What are the specific classifications of electric actuators?

I. Electric Multi-Turn Actuators
Electrically driven multi-turn actuators are one of the most commonly used and reliable types of actuators. A single- or three-way electric motor drives a gear or worm gear, which in turn drives a valve stem nut. The valve stem nut causes the valve stem to move, opening or closing the valve.

Multi-turn electric actuators can quickly drive large-size valves. To protect the valve from damage, a limit switch installed at the end of the valve stroke cuts off the motor power. Simultaneously, a torque sensor cuts off the motor power when the safety torque is exceeded. A position switch indicates the valve's open/closed state, and a handwheel mechanism with a clutch allows for manual valve operation in case of power failure.

The main advantage of this type of electric actuator is that all components are housed within a single, waterproof, dustproof, and explosion-proof enclosure, integrating all basic and advanced functions. The main disadvantage is that in the event of a power failure, the valve can only remain in its original position; a fail-safe position can only be achieved using a backup power system.

II. Electric Single-Turn Actuator
This actuator is similar to an electric multi-turn actuator, the main difference being that the final output is a 1/4 turn, or 90-degree motion. New generation electric single-turn actuators combine most of the complex functions of multi-turn actuators, such as high-temperature solenoid valves, using a non-entry, user-friendly interface for parameter setting and diagnostics.

Single-turn gas solenoid valve actuators are compact and can be installed on small valves. They typically have an output torque of up to 800 Nm. Furthermore, due to their lower power requirements, they can be battery-powered for fail-safe operation.

III. Fluid-Driven Multi-Turn or Linear Output Actuators
This type of actuator is frequently used to operate straight-through valves (gate valves) and shut-off valves. They use pneumatic or hydraulic operation. They are simple in structure, reliable in operation, and easily implement fail-safe operation.

Generally, electric multi-turn actuators are used to drive gate valves and shut-off valves; hydraulic or pneumatic actuators are only considered when there is no power supply.

IV. Fluid-Driven Single-Turn Actuators
Pneumatic and hydraulic single-turn actuators are very common. They do not require a power supply, have a simple structure, and are reliable. They have a wide range of applications. Output typically ranges from a few kilograms per meter to tens of thousands of kilograms per meter. Magnetic level gauges use cylinders and transmission devices to convert linear motion into right-angle output. Transmission devices typically include: forks, racks and pinions, and levers. Racks and pinions output the same torque throughout the entire stroke, making them suitable for small-diameter valves. Forks have higher efficiency and high torque output at the beginning of the stroke, making them suitable for large-diameter valves. Pneumatic actuators generally use accessories such as solenoid valves, positioners, or position switches to control and monitor valves.