Classification of pneumatic actuators and identification of quality grades

Actuators are divided into three categories according to the form of energy: pneumatic actuators, electric actuators andHydraulic Actuators, they have their own characteristics, respectively, suitable for different occasions, pneumatic actuators refer to the use of air pressure as the driving force to drive or mediate the valve of the actuator, pneumatic actuators are a more widely used category of actuators. In the future, pneumatic actuators account for 50% of the types of actuators.
Pneumatic Actuators have membrane type and piston type according to the different actuators. Fork type and rack and pinion type, their formation and torque are more different, among which the rack and pinion typePneumatic Actuatorhas a wide range of applications in petroleum, chemical and power generation industries with high safety requirements because of its simple structure, safety and explosion-proof characteristics.

1. Membrane actuator
Diaphragm actuator is the most commonly used imported pneumatic actuator, which can be used as a pushing device for generalControl Valves to form a pneumatic diaphragm actuator. The signal pressure p of the pneumatic diaphragm actuator acts on the diaphragm to deform it, drives the push rod on the diaphragm to move, and displaces the valve core, thereby changing the opening of the valve. It has simple structure, cheap price, easy maintenance and wide application.
Pneumatic membrane actuators are available in two forms: positive and reactive.
When the signal pressure from the controller or valve positioner increases, the downward action of the valve stem is called the positive action actuator; When the signal pressure increases, the valve stem moves upwards is called a reaction actuator. The signal pressure of the positive-acting actuator is through the membrane air chamber above the corrugated diaphragm; The signal pressure of the reaction actuator is through the membrane air chamber below the corrugated diaphragm. By replacing individual parts, the two can be retrofitted with each other.
Pneumatic actuators can also be divided into two types: single-acting and double-acting according to the air source drive mode: the switching action of the actuator is driven by the air source, which is called DOUBLE ACTING. The switching action of SPRING RETURN (single acting) is only driven by air when it is on, and the spring returns when it is closed.

2.Piston Actuator
The pneumaticPiston Actuatorcauses the piston to move in the cylinder to generate thrust, and obviously, the output force of the piston type is much greater than that of the diaphragm type. Therefore, the film type is suitable for occasions with small output and high precision; The piston type is suitable for applications with large output forces, such as large diameters, high pressure drop control or push devices for butterfly valves. In addition to the diaphragm type and piston type, there is also a long-stroke actuator, which has a long stroke and large torque, and the piston type imported pneumatic actuator is suitable for the occasion of output angular displacement and high torque.
The standard for the signal received by the pneumatic actuator is 0.02 to 0.1MPa.
The main components of the pneumatic piston actuator are cylinders, pistons, and push rods. The piston in the cylinder moves with the change in the pressure difference between the two sides of the cylinder. According to the characteristics, it can be divided into two types: proportional and two-digit. The two-position type pushes the piston from the high-pressure side to the low-pressure side according to the amount of operating pressure on both sides of the input piston. The proportional type is based on the two-position type with a valve positioner, so that the displacement of the push rod and the signal pressure are proportional.

3. Rack and pinion actuator
Rack and pinion type (double piston rack and pinion type) pneumatic actuator has the characteristics of compact structure, beautiful appearance, fast response, stable operation and long service life. All fittings are treated with the most advanced anti-corrosion treatment technology and can adapt to a variety of harsh working conditions. Its actuators with high and low temperatures and various special strokes have good performance in various applications.
From the perspective of technical performance, pneumatic actuators have many advantages such as large load, fast action and good environmental adaptability, among which the advantages of large load make pneumatic actuators suitable for applications with high torque output. Because pneumatic actuators have so many advantages, the quality of pneumatic actuators on the market is uneven, so how can we distinguish the quality of pneumatic actuators from the appearance? Generally speaking, the paint layer or chemical treatment layer on the outer surface of a good pneumatic actuator will be smooth and smooth, and the color of the surface will be very uniform, while the pneumatic actuator with poor texture is just the opposite, because the small manufacturer is convenient in the production process diagram and saves many steps.