Pneumatic Systems PDF

PNEUMATIC SYSTEM Introductio n  Pneumatics may be defined as branch of engineering science which deals with the study of the behaviour and application of compressed air to power machine or control or regulate machines. It deals with generation, transmission and cont...

PNEUMATIC SYSTEM Introductio n  Pneumatics may be defined as branch of engineering science which deals with the study of the behaviour and application of compressed air to power machine or control or regulate machines. It deals with generation, transmission and control of power using pressurized air. Gas in a pneumatic system behaves like a spring since it is compressible. Any gas can be used in pneumatic system but air is the most usual, for obvious reasons. Exceptions are most likely to occur on aircraft and space vehicles where an inert gas such as nitrogen is preferred or the gas is one which is generated on board. Actuation of the controls can be manual, Pneumatic or Electrical actuation. DIFFERENCES BETWEEN HYDRAULIC AND PNEUMATIC SYSTEMS One of the main differences between the two systems is that in pneumatics, air is compressible. In hydraulics, liquids are not. Other two distinct differences are given below. The hydraulic systems also have two main features:  Hydraulic systems use liquids such as oil and water to perform work processes.  Hydraulic systems are closed systems, recirculating the oil or water after use. S.NO HYDRAULIC PNEUMATIC. SYSTEM SYSTEM 1 It employs a pressurized It employs a liquid as fluid compressed gas usually air as a fluid 2 Oil hydraulics system Pneumatic systems operates at usually operate at 5 to pressure upto 700 bar 10 bar 3 Generally designed for Pneumatic closed systems systems are usually designed as open system 4 System get Leakage does not slowdown of affect the system much leakage occurs more 5 Valve operation are Easy to operate the difficult valves 6 Heavier in weight Light in weight 7 Pumps are used to Compressors are used provide pressurized to provide compressed liquids gas 8 System is unsafe to fire System is free from fire hazards hazards 9 Automatic lubrication is Special arrangements provided for lubrication needed. Table 1.1 Comparison between Hydraulic and Pneumatic Systems ADVANTAGES OF PNEUMATIC SYSTEM  Low inertia effect of pneumatic components due to low density of air.  Pneumatic Systems are light in weight.  Operating elements are cheaper and easy to operate  Power losses are less due to low viscosity of air  High output to weight ratio  Pneumatic systems offers a safe power source in explosive environment  Leakage is less and does not influence the systems. Moreover, leakage is not harmful DISADVANTAGE S OF PNEUMATIC SYSTEMS  Suitable only for low pressure and hence low force applications  Compressed air actuators are economical up to 50 KN only  Generation of the compressed air is expensive compared to electricity  Exhaust air noise is unpleasant and silence has to be used APPLICATIONS Pneumatic systems are used in many applications. In construction, it is indispensable source of power for such tools as air drills, hammers, wrenches, and even air cushion supported structures, not to mention the many vehicles using air suspension , braking and pneumatic tires. In manufacturing, air is used to power high speed clamping, drilling, grinding, and assembly using pneumatic wrenches and riveting machines. Plant air is also used to power hoists and cushion support to transport loads through the plant. Many recent advances in air – cushion support are used in the military and commercial marine transport industry. MATERIAL MANUFACTURING OTHER HANDLING APPLICATIONS Clamping Aircraft Drilling Shifting Cement Positioni Turning Plants ng Chemical Milling Orientin Plants Coal Sawing g Mines Feeding Finishin Cotton Mills Ejection g Diaries Braking Forge Shops Formin Bonding Machine g Locking Tools Door Packaging Control Quality Control Feeding Turning Stamping Sorting Parts Stacking Embossin g Filling Table 1.2 Applications of Pneumatic Systems COMPONENTS Pneumatic system carries power by employing compressed gas generally air as a fluid for transmitting the energy from an energy- generating source to an energy – use point to accomplish useful work. Figure 1.1 Arrangement of Pneumatic System a) Air filters These are used to filter out the contaminants from the air. b) Compressor Compressed air is generated by using air compressors. Air compressors are either diesel or electrically operated. Based on the requirement of compressed air, suitable capacity compressors may be used.  c) Air cooler During compression operation, air temperature increases. Therefore coolers are used to reduce the temperature of the compressed air. d) Dryer The water vapor or moisture in the air is separated from the air by using a dryer. e) Control Valves Control valves are used to regulate, control and monitor for control of direction flow, pressure etc. f) Air Actuator Air cylinders and motors are used to obtain the required movements of mechanical elements of pneumatic system. g) Electric Motor Transforms electrical energy into mechanical energy. It is used to drive the compressor h) Receiver tank The compressed air coming from the compressor is stored in the air receiver. FUNCTIONS OF COMPONENTS  Pneumatic actuator converts the fluid power into mechanical power to do useful work.  Compressor is used to compress the fresh air drawn from the atmosphere.  Storage reservoir is used to store a given volume of compressed air.  Valves are used to control the direction, flow rate and pressure of compressed air.   External power supply (Motor) is used to drive the compressor.  Piping system carries the pressurized air from one location to another. Air is drawn from the atmosphere through air filter and raised to required pressure by an air compressor. As the pressure rises, the temperature also rises and hence air cooler is provided to cool the air with some preliminary treatment to remove the moisture. Then the treatment pressurized air needs to get stored to maintain the pressure. With the storage reservoir, a pressure switch is fitted to start and stop the electric motor when pressure falls and reached the required level, respectively. The cylinder movement is controlled by pneumatic valve. One side of the pneumatic valve is connected to the compressed air and silencers for the exhaust air and the other side of the valve is connected to port A and Port B of the cylinder.