| 摘要 |
PROBLEM TO BE SOLVED: To allow a main piston to easily and surely release a neutral condition. SOLUTION: A main piston 3 is slidably arranged inside a cylinder 2. A piston rod 5 for driving a tool 4 on its front end is relatively slidably penetrated into this main piston. The front and rear pistons 7F and 7R for forming the front air chamber 6F and the rear air chamber 6R between the main piston are provided in this piston rod. The front and rear energizing members 8F and 8R for energizing the front and rear pistons on the main piston side are provided in between the front and rear pistons and the cylinder. An air supply port 10 connected to a compressed air supply source 9 is formed in the cylinder. An air supply means 11 to be in a communicating state of the air supply port with the front air chamber, a communicating state of the air supply port with the rear air chamber, or an equilibrium state of both the front and rear chambers is provided in the main piston. A reset means 12 for pressing the piston rod when the air supply means comes to be in the equilibrium state of both the front and rear chambers is provided in the cylinder.
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