Pneumatic systems advantages, disadvantages, components and gas terminology

Definition of gas state terms of pneumatic components

1. Density ρ: The mass of gas contained in unit volume is called density. The unit is kg/m3.
2. Pressure p: Pressure can be measured by absolute pressure, gauge pressure and vacuum degree.
3. Absolute pressure: the pressure value based on absolute vacuum as the starting point. Generally, "ABS" is marked on the lower right foot of the symbol indicating absolute pressure, which is PABS.
4. Gauge pressure: the pressure value higher than the local atmospheric pressure. The pressure value measured by the pressure gauge is the gauge pressure. In engineering calculations, the local atmospheric pressure is often replaced by the standard atmospheric pressure, that is, Pa=101325Pa.
5. Vacuum degree: the pressure value lower than the local atmospheric pressure.
6. Vacuum pressure: the difference between absolute pressure and atmospheric pressure. Vacuum pressure is numerically the same as vacuum degree, but should be preceded by a negative sign.

7. Temperature T: The thermodynamic temperature T is commonly used in engineering calculations. Its unit name is Kelvin [Irvin] and its unit symbol is K. The conversion relationship with the Celsius temperature (℃) in our lives is: T=t-T0, T0 =273.15K.





8. Standard state: refers to the state of air when the temperature is 20°C, the relative humidity is 65%, and the pressure is 0.1Mpa.
Under standard conditions, the density of air is ρ=1.185kg/m3. According to the international standard ISO8778, "(ANR)" can be marked after the unit in the standard state.
9. Baseline state: refers to the state of dry air with a temperature of 0°C and a pressure of 101.3Kpa. In the base state, the density of air is ρ=1.293kg/m3.
10. Ideal gas: A gas without viscosity is called an ideal gas. The purpose is to simplify problem solving.
11. Complete gas: It is an imaginary gas whose molecules are elastic particles that do not occupy a volume. There is no interaction force between the molecules except for collisions with each other. It is a completely different concept from an ideal gas without viscosity.
Any actual gas can be regarded as a perfect gas as long as it is not at a very high pressure or a very low temperature. Calculated according to the complete gas equation of state, the error will not be too large.

Advantages and Disadvantages of Pneumatic Systems

1. Advantages of pneumatic systems
(1) Applicability Most factories and workshops are equipped with compressed air sources in the working area, and mobile compressors can be used in farther locations.
(2) Storage: Easily store large volumes of compressed air as needed.
(3) Simple design and control. The use of pneumatic components is a simple design, so it is easily suitable for automatic systems with simpler controls. Compared with hydraulic transmission, pneumatic transmission has fast response and rapid action, and generally only needs to establish the required pressure and speed;therefore, it is particularly suitable for realizing automatic control of the system. It is easy to adjust and control. It can not only form a full pneumatic control loop, but also can be combined with electrical and hydraulic to achieve hybrid control.
(4) Selection of motion Pneumatic components are easy to realize linear and rotary motion with stepless speed regulation.
(5) Economical Since the price of pneumatic components is appropriate, the cost of the entire device is low, and the pneumatic components have a long life and do not require maintenance, so the maintenance cost is low.
(6) Reliability Pneumatic components have a long working life, so the system has high reliability.
(7) Adaptability to harsh environments Compressed air is largely unaffected by high temperature, dust, and corrosion, which is beyond the reach of other systems.
(8) Clean environment: Pneumatic components are clean and have special exhaust air treatment methods, and can be installed in a standard clean workshop.
(9) Safety: It will not cause fire in dangerous places. If the system is overloaded, the actuator will only stop or slip. Pneumatic actuators do not generate heat.

2. Disadvantages of pneumatic systems
(1) Due to the compressibility of air, the motion is slightly less smooth when the load changes.
(2) Due to low working pressure, it is difficult to obtain large output force or torque;therefore, pneumatic transmission is not suitable for heavy-load systems.
(3) There is loud exhaust noise.
(4) Since air has no lubricating properties, an oil lubrication device should sometimes be installed in the air circuit.
(5) The signal transmission speed in pneumatic devices is limited to the speed of sound, which is slower than optical and electrical signals, so it is not suitable for use in situations where the signal transmission speed is very high. At the same time, it is also difficult to achieve remote control of the production process.
(6) There is leakage in the pneumatic system, which is a loss of energy. A certain amount of external leakage is also allowed. However, leakage should be minimized as much as possible.

Composition of pneumatic system:
1. Air compressor
2. Main road purification equipment
3. Three major parts of air source treatment: filter, pressure regulating valve, and lubricator