Abstract: A simple lock device for use on a valve of the push-pull or plunger operated type includes a tubular casing defined by a outer shell and an inner core, which is connected to the plunger of a valve so that the valve can be operated by pushing the casing against the valve plunger, a sleeve slidable into one end of the casing between the outer shell and the core, permitting plunger operation and actuation of the valve, and out of the casing against a fixed element such as the valve casing carrying the plunger, pins radially movable in the casing for engaging the sleeve to prevent movement thereof into the casing, and consequently to prevent actuation of the valve, and a lock in the other end of the casing for controlling movement of the pins, and thereby to control actuation of the valve.