Hydraulic circuit for swivel working machine

A swivel working machine comprising a swiveling body, a swiveling hydraulic motor for swiveling said swiveling body, a working unit, a hydraulic cylinder for operating said working unit, and a hydraulic circuit for supplying hydraulic fluid to said swiveling hydraulic motor and to said hydraulic cylinder, said swiveling hydraulic motor having first and second ports, said hydraulic cylinder having first and second ports, said hydraulic circuit comprising:

• a hydraulic pump having an outlet;
• a first operating valve, said first operating valve having at least one inlet port and first and second output ports, said first operating valve having first and second operating positions and a neutral position;
• a second operating valve, said second operating valve having at least one inlet port and first and second output ports, said second operating valve having first and second operating positions and a neutral position;
• a first pressure compensating valve, a second pressure compensating valve, a third pressure compensating valve, a fourth pressure compensating valve, each of these pressure compensating valves having at least a first pressure receiving section;
• a first conduit connecting said outlet of said hydraulic pump to said at least one inlet port of said first operating valve;
• a second conduit connecting said output of said hydraulic pump to said at least one inlet port of said second operating valve;
• a third conduit connecting said first output port of said first operating valve through said first pressure compensating valve to said first port of said swiveling hydraulic motor;
• a fourth conduit connecting said second output port of said first operating valve through said second pressure compensating valve to said second port of said swiveling hydraulic motor;
• a fifth conduit connecting said first output port of said second operating valve through said third pressure compensating valve to said first port of said hydraulic cylinder;
• a sixth conduit connecting said second output port of said second operating valve through said fourth pressure compensating valve to said second port of said hydraulic cylinder;
• first and second load pressure introduction check valves, each of said first and second load pressure introduction check valves having an inlet and an outlet;
• a seventh conduit connecting said first port of said swiveling hydraulic motor through said first operating valve to said inlet of said first load pressure introduction check valve when said first operating valve is in its first operating position;
• an eighth conduit connecting said second port of said swiveling hydraulic motor through said first operating valve to said inlet of said first load pressure introduction check valve when said first operating valve is in its second operating position;
• a ninth conduit connecting said first port of said hydraulic cylinder through said second operating valve to said inlet of said second load pressure introduction check valve when said second operating valve is in its first operating position;
• a tenth conduit connecting said second port of said hydraulic cylinder through said second operating valve to said inlet of said second load pressure introduction check valve when said second operating valve is in its second operating position;
• a load pressure introduction conduit connecting the outlet of said first load pressure introduction check valve and the outlet of said second load pressure introduction check valve to the first pressure receiving section of each of said first, second, third, and fourth pressure compensating valves to set these pressure compensating valves;
• a first controller for actuating said first operating valve from one of its positions to another of its positions;
• a second controller for actuating said second operating valve from one of its positions to another of its positions;
• and
• means for applying a closing pressure to said first load pressure introduction check valve to close said first load pressure introduction check valve when said second controller actuates said second operating valve to one of its operating positions.