Working principle and system composition of hydraulic transmission

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Hydraulic transmission uses a liquid sealed within the system as a medium to convert hydraulic energy into mechanical energy; transmission that relies solely on the pressure energy of the liquid is known as hydraulic transmission. 1. Working principle of hydraulic transmission: The working principle of a hydraulic transmission system is based on Pascal’s principle. The hydraulic jack shown in Figure 11.1 illustrates the working principle of hydraulic transmission. In Figure 11.1, the large and small cylinders are connected to each other. As is known in physics, liquids have two important properties ； Liquids are almost incompressible ； The pressure of a stationary liquid in a closed container is transmitted in all directions with equal magnitude. When the handle is pulled upward by hand, the small piston moves upward, causing the volume chamber at the bottom of the small piston to expand and creating a vacuum. Under atmospheric pressure, the oil enters the lower chamber of the small cylinder through oil pipe 5 and check valve 4 ； By pressing down on the handle with force, the small piston moves downward; the oil in the sealed volume chamber is compressed, and the oil from the lower chamber is forced into the lower chamber of the large cylinder through pipe 6 and check valve 7 (at this point, check valve 4 is closed, preventing flow from the oil tank). This action forces the large piston 8 to move upward, thereby lifting the load W. By repeatedly pushing the handle, oil is continuously pumped into the lower chamber of the large cylinder, causing the large piston to rise slowly. II. Basic Components of a Hydraulic Transmission System A hydraulic system consists of the following five components: 1) Transmission medium – the medium that transfers energy, namely hydraulic oil ； 2) Power elements – hydraulic components that convert mechanical energy into hydraulic energy of the oil. Here it usually refers to a hydraulic pump, which supplies pressurized oil to the system ； 3) Actuator – A hydraulic component that converts the hydraulic energy of the oil into mechanical energy. Refers to hydraulic cylinders that move in a straight line or hydraulic motors that rotate, etc ； 4) Control elements – Hydraulic components that are used to control or regulate the pressure, flow rate, or direction of fluid flow in a system. Such as check valves, globe valves, etc. in the examples above ； 5) Auxiliary components — other components besides the three mentioned above. III. Graphic symbols and schematic diagrams of hydraulic transmission systems Internationally, corresponding graphic symbols have been established for hydraulic (pneumatic) components and accessories to represent their functions; however, these symbols do not indicate their specific structure, which is why they are also referred to as functional symbols. Figure 11.3 shows the hydraulics of the machine tool table, drawn according to the hydraulic and pneumatic functional graphic symbols specified in GB786.1-1993