Introduction To The Classification Of Pneumatic Actuators

A pneumatic actuator is an actuator that uses pneumatic power to drive the opening and closing or adjustment of a valve. It is also called a pneumatic actuator or a pneumatic device, but is usually called a pneumatic head. The actuator and adjustment mechanism of the pneumatic actuator are a whole, including diaphragm type, piston type, fork type and rack and pinion type actuators.

The piston type has a longer stroke and is therefore suitable where greater thrust is required. On the other hand, the diaphragm has a small stroke and can only directly drive the valve stem. Fork-type pneumatic actuators are characterized by high torque, small space, and the torque curve matches that of the valve, but they are not very beautiful and are usually used for high-torque valves. Rack-and-pinion pneumatic actuators have the advantages of simple structure, stable and reliable operation, safety, and explosion-proof. They have been widely used in power plants, chemical industries, oil refining and other manufacturing processes with high safety requirements.

1. Thin film actuator

Diaphragm actuators are commonly used and can be used as universal control valve drivers to form pneumatic diaphragm actuators. The signal pressure p of the pneumatic diaphragm actuator acts on the diaphragm, deforming the diaphragm, driving the push rod of the diaphragm to move the valve core, and changing the opening of the valve. It has the characteristics of simple structure, low price, easy maintenance and wide application range.

Pneumatic diaphragm actuators come in two forms: direct acting and reverse acting. When the signal pressure from the controller or valve positioner increases, the downward movement of the valve stem is called a forward actuator, while when the signal pressure increases, the upward movement of the valve stem is called a reaction actuator. The signal pressure of the positive actuator is transmitted to the diaphragm air chamber above the corrugated diaphragm, and the signal pressure of the reaction actuator is transmitted to the diaphragm air chamber below the corrugated diaphragm. Both can be retrofitted by swapping individual parts.

2. Piston actuator

Pneumatic piston actuators move a piston within a cylinder to create thrust. Obviously, the power of the piston type is much higher than that of the diaphragm type. Therefore, the diaphragm type is suitable for low output and high precision, while the piston type is suitable for large diameter, high pressure drop control, butterfly valve extrusion device, etc. In addition to diaphragm type and piston type, there are also long-stroke actuators with long stroke and large torque, which are suitable for outputting angular displacement and large torque.

The pneumatic actuator receives signals from 0.02 to 0.1MPa.

The main components of a pneumatic piston actuator are the cylinder, piston and push rod. The piston in the cylinder moves based on the pressure difference on either side of the cylinder. According to characteristics, it can be divided into two types: proportional type and two-position type. In the two-position type, the piston is pushed from the high-pressure side to the low-pressure side according to the operating pressure on both sides of the input piston. The proportional type adds a valve positioner on the basis of the 2-position type, so that the displacement of the push rod is proportional to the signal pressure.

3. Rack and pinion actuator

Rack-and-pinion (double-piston rack-and-pinion) pneumatic actuator has compact structure, beautiful appearance, fast response, stable operation, and long service life. All accessories adopt the most advanced anti-corrosion technology and can adapt to various harsh working conditions. Its high and low temperature and various special stroke actuators provide excellent performance in a variety of applications.