The hydraulic drive system mainly has two types: pump direct drive and pump-accumulator drive. The pump directly drives the drive system to provide high pressure working fluid to the hydraulic cylinder. The valve is used to change the direction of the liquid supply. The overflow valve is used to regulate the system's limiting pressure and at the same time acts as a safety overflow. This kind of drive system has few links, simple structure, and the pressure can automatically increase or decrease according to the required work force, reducing the power consumption. However, the maximum work force and the maximum working speed of the hydraulic press must be used to determine the capacity of the pump and its drive motor. This type of drive system is mostly used for small and medium-sized hydraulic presses, and also has a large-sized (for example, 120,000 kN) free-forging hydraulic press directly driven by a pump. Pump-accumulator drive There is one or a group of accumulators in this drive system. When the high pressure working fluid supplied by the pump has a surplus, it is stored by the accumulator, and when the supply amount is insufficient, it is replenished by the accumulator. With this system, the pump and motor capacity can be selected according to the average amount of high-pressure working fluid. However, because the pressure of the working fluid is constant, the power consumption is large, and the system has many links and the structure is complicated. This type of drive system is mostly used for large hydraulic presses, or it can drive several hydraulic presses with a single drive system.