What is Pneumatic System? Working Principle, Components, Pros & Cons

different types of pneumatic system components
Figure 1: Pneumatic system components.

Pneumatic technology uses compressed air as the working medium to transmit energy and signals. It is a technology that realizes the mechanization and automation of various production processes. The following describes in detail the working principle, components and advantages and disadvantages of the pneumatic system (pneumatic control system).

1. How Pneumatic Systems Work

The working process of pneumatic transmission is to use an air compressor to convert the mechanical energy output by an electric motor or other prime mover into the pressure energy of the air. Then under the action of the control component, the pressure energy is converted into mechanical energy in the form of linear or rotary motion through the actuator, thereby completing various actions.

2. Pneumatic System Components

According to the different functions of pneumatic components and devices, they can be divided into four types.

pneumatic system diagram and components
Figure 2: An example of a pneumatic system.

2.1 Air Source Devices

The air source devices include an energy device for obtaining compressed air whose main part is an air compressor, and also include an air source purification device.

Air Compressor
The air compressor is the power source of the pneumatic system and the "heart" part of the pneumatic transmission. It is an energy conversion device that converts the mechanical energy output by the motor into air pressure energy.

Air compressor types and selection principles:
According to the output pressure, air compressors can be divided into 4 types.
●Low pressure air compressor (0.2-MPa)
●Medium pressure air compressor (1.0-10Mpa)
●High pressure air compressor (10-100Mpa)
●Ultra-high pressure air compressor (>100Mpa)

According to the output flow (displacement), they can be divided into 4 types.
●Micro air compressor (<1 m³/min)
●Small air compressor (1-10 m³/min)
●Medium air compressor (10-100 m³/min)
●Large air compression (>100 m³/min)

Air compressor set including air tank
Figure 3: Air compressor set.

Air Source Purification Device
Function: The aftercooler reduces the temperature of compressed air and removes liquid water from it.

②Oil-water separator
The oil-water separator is installed on the outlet pipe of the aftercooler. Its function is to separate and discharge the oil, moisture, dust and impurities from the compressed air, so that it can be initially purified.

③Air storage tank /air receiver
Function: It stores a certain amount of compressed air, reduces air flow pulsation, weakens pipe vibration caused by air flow pulsation, and further separates the moisture and oil from the compressed air.

Function: It further removes moisture, oil, particle impurities, etc. contained in compressed air to dry it for use in pneumatic devices, pneumatic instruments, etc. that require higher air source quality. Adsorption, centrifugation, and freezing methods are mainly used.

Including air filter, pressure reducing valve (pressure regulator) and lubricator

air source treatment component, F.R.L. unit
Figure 4: F.R.L. unit.

2.2 Pneumatic Control Component

It is a component used to control the pressure, flow rate and flow direction of the compressed air flow so that the actuator can complete the predetermined movement, including various pressure control valves, solenoid directional control valves, flow control valves, stroke valves, sensors, etc.

2.3 Pneumatic Actuator

It is an energy conversion device that uses compressed air as the working medium and converts its pressure energy into mechanical energy, including air cylinder with linear reciprocating motion, pneumatic motor with continuous rotary motion, and swing motor with reciprocating swing motion.

The air cylinder is one of the main pneumatic components and it comes in many types. According to the mode of action, it can be divided into: single-acting cylinder and double-acting cylinder.

air cylinders of different types
Figure 5: Air cylinders.

2.4 Pneumatic Auxiliary Components

Auxiliary components in pneumatic systems include mufflers, pipes, joints, etc.

When the cylinder, valve, etc. are working, the air exhaust velocity is high and the air volume expands rapidly, which will produce harsh noises. The intensity of the noise changes with the exhaust speed, exhaust volume and the shape of the air channel. The greater the air exhaust speed and power, the greater the noise, which can generally reach 100 to 120dB. In order to reduce the noise, a muffler must be installed at the exhaust port.

②Piping and fittings
Pipes (channels for compressed air)
Hard pipes: steel pipes, copper pipes, aluminum pipes, PVC pipes, etc.
Hoses: plastic, nylon, rubber, metal braided and other types.

pipe connectors for different uses
Figure 6: Pipe connectors.

Pipe connectors
Function: Connecting air pipelines.
Requirements: Reliable and fast connection, and long service life.
Type: welding type, ferrule type, clamp type, flared type, quick change type.

③Sealing components
Function: Preventing transmission medium (air) leakage (external and internal leakage).
1. Within a certain working pressure and temperature range, it should have good sealing performance, which can automatically improve as the pressure increases.
2. The friction between the sealing device and the moving parts should be small with a stable friction coefficient.
3. Strong corrosion resistance, not easy to age, long working life, good wear resistance, and to a certain extent automatic compensation after wear.
4. Simple structure, easy to use and maintain, and low price.

Pneumatic system components

Air source devices

Air compressor, cooler, dehydrator, dryer, filter, F.R.L. (Filter, Regulator, Lubricator)

Pneumatic control component

Solenoid directional control valve, pressure control valve, flow control valve, logic valve

Pneumatic actuator

Air cylinder, air motor, vacuum suction cup

Pneumatic auxiliary components

Mufflers, pipeline components, seals, instruments (pressure gauges, vacuum gauges, thermometers, flow meters), etc.

Table 1: Pneumatic system components.

3. Characteristics of Pneumatic Systems

3.1 Advantages of Pneumatic Systems

a. Air is available everywhere and is inexhaustible, saving the cost of purchasing, storing, and transporting. The used air is directly discharged into the atmosphere, which causes no pollution to the environment and is easy to handle. There is no need to set up a recovery pipeline, and no problems such as medium deterioration, replenishment and replacement.

b. Due to the small viscosity of air (about one ten thousandth of hydraulic oil), the flow resistance in the pipe is small and the pressure loss is small, which facilitates centralized air supply and long-distance transportation. Even if there is a leak, it will not pollute the environment like hydraulic oil.

c. Compared with hydraulic transmission, pneumatic transmission has fast response, rapid action, simple maintenance, and the pipeline is not easily blocked.

d. Pneumatic components have simple structure and are easy to manufacture, and are suitable for standardization, serialization and generalization.

e. The pneumatic system has good adaptability to the working environment. Especially when working in harsh working environments such as flammable, explosive, strong magnetism, radiation, vibration, etc., its safety and reliability are better than hydraulic, electronic and electrical systems.

f. The compressibility of air enables the pneumatic system to achieve automatic overload protection and also facilitates the storage of energy in the air tank in case of urgent needs.

g. When exhausting, the temperature of the air decreases due to expansion, so the pneumatic equipment can automatically cool down and will not overheat during long-term operation.

Pneumatic components, new thin air cylinders with guide rods
Figure 7: Air cylinders.

3.2 Disadvantages of Pneumatic Systems

a. Air is compressible and when the load changes, the action stability of the pneumatic system is poor. However, a gas-liquid linkage actuator can be used to solve this problem.

b. The working pressure is low (generally 0.4-0.8MPa), and the structural size should not be too large, so the output power is small.

c. The transmission speed of air signals is slower than that of light and electrons, so it is not suitable for use in complex circuits that require high transmission speeds. But for general mechanical equipment, it can meet the speed requirements.

d. The air exhaust noise is large and mufflers need to be installed.

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