There are actually two meanings in the middle. First, according to the working medium, the hydraulic valve is used to pass hydraulic oil, and the pneumatic valve is used to pass compressed air. Secondly, according to the operation mode of the valve, it can be divided into solenoid valve (electric drive operation), manual valve and valves operated in other ways. So before and after the combination, the hydraulic solenoid valve and pneumatic solenoid valve have different combinations and differences. In addition, according to the different functions of the controlled fluid, it can be divided into different valves such as reversing, pressure regulating and speed regulating (intercepting). I won't go into details.