Proportional Control Valves
Advanced hydraulic control components that bridge the gap between on-off electro-hydraulic control elements and servo-type electro-hydraulic control elements
Introduction to Proportional Control Valves
A proportional control valve is a type of hydraulic control valve that can make the parameters of the output oil (pressure, flow, and direction) change proportionally with the input electrical signal parameters (current, voltage). This innovative hydraulic control element combines the advantages of switching electro-hydraulic control elements and servo-type electro-hydraulic control elements, offering precise control over hydraulic systems with enhanced efficiency.
These valves play a crucial role in regulating hydraulic transmission oil within various industrial systems, ensuring that the flow and pressure of hydraulic transmission oil are maintained at optimal levels for specific operational requirements. The ability to precisely control hydraulic transmission oil parameters makes proportional control valves indispensable in modern hydraulic systems.
Proportional control valve integrated within a complex hydraulic system, controlling the flow of hydraulic transmission oil
Similar to the classification of ordinary hydraulic components, proportional control valves can be categorized based on the types of parameters they control. This includes proportional pressure valves, proportional flow valves, proportional directional valves, and proportional composite valves. The versatility of these valves allows for precise regulation of hydraulic transmission oil in various applications, from simple to complex hydraulic systems.
Another classification method is based on the number of parameters controlled, dividing proportional control valves into single-parameter control valves and multi-parameter control valves. Proportional pressure valves and proportional flow valves fall into the single-parameter control valve category, primarily regulating specific aspects of hydraulic transmission oil behavior. In contrast, proportional directional composite proportional valves belong to the multi-parameter control valve category, offering more comprehensive control over hydraulic transmission oil characteristics.
Because proportional control valves can make the controlled parameters change proportionally, they can greatly simplify hydraulic systems while significantly improving the precision of the controlled parameters. The emergence of high-performance electro-hydraulic proportional valves has particularly expanded the application scope of proportional control valves, enabling more efficient and accurate control of hydraulic transmission oil in diverse industrial settings.
Basic Structure of Proportional Control Valves
A proportional control valve consists of two main parts: the proportional adjustment mechanism and the hydraulic valve. The former has a relatively special structure and performance different from the solenoid valves commonly encountered, while the latter is very similar to ordinary hydraulic valves. This combination allows for precise electrical control over the hydraulic functions, ensuring accurate regulation of hydraulic transmission oil parameters.
Proportional Adjustment Mechanism
This component converts electrical signals into mechanical displacement or force, providing the precise control input necessary for regulating hydraulic transmission oil. The mechanism's design ensures linearity between input signals and output mechanical actions, critical for accurate proportional control.
Hydraulic Valve Component
Similar to conventional hydraulic valves but designed to work in harmony with the proportional adjustment mechanism, this part controls the actual flow, pressure, and direction of hydraulic transmission oil within the system based on the mechanical input received.
I. Proportional Solenoid
Proportional solenoid valves belong to the category of DC solenoid valves. The attractive force or displacement of a proportional solenoid is directly proportional to the input current, making it an essential component for converting electrical signals into precise mechanical actions that control hydraulic transmission oil parameters.
Figure 5-52a: Structural diagram of a proportional solenoid, highlighting the components that control hydraulic transmission oil flow through precise electromagnetic actuation
In the proportional solenoid structure, the coil is installed in the housing and fixedly connected to the pole piece. A spacer ring concentrates the magnetic lines of force in the magnetic circuit between the armature, air gap, and pole piece, enabling the pole piece to generate a relatively large attractive force on the armature. This design ensures efficient conversion of electrical energy to mechanical force, critical for accurate control of hydraulic transmission oil.
The armature can slide freely within the guide sleeve. An adjusting screw is used to adjust the thrust of the spring, thereby adjusting the output characteristics of the armature. The electromagnetic force generated by the armature pushes the valve core through the push rod, directly influencing the flow and pressure of hydraulic transmission oil in the system.
