Abstract: Dual coaxial bidirectional valves are provided for use in fluid systems such as hydrostat systems where flow can proceed in opposite directions, and which direct flow through a unidirectional or multidirectional function such as a filter assembly in such a system in the normal direction, regardless of the direction of flow in the system. The valve includes two opposed coaxial valves intercepting and controlling flow through a box junction of the fluid line with the lines leading to and from the filter assembly, in a manner such that, regardless of the direction of flow in the fluid line, flow proceeds in the same direction in the connecting fluid lines to and from the function.