A flush valve for a multiple line hydraulic system includes a bifurcated manifold, the bifurcation being provided by a piston actuatable hydraulically, mechanically, electrically magnetically or by fiber optic means. The piston or gate is provided with a port extending diametrically therethrough and oriented to become coaxial with an inlet and outlet of the manifold upon actuation of the piston. With the port aligned the hydraulic fluid in the system can be displaced by fresh fluid. The piston is then deactivated which results in the port becoming misaligned with the inlet and outlet of the manifold. In this condition the hydraulic system is again sealed and functions normally.