Generally, a valve cannot control a process by itself, so they need an operator to place them for controlling a process variable. A special device like an actuator is required to operate valves remotely & automatically to move them. An actuator is one kind of device used to make something operate or move. Actuators are available in three types which are defined by their source of energy and used in industries like Electric, Hydraulic & Pneumatic. So this article discusses an overview of Pneumatic Actuator – working and their applications.
A pneumatic actuator definition is; a type of actuator that is used to change the energy which is in the compressed air form to motion. There are different manufacturers which offer different forms of pneumatic actuators where some actuators convert the energy of compressed air into linear motion & some actuators changes to rotary motion. These actuators have different names in the industry like air cylinders, air actuators & pneumatic cylinders.
A Pneumatic actuator mainly depends on some form of pressurized gas like compressed air which enters into a chamber to build up pressure. Once this air builds up sufficient pressure as compared to the external atmospheric pressure, then it results in the controlled kinetic movement of a device like a gear or a piston. So this resulting movement is directed in either a circular motion or in a straight line. These actuators are one of the most frequently used mechanical devices in a wide range of current industries when compressed gas is converted into energy is extremely controlled and repeatable and reliable.
The pneumatic actuator is constructed by using different components like a spring, compressor, reservoir, diaphragm, and valve. The following diagram represents the construction of a pneumatic actuator. To drive this system, the energy of the fluid is changed to mechanical. In this system, the fresh air is compressed through the compressor & this air is simply stored within the storage reservoir.
Here, a flow control valve is used to control the air direction and its flow speed. The spring unit in this actuator handles the airflow from one place to another & also gives a return stroke toward the piston.
At first, the control valve will stay open & the diaphragm is pulled up through the spring action in the need of air supply. Then the air is drawn from the atmosphere it is filtered by a filter & is given to the compressor. Now, the compressor will compress the air and increases the level of pressure.
Here we have to notice that, when the air pressure level is increased then the temperature of the air is also be increased. Thus, air coolers are utilized to keep the temperature to a modest range. After that, the pressurized air is simply stored within a storage reservoir so that the level of pressure can be maintained. In addition, this pressurized air within the system applies energy to the diaphragm of the pneumatic actuator. Once the force overcomes the spring’s force because of the pressurized air then it keeps the diaphragm at the top to cause the diaphragm moves downward to close the control valve.
When air supply pressure is increased, the diaphragm moves continuously in the down direction & this closes the control valve totally at a particular point. Similarly, once air supply pressure is decreased, then the applied force on the diaphragm by the spring overcomes the force because of the supplied force. This can cause motion in the up direction of the diaphragm to open the control valve.
Here, it is also noted here that the control valve’s position mainly depends on the pressure of air. As a result, the control valve opening & closing is related to the diaphragm’s movement with the pressure of air.
We know that after a controller, actuators are there to provide a control signal for the preferred action to take place. So the air pressure will be changed based on the obtained control signal & this changes the position of the control valve simultaneously. In this way, this actuator works according to the control signal received & drives the process.
There are different types of pneumatic actuators like pistons, rotary vanes & springs, or diaphragms.
This type of pneumatic actuator uses a piston within a cylinder. The piston movement can be caused by simply applying less or more power on one face of the piston.
Single-acting based piston style pneumatic actuator uses a spring on one face & changes force to the other face whereas a Double-acting based piston style pneumatic actuator has air pressure that is applied to both faces of the piston. The piston’s linear motion can be directly used for the actuation of linear motion otherwise it can be changed into rotary motion with a pinion & rack or related mechanical arrangement. These actuators are simply recognized with a diameter of cylinder & length of stroke. A pneumatic actuator with a large cylinder is capable of exerting more force.
The rotary vane type pneumatic actuator simply works like a piston pneumatic actuator with two pressurized chambers. The housing of this actuator is shaped like a pie wedge rather than a cylinder form. A paddle including an output shaft simply divides the two pressurized chambers. Changing the degree of difference across the paddle moves the output shaft accordingly throughout its 90 degrees of movement.
This kind of pneumatic actuator needs compressed air to thrust a diaphragm against a plate that is opposed by a spring. Once the pressure is decreased then the spring will pull back the diaphragm. So by changing the force, the position can be attained. This kind of actuator can fail-open/fail-closed once air force is lost by the spring returning the actuator to the break position.
The advantages of pneumatic actuators include the following.
The disadvantages of pneumatic actuators include the following.
The applications of pneumatic actuators include the following.
Generally, Pneumatics uses pressurized gas for controlling physical systems. These are widely used on robots with compressed air to produce mechanical motion.
The pneumatic robotic arm works like a human hand and it includes two arms namely; the upper arm & forearm. The upper arm is permanent with hinged support to the rotatable base & activated with a pneumatic cylinder whereas the forearm is fixed to the upper arm by hinged support. Therefore the robotic arm works like a human hand using a pneumatic cylinder.
Thus, this is an overview of a pneumatic actuator – working with applications. These actuators are efficient, highly reliable & secure motion control sources that utilize gas or pressurized air for converting energy into linear or rotary motion. These are particularly suitable for frequent valve opening & closing and are also used in other industrial-based applications wherever the utilization of electricity may cause an ignition or fire hazard. Here is a question for you, what are the examples of actuators?