The electromagnetic force generated by the armature is directly proportional to the current input into the coil, creating a linear relationship between electrical input and mechanical output. This linearity is fundamental to the proportional control of hydraulic transmission oil parameters, allowing for precise and predictable system behavior.
Key Advantages of Proportional Solenoids
- Linear relationship between input current and output force/displacement
- Precise control over hydraulic transmission oil parameters
- Compact design suitable for integration into various valve configurations
- High repeatability ensuring consistent performance
- Energy-efficient operation compared to alternative actuation methods
II. Electro-Hydraulic Proportional Valves
There are many types of proportional valves, and almost all types and functions of ordinary hydraulic valves have corresponding types and functions of electro-hydraulic proportional valves. These valves are specifically designed to control the behavior of hydraulic transmission oil with high precision, adapting to varying operational demands through electrical signal input.
Electro-hydraulic proportional valve with visible electrical connections for signal input and hydraulic ports for hydraulic transmission oil
Cutaway view revealing internal structure of an electro-hydraulic proportional valve, demonstrating how hydraulic transmission oil is controlled
Classification by Function
According to different functions, electro-hydraulic proportional valves can be divided into electro-hydraulic proportional pressure valves, electro-hydraulic proportional directional valves, electro-hydraulic proportional flow valves, and composite function valves. Each type is designed to control specific aspects of hydraulic transmission oil behavior, providing tailored solutions for various hydraulic system requirements.
| Valve Type | Primary Function | Key Application |
|---|---|---|
| Electro-hydraulic Proportional Pressure Valves | Control pressure of hydraulic transmission oil | Presses, clamping systems |
| Electro-hydraulic Proportional Directional Valves | Control flow direction of hydraulic transmission oil | Material handling, robotics |
| Electro-hydraulic Proportional Flow Valves | Control flow rate of hydraulic transmission oil | Speed control in machinery |
| Composite Function Valves | Control multiple parameters of hydraulic transmission oil | Complex industrial machinery |
Classification by Feedback Method
According to the feedback method, electro-hydraulic proportional valves can be further divided into those without displacement electrical feedback and those with displacement electrical feedback. This classification is crucial as it directly impacts the precision and performance characteristics of the valve in controlling hydraulic transmission oil.
Without Displacement Electrical Feedback
These valves use ordinary proportional solenoids, offering simpler control, lower cost, and reduced current requirements which simplifies the electrical circuitry. However, their performance in terms of power parameters and repeatability is relatively poor when controlling hydraulic transmission oil.
Suitable for: Control systems with lower requirements
With Displacement Electrical Feedback
These valves offer higher control precision and better dynamic characteristics, making them ideal for applications requiring accurate regulation of hydraulic transmission oil parameters. The feedback mechanism allows for continuous adjustment and correction, ensuring consistent performance.
Suitable for: Various control systems with higher requirements
Due to space limitations, we will focus on several representative electro-hydraulic proportional valves to provide a comprehensive understanding of these components. Each type offers unique advantages in controlling hydraulic transmission oil, and selecting the appropriate valve depends on the specific application requirements, performance needs, and budget constraints.
III. Applications of Proportional Valves
Like ordinary hydraulic valves, proportional valves are widely used in engineering practice across various industries. Their ability to precisely control hydraulic transmission oil parameters makes them invaluable in applications requiring accurate, responsive, and efficient hydraulic systems. From manufacturing machinery to mobile equipment, proportional valves enhance performance while reducing energy consumption and system complexity.
1. Applications of Proportional Pressure Valves
When using proportional valves to control a circuit, there are generally two approaches: one is to use proportional pressure valves to control ordinary pressure valves; the other is to use specially designed and manufactured pilot-operated proportional pressure valves for direct pressure control. Both methods effectively regulate the pressure of hydraulic transmission oil, but each offers distinct advantages depending on the application scenario.
