In the hydraulic system, the hydraulic valve is the key element to control the pressure, flow and direction of fluid, which is of great significance for the normal operation and performance optimization of the system. In order to standardize the design, manufacture and application of hydraulic valves, relevant international and domestic standards bodies have formulated a series of classification standards for hydraulic valves. These standards not only provide a basis for the selection of hydraulic components, but also lay a foundation for technical exchange, product exchange and quality control.

# 1. Classification by function

According to the functions of hydraulic valves, they can be mainly divided into three categories:

1. Pressure control valve: used to control the pressure in the hydraulic system. Common types include overflow valve, pressure reducing valve, sequence valve and pressure relay. This kind of valve ensures the safe and stable operation of the system within the set pressure range.

2. Flow control valve: used to adjust the flow through the valve to control the movement speed of the actuator. Typical products include throttle valve, speed regulating valve and so on.

3. Direction control valve: it is mainly used to control the direction of liquid flow, thus controlling the movement direction of the actuator. Common ones include directional valves (such as electromagnetic directional valves) and one-way valves.

# 2. Classification by structural form

Structurally, hydraulic valves can be divided into the following categories:

-Slide valve: the liquid flow path is changed by the sliding of the valve core in the valve body, which is suitable for occasions requiring continuous adjustment.
-Ball valve and cone valve: the on-off control is realized by the rotation or movement of the ball or cone valve core, which has good sealing performance.
-Cartridge valve: The valve installed in the manifold block has the characteristics of compact structure, quick response and easy combination, and is widely used in modern hydraulic system design.

# 3, according to the control mode classification

According to the control mode, hydraulic valves can be divided into:

-Manual valve: It depends on manual operation, such as manual reversing valve.
-Mechanical control valve: driven by mechanical displacement or force, such as travel valve.
-Hydraulic control valve: using hydraulic pressure as control signal, such as hydraulic directional control valve.
-Electro-hydraulic control valve: Combining electrical and hydraulic control, such as electromagnetic directional valve, electro-hydraulic proportional valve and servo valve, it has the advantages of high precision and quick response.
-Proportional valve and servo valve: used in precise control occasions, which can realize continuous adjustment and high dynamic response.

# 4. Classification by connection mode

The connection mode of hydraulic valves is also one of the classification standards, mainly including:

-Tubular connection
-Plate connection
-Plug-in connection
-Overlapping connection

Different connection methods adapt to different system layout and installation requirements.

# 5, standardization system

At present, ISO standards are mainly adopted in the world (such as ISO 1219 on graphic symbols of fluid transmission systems), while China mainly follows GB/T series standards (such as GB/T 786.1 Graphic symbols and circuit diagrams of fluid transmission systems and components). These standards unify the graphic symbols, naming rules, performance parameters and testing methods of hydraulic valves, which is convenient for technical exchange and product exchange around the world.

# Conclusion

As the core control component in hydraulic system, the classification standard of hydraulic valve not only contributes to the standardization and serialization of products, but also provides great convenience for engineering design and maintenance. With the continuous improvement of industrial automation level, the types and functions of hydraulic valves are also developing, and the future standardization work will pay more attention to the development of intelligence, modularization, energy saving and environmental protection.