Abstract: A fluid-actuated interlock system for automatically controlling a plurality of remotely located valve assemblies. A fluid switch and a locking device are disposed for cooperation with each valve operator. The fluid switches are connected to a supply line for a pressure fluid, and the locking devices are connected to a manifold. Communication is permitted between the supply line and the manifold only when one of the fluid switches is moved into an open position. Each fluid switch is maintained in a closed position by its respective valve operator in a preselected position. When one valve operator is moved away from this preselected position, the associated fluid switch is opened whereby pressure fluid flows from the supply line into the manifold which in turn supplies pressure fluid to the locking devices associated with the remaining valve operators.