Industrial hydraulic system incorporating proportional pressure valves for precise control of hydraulic transmission oil pressure
The first approach uses the proportional pressure valve as a pilot stage, connected to the pilot port of an ordinary pressure valve to indirectly adjust the working pressure of the ordinary pressure valve. This method features smaller proportional valves, lower cost, smaller control current, and simplified circuitry. However, due to the influence of the ordinary main valve's performance, the circuit control precision for hydraulic transmission oil is not as high, and the circuit has more pipelines.
The latter method, using specially designed valves, ensures better performance and higher control precision over hydraulic transmission oil pressure but comes with a higher cost. This approach is preferred in applications where precise pressure control is critical to operational success, such as in precision machining, material testing, and automated manufacturing processes where consistent hydraulic transmission oil pressure directly impacts product quality and process reliability.
2. Proportional Speed Control Circuits
Figure 5-58 shows a comparison between a speed control circuit using an ordinary flow valve and one using a proportional flow valve. The diagram clearly illustrates the advantages of proportional valves in simplifying system design while improving performance in controlling hydraulic transmission oil flow rates.
Figure 5-58a: Multi-stage speed control circuit using ordinary flow valves, requiring numerous components to regulate hydraulic transmission oil
Figure 5-58b: Multi-stage speed control circuit using a proportional flow valve, demonstrating simplified design for controlling hydraulic transmission oil
As can be seen from the figures, to achieve multi-stage speed control for the actuating element, using ordinary flow valves requires more hydraulic components, resulting in a complex system with lower efficiency that can only achieve several discrete speed levels. This complexity increases energy consumption and maintenance requirements while reducing the precision of hydraulic transmission oil control.
In contrast, using a proportional flow valve can greatly simplify the system while offering infinitely variable speed control within the valve's range. This simplification reduces the number of components, lowers energy consumption, and improves system reliability. The precise control over hydraulic transmission oil flow rates enables smoother operation, increased efficiency, and better overall performance of the hydraulic system.
Advantages of Proportional Valves in Industrial Applications
- Reduced system complexity through fewer components while maintaining precise control of hydraulic transmission oil
- Improved energy efficiency by optimizing hydraulic transmission oil flow and pressure according to real-time demands
- Enhanced control precision enabling better product quality and process repeatability
- Greater flexibility in system operation through easy adjustment of hydraulic transmission oil parameters
- Reduced maintenance requirements due to simplified system design and optimized hydraulic transmission oil flow
- Improved safety through more precise control over hydraulic transmission oil in critical operations
3. Emerging Applications in Modern Industry
With advancements in control technology, proportional control valves are finding new applications in emerging industrial sectors. Their ability to precisely meter hydraulic transmission oil makes them ideal for renewable energy systems, such as in the control mechanisms of wind turbines and solar tracking systems. In these applications, proportional valves ensure efficient operation by maintaining optimal hydraulic transmission oil parameters under varying environmental conditions.
Another growing application area is in mobile hydraulic systems, where proportional valves contribute to improved fuel efficiency and performance. Construction equipment, agricultural machinery, and material handling vehicles benefit from the precise control of hydraulic transmission oil, resulting in smoother operation, reduced operator fatigue, and lower maintenance costs.
The integration of proportional control valves with digital control systems and industrial IoT (Internet of Things) platforms is further expanding their capabilities. This connectivity allows for real-time monitoring and adjustment of hydraulic transmission oil parameters, predictive maintenance, and performance optimization. As industries continue to embrace automation and smart manufacturing, the role of proportional control valves in ensuring precise, efficient control of hydraulic transmission oil will only become more critical.
Conclusion
Proportional control valves represent a significant advancement in hydraulic system technology, offering precise control over hydraulic transmission oil parameters through electrical signal input. By combining the advantages of on-off valves and servo valves, they provide an optimal balance of performance, cost-effectiveness, and simplicity in a wide range of applications.
From simple pressure control to complex multi-parameter regulation, proportional valves continue to evolve, enabling more efficient, accurate, and reliable hydraulic systems. Their ability to precisely control hydraulic transmission oil ensures that modern industrial machinery operates at peak performance while minimizing energy consumption and maintenance requirements.