What is the reason why the pressure setting value of the four-column hydraulic press cannot be reached?

1. The flow rate of the hydraulic pump of the four-column hydraulic machine is insufficient. The pressure oil of the hydraulic system is supplied by the hydraulic pump. Generally, a suitable pump will not cause insufficient oil supply. D. Due to oil contamination, oil filter blockage and other reasons, the pump will not absorb enough oil. Therefore, the pump flow rate must be insufficient. The hydraulic pump has been used for a long time, or the parts in the pump have been severely worn due to oil contamination, resulting in serious internal leakage and a sharp decline in volumetric efficiency. This is also the reason for insufficient oil discharge from the pump.
2. The internal leakage of the reversing valve is serious. The internal seal of the reversing valve is guaranteed by the gap between the valve core and the valve hole. Due to various reasons, the gap between the valve core and the valve hole increases. Therefore, after the pressure oil from the pump enters the reversing valve, The internal annular gap will flow from the high-pressure chamber to the low-pressure chamber, greatly reducing the oil flow through the reversing valve, thereby reducing the flow into the hydraulic cylinder.

3. The hydraulic cylinder of the four-column hydraulic machine has serious internal leakage. When the hydraulic cylinder moves, the pressure oil in the high-pressure chamber of the hydraulic cylinder leaks to the low-pressure chamber. The cause of the leakage is that the gap between the piston and the cylinder is too large due to wear, or the piston seal is damaged. The movement speed of a hydraulic cylinder is the ratio of the flow rate input to the hydraulic cylinder to the effective area of the piston.
Since leakage reduces the actual flow that drives the piston movement, the movement speed of the hydraulic cylinder of the four-column hydraulic machine decreases. At this time, the piston should be replaced to ensure a reasonable clearance between the piston and the cylinder barrel. If the piston seal is damaged, replace it with a new one. Checking the above system failures does not belong to the reasons analyzed above. When inspecting the oil return pipe of M, it was found that when the hydraulic cylinder 6 moves, a large amount of oil flows out of the oil return pipe, and it can be seen that the relief valve begins to overflow, indicating that the pressure setting values of the relief valve and the sequence valve do not match. When the pressure of the relief valve is adjusted to 0. 5 ~ 0. 8 MPa higher than the pressure of the sequence valve, the circuit fault is eliminated immediately.

In the pressure control system, the matching of the pressure setting value of the pressure valve is very important. Different systems should reasonably adjust various pressure valves according to actual conditions. In the above system, the regulating pressure of sequence valves 4 and 5 should be 0.4 to 0.5 MPa higher than the working pressure of hydraulic cylinder 7. If the pressure of relief valve 2 is also adjusted according to this value, then the pressure will increase when the sequence valve opens. When the oil is flowing out, the relief valve also begins to overflow. Or the pressure of the relief valve is adjusted higher than that of the sequence valve, but the higher value is not enough. In this way, when the external load increases during the movement of the hydraulic cylinder 6, that is, the working pressure of the hydraulic cylinder 6 reaches the setting of the relief valve. When the pressure is high, the relief valve will start to overflow, and the movement speed of hydraulic cylinder 6 will slow down. Therefore, for such a system, it is appropriate to set the regulating pressure of the relief valve and sequence valve according to the above values.