The rotary reducer in the concrete pump trucks manufactured by Zoomlion Heavy Industry and Sany Heavy Industry serves a crucial function in facilitating the rotation and positioning of the boom arm or the entire upper structure of the vehicle.

The primary role of the rotary reducer is to provide the necessary torque and reduction gear ratio for smooth and controlled rotation. It is responsible for transmitting power from the hydraulic system to the rotating components, allowing the boom arm or upper structure to rotate horizontally or vertically as required during concrete pumping operations.

The rotary reducer ensures precise and accurate positioning of the boom arm, allowing for efficient concrete placement at the desired locations. It enables the operator to control the movement and orientation of the boom arm with precision, enhancing productivity and construction quality.

The specific model numbers provided, such as "PG1003," "PG1002," "RE1022," "RE1023," "WHBH-100C," "EL1512," "EL1513," "GS9T99," and "310 L3 101HZ 5B," correspond to different variants or specifications of the rotary reducers used in the concrete pump trucks. These model numbers help to identify the specific type or configuration of the rotary reducer for maintenance, replacement, or compatibility purposes.