In the hydraulic system, the pressure control valve of the four-column hydraulic press is used to control and adjust the pressure of the system, which is based on the principle of balancing the liquid pressure on the valve core and the spring force. Pressure control valves mainly include relief valves, pressure reducing valves, sequence valves and pressure relays, etc. Among them, the relief valve is the overflow through the opening of the valve port, which keeps the pressure of the controlled system constant, and realizes the role of pressure regulation, pressure regulation and pressure limiting. The main characteristics of the relief valve are: large pressure regulation range, small pressure regulation deviation, small pressure oscillation, sensitive action, large overflow capacity, and small noise. It can be divided into direct acting relief valve and pilot relief valve two kinds. In the case of medium and high pressure and large flow, pilot operated relief valves are generally used.
The working principle of pilot operated relief valve. This kind of structure is divided into two parts, the main valve part below, the pilot pressure regulator part above, which uses the pressure difference between the upper and lower ends of the main valve spool to move the main valve spool. Pressure oil enters from the inlet, acts on the lower end of the main valve spool, and enters the upper cavity of the main valve spool through the damping hole in the main valve spool, acts on the upper end of the main valve spool, and acts on the left end of the pilot valve spool through the oil inlet channel. When the pressure of the oil inlet is low, the hydraulic force on the pilot valve spool is less than the preload force of the pressure regulating spring of the pilot valve, and the valve port of the pilot valve is closed. The oil in the damping hole does not flow, so the oil pressure at both ends of the main spool is equal, and the main spool is at the bottom position under the action of the reset spring, and the overflow port is closed.
When the pressure of the oil chamber rises, the liquid pressure acting on the pilot valve spool is greater than the preload force of the pilot valve regulating spring, the pilot valve spool moves to the right, the compression spring opens the pilot valve port, and the pressure oil flows into the return oil port through the pilot valve return oil hole. Because the pressure drop occurs when the oil flows through the damping hole, the oil pressure at the upper end of the main spool is less than the oil pressure at the lower end. When the pressure difference on the main spool exceeds the pre-tightening force of the return spring, the main spool moves upward and the overflow port is opened to realize the overflow effect.
Adjusting the adjusting screw can change the preload force of the pressure regulating spring, so as to adjust the oil inlet pressure of the relief valve.
There is a remote control port on the valve body, using different control methods, can be pilot-operated relief valve to achieve different roles.
The main use of the relief valve has two points, one is used to keep the pressure of the system or loop constant, such as in the quantitative pump throttling speed regulation system as a constant pressure relief valve, to keep the pump outlet pressure constant, but in the system as a safety valve, in the normal work of the system, the relief valve is closed, and when the system pressure is greater than or equal to its set pressure, the relief valve to open the overflow. Provides overload protection for the system. In addition, the relief valve can also be used as back pressure valve, unloading valve, brake valve, balance valve and speed limiting valve. The pressure stability of the four-column hydraulic press depends on the stability of these valves. If the hydraulic components are damaged or have problems, they must be repaired or replaced in time, because some minor problems are not handled properly, and if they are not timely, they will bring greater harm.
The relief valve high and low pressure regulation method is as follows:
1. Loosen all the screw of the relief valve, the equipment is running, slowly tighten the screw, look at the pressure gauge, and stop after a few mpa of pressure, let the equipment run statically for a few minutes under this pressure, and then repeat the process of boosting and running until the set pressure is adjusted.
2. Each hydraulic station oil pump outlet will have an overflow valve, sometimes for some reason, the pump outlet pressure may be greater than the pressure required by the system, this time you need the overflow valve to remove the excess pressure, the oil discharged back to the tank.