Throttle valve construction for a percussion tool

In a percussion tool including an elongated tool body having a cylinder therein and handle means at one end of said body for manipulating said tool, a piston mounted in said cylinder for reciprocating movement and operable to impart impact blows to a workpiece or the like mounted in one end of said body, said tool body also having passage means therein for conveying fluid under pressure to the opposite ends of said cylinder and control valve means for controlling the direction of the flow of fluid under pressure through said passage means so as to effect reciprocation of said piston in said cylinder, the improvement of throttle valve means including a throttle valve member adapted to be operatively connected to said passage means for controlling the quantity of fluid under pressure flowing therethrough, said throttle valve member having a first position preventing fluid flow through said passage means and into said cylinder to prevent operation of said tool, a second position permitting substantially unrestricted fluid flow through said passage means to permit normal operation of said tool, and a third position restricting the flow of fluid under pressure through said passage means so that the frequency of reciprocation and kinetic energy of said piston are substantially reduced, lever means mounted on said body adjacent to said handle means, said lever means being pivotal about an axis perpendicular to tool movement and operable to move said throttle valve member to said first, second and third positions, said lever means being positioned so as to hold said throttle valve member in said second position when said lever means is fully depressed by the operator, and said lever means also being positioned so as to permit movement of said throttle valve member to and to hold the same in said third position when a pulling force is applied to said handle means by the operator, whereby the magnitude and frequency of the vibrations generated by said tool and transferred to the operator thereof, and the operating noise level of the tool, when said throttle valve member is in said third position, are substantially less than when said throttle valve member is in said second position, said throttle valve member having a constant flow area for a substantial length of movement thereof adjacent said third position.