Electromagnetic hydraulic valves are used to control the flow of oil in hydraulic systems or regulate their pressure and flow rate, and can therefore be divided into three categories: directional valves, pressure valves, and flow valves. Due to different mechanisms of action, valves of the same shape have different functions. Pressure and flow valves control the pressure and flow of the system through cross-sectional throttling, while directional valves control the direction of oil flow by changing the flow path. That is to say, although there are many types of solenoid valves, they have some basic similarities. For example:

(1) Structurally, all valves consist of a valve body, a spool (rotary valve or slide valve), and components and parts that drive the spool (such as springs and electromagnets);

(2) In terms of working principle, the opening size of all valves, the pressure difference between the valve inlet and outlet, and the flow rate through the valve all conform to the orifice plate flow formula, but the parameters controlled by different valves are different.