1.5 Basic composition of pneumatic system
The pneumatic system mainly consists of a power source (the energy conversion process that converts mechanical energy into pressure energy, completing the compression, distribution, and treatment of compressed air); Power control part (including directional control valve, flow control valve, one-way valve, pressure control valve); Control part (including manual control, electrical control, electronic control, and pneumatic control); The execution component (i.e. energy conversion part, including cylinder, air motor, and combination unit, which refers to the gas-liquid combination feed device, clamping device, belt feed device, stepper table, drilling device, thread processing device, multi-purpose pneumatic screwdriver, etc.) and auxiliary components are composed. A typical pneumatic transmission system is shown in Figure 1-4.
Figure 1-4 Schematic diagram of pneumatic transmission system
(1) Power source
It is a device for obtaining compressed air. The main part is an air compressor or vacuum pump, which converts the mechanical energy supplied by the prime mover into the pressure energy of the gas. There are two types of air compressors: volumetric and velocity.
There are two types of vacuum pumps: rotary and jet.
The working principle of a volumetric air compressor is to change the working volume through a reciprocating piston or rotary rotor in the cylinder, thereby compressing the volume of gas and increasing the density of gas per unit volume, thereby increasing the pressure of compressed air. The working principle of a speed air compressor is to increase the speed of gas movement through the action of a high-speed rotating impeller, and then convert the kinetic energy of the gas into pressure energy to increase the pressure of compressed air.
A reciprocating air compressor compresses gas through the reciprocating motion of the piston and is controlled by the gas distribution system. Suitable for medium displacement and various pressure situations.
A rotary air compressor compresses gas through the mechanical movement of a rapidly rotating rotor, which transmits speed and pressure to the flowing gas. Suitable for small displacement, medium and low pressure applications.
In an axial flow air compressor, the gas is accelerated by a rotor equipped with blades, and the main airflow is axial. It is generally used as a low pressure, large displacement compressor.
In a centrifugal air compressor, there are one or more rotating impellers (usually on the side) that accelerate the airflow, and the airflow is radial. Suitable for occasions with large displacement and low pressure.
The shape of the rotor of a mixed flow air compressor combines some characteristics of both centrifugal and axial flow, and its usage range is narrow, suitable for production situations that require medium pressure and medium displacement.
The energy components of the pneumatic system are generally located in the compressor station far away from the control and execution components, and transported over long distances through pipelines. In recent years, there have also been small low noise compressors or booster pumps installed near control and execution components,implementing single unit single pump supply or local pressurization. Rotary vacuum pumps are generally installed near control and actuator components, while jet vacuum pumps are generally installed near vacuum actuators such as suction cups as much as possible to reduce vacuum volume and save air consumption.
(2) Power control part
It is used to control the pressure, flow rate, and flow direction of compressed air, in order to enable the actuator to complete the predetermined working cycle. It includes various pressure control valves, flow control valves, directional control valves, and logic components.
(3) Control section
Complete the stroke program action through manual control, relay control, PLC control, and pure pneumatic control.
(4) Actuating element
Pneumatic actuator is an energy conversion device that uses compressed air as the working medium to convert the pressure energy of gas into mechanical energy. It includes a cylinder that achieves linear reciprocating motion and an air motor or swing motor, air claw, etc. that achieves continuous rotary motion or swing.
(5) Auxiliary components
It is necessary to ensure the purification of compressed air, lubrication of components, connection between components, and noise reduction, including filters, oil misters, pipe joints, and mufflers.