Pneumatic drive general knowledge

(a) Overview of pneumatic transmission

Pneumatic transmission and hydraulic transmission collectively referred to as fluid transmission, are the use of pressurized fluid (gas or liquid) as a working medium to transfer power or control signals of a transmission mode. Pneumatic transmission is a compressed air as a working medium for pressure or signal transmission and control, and then realize the production of mechanization and automation of a technology. Its transmission and control principle and hydraulic transmission is basically the same, but because of the working medium in the system and its characteristics are very different, therefore, the working characteristics of the two systems and their applications are different.

(B) the basic principle of pneumatic transmission, composition and characteristics

1. The working principle of pneumatic transmission

Pneumatic transmission and hydraulic transmission is similar to the basic principle of work (omitted).

2. Composition of pneumatic transmission system

The typical pneumatic transmission system consists of pneumatic pressure generator, actuating elements, control elements and auxiliary components of four parts (Figure 2-70).

Figure 2-70 Composition of pneumatic drive and control system

1-motor; 2-air compressor; 3-tank; 4-pressure control valve; 5-logic element; 6 -directional control valve;7-flow control valve;8-travel valve;9-cylinder;10-muffler;11-oil mister;12-water separator Air filter

(1) air pressure generator

Air pressure generator, referred to as air source device, is to obtain compressed air energy device, the main part of which is the air compressor, in addition to air purification equipment. Air compressor will be supplied by the prime mover mechanical energy into the air pressure energy, and air purification equipment to reduce the temperature of compressed air, remove the compressed air in the water, oil and pollution impurities. The use of pneumatic equipment more factories and mines will often be gas source devices concentrated in the pressurized air station (commonly known as air pressure station), the pressurized air station and then unified to the gas point (sub-factorys, workshops and gas equipment, etc.) to allocate the supply of compressed air.

(2) executive element

Executive element is compressed air as a working medium, and the compressed air pressure can be changed into mechanical energy conversion device, the executive element includes: to do the linear reciprocating motion of the cylinder, to do the continuous rotary motion of the air motor and to do the discontinuous rotary motion of the oscillating motor and so on.

(3) control components

Control components, also known as manipulation, arithmetic, detection components, is used to control the compressed air flow pressure, flow and flow direction, in order to make the actuator to complete the pre-determined rules of motion components. Control components include: a variety of pressure valves, directional valves, flow valves, logic components, injection components, travel valves, converters and sensors.

(4) auxiliary components

Auxiliary components are compressed air purification, lubrication, muffling, and connection between the components of some of the devices required. Auxiliary components include: water filter, oil mist, muffler and various piping accessories.

3. Characteristics of pneumatic transmission

Pneumatic transmission and other transmission and control methods, compared with its main advantages and disadvantages are as follows:

(1) the advantages of pneumatic transmission

1) pneumatic device structure is simple, lightweight, simple installation and maintenance. Low pressure level, so the use of safety.

2)Output force and working speed adjustment is very easy. Cylinder action speed is generally 50 ~ 500mm / s, faster than the hydraulic and electrical mode of action.

3)High reliability and long service life.

4)Compressibility of air can be used to store energy to achieve centralized air supply.

5)Pneumatic control with fire, moisture, explosion-proof ability. Compared with the hydraulic, pneumatic method can be used in high temperature occasions.

6)Because of the small loss of air flow, compressed air can be centralized supply, long-distance transmission.

(2) the shortcomings of pneumatic transmission

1) due to air compression, the cylinder's speed of action is susceptible to changes in the load and change.

2)Cylinder in low-speed movement, due to friction accounted for a larger proportion of the thrust, the low-speed stability of the cylinder is not as good as the hydraulic cylinder.

3) Although in many applications, the output force of the cylinder can meet the work requirements, but its output force is smaller than the hydraulic cylinder.

4)The current pneumatic transmission efficiency is low.