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The working principle and function of proportional valve

Author: Hou

Feb. 07, 2024

Proportional valves are a technical solution developed to solve those complex oil circuits. These revolutionary hydraulic proportional valves allow for continuous positioning of the spool, thereby providing continuously adjustable flow. Stroke-controlled or force-controlled solenoid coils are used to achieve continuous positioning of the spool.

This variable positioning method allows the valve core to be designed as a metering groove, integrating flow/speed control and direction control functions into one valve body, without the need to add separate valve bodies for direction control and speed control. Another major benefit is that when the oil circuit requires more than one speed, by changing the electrical signal level to provide the required flow/speed, different speed adjustments can be achieved without the need for additional hydraulic components. The proportional valve is composed of a DC power control.

Proportional controls, used together with their associated electronic controls, also provide ideal acceleration and deceleration characteristics. This feature provides a variety of machine cycles that allow the machine to operate safely at higher speeds but with controlled start and stop characteristics. Adjusting acceleration and deceleration can improve the overall cycle time and productivity of the entire machine.

The working principle of the proportional valve is very simple. In fact, there are still a lot of details to be done if you want to make a proportional valve. The casting requirements for the valve body are very high. Generally, hydraulic valves have to withstand high pressures. Generally, cast iron will suffer when the internal pressure is high. Leakage occurs, which is what we often call "sweating".

The valve cavity and valve core require high machining accuracy, roundness, and coaxiality of different cylindrical surfaces, because the cooperation between the valve core and the valve body must ensure both good sealing performance and low friction. Once the roundness is Or if the coaxiality error is large, the valve core may get stuck during operation. Once the proportional valve is stuck, it may fail.

Lets talk about springs. Proportional valves have very high requirements for spring stiffness. The dispersion of spring stiffness of the same batch must be controlled within a small range. Once the spring stiffness dispersion is large, the characteristics of the proportional valve will change. The input voltage signal or current intensity of the valve is proportional to the flow rate or pressure of the proportional valve. This proportional relationship is based on a relatively fixed spring stiffness. If the spring stiffness changes over time, the characteristics of the proportional valve will also change. Changed, so a good proportional valve needs to be able to maintain this proportional relationship after working for a long time.

The purpose of using proportional valves or servo valves is to achieve throttling control of flow through electronic control (of course, pressure control can also be achieved through structural changes). Since it is throttling control, there must be energy loss. Servo valves Different from other valves, its energy loss is larger because it requires a certain flow rate to maintain the work of the pre-stage control oil circuit. Proportional valves are mostly used for open-loop control; secondly, there are many types of proportional valves, including proportional pressure, flow control valves, etc. The control is more flexible than servo. Automatic control can be divided into intermittent control and continuous control. Intermittent control is switch control. In the pneumatic control system, a switch-type (ON-OFF) reversing valve with a low operating frequency is used to control the on-off of the air path. The pressure reducing valve is used to adjust the required pressure, and the throttle valve is used to adjust the required flow rate. If this traditional pneumatic control system wants to have multiple output forces and multiple movement speeds, it requires multiple pressure reducing valves, throttle valves and reversing valves. In this way, not only are many components required, the cost is high, and the system is complex, but many components also need to be manually adjusted in advance. Electric proportional valve control is a continuous control, and its characteristic is that the output changes with the change of the input, and there is a certain proportional relationship between the output and the input. Proportional control can be divided into open-loop control and closed-loop control. The valve opening size of the proportional directional valve is controlled proportionally by the input signal, and the proportional valve spool is adjusted by a position sensor. Proportional directional valves are suitable for control systems and control loops. Proportional directional valves are available with valve-mounted amplifiers. For proportional directional valves without this type of amplifier, different external control amplifier options are available. The three-position four-way proportional directional valve is combined with a pilot check valve and is suitable for controlling single-acting hydraulic cylinders. Proportional relief valves control the maximum pressure of the system in proportion to the input signal. Proportional pressure reducing valve controls secondary pressure. Proportional pressure reducing valves and proportional relief valves are available as direct-acting valves or pilot-operated valves. The 2-way pressure compensator and the 3-way pressure compensator maintain a constant pressure drop and are matched with the integrated load-sensitive directional valve and are provided in the form of superimposed valve plates.

Electro-hydraulic proportional valve is referred to as proportional valve. Ordinary hydraulic valves can only control the pressure and flow of liquid flow at fixed values through pre-adjustment. However, when the equipment mechanism requires the pressure and flow parameters of the hydraulic system to be adjusted or continuously controlled during the work process, for example, the workbench is required to feed at a continuously changing speed of slow, fast, and slow during work, or at a certain speed. Accurately simulate an optimal control curve to achieve brigade force control. Ordinary hydraulic valves cannot achieve this. At this time, an electro-hydraulic proportional valve can be used to control the hydraulic system.





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