When compressed air is admitted into the lower end of cylinder 1, piston 2, to which load hook 3 is attached, travels upward. When the lower end of cylinder 1 is connected to the atmosphere, piston 2 is lowered by gravity. Air is delivered to the lower end of cylinder 1 through pipeline 4, opening check valve 5, and through rotary valve 6 and channel a. Valve 6 is controlled by two chains which are attached to the ends of control lever 7. Lever 7 is mounted on one end of shaft A with the valve member on the other end. The valve member is spring-loaded. Thus, the lower end of cylinder 1 can be connected either to the compressed air main or to the atmosphere. Spring 8 holds control lever 7 in the position in which the lower end of the cylinder is closed off. In case of damage to the pipeline or other failure of the compressed air supply, the pressure above check valve 5 drops and this valve blocks reverse flow of compressed air out of the cylinder, thereby preventing the dropping of the load. The speed at which the load is lowered in normal operation can be regulated by adjusting screw 9 which changes the rate of flow of air from under piston 2.
$3700$SHP,MH$