The control valve system consists of a traveling shuttle valve, a four-way reversing valve (with a linear traveling valve and a stick throttle valve), a five-way reversing valve (with a swing priority valve), and a boom holding valve. The four-way reversing valve and the five-way reversing valve are connected together by bolts, and the oil passages are connected in the valve. The structure is compact and easy to maintain.
1. Traveling shuttle valve
The valve consists of a return spring 2, a slide valve 4, and a valve body 3. The structure is shown in Figure 3.12. The travel shuttle valve is installed on the top of the four-way reversing valve and is controlled by the left travel oil circuit. When the traveling and working device (or rotating) are simultaneously operated, the pressure oil from the shuttle valve of the working device (or rotating) pilot control valve (PPC valve) flows to the linear traveling valve through the traveling shuttle valve. The working principle of the traveling shuttle valve is shown in Figure 3-13.
Figure 3-13 Working principle of traveling shuttle valve
① Only operate the walking joystick. When the travel joystick is in the "forward" position, the control pressure oil from the left travel forward circuit flows to port P1 and pushes the spool valve to the right, so ports P3, P4, P5 and Po pass through the grooves on the spool valve All are connected, and all communicate with the linear travel valve. Because there is no pilot pressure oil from the pilot control valve (PPC valve), the linear travel valve does not work.
When the travel joystick is in the "reverse" position, the control pressure oil flows from the left travel retreat oil path to P2, pushing the slide valve to the left. Ports P3, P4, P5, and Po are all connected through the grooves on the slide valve, and all communicate with the linear travel valve. Because there is no pilot pressure oil from the pilot control valve (PPC valve), the linear travel valve does not work.
② Simultaneously operate the walking and working (or turning) devices. Make the walking joystick in the "forward" position, while operating the stick joystick to control the pressure oil to flow from the oil path to the P1 port when walking on the left, and push the slide valve to the right, the shuttle valve pilot pressure oil from the stick PPC valve It flows to the P3 port, then passes through the groove on the slide valve to the Po port, and then flows to the linear travel valve.
When the boom (or bucket) and the walking device are operated at the same time, the pilot pressure of the shuttle valve of the automatic arm (or bucket) PPC valve flows to the P4 port-P4a port-Po port straight line travel valve.
When the swing and travel devices are operated at the same time, the pilot pressure oil from the shuttle valve of the swing PPC valve flows to the P5 port-*P4a port f Po port straight travel valve.
2. Linear travel valve
The linear travel valve travels on the left side of the control spool in the four-way reversing valve. When the travel and working (or rotating) devices are simultaneously operated, the valve makes the left and right sides travel. Its working principle is shown in Figure 3-14.
① When only traveling, the pilot pressure oil from the shuttle valve of the PPC valve does not flow to the linear travel valve, so the left and right travel oil paths are closed, and the oil paths on both sides remain independent.
② When operating the walking and working (or rotating) devices at the same time, the pilot pressure oil from the traveling shuttle valve pushes the slide valve of the linear travel valve to the right. At this time, the left side travels oil through the groove on the slide valve. The road is connected to the right-hand travel oil path, and equal pressure oil is supplied to the left and right travel motors, so that the two travel motors rotate at the same speed and the excavator travels straight.
3. Swing priority valve
The swing priority valve is next to the swing control spool in the five-way reversing valve. When the swing device and the stick are operated at the same time, most of the pressure oil flows to the stick with a smaller load, and the flow to the swing oil circuit is reduced, so the speed of the stick is faster than the rotating speed, which makes joint operation difficult . The function of the swing priority valve is to limit the pressure oil flow to the stick-low-speed control valve during joint operation, which limits the speed of the stick and improves the joint operation performance. Its working principle is shown in Figure 3-15.
① When the swing control lever is in the neutral position, there is no pilot pressure oil from the travel shuttle valve, and the swing priority valve does not work. At this time, all the pressure oil output from the front main pump flows through the Pr port to a low-speed control valve of the stick.
② When operating the turning device. The pilot pressure oil from the travel shuttle valve pushes the spool valve of the swing priority valve to the left. Therefore, when the pressure oil from the front main pump flows to the stick-low-speed control valve through the Pr port, it is throttled and the stick speed is controlled. Improved joint operation performance.
4. Stick throttle
The stick throttle valve is beside the bucket control spool in the four-way reversing valve. When the boom and stick are manipulated at the same time, most of the pressure oil flows to the stick oil path with a smaller load, so the speed of the stick is faster than the speed of the boom, making joint operations difficult. When the stick and the bucket are operated at the same time, since the stick is operated by dual pumps and the bucket is operated by a single pump, the speed of the stick is much faster than that of the bucket, which makes joint operation difficult . The function of the stick throttle valve is to open the stick throttle valve to limit the flow of pressure oil flowing to a high-speed control valve of the stick during joint operation, which limits the speed of the stick and improves the joint operation performance. The working principle of the lever throttle is shown in Figure 3-16.
① When the stick is operated alone, the travel shuttle valve has no pilot pressure oil flowing out, and the stick throttle valve does not work. The pressure oil from the rear main pump flows to the stick high-speed control valve through the PL port.
② When the stick and boom or stick and bucket are operated at the same time, the pilot pressure oil from the traveling shuttle valve pushes the spool valve of the stick throttle valve to the right. Therefore, the pressure oil flowing from the main rear pump to the high-speed control valve of the stick is throttled, and the speed of the stick is controlled, which improves the joint operation performance.
5. Boom holding valve
① Function: When the boom is in the raised position, it prevents the boom from sliding down naturally.
② The boom holding valve consists of a safety charge valve, a pilot spring, a pilot spool, a poppet spring, and a spool valve, as shown in Figure 3-17.
③ The working principle is shown in Figure 3-18.
(a) When the boom is raised, after the pressure oil from the main operating valve flows to the V port, it overcomes the force of the poppet spring 4 to push the spool valve 5 upward and flows to the lower cavity of the boom cylinder through the Cv port. The boom starts to lift.
(b) When the boom is in the raised position and the joystick returns to the neutral position, the spool valve 5 is moved downward by the force of the lift spring 4, closing the oil circuit of the lower chamber of the boom cylinder, and at the same time the lower chamber of the boom cylinder After the pressure oil enters the inner b cavity of the slide valve 5 through the throttle hole a on the slide valve 5, it is closed by the pilot valve core 3, and the boom remains in the raised position to prevent the boom from sliding down.
(c) When the boom is lowered, the pilot pressure oil from the PPC valve pushes the pilot spool 3 to move to the left, so that the pressure oil in the b cavity of the spool valve 5 moves to the left through the channel opened by the pilot spool 3 to drain back to the tank. The pressure oil in the lower cavity of the boom cylinder enters the b cavity through the orifice a on the spool valve 5. When the pressure oil passes through the orifice a, a pressure drop occurs. When the pressure in the b cavity drops below the pressure of the V port, the sliding Valve 5 is opened, and the pressure oil from the lower chamber of the boom cylinder flows through the Cv port to the V port, and then flows into the main operating valve. When the boom cylinder is down.
