AUTOMATION AND CONTROLLERS HCU - HYDRAULIC CONTROL UNIT Hydraulic Control Unit Our HCU activates the opening and closing of valve gates on your hot runner system. This hydraulic control unit works independent of your injection molding machine. The hydraulic control unit has its own electrical board, motor, hydraulic tank, solenoids and cooling system. A manometer enables you to check the hydraulic control unit operating pressure and the thermostat indicates any excessive temperature in the solenoids. The hydraulic control unit works through a 24 pin Harting mounted on the side wall of the electrical board.