A pneumatic motor-controlled valve of a screwdriver is installed between an air guide hole of a pneumatic motor and a main air valve gate in the screwdriver. A valve hole is formed on a guide seat and is communicated to an air guide hole of the motor. A plug is formed on an outer wall of a cylinder; and the cylinder is movably mounted within the guide seat. A lower spring resists against the cylinder. At least one ventilating hole is formed on a wall of the cylinder for communicating the valve hole to one of the upper valve opening and the lower valve opening of the main air valve gate. The plug drives the cylinder to actuate with the descending and rising of the piston valve so as to open or close the valve hole of the guide seat, thereby, the rotation of the motor is controlled. In one prior art screwdriver, a body of the screwdriver is installed with a cylinder, a piston rod, a pneumatic motor, etc. The piston rod is movably installed to the cylinder. The piston rod has a plug for opening or closing the motor air inlet valve. Thereby, high pressure air in the cylinder can push the pneumatic piston rod to linearly reciprocate and the high pressure air can drive the pneumatic motor to rotate and thus to drive the moving piston rod to rotate. Meanwhile, the plug on the piston rod can open or close the motor air inlet valve so as to control the motor to rotate or stop. Thereby, the piston rod can rotate and displace linearly as desired for locking a screw nail. However, in above mentioned prior art, the plug for controlling the rotation of the motor is arranged on the piston rod which is rotatable and linearly movable. When the plug moves to motor air inlet valve for closing the valve opening, the plug of the piston rod still rotates, as a result, the air stop washer of the plug will wear easily so as to reduce the lifetime of the plug. Thereby, the prior art design has a short lifetime. These prior arts still exist in other prior art and can not be over-come effectively. Accordingly, the primary object of the present invention is to provide a pneumatic motor-controlled valve of a screwdriver, wherein a plug is mounted to an outer wall of a movable cylinder so that the plug has only the effect of linearly movement (no rotation power) for closing the valve hole of inputting air to motor. Thereby, the lifetime of the plug is increased. Another object of the present invention is to provide a pneumatic motor-controlled valve of a screwdriver, wherein a guide seat is installed in the head. At least one valve hole is formed on the wall of the guide seat so that the valve hole is communicated to the air guide hole of the pneumatic motor in the screwdriver, and the cylinder is linearly moved in the guide seat so that the plug serves to open and close the valve hole of the guide seat so as to control the rotation and stopping of the pneumatic motor. To achieve above objects, the present invention provides a pneumatic motor-controlled valve of a screwdriver is installed between an air guide hole of a pneumatic motor and a main air valve gate in the screwdriver. A valve hole is formed on a guide seat and is communicated to an air guide hole of the motor. A plug is formed on an outer wall of a cylinder; and the cylinder is movably mounted within the guide seat. A lower spring resists against the cylinder. At least one ventilating hole is formed on a wall of the cylinder for communicating the valve hole to one of the upper valve opening and the lower valve opening of the main air valve gate. The plug drives the cylinder to actuate with the descending and rising of the piston valve so as to open or close the valve hole of the guide seat, thereby, the rotation of the motor is controlled. The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing. The present invention relates to screwdrivers, and particularly to a pneumatic motor-controlled valve of a screwdriver, wherein a valve hole and a plug are installed to a movable cylinder and a guide seat for controlling the opening and closing of the pneumatic motor.
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