In a double-rod hydraulic cylinder, the single-column hydraulic press will have unstable speed due to the unequal leakage of the two chambers and the different friction resistance of the reciprocating motion. In the hydraulic system, when the three-position four-way reversing valve is in the neutral position , the oil path leading to the hydraulic cylinder is blocked, the two chambers of the hydraulic cylinder are interconnected, and the return oil path is connected. The design of the hydraulic system of the four-column press is imperfect and the components are not selected properly. The smooth passage is sometimes blocked and sometimes open, and the leakage inside and outside the system is serious. If excessive air enters the oil and friction resistance changes, the hydraulic machine will also cause the actuator to become unstable at low speeds and even crawl.
The hydraulic pumps in the single-column hydraulic machine pump direct drive system are selected according to the maximum working speed and working pressure of the single-column hydraulic machine. When the single-column hydraulic machine has a small filling stroke, return stroke, auxiliary process and required working pressure, the hydraulic pumps are all selected. The single-column hydraulic press, especially the large-tonnage single-column hydraulic press, has a very low utilization coefficient; the stroke speed of the flow beam of the four-column hydraulic press depends on the liquid supply volume of the pump, and has nothing to do with the forging deformation resistance during the process. The characteristics of the constant stroke speed of the flow beam and the changing liquid supply pressure of the pump can be used as a signal to operate the distributor to realize the automatic control of the single-column hydraulic press. If the liquid supply volume of the pump is constant, the working speed of the press is a fixed value, therefore, single-column hydraulic presses tend to carry out step-by-step transmission of working speed and working pressure.
