Abstract: This invention relates to accumulator conveyors. During the past two decades many types of accumulator conveyors have been developed. These utilize a variety of different operating mechanisms and principles. This invention is in the field of accumulator conveyors which rely upon shifting the primary propelling member vertically between a raised position in which the propelling member is in driving contact with the lower faces of the article supporting and propelling rollers and a lowered position in which it is disengaged from these rollers. The invention is further directed to the type of accumulator in which the shift of the conveyor from conveying to accumulation mode and return to conveying mode is automatically controlled in response to the presence of the motion or lack of motion of an article on the conveyor. Heretofore, all conveyors of this type have had some type of sensor in the form of a roller, lever, wheel or pneumatic valve which is moved or triggered by an article near or over it.