新闻中心

24

2023

-

04

Comparative analysis of three types of valve actuators

Classification:


【Summary description】A large number of valves are needed to control fluid movement in fields such as environmental protection, water conservancy, petrochemicals, metallurgy, papermaking, power, aerospace, pipelines, industrial equipment, and industrial processing. The driving device that controls the opening, closing, or partial opening of a valve is usually referred to as a valve actuator or valve driver. As the terminal actuator for valve control, the reliability, controllability, and functionality of the actuator directly affect the success or failure of regulation and control results, as well as the safety of the equipment, and restrict the overall level of automation.

A large number of valves are needed to control fluid movement in fields such as environmental protection, water conservancy, petrochemicals, metallurgy, papermaking, power, aerospace, pipelines, industrial equipment, and industrial processing. The driving device that controls the opening, closing, or partial opening of a valve is usually referred to as a valve actuator or valve driver. As the terminal actuator for valve control, the reliability, controllability, and functionality of the actuator directly affect the success or failure of regulation and control results, as well as the safety of the equipment, and restrict the overall level of automation.

Traditional actuators are divided into three types: electric, pneumatic, and hydraulic, as well as derived gas-liquid combination and electro-hydraulic combination drive. Each type of drive has its own advantages and disadvantages. This article briefly explains the advantages and disadvantages of electric, pneumatic, and hydraulic drives, making it easy for everyone to quickly understand.

1: Electric actuator

Electric actuators, as the name suggests, are powered by electricity and use single-phase or three-phase motors to drive gears or worm gears to output linear or rotational motion. Electric actuators can output relatively constant driving force, have strong resistance to deviation, and have higher control accuracy than pneumatic actuators. They can automatically maintain position without the need for other auxiliary systems. Electric actuators have the characteristics of simple operation and easy implementation of remote control, but their structure is complex, prone to load failures, often resulting in low positioning accuracy, over opening and closing, motor burning, gear box wear, and high maintenance costs. Adjusting too frequently can cause the motor to heat up and the reduction gear to wear easily. In addition, the electric actuator runs slowly, making it difficult to achieve high driving power, and it is also difficult to achieve overcurrent protection and poor positioning.

2: Pneumatic actuator

The pneumatic actuator is powered by compressed air and has the characteristics of simple structure and convenient maintenance, but it has a large volume and requires an air source and air purification device; The actuating mechanism and regulating mechanism of pneumatic actuators are a unified whole, and their actuating mechanisms include diaphragm type, piston type, fork type, and gear rack type. Using gas as the power medium has the advantage of high safety and low environmental requirements. However, due to the compressibility of the gas, the pneumatic actuator with relatively low stiffness has slow response, poor resolution, low control accuracy, and weak anti deviation ability. When it is applied in the case of large dynamic force or friction, it is very easy to cause adverse vibration of the equipment. And its energy to weight ratio is poor, power density is low, and pneumatic actuators with large driving force are extremely complex, bulky, and expensive.

3: Hydraulic actuator

Ordinary hydraulic actuators are powered by high-pressure oil and have the characteristics of large load capacity and high adjustment accuracy. However, they require a large independent oil supply equipment and relatively large maintenance workload Hydraulic actuator structures include blade type, gear rack type, and screw type actuators. Each of the three has its own advantages and disadvantages. The blade structure has low load-bearing capacity and high oil leakage; The gear and rack type has a large load-bearing capacity, simple structure, large volume, precise positioning of the spiral type, and high processing difficulty. The following figure shows the installation of the gear and rack actuator on the valve. The existing hydraulic actuators usually require the use of a hydraulic station, resulting in their large volume, long hydraulic pipelines, large throttling losses, and inconvenient maintenance.

 

Below, use a table to compare the characteristics of three types of actuators.

Compare items

Electric actuator

Pneumatic actuator

Hydraulic actuator

Torque

Medium

Less

More

Control accuracy

Average accuracy

Low accuracy

High precision

Output stroke

Big

Small

Big

Output speed

Slow

Faster

Fast

Positioning effect

High stability

Poor stability

High stability

Response speed

Slower

Faster

Fast

Install

Simple

Air supply required

Liquid source required

Maintenance

Maintenance required

Less maintenance

Maintenance-free

Operating Distance

Remote

Close range

Remote

Cost

Low

Higher

Tall

 

4: Electrohydraulic actuator

As a power device derived from hydraulic actuators, electro-hydraulic actuators combine hydraulic, control, electromechanical, computer, communication and other technologies to quickly and stably control the position of the controlled object, and are applied to the driving and control of various valves. The electro-hydraulic actuator integrates the hydraulic power module and control module into one. The electro-hydraulic actuator integrates the advantages of simple electrical operation, fast hydraulic power, and reliable electrical control board, with fast response speed, high control accuracy, large output power, and compact structure; At the same time, electro-hydraulic actuators overcome the problems of low control accuracy of pneumatic actuators and poor controllability of electric actuators. There are generally two types of electro-hydraulic actuators: one is controlled by servo valves, which is a traditional electro-hydraulic servo actuator that uses an open hydraulic system to adjust the direction and flow rate of hydraulic oil through the control of servo valves, achieving the adjustment of the controlled object; One type is electric motor control, which uses a closed hydraulic system to control the direction and flow rate of the bidirectional pump pressure oil output by adjusting the direction and speed of the stepper motor or servo motor, and precisely regulate the controlled object.

The new electro-hydraulic actuator has the advantages of simple structure, compactness, small size, stable transmission, large output torque, convenient speed adjustment, easy control, and overload prevention. It has the advantages of overall low price, easy maintenance, and wide applicability.

The control box integrates a hydraulic micro power unit and control board, making the entire actuator intelligent and mini. The above diagram shows an angular stroke electro-hydraulic actuator, while the following diagram shows a straight stroke electro-hydraulic actuator.

Electrohydraulic actuators are important control components in industrial automatic control systems, which can regulate valve pressure, flow rate, temperature, etc. They are widely used in industrial process control systems such as chemical, petroleum, metallurgy, power, coal, etc.

The development of electro-hydraulic actuators is trending towards small size, lightweight, high-efficiency, energy-saving, and high reliability.

Pre

Next

Pre

Next

Related suggestion