The function of a shuttle valve is to allow two independent signal sources to be connecteected to a common pilot line, e.g. a pressure operated valve may then be controlled from two different points. In this respect the unit performs an 'OR' logic function.

Shuttle valves may be used in combination to provide operation from three or more independent sources.

When a signal is applied to one inlet port of the shuttle valve a piston moves over, and the inlet is connected to the outlet, the other inlet port remaining sealed.