a control valve structure and combined visual indicator for controlling fluid and visually indicating the operating condition of a portion of a fluid system . the control valve has a slide valve mounted in a housing and biased toward a retracted position with one end portion thereof extending from the housing . the extended end portion of the slide valve has a knob adapted to be manually gripped for moving of the slide valve outwardly for setting same . a visual indicator is mounted on the knob . a port in the housing communicates with the slide valve to permit the application of fluid pressure to the slide valve to move same outwardly . the visual indicator has a visually observable indicator member movable between two positions for indicating the presence of either of two associated conditions in a system containing the control valve . the visual indicator displays one position when less than a predetermined fluid pressure is applied to the visual indicator and it displays the other position when a larger predetermined fluid pressure is applied to the visual indicator .