The injection pressure of the injection molding machine is adjusted by the pressure regulating valve. Under the condition of setting the pressure, the injection pressure in the front and back stages is controlled through the on-off of the high-pressure and low-pressure oil circuits. Ordinary injection molding machines above medium-sized are equipped with three pressure options, namely high pressure, low pressure and high pressure before low pressure. 

High pressure injection is realized by injecting high pressure oil into the injection cylinder. Due to the high pressure, the plastic enters the mold cavity at high pressure and high speed from the beginning. During high-pressure injection, the plastic enters the mold quickly, and the reading of the pressure gauge of the injection cylinder rises quickly. Low pressure injection is realized by injecting low-pressure pressure oil into the injection cylinder. During the injection process, the reading of the pressure gauge rises slowly, and the plastic enters the mold cavity at low pressure and low speed. 

High pressure first and then low pressure is realized by controlling the pressure of the pressure oil into the oil cylinder in time according to the actual requirements of plastic types and molds. In order to meet the requirements of different plastics, there are different injection pressures, and the method of replacing screws or plungers with different diameters can also be adopted, which not only meets the injection pressure, but also gives full play to the production capacity of the machine. In large injection molding machines, there are often multi-stage injection pressure and multi-stage injection speed control functions, which can better ensure the quality and accuracy of products.