As a key control element in hydraulic system, servo valve is widely used in high precision and high response control system. In large-flow application scenarios, such as large-scale construction machinery, aerospace, ship propulsion system, etc., it is particularly important to choose a large-flow servo valve with appropriate diameter. Reasonable path can not only ensure the response speed and stability of the system, but also effectively reduce energy consumption, heat generation and system pressure loss. Therefore, scientifically determining the size of large-flow servo valve is an indispensable and important link in the design of hydraulic system.
First, the basic principles of path selection
The selection of path mainly depends on the flow rate, working pressure, fluid properties and dynamic response requirements of the system. Generally speaking, the rated flow of servo valve should be slightly higher than the maximum flow required by the system to ensure good control performance under high load conditions. At the same time, the selection of diameter should also avoid pressure loss and cavitation caused by high flow rate and prevent damage to valve body and system components.
Second, the main factors affecting the path
1. Maximum working flow
When designing the system, the minimum diameter of the servo valve should be calculated according to the maximum required flow of the actuator (such as hydraulic cylinder or motor). It is generally recommended that the rated flow rate of the valve is 1.2~1.5 times of the maximum flow rate of the system, so as to leave a certain safety margin.
2. System working pressure and pressure drop
In high-pressure system, the actual flow capacity of servo valve at rated pressure drop should be considered. Too small a path diameter will increase the pressure difference between the front and rear of the valve, affect its control accuracy and efficiency, and even cause system instability.
3. Response speed requirements
For the system with high dynamic response, increasing the path appropriately can improve the response speed of the system, but it will also increase the control difficulty and cost. Therefore, there is a trade-off between performance and cost.
4. Medium characteristics
The viscosity and cleanliness of hydraulic oil will also affect the flow state, so different requirements are put forward for the diameter. For example, the diameter of high viscosity oil should be appropriately increased to reduce the resistance.
Third, the path calculation method
Generally, the following formula is used for preliminary estimation:
$$
Q = C_v cdot sqrt{frac{Delta P}{
ho}}
$$
Among them:
-$ Q $: flow (l/min);
-$ C_v $: flow coefficient;
-$ Delta P $: pressure drop (MPa);
-$
ho $: hydraulic oil density (kg/m);
Based on the known system flow and pressure drop, the required $ C_v $ value is deduced, and the appropriate size is selected by combining the sample data of the servo valve.
Iv. Selection Suggestions and Precautions
1. Refer to the manufacturer’s sample: the flow-path relationship of different brands of servo valves is different, so the selection should be based on the technical parameters provided by the manufacturer.
2. Simulation verification: With the help of hydraulic simulation software (such as AMESim, MATLAB/Simulink), the system is modeled and analyzed to verify whether the path meets the dynamic performance requirements.
3. Consider redundancy design: In important systems, products with larger diameters can be appropriately selected to improve system reliability and service life.
4. Regular maintenance and management: Large-flow servo valves are sensitive to the cleanliness of oil, and must be equipped with an efficient filtration system to regularly detect the oil quality and the state of the spool.
V. Conclusion
To sum up, the determination of the size of large-flow servo valve is a systematic project that comprehensively considers flow, pressure, response speed and medium characteristics. Designers need to make scientific calculation according to actual working conditions, and make reasonable selection by combining simulation analysis with manufacturer’s data to ensure the efficiency, stability and reliability of system operation. With the continuous development of hydraulic technology, the performance of servo valve is also improving, and its application in large flow and high response system will be more extensive and in-depth in the future.