How does the equal percentage regulating valve curve

In industrial automation control systems, the regulating valve acts as an actuator, and its performance directly affects the control effect of the system. The equal percentage (Equal Percentage) regulating valve is widely used in the field of process control due to its unique flow characteristics. This article will focus on the characteristic curve, working principle, and application advantages of the equal percentage regulating valve.

Basic Concept of Equal Percentage Regulating Valve

What is meant by 'equal percentage' is that the percentage change in flow of a regulating valve remains constant when its opening changes. Specifically, when the opening of the valve changes by equal percentage, the change in flow is a fixed percentage of the flow at the previous opening. This characteristic allows the regulating valve to have a smaller gain at low openings and gradually increase the gain as the opening increases, thus maintaining high stability and sensitivity during the control process.

Two, Mathematical Expression of Equal Percentage Control Valve

The flow characteristics of the equal percentage control valve can be expressed by the following formula:


Q = Q_max * (R - 1)/R)^x


Among which:
- Q: The flow at a certain opening;
- Q_max: The maximum flow when fully open;
- R: Rangeability (Rangeability), that is, the ratio of the maximum controllable flow to the minimum controllable flow;
- x: The relative opening of the valve, ranging from 0 to 1.

From the formula, it can be seen that as the opening x increases, the flow shows an exponential growth trend, which is the key difference between the equal percentage valve and the linear valve.

Three, Characteristics of Equal Percentage Curves

Different from the linear control valve's 'flow varies proportionally with opening', the flow-opening curve of the equal percentage valve is an exponential curve. Initially when the valve is opened, the flow change is slow, and as the opening increases, the flow rises rapidly. This characteristic makes it particularly suitable for conditions with large load changes and large system gain changes.

In practical applications, when there are nonlinear objects in the control loop, the use of equal percentage valves can compensate for the nonlinear characteristics of the objects, thereby improving control accuracy and stability.

Four, Application Advantages of Equal Percentage Valves

1. Good stability: In the small opening area, the flow change is small, which avoids the system from experiencing severe fluctuations due to minor adjustment actions;
2. High control accuracy: In the large opening area, the regulation is sensitive, and the response is rapid;
3. Strong adaptability: Suitable for a variety of complex operating conditions, such as temperature control, pressure regulation, and liquid level control, etc.;
4. Significant energy-saving effect: By reasonably selecting the adjustable ratio R, energy consumption can be reduced while ensuring control performance.

Five, Selection and Usage Recommendations

When selecting an equal percentage control valve, it should be determined reasonably according to the actual needs of the system, the adjustable ratio parameter R, and matched with the output capacity of the actuator. In addition, factors such as the nature of the medium (such as viscosity, corrosiveness), working temperature, and pressure should also be considered to ensure the reliability and safety of the valve during long-term operation.

Six, Conclusion

In summary, the equal percentage control valve, with its superior flow characteristics and wide application adaptability, has become an indispensable and important component in modern process control. By deeply understanding its characteristic curve and working principle, and combining with scientific selection based on actual operating conditions, it can effectively improve the stability and operation efficiency of the control system, providing strong support for enterprises to achieve intelligent and refined management.