HYDRAULIC CIRCUIT FOR PREVENTING LIFTING DOWN OF BOOM IN HEAVY EQUIPMENT SUCH AS EXCAVATOR WITH BOOM FLOAT POSITION VALVE

摘要

PURPOSE: A hydraulic circuit with a boom float position function is provide to improve the convenience by turning off the float position function in turning on the electric switch in increasing pressure of a small chamber over the predetermined value and preventing the boom from lifting down against the purpose of a driver. CONSTITUTION: A hydraulic circuit comprises a pilot pump(1), a main pump(2), a boom cylinder(5) connected to the main pump, a main control valve(3) installed between the main pump and the boom cylinder and composed of a boom control spool and an actuator control spool controlling operation, stop and direction change of the boom cylinder, a remote control valve(4) controlling the main control valve according to the pilot signal pressure from the pilot pump, a float position valve(6) communicating and shutting off the connection passages of the large chamber and the small chamber and the return passage of an oil tank to lift up and down the boom, an electric switch(11), a solenoid valve(7) controlling the pilot signal pressure to the main control valve and the float position valve, a pressure detecting unit(9) sensing pressure of the small chamber, and a controller(10) turning off the float position function by shutting off the electric signal to the solenoid valve in detecting the pressure over the predetermined value.