Hitachi Excavator Brake Valve
(1) Working principle
When the slewing action stops, if the upper slewing platform is still rotating due to the inertial force of the slewing, the slewing motor will continue to rotate and suck oil from the oil pump, thereby forming air pockets in the motor. The supplement valve sucks hydraulic oil in the oil return path (oil port C) to compensate for the lack of hydraulic oil in the motor, which can prevent the generation of air pockets and enable the upper turntable to rotate smoothly.
(2) Safety valve
The structure of the safety valve is shown in Figure 5-8. When the turning operation starts or stops, the oil pressure in the turning oil circuit rises, and the safety valve can prevent the oil pressure in the pipeline from rising to greater than the specified pressure. The pressure P of the oil port P and the pressure of the pressure zone A2 will be The plug 5 is pushed to the left, but the plunger 5 is pushed back to the right due to the force of the spring 8, the pressure p of the oil chamber g, and the pressure of the pressure zone A3.
The oil cavity g communicates with the oil port P through the small hole m. When the force on the left is higher than the force on the right, the safety valve starts to act.
(1) Action when pressure rises. When the pressure p of the oil port P increases, the pressure p of the oil chamber g also increases. Because the oil cavity g communicates with the oil port P through the small hole m of the plunger, the increased pressure acts on the pressure area A4 of the piston 2. When the force pushing the piston 9 to the left exceeds the force of the spring 1, the piston 9 moves to the left, and the pressure p of the oil chamber g drops below the pressure P. As a result, the plunger 5 moves to the left, the port P communicates with the port R, and the pressure at the port P drops.
When the pressure of the oil port P drops, the plunger 5 returns to the right again, the passage between the oil port P and the oil port B is closed, the pressure P of the oil port P and the pressure p in the oil chamber g increase until Piston 9 starts to move to the left again. This action is repeated until the piston 9 reaches the end of its stroke
When the piston 9 moves to the left, the oil behind the piston 2 is squeezed out through the small hole n, and slowly flows back to the oil port R, so that the overflow pressure is slowly increased.
When the piston 9 reaches the end of its stroke, the piston 2 starts to move to the right. This is the result of the force generated by the pressure p in the oil chamber g acting on the pressure zone A1. At the same time, the spring 8 is compressed. When the piston 4 starts to move to the right, the oil remaining in the oil chamber leaks out through the oil groove h on the sliding surface between the adjustment valve 10 and the piston 2. Therefore, the pressure p of the oil chamber g gradually rises until the piston 2 reaches the end of the stepped hole of the regulating valve 10. As the spring is compressed, its spring force increases, so the overflow pressure slowly rises. When the piston 2 reaches the end of the stepped hole of the regulating valve 10, it can no longer move to the right, and the pressure of the oil chamber g becomes equal to the prescribed pressure p. After reaching this position, the continuous overflow action begins
(2) The action of pressure reduction. When the pressure P of the oil port P drops, the pressure P of the oil chamber g also drops to the tank pressure, the plunger 5 moves to the right, and the valve seat 6 is closed. The spring 1 is pushed to the right. At the same time, the non-return ball valve installed on the sleeve 3 is opened, and oil is obtained from the oil port R, which prevents a vacuum from appearing behind the piston 2, which helps the piston 2 to return immediately without delay.
