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Chapter 1
INTRODUCTION
A fluid power system is one that transmits and controls energy through the use of pressurized liquid or gas.In Pneumatics, this power is air. This of course comes from the atmosphere and is reduced in volume bycompression thus increasing its pressure.Compressed air is mainly used to do work by acting on a piston or vane. While this energy can be used in many facets of industry, the field of Industrial Pneumatics is considered here.The correct use of pneumatic control requires an adequate knowledge of pneumatic components and theirfunction to ensure their integration into an efficient working system.Although electronic control using a programmable sequencer or other logic controller is currently specified it is still necessary to know the function of the pneumatic components in this type of system.This project deals with the technology of the components in control systems, describing types and design features of air treatment equipment, actuators and valves, methods of interconnection and introduces the basic pneumatic circuits. An incredible range of manufacturing systems use the force and power of fluids such as water, oil and air. Powered clamps open and close with the force of pressurized air or oil, large presses works on hydraulic pressure, and assembly torque tools to fasten components with pressurized air. In each example, fluid power provides the energy necessary to exert significant mechanical forces.
Systems that use air are called pneumatic systems while systems that use liquids like oil or water are called hydraulic system. Pneumatics is all about using compressed air to make a process happens. Compressed air is simply the air we breathe squeezed into a small space under pressure. Air under pressure possesses potential energy which can be released to do useful work.
1.1 Basic Pneumatic System
Pneumatic cylinders, rotary actuators and air motors provide the force and movement of most pneumatic controlsystems, to hold, move, form and process material.To operate and control these actuators, other pneumatic components are required i.e. air service units to preparethe compressed air and valves to control the pressure, flow and direction of movement of the actuators.
A basic pneumatic system, shown in fig., consists of two main sections:
Air Production and distribution System
• Air Consuming System
The component parts and their main functions are:
Compressor: Air taken in at atmospheric pressure is compressed and delivered at a higher pressure to the pneumatic system. Itthus transforms mechanical energy into pneumatic energy.
Electric Motor: Supplies the mechanical power to the compressor. It transforms electrical energy into mechanical energy.
Pressure Switch: Controls the electric motor by sensing the pressure in the tank. It is set to a maximum pressure at which it stopsthe motor, and a minimum pressure at which it restarts it.
Check Valve: Lets the compressed air from the compressor into the tank and prevents it leaking back when the compressor is stopped.
Tank: Stores the compressed air. Its size is defined by the capacity of the compressor. The larger the volume, the longer the intervals between compressor runs.
Pressure Gauge: Indicates the Tank Pressure.
Auto Drain: Drains all the water condensing in the tank without supervision.
Safety Valves:Blows compressed air off if the pressure in the tank should rise above the allowed pressure.
1.2 Properties of compressed air
Availability:Most factories and industrial plants have a compressed air supply in working areas, and portable compressors can serve more remote situations.
Storage:It is easily stored in large volumes if required.
Simplicity of Design and Controlneumatic components are of simple design and are easily fitted to provide extensive automated systems with comparatively simple control.
Choice of Movement: It offers both linear movement and angular rotation with simple and continuously variable operational speeds.
Economy: Installation is of relatively low cost due to modest component cost. There is also a low maintenance cost due tolong life without service.
Reliability: Pneumatic components have a long working life resulting in high system reliability.
Resistance to Environment: It is largely unaffected in the high temperature, dusty and corrosive atmospheres in which other systems may fail.
Environmentally Clean: It is clean and with proper exhaust air treatment can be installed to clean room standards.
Safety:It is not a fire hazard in high risk areas, and the system is unaffected by overload as actuators simply stall or slip. Pneumatic actuators do not produce heat.
1.3 Advantages of Pneumatic system
Availability:Air is available practically everywhere in unlimited quantities.
Transport: Air can be easily transported in pipelines, even over large distances.
Storage: Compressed air can be stored in reservoirs and removed as required. In addition, the reservoir is transportable.
Temperature: Compressed air is relatively insensitive temperature fluctuations. This ensures reliable operation, even under extreme conditions.
Explosion Proof: Compressed air offers no risk of explosion or fire.
Cleanliness: Un-lubricated exhaust air is clean. Any un-lubricated 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.
Overloads Safe: Pneumatic tools and operating components can be loaded to the point of stopping and are therefore overload safe.
1.4 Engineering applications
The applications for compressed air are limitless, from the optician’s gentle use of low pressure air to test fluid pressure in the human eyeball, the multiplicity of linear and rotary motions on robotic process machines, to the high forces required for pneumatic presses and concrete breaking pneumatic drills.
The short list below serves only to indicate the versatility and variety of pneumatic control at work, in a continuously expanding industry.
Operation of system valves for air, water or chemicals
Operation of heavy or hot doors
Unloading of hoppers in building, steel making, mining and chemical industries
Ramming and tamping in concrete
Lifting and moving in slab moldings machines
Crop spraying and operation of other tractor equipment
Spray painting
Holding and moving in wood working and furniture making
Holding in jigs and fixtures in assembly machinery and machine tools
Holding for gluing, heat sealing or welding plastics
Holding for brazing or welding
Forming operations of bending, drawing and flattening
Spot welding machines
Riveting
Bottling and filling machines
Wood working machinery drives and feeds
Test rigs
Machine tool, work or tool feeding
Component and material conveyor transfer
Pneumatic robots
Auto gauging
Air separation and vacuum lifting of thin sheets
Dental drills
1.5 Problem definition/ Scope/ Objective
There was a need of a pneumatic trainer in our college for practical purpose. It will be beneficial for the mechanical department. So we decided to develop a pneumatic trainer as our diploma final year project.
Components of Pneumatic System
2.1 Air Compressor
A compressor is a device which is used to produce pressure head on the expense of mechanical energy. In case the working fluid is an air, it is called an air compressor.
2.2 Flow control valve
Flow control valves are used to control the flow rate of the working fluid. Since the energy is contained in the fluid in the form of pressure energy, the flow control valves also controls the rate of energy transfer in a fluid power system. The rate of flow of fluid controls the rate of movement of machine elements. Thus it is possible to control the speed of actuators like cylinder or motor by flow control.
The basic principle of flow control:
A flow control valve controls the rate of flow of air through it. It is achieved by varying the area of flow, therefore a flow control valve is basically a variable area orifice. However, when the orifice area is varied, it is subjected to change in the differential pressure. This change in the differential pressure also causes the flow to change.
2.3 Directional control valve
Direction control valves (DCV) are used for distribution of energy to various actuators by controlling the direction of flow of pressurized air in the system