How should one choose between on-off and control types of electric valve actuators? The price difference is huge depending on the function!

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In industrial automation control systems, electric valves serve as the core actuating elements for medium transfer and parameter regulation; the rationality of their selection directly affects the stability, accuracy, and cost-efficiency of system operation. Depending on the control requirements, electric valves are mainly divided into two categories: on-off type and control type. There are significant differences between the two in terms of structural design, working principle, control method, and application scenarios. This article will provide an in-depth technical analysis of these differences and offer tailored selection recommendations to assist in making accurate choices for industrial applications. In terms of core functions and working principles, the essential difference between on-off and control-type electric valves lies in \"control precision\" and \"operating state\". The primary function of a on-off electric valve is to enable or disable the flow of fluid; it has only two fixed operating states: \"fully open\" and \"fully closed\". It functions similar to a light switch in an electrical circuit – precise control over the degree of opening is not required, as long as the flow can be switched on or off. Its actuators are typically ordinary asynchronous motors equipped with limit switches; when the valve reaches the fully open or fully closed position, the limit switch sends a signal that causes the motor to stop running. It features a simple structure and a straightforward control logic, requiring no complex feedback or adjustment mechanisms. Adjustable electric valves focus on precise control of medium parameters; they can maintain the valve opening at any position within the 0–100% range in accordance with the instructions from the control system, thereby enabling continuous adjustment of process parameters such as flow rate, pressure, liquid level, and temperature. The actuator’s core is equipped with a servo positioning module and a precise position feedback device; it is capable of receiving analog control signals in the 4-20mA or 0-10V range sent by PLC or DCS systems. At the same time, it sends back the actual valve position as a feedback signal to the control system, thereby enabling closed-loop control. This ensures high precision and stability in valve opening adjustment, with a fast response time, and the adjustment error can be kept within ±1%. In terms of structural composition, the differences between the two mainly lie in the actuator and the control module. Switch-type electric actuators do not have a positioning function; they consist only of a drive motor, a reduction mechanism, and travel limit switches. Some simpler models even lack valve position feedback functionality. Their manufacturing cost is low, and their failure rate is relatively low as well. Adjustable electric actuators build on the basic switch-type design by adding core components such as servo amplifiers and position sensors (such as potentiometers and encoders). Some high-end models also come equipped with functions like overload protection and power-off reset; their structure is more complex and they require higher manufacturing standards, which is why their cost is much higher than that of switch-type actuators. In terms of control signals and operating conditions, on-off electric valves use digital control (such as relay signals), requiring only two commands – “on” and “off”. They are suitable for applications that do not need parameter adjustment and only require on/off control, such as industrial wastewater discharge, gas transmission, equipment bypass switching, and pipeline maintenance shutdowns. Common valve types include gate valves, globe valves, and ordinary ball valves; no special requirements are placed on the flow profile. Adjustable electric valves use analog control and can be integrated into automated control systems for continuous adjustment. They are suitable for applications where high precision in process parameters is required, such as flow rate regulation in chemical manufacturing, temperature stabilization in thermal systems, maintaining constant liquid levels in water treatment, and pressure control in the petrochemical industry. The valve body used in such applications must possess good flow characteristics; valves with equal percentage or linear flow characteristics, such as control butterfly valves, V-ball valves, and eccentric hemispherical valves, are preferred, to ensure a linear relationship between the degree of opening and the flow rate, thereby improving the accuracy of regulation. During the selection process, it is necessary to make a comprehensive assessment based on operational requirements, control accuracy, and cost considerations: if only the on/off operation of the medium is required without any need for parameter adjustment, switch-type electric valves should be preferred, as this helps to reduce equipment costs and maintenance difficulties ； To achieve precise control of parameters such as flow rate and pressure and to integrate with automated systems, regulated electric valves must be used, with the corresponding control signals matched to the valve’s flow characteristics. In addition, factors such as medium type, operating pressure, and pipe diameter also need to be considered to prevent system malfunctions resulting from improper selection. In summary, on-off and control type electric valves are not one better than the other; rather, they are two types of core actuating elements designed to suit different operating conditions. Only by clarifying the technical differences between the two and selecting the appropriate option based on actual process requirements can the advantages of electric valves be fully utilized, thereby improving the operational efficiency and stability of industrial automation systems and reducing maintenance costs.