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This article covers the fundamentals of pneumatics, pneumatic circuits and pneumatic circuit diagrams. Pneumatics is an area of fluid engineering that deals with compressed air and its application in various systems. Pneumatic control technology is used in many industries and sectors, such as material handling, robotics, or transportation.
Pneumatics is a sub-area of mechanics that deals with the behavior of gases. In particular, it is fluid engineering that makes use of compressed air or air-operated systems to generate motion and drive power.
In typical compressed air systems, the air has a positive pressure of 6 bar. The pressure level is up to 18 bar in high pressure applications, such as pneumatic applications with high power input requirements. In special cases, the pressure can even be up to 40 bar.
There are many uses for compressed air that can be used as needed and required. For example, it can act as active air to convey substances and materials. It is also used as process air and supports drying processes and other processes. In addition, compressed air may be used in potentially explosive or wet locations, for example to operate motors or the like. A typical application example is a compressed air an eccentric orbital sander in a painting booth.
Pneumatic controls and systems find a wide range of applications in mechanical engineering, custom machine construction and mass production. In addition to their simplicity and reliability, the advantages of pneumatic systems also include fast response times and relatively cost-effective implementation.
Typical application examples of pneumatic controls include:
Pneumatic systems have numerous advantages. The material used, i.e. air, has an infinite supply, is available virtually anywhere, and can be transported over long distances.
Various mechanical processes can be operated efficiently by using compressed air as a power source, making it a cost-effective alternative to other power systems.
Compressed air is supplied to the desired location using valves. The energy stored in the compressed air is used to generate motion energy. An example for this is the use of compressed air to control a cylinder piston in a particular direction.
Each pneumatic control system basically consists of the following sub-components:
One or more compressors are used to generate the required process pressure. They draw in and compress the air as needed to a pressure between 6 and 40 bar.
The mechanical and thermodynamic processes in use to compress the air generate a large quantity of heat that must be evacuated from the compressed air. The compressed air is therefore routed through an air chiller to lower the temperature.
However, cooling down the air also reduces the ability of the air to absorb water. As the air cools it often releases water, which can damage the system. The air is passed through an air dryer to prevent this. There are several types of air dryers, such as refrigeration dryers and adsorption dryers, that remove moisture from the air. It is equally important to remove contaminants from compressed air to ensure optimum compressed air quality and long service life of compressed air systems. This is accomplished by passing the air through filters to remove contaminants, such as dust, particles, and oil. However, because oil is required to lubricate drives, compressed air is enriched with oil by using specialized oilers.
The conditioned air is stored in compressed air tanks. These tanks simultaneously compensate for pressure fluctuations when compressed air is removed from the system. The air accumulator is refilled when the pressure drops below a certain value.
The air pressure is adjusted with a pressure regulator before the compressed air is used in the pneumatic circuit. The air is then distributed in the system over a network of piping and hoses. The compressed air system must be planned by taking into account various requirements, such as the diameter of the lines. The smaller the diameter of a pipe, the higher the flow resistance. The diameter must be selected such that the flow resistances remain as low as possible.
Leaks are yet another risk in compressed air systems. These are common in unions or manifolds. Such leaks lead to a continuous loss of compressed air, resulting in increased power consumption and reduced system performance. In addition to such direct losses, the system can also exhibit indirect losses. Over-sized compressors, overly restrictive or excessively long lines, unfavorable tank placement - all of which leads to performance degradation and inefficiencies in the system. Purposeful planning of the compressed air distribution is therefore a condition for optimizing the compressed air system for durability and performance.
Various components in pneumatic circuits wok together to create motion and to transfer force. Valves control the direction, pressure and flow of compressed air. Pneumatic drives, such as cylinders or air motors, perform the actual work in a pneumatic circuit. They convert the energy contained in the compressed air into mechanical motion. Compressed air moves the piston inside the cylinder, transferring force, usually in a linear direction.
The mechanical work is performed by specialized working elements, which mainly come in the form of pneumatic cylinders - for example as pneumatic grippers.
Industrial conveyors move or transport material to various destinations in shop floors or warehouses. Pneumatic conveyors use compressed air to transport materials or components, such as granules, powders, or bulk materials through piping for further processing or disposal. These systems are used at different stages of production since they simplify and facilitate material handling.
Pneumatic circuit diagrams are graphical representations of pneumatic controls. They show the function and connection of the individual components of a pneumatic system.
Pneumatic circuit diagrams include supply elements, actuators and process elements. Supply elements are responsible for supplying compressed air, and for processing, storing and distributing compressed air. Actuators are the control elements in a pneumatic circuit diagram. These includes, for example, directional valves, pressure valves, or check valves. They determine the flow and direction of the compressed air. Process elements are the components that perform the physical work in the circuit. They convert the energy stored in the compressed air into mechanical motion. Cylinders, motors or actuators are process elements.
In general, the circuits are arranged so that the power flows from bottom to top, i.e. from the power supply of the compressed air source to the process element. The compressed air source is therefore the first or lowest element and the power element is the uppermost or last element.
The following practical application example shows a piston rod to be extended (fully-deployed position) and retracted after a defined time (home position). For safety reasons, practitioners usually use 2 hand buttons to prevent unintentional piston deployment.
The application basically consists of the following components:
The operating principle of the planned circuit causes several things to happen at the same time during the switching action.
The elements of the circuit diagram are labeled according to the labeling key specified in DIN ISO 1219-2. Depending on the application, the symbols contained in the standard can be combined accordingly. The following overview shows some examples.
The description of the directional valves is based on the number of ports, the number of switch positions and the flow path. Directional valves are assigned two numbers. The first indicates how many ports the valve has, and the second number indicates the number of switch positions. A 3/2-way valve, for example, has three ports and two switch positions. In practice, 2/2, 3/2, 5/2, and 5/3 directional valves are most commonly used.
Pneumatic actuators (for example, cylinders, etc.) are controlled by pneumatic valves. The function of the valves is to control the direction of action, the speed (via the flow rate) and the force.
Directional valves are one of the most important elements of pneumatic controls. They are used to determine the flow direction and to open or block the path for the medium. For example, they are used to actuate and control cylinders, valves, or pneumatic tools. Directional valves can be grouped according to different criteria:
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