Wireless sensor networks for machine condition based monitoring

A hydraulic positioner for maintaining a given separation between its attachment points and having a bidirectional detenting action whereby the given separation can be altered only by application of a sufficiently large overriding force. A closed cylinder is divided into two closed fluid-filled chambers by a slidable piston. Motion of the piston requires transfer of fluid between the chambers. The transfer flow is determined by preloaded check valves in the transfer flow path. The check valves are preloaded in opposite directions to achieve the bidirectional detenting action. A reservoir supplies fluid under a small positive pressure to one of the closed fluid-filled chambers to replace fluid lost through leakage.