A valve comprises a body having a first inlet, a second inlet, and an outlet. A shuttle is shiftable between: a first position permitting communication between the first inlet and the outlet and blocking communication between the second inlet and the outlet； and a second position permitting communication between the second inlet and the outlet and blocking communication between the first inlet and the outlet. One or more permanent magnets are positioned to bias the shuttle away from a neutral position between the first position and the second position, wherein the valve further comprises: one or more electromagnets positioned to, in at least one condition of energization, counter said bias.
