cylinder, and dividing the cylinder into a first chamber communicating with the inlet port and a second chamber communicating with the outlet port, a cylindrical cavity defined in the piston facing the second end cover, a hole defined in the piston to communicate with the first chamber and the cylindrical cavity in the piston, the hole in the piston having a diameter smaller than that of the cylindrical cavity in the piston, an annular groove defined around the hole in the piston and communicating with the first chamber of the cylinder, an exhaust passage defined in the piston and communicating with the second chamber and the annular groove, a fixing block mounted on an outlet end of the piston to close the cavity in the piston and having a through hole defined in the fixing block;
• and
• an actuating piston movably received in the cavity of the piston and having a diameter slightly smaller than that of the cavity in the piston, a rod extending from the actuating piston and entering the second chamber through the through hole in the fixing block, a shaft extending from the actuating piston and entering the first chamber through the hole in the piston, a valve disk attached to one end of the shaft in the first chamber to selectively close the exhaust passage.