A pneumatic driven ratchet wrench having a spindle and capable of preventing mis-switching of rotational directions of a spindle, said pneumatic driven ratchet wrench comprising:
- a wrench housing having first and second sections and a middle section disposed between and interconnecting said first and second sections, said first section being formed with a first fluid passage, said middle section being formed with a second fluid passage, a rotor-driving chamber separated from said second fluid passage, and third and fourth fluid passages separated from said rotor-driving chamber;
- a spindle-engaging unit mounted to said second section and including a ratchet wheel that is adapted to be associated with the spindle for switching rotational directions of the spindle;
- a rotation-driving unit including a pneumatic rotor that is mounted rotatably in said rotor-driving chamber, that is adapted to be connected to said spindle, and that is adapted to be driven to rotate by a compressed air entering from said first fluid passage into said rotor-driving chamber so as to drive rotation of the spindle;
- a direction-driving unit mounted in said wrench housing and adapted to be driven to move by the compressed air entering from said first fluid passage through said second fluid passage into a selected one of said third and fourth fluid passages;
- a reverse gear unit mounted movably in said wrench housing and driven to move by said direction-driving unit to engage said ratchet wheel so as to switch rotational directions of the spindle;
- a first valve unit operatively mounted in said wrench housing and operable to permit fluid communication between said first fluid passage and a selected one of said rotor-driving chamber and said second fluid passage while preventing fluid communication between said first fluid passage and the other of said rotor-driving chamber and said second fluid passage;
- and
- a second valve unit operatively mounted in said wrench housing for controlling fluid communication between said second fluid passage and a selected one of said third and fourth fluid passages so as to control switching of the rotational directions of the spindle.