Control mechanism for a pneumatic tool

摘要

Control mechanism for a pneumatic hand tool which provides improved performance, speed regulation and control of the tool in air pressure ranges up to at least 116 pounds per square inch gauge (psig). A pneumatic hand tool embodying subject control mechanism includes a cylinder having an implement, such as a chisel, secured thereto and a reciprocating piston in the cylinder, the piston adapted to be driven by pressurized air into impact engagement with the front head of the cylinder, and returned to the rear cylinder end without impact. The control mechanism comprises an adjustable control valve which meters the volume of incoming pressurized air to that amount which produces desired tool operation, and an improved ball valve between the control valve and the cylinder. The control valve includes a radially movable spring-biased valve pin which cooperates with a valve seat, and a rotatable control ring in effective relation with the valve pin. The control ring has an internal spiral cam surface extending through about 90 DEG adapted to move the valve pin from a radially outward fully opened position to a radially inward closed position where the valve pin firmly engages the valve seat. Intermediate settings of the control ring provide intermediate valve actions. The internal cam surface has a scallop configuration providing discrete valve pin detent positions between closed and fully opened positions.