Classification of Pneumatic Actuators

Pneumatic actuators are actuators that use pneumatic power to drive the opening and closing or adjustment of valves, also known as pneumatic actuators or pneumatic devices, but are often referred to as pneumatic heads. The actuator and adjustment mechanism of the pneumatic actuator are integrated, and there are diaphragm type, piston type, shift fork type and rack and pinion type actuators. The piston type has a longer stroke and is therefore suitable for situations where higher thrust is required. On the other hand, the diaphragm travel is small and can only drive the valve stem directly. Fork-type pneumatic actuators are characterized by high torque, small space, and a torque curve that matches that of the valve, but they are not very pretty and are typically used for high torque valves. The rack and pinion pneumatic actuator has the advantages of simple structure, stable and reliable operation, safety and explosion-proof, and has been widely used in power plants, chemical industry, oil refining and other manufacturing processes that require high safety. 1. Membrane actuators Membrane actuators are commonly used and can be used as general-purpose control valve drivers to form pneumatic diaphragm actuators. The signal pressure p of the pneumatic diaphragm actuator acts on the diaphragm, which deforms the diaphragm, drives the push rod of the diaphragm to move the valve core, and changes the opening of the valve. It has the characteristics of simple structure, low price, convenient 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 positive actuator, and 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 actuator moves the piston in the cylinder to generate thrust. Obviously, the power of the piston type is much higher than that of the film 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 devices, etc. In addition to diaphragm type and piston type, there are also long-stroke, high-torque long-stroke actuators, which are suitable for outputting large torque of angular displacement. Pneumatic actuators receive 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 according to the pressure difference across the cylinder. According to the 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 working 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 speed, stable operation and long service life. All accessories use the most advanced anti-corrosion technology, which can adapt to various harsh working conditions. Its high and low temperature and various special stroke actuators provide excellent performance in various application fields.