Abstract: A wiper device is provided comprising a container having a central opening through which the well string may pass. A pair of opposed wiper pads disposed in a horizontal attitude are mounted in spaced vertical relationship within the container for longitudinal movement toward each other, to engage the vertical string. A double-acting pneumatic cylinder actuates each pad. Each cylinder is mounted in the plane of the pad, said cylinder being connected at its front end with the rear portion of the wiper pad and being pivotally connected at its rear end with a support member. The front end of the cylinder is thus adapted to rotate in a horizontal plane about its pivot connection, to accommodate transverse movement of the attached wiper pad. The container side walls are spaced from the wiper pad edges to permit such transverse movement to take place. Arrays of anti-friction rollers support each of the pads.