A complete hydraulic system consists of five parts, namely power components, actuators, control components, auxiliary components, and hydraulic oil.

　　The function of the power component is to convert the mechanical energy of the prime mover into the pressure energy of the liquid. It refers to the oil pump in the hydraulic system, which provides power to the entire hydraulic system. The structural forms of hydraulic pumps generally include gear pumps, vane pumps, and plunger pumps, and their performance comparison is shown in 1-1.

　　The function of actuators (such as hydraulic cylinders and hydraulic motors) is to convert the pressure energy of the liquid into mechanical energy, driving the load to perform linear reciprocating motion or rotary motion.

　　Control components (i.e., various hydraulic valves) control and regulate the pressure, flow, and direction of the liquid in the hydraulic system. According to different control functions, hydraulic valves can be divided into pressure control valves, flow control valves, and directional control valves. Pressure control valves are further divided into relief valves (safety valves), pressure reducing valves, sequence valves, pressure relays, etc.; flow control valves include throttle valves, regulating valves, flow divider-combiner valves, etc.; directional control valves include check valves, pilot-operated check valves, shuttle valves, directional valves, etc. According to different control methods, hydraulic valves can be divided into on-off control valves, fixed-value control valves, and proportional control valves.

　　Auxiliary components include oil tanks, oil filters, oil pipes and pipe joints, sealing rings, pressure gauges, oil level and oil temperature gauges, etc.

　　Hydraulic oil is the working medium that transmits energy in the hydraulic system, and there are several major categories such as various mineral oils, emulsions, and synthetic hydraulic oils.