Objectives: The purpose of this chapter is to describe: 1. Advantages and disadvantages of pneumatic transmission 2. Operation and performance of various pneumatic elements. 3. Operation and performance of some usually used circuits.Upon completing this chapter, you should be able to: Be familiar with the main pneumatic components and standardized symbols used for their representation on circuit diagrams. Explain the operation principle and performance characteristics of some usually used circuits. Describe the function of each basic component in a practical pneumatic circuit Design a circuit to perform a desired function.

CHAPTER 11CHAPTER 11 PNEUMATICS PNEUMATICS TRANSMISION TRANSMISION

11.1 Pneumatics Overview

11.1.1 Pneumatic System Structure & Its Operation Principle

In pneumatic system, compressors are used to compress and supply the necessary quantities of air that comes from the atmosphere. To operate and control these actuators, other pneumatic components are required i.e. air service units to prepare the compressed air and valves to control the pressure, flow and direction of movement of the actuators.

CHAPTER 11CHAPTER 11 PNEUMATICS PNEUMATICS TRANSMISION TRANSMISION

Fig.11.1 A Basic Pneumatic SystemIn production section: compressor, electric motor, pressure ① ② ③switch, check valve, tank, pressure gauge, auto drain, ④ ⑤ ⑥ ⑦

safety valve, refrigerated air dryer, line filter⑧ ⑨ ⑩In consumption section: air take-off, auto drain, air service ① ② ③unit, directional valve, actuator, speed controllers④ ⑤ ⑥

11.1.2 Pneumatics Properties Table 11.1.Advantages of Pneumatics

Availability Air is available practically everywhere in unlimited quantities.

Transport Air can be easily transported in pipelines, even over long distances.

Storage Compressed air can be stored in a reservoir and removed as required.

Temperature Compressed air is relatively insensitive to temperature fluctuations.

Explosion proof

Compressed air offers no risk of explosion of fire.

CleanlinessUnlubricated exhaust air is clean. Any unlubricated air that escapes through leaking pipes or components does not cause contamination.

Components The operating components are of simple construction and therefore relatively inexpensive.

Speed Compressed air is a very fast working medium. This enables high working speeds to be attained.

Overload safe Pneumatic tools and operating components can be loaded to the point of stopping and are therefore overload safe.

Preparation Compressed air requires good preparation. Dirt and condensate should not be present.

Compression It is not always possible to achieve uniform and constant piston speeds with compressed air.

Force requirement

Compressed air is economical only up to a certain force requirement. Under the normal working pressure of 600 to 700 kPa (6 to 7 bar) and dependent on the travel and speed, the output limit is between 40000 and 50000 N.

Noise level The exhaust air is loud. This problem has now, however been largely solved due to the development of sound absorption material and silencers.

Table 11.2.Disdvantages of Pneumatics

CHAPTER 11CHAPTER 11 PNEUMATICS PNEUMATICS TRANSMISION TRANSMISION

11.2 Air Generation and Treatment

Fig.11.2 Structure of Air Preparation System

11.2.1.2 Air generation equipments and preparation

Fig.11.4 Two Stage Piston Compressor

Fig.11.5 Rotary sliding vane compressor

11.2.1.2 Air generation equipments and preparation

Fig.11.6 Screw Compressor

11.2.1.2 Air generation equipments and preparation

11.3 Actuators

11.3.1. Linear Cylinder

Fig.11.15 Construction of a Cylinder

11.3.2 Rotary Actuators

 11.3.3. Air Motors

Air motors are similar in construction and function to hydraulic motors, and are most commonly of the rotary vane, gear, radial piston, or axial piston type. They can operate at speeds in excess of 10,000rpm. Air motors have several advantages that are important in some applications. One advantage is that air motors can stall under full load for indefinite periods of time, another is that they can be used in applications where electric motors would constitute a fire hazard.

11.4 Pneumatic Control Valves

11.4.1 Pressure Control Valves

Fig.11.20 Safety Valve

11.4.3 Directional Control Valves11.4.3 Directional Control Valves

Fig.11.38 Solenoid Valves

11.5 Basic Pneumatic Circuits11.5 Basic Pneumatic Circuits

Fig.11.50 Automatic Reciprocate