The control valve has two relief valves to limit the pressure in the oil road.
(1) Main safety valve
The main safety valve is used to limit the pressure of the main hydraulic system.
The hydraulic oil of the pump P1 and the pump P2 enters the control valve via the port P1 and P2. The main relief valve is directly entered by the check valve CMR1 or CMR2 and channels. The pressure setting of the channel is limited by the main overflow valve.
The principle of main overflow valve work is as follows.
When the pressure of the channel is smaller than the pressure set by the mainflow valve, the thimble 10 is fixed, and the hydraulic oil of the passage does not flow to the oil port. When the pressure of the channel is close to the set pressure, the top needle 10 is pushed open by the pressing spring 11. The oil volume of the oil chamber leaks to the retraction port through the channel, and the pressure decreases. At the same time, since the pressure drops in the passage, the hydraulic oil of the passage flows into the channel, and then, since the pressure is discharged, the pressure of the spring chamber 3 is lowered. The pressure of the passage pushes the plunger 8 to move the spring 9 to the right. Then, the plunger 8 opens, the hydraulic oil of the passage enters the oil port and holds the set pressure value. The pressure setting is adjusted by the adjustment screw 12.
(2) Modern excavator oil mouth relief valve
Used to limit the impact pressure of the cylinder oil.
Oil port overflow valve and replenishing valve are mounted between the cylinder port of the working device (the arms, the arm and bucket) and their spools, since the spool is located in the median, the external force acts on the cylinder rod, the cylinder pressure may Excessive, therefore the pressure setting of the oil port overflow valve limit valve.
Oil port relief valve also has a function of supplementate valve. In the case where external force acts on the cylinder, it may not be able to cooperate with the cylinder without the amount of oil supply. If this happens, there may be vacuum and cavitation. In order to avoid this, the supplemental valve work is cut off because of the vacuum generated by the backflow to the cylinder. Supplement oil from the hydraulic tank.
The hydraulic oil flow in the cylinder and the spool flows in the channel to boost the oil port overflow valve. The hydraulic oil of the passage flows into the spring chamber 3 through the passage. If the needle 2 is lower than the set pressure, the thimble 2 is turned off because the force of the spring is greater than the pressure. Therefore, the channels and spring chains remain the same pressure. Since the pressure of the spring chamber is greater than the pressure of the plunger than the channel, the valve seat and the plunger are pushed to the left, and then the hydraulic oil of the channel does not leak into the oil return channel.
1 Oillet overflow function. When the pressure of the channel is increased to the set pressure, the thimble is pushed away from the spring. Due to the decrease in pressure, the hydraulic oil of the oil port has flowed into the return passage through the channel. Because the pressure of the channel, the plunger moves to the left and stops at the end of the plug.
The hydraulic oil of the passage flows through the passage 6 into the oil chamber and the spring chamber. The hole between the outer diameter chamber and the inner diameter chamber of the plunger generates different pressure acts to the passage, so the pressure of the spring is low, so the plunger is pushed to the right due to the opening of the channel, so the hydraulic oil of the passage Flowing into the oil return channel.
2 supplementary function. The hydraulic oil of the cylinder rod (top) is leaked from the oil exit overflow valve because the vacuum needs to supply hydraulic oil during the cylinder rod (top). When there is a vacuum in the channel, a vacuum occurs through the spring chamber of the channel. The pressure of the oil return channel acts on the seat. Because the spring chamber and the plunger are in vacuo, the backlare pressure base is shifted to the right. Hydraulic oil flowing in the oil return to cut off the vacuum of the passage.
