JABATAN KEJURUTERAAN MEKANIKAL POLITEKNIK UNGKU OMARRusmay Bin AbdullahJJ512 PNEUMATIC & HIDRAULICAir Generation and DistributionAIRAir generation and distributionThe Perfect Gas LawsCompressorCompressorsA compressor is a machine that compresses air or anothertype of gas from a low inlet pressure (usually atmospheric) toa higher desired pressure level. This is accomplished byreducing the volume of the gas. Air compressors aregenerally positive displacement units and are either of thereciprocating piston type or the rotary screw or rotary vanetypes.Positive DisplacementReciprocatingSingle Acting/Single Stage CompressorPiston compressorIn this type of compressor a cylinder bore encloses a moving piston. As the crankshaft of the compressor rotate, the piston moves within the cylinder, similar to the piston in a car engine. As the piston is pulled down, the volume increases, creating a lower atmospheric pressure in the piston chamber. This difference in pressure causes air to enter via the inlet valve. As the piston is forced upwards the volume of air reduces. The air pressure therefore increases. Eventually the pressure forces the outlet valve to open.Single Acting/Single StageTo avoid an excessive rise in temperature. Multi-stage compressors with INTERCOOLERS have been developed. These compressors can generate higher pressures than single stage compressors. The most common type is the Two-Stage compressor. The following figures show how this compressor works.Positive DisplacementReciprocatingDouble Acting/Double Stage Piston CompressorDouble Acting/Double StagePositive DisplacementReciprocatingDiaphragm CompressorA diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in contact with the gas being compressed.DiaphragmPositive DisplacementRotoryLobe CompressorIn this type of compressor the rotors do not touch and certainamount of slip exists. This slip increases as the output pressureincreases. It is therefore operated at maximum speed for thehighest efficiency. 17.3 bar is obtainable with this type ofconstant displacement compressor.LobePositive DisplacementRotoryScrew CompressorThere is a current toward increased use of the rotary-typecompressor due to technological advances, which have producedstronger materials and better manufacturing process. Thefollowing figure shows a cutaway view of a single-stage screwtype compressor. Precise positioning of the screw is essential forits performance. Oil provides a seal between the rotating screwsas well as lubricating the parts and cooling the air. The oil is thenseparated from the air before it enters the system.ScrewPositive DisplacementRotoryVent CompressorThe following figure shows a cutaway view of the sliding-vane-type rotary compressor. The air inlet is placed where the volumeof the compression chamber is greatest, the outlet where thevolume is smallest. Consequently, as the vanes turn, the spacebetween them is reduced. This reduction in volume compressesthe air as it travels from the inlet to the outlet.VaneDynamicThe dynamic type air compressorsmechanically impart velocity to the air. Theimpellers rotating at a high speed, inenclosed casing, produce this action. Theair is forced into a progressively reducedvolume. The volumetric flow will varyinversely with the differential pressureacross the compressor. This type ofcompressor is further classified as:1. Centrifugal Air Compressor2. Axial FlowAir CompressorCentrifugal Air CompressorAxial Flow Air Compressor