Abstract: A reciprocating cylinder assembly for self-propelled sprinkler systems and the like comprising a cylinder tube having hollow plugs at each end having slidably engaged therein, a piston rod, said piston rod being surrounded by a repositionable valve slide and a piston. The piston rod projects through the hollow plugs at each end of the cylinder tube and have fluid inlet and outlet means at each end of the piston rod. When pressurized fluid is delivered to one end of the piston rod, the piston rod moves relative to the cylinder in a direction opposite to the direction of the entering fluid, and fluid is forced from the outlet at the opposite end of the piston rod until the valve slide engages the end plug of the cylinder tube whereupon pressure causes valve detents to slidably change positions thereby causing a reversal of fluid flow and the change of direction in the movement of the piston rod.