Abstract: In a track tamping machine, opposed pivotally mounted tamping arms are oscillated by respective single acting hydraulic cylinders controlled by one or more hydraulic duplex rotary distributing valves. Fluid supply and return lines for each piston assembly are connected to a source of pressurized hydraulic fluid by way of a respective rotary valve. Each valve has a stationary ported shell which receives a rotary cylindrical spool having a pair of axially displaced supply and return throughports which alternately register with supply and return line ports in the shell to open and close the connections between the oscillating cylinder and the supply and return lines. Such oscillating cylinders are useful in controlling the vibration of the tamper arms in a track tamper unit.

Abstract: Opposed pivotally mounted tamper arms are oscillated by respective single-acting hyraulic piston assemblies controlled by separate hydraulic duplex rotary distributing valves. Fluid supply and return lines for each piston assembly are connected to a source of pressurized hydraulic fluid via the respective rotary valve. Each valve has a stationary ported shell which receives a rotary cylindrical spool having a pair of axially displaced supply and return throughports which alternately register with supply and return line ports in the shell to open and close the connections between the respective piston assembly and the supply and return lines. While the rotary valves are preferably driven by a common drive unit, the relative phase of the oscillations of the arms can be determined by rotationally offsetting one of the spools with respect to the other by the desired phase angle.

Abstract: Opposed pivotally mounted tamper arms are oscillated by respective single-acting hydraulic piston assemblies controlled by separate hydraulic duplex rotary distributing valves. Fluid supply and return lines for each piston assembly are connected to a source of pressurized hydraulic fluid via the respective rotary valve. Each valve has a stationary ported shell which receives a rotary cylindrical spool having a pair of axially displaced supply and return throughports which alternately register with supply and return line ports in the shell to open and close the connections between the respective piston assembly and the supply and return lines. While the rotary valves are preferably driven by a common drive unit, the relative phase of the oscillations of the arms can be determined by rotationally offsetting one of the spools with respect to the other by the desired phase angle.