Hydraulic system

1. A hydraulic system, comprising:

a variable displacement hydraulic pump;

a control valve configured to control a supply state of a hydraulic fluid from the hydraulic pump to a hydraulic actuator;

a sensing oil passage configured to extract a pilot hydraulic fluid portion branching from the hydraulic fluid being supplied from the control valve to the hydraulic actuator;

a pump operating unit configured to control a discharge amount of the hydraulic pump to an increase side in response to increasing of a pressure of the pilot hydraulic fluid portion in the sensing oil passage and to control the discharge amount of the hydraulic pump to a decrease side in response to decreasing of the pressure of the pilot hydraulic fluid portion in the sensing oil passage; and

an operating valve provided in the sensing oil passage, and

wherein:

the operating valve is switchable between an open state allowing the sensing oil passage to be open and a closed state blocking the pilot hydraulic fluid portion from flowing toward the control valve in the sensing oil passage,

the operating valve is maintained in the open state while an operation pressure is less than a setting pressure, and the operation pressure is a pressure of the pilot hydraulic fluid portion in a portion of the sensing oil passage which portion is between the operating valve and the control valve, and

the operating valve is switched to the closed state in response to increasing of the operation pressure to the setting pressure or more.

2. The hydraulic system according to claim 1 , wherein;

the closed state blocks the pilot hydraulic fluid portion from flowing toward the control valve and allows the pilot hydraulic fluid portion to flow toward the pump operating unit.

3. The hydraulic system according to claim 1 , wherein:

the operating valve comprises:

a spool movable between an open position causing the open state and a closed position causing the closed state;

a biasing section configured to bias the spool to the open position; and

a pressure receiving section configured to receive the operation pressure,

wherein the spool is maintained at the open position due to a biasing force of the biasing section while the operation pressure applied to the pressure receiving section is less than the setting pressure, and

wherein the spool is operated to the closed position against the biasing force of the biasing section in response to increasing of the operation pressure applied to the pressure receiving section to the setting pressure or more.

4. The hydraulic system according to claim 3 , wherein;

the operating valve comprises:

a first internal space;

a second internal space connected to the first internal space;

a first port allowing the first internal space to communicate with a portion of the sensing oil passage which portion is adjacent to the pump operating unit;

a second port allowing the second internal space to communicate with a portion of the sensing oil passage which portion is adjacent to the control valve;

the spool comprising a first land disposed on a side opposite from the second port across the first port, a second land disposed closer to the second port than the first port, and a notch provided in a peripheral end of the second land which peripheral end is adjacent the first land, the spool supported movably in the first internal space;

a communication passage provided in the spool separately from the second land and the notch and allowing the first port to communicate with the second port; and

a check valve configured to block the pilot hydraulic fluid portion from flowing from the first port to the second port in the communication passage and to allow the pilot hydraulic fluid portion to flow from the second port to the first port in the communication passage, and

wherein:

the pressure receiving section is a portion of the second land which portion faces the second internal space,

the spool moves due to the biasing force of the biasing section to the open position allowing the first port to communicate with the second port via the notch, in response to decreasing of the operation pressure applied to the pressure receiving section to be less than the setting pressure, with the first land and the second land being-supported in the first internal space, and

the spool moves against the biasing force of the biasing section to the closed position causing the second land to block the communication between the first port and the second port via the notch, in response to increasing of the operation pressure applied to the pressure receiving section to the setting pressure or more, with the first land and the second land being-supported in the first internal space.

5. The hydraulic system according to claim 4 , further comprising:

a stopper configured to, in response to the spool moving to the open position due to the biasing force of the biasing section, stop the spool at a position allowing the first port to communicate with the second port via the notch and maintaining the second land in the first internal space.

6. The hydraulic system according to claim 4 , wherein:

the second internal space has a diameter larger than a diameter of the first internal space.