Patent ID: 7398647

Claim:
A fastener driving tool comprising: a frame defining therein an accumulator that accumulates compressed air; a cylinder disposed within the frame; a piston disposed within the cylinder and movable between a top dead center and a bottom dead center, a piston upper chamber being defined by an inner peripheral surface of the cylinder and an upper surface of the piston; a main valve section disposed in the frame and having a main valve movable between a top dead center and a bottom dead center to alternately open and block fluid communication between the piston upper chamber and the accumulator, a main valve chamber being defined by an upper surface of the main valve and a part of the frame; a trigger valve section having a plunger movable between a top dead center and a bottom dead center so as to alternately open and block fluid communication from the accumulator to the main valve chamber, and fluid communication from the main valve chamber to atmosphere; a first channel providing a fluid communication between the main valve chamber and the trigger valve section; and a trigger adapted to press the plunger when operated by a user; wherein a ratio obtained from dividing a maximum internal volume of the main valve chamber measured in m 3 by a cross sectional area of the first channel measured in m 2 is no greater than 0.8.