Hydraulic variable control apparatus for heavy construction equipment

A hydraulic control apparatus for heavy construction equipment having an actuator driven in connection to a pump line of a hydraulic pump, a hydraulic control valve mounted to a hydraulic line between the hydraulic pump and the actuator and switched upon an application of a pilot signal pressure to control flows of hydraulic fluid, and a seat valve body mounted in a hydraulic line between the pump line and hydraulic feeders to auxiliarily control hydraulic fluid flowing in a load line, the seat valve body comprising:

• a first seat valve displaced by a difference between a load pressure of the load line and a discharge pressure of the hydraulic pump in the hydraulic line between the pump line and the feeder lines, and varying an opening area between the pump line and the feeder lines based on a displacement amount thereof;
• a second seat valve displacing with respect to the first seat valve and determining a displacement amount of the first seat valve;
• and
• a pilot spool having a pilot variable throttle, and controlling an opening degree of the pilot variable throttle with switching and determining a displacement amount of the second seat valve.