Compressor
Compressor is a device for compression and supply of air or other gas under pressure.
Compressor is used for conversion of electrical energy into the energy of compressed air. The transformation of energy into pneumatic gives incontestable advantage in safety and economy of equipment and tools use.
Per principle of operation and main constructive peculiarities they differ piston-type compressors, rotary screw compressors, centrifugal-flow compressors, axial-flow compressors and jet compressors. Nowadays the most wide spread in industry are piston-type compressors and rotary screw compressors.
Piston-type compressors are the most common used in Ukraine among installed compressors with productivity up to 100 ì³/min.
Main advantages of piston-type compressors are their low price in comparison with compressors of other types, relative simplicity of production, high maintainability.
Under the condition of due maintenance, piston-type compressor is a machine for practically “perpetual tenure”. Inter-service interval of piston-type compressors does not exceed 500 working hours.
Piston-type compressor mainly consists of working cylinder and piston; it also has a suction-valve and a pressure valve, which usually are situated in cylinder head. For putting the piston in alternate/reciprocal motion there is a connecting rod gear with a crankshaft in majority of piston-type compressors.
Piston-type compressors come in various types: single-cylinder and multicylinder, with vertical, horizontal, V- or W-type of cylinder arrangement, single and double action (when piston is working by both sides), and also single compression or compound compression.
Piston-type compressors are usually provided with automatic control of productivity depending on compressed gas flow for providing constant pressure in delivery conduit. There are several ways of control. The easiest one is by intermittent switching on, i.å. when pressure drops to the level of bottom end in receiver (in the system) compressor switches on and switches off (rotary screw compressor turns to no-load condition) while reaching prescribed superior limit up to the next switching on.
Piston-type compressors are more preferable than compressors of other types in the following cases:
• if low productivity is required, in such cases piston-type compressors surpass rotary screw compressors;
• if there are big gaps in compressed air consumption. Industrial piston-type compressors work well in intermittent cycle, ensuring big economy in comparison with rotary screw compressors.
• if a compressor runs in adverse conditions: if used in cement packing premises, in coal storage or grain grinding mills, or under wide temperature fluctuation and etc. In such conditions piston-type compressors ensure longer life time period and demand less costs for maintenance.
• if compressors are used for compressing a corrosive gas and etc.
So, for the cases when low (up to 200 l/min) productivity and high (above 20-30 atmosphere) pressure is needed, piston-type compressors are more effective and much cheaper than compressors of other compression technologies with the exception of turbine compressor, which are effective on the big need in compressed air.
Rotary screw compressors differ from the traditional piston-type compressors by principle of operation.
While piston-type compressor has percussive air compression, rotary screw compressor is boosting smoothly, by means of screw pair. Screw pair sucks in air, rotating in oil reservoir, which ensures practically total absence of friction, additional oil seal, which guarantees the containment of the system, and also effective heat eliminating from working area. As a result - high efficiency factor (~92%) and slight exceeding in temperature (on 10-15ºÑ) of compressed air in comparison with the temperature at the input.
High operational characteristics and effective system of oil cooling ensures around-the-clock work of rotary screw compressor under optimal temperature. At the same time the system of oil catching, provided in standard integration of rotary screw compressors, ensures from 1 to 3 mg/m³ oil content at the output.
As compared to piston-type compressors, rotary screw compressors have a whole series of advantages:
• low noise and vibration level, small dimension and weight and may be installed directly in workshops, where air is being consumed,
• do not special base for this;
• practically do not have oil consumption (2-3 mgr/m³), in contrast to large piston-type compressors with lubrication grease, that is why they produce more clear air, and this allows to use them for the most modern pneumatic equipment;
• provided with automatic system of management and efficiency control, that is why they are secure, and do not need to be looked after, reliable, capable for long functioning without maintenance;
• air-cooling of rotary screw compressors allows to refuse from bulky system of water recycling (cooler), and, besides, gives possibility of the second time use of heat evolving from a working compressor, for example for heating premises during winter time;
• repair-free service life of rotary screw compressors is much longer than of standard piston-type compressors;
• rotary screw compressors do not need to be maintained and served by specially trained staff;
• screw block in compressors has minimal noise and vibration level;
rotary screw compressor is fully automatized;
• compressed air at the output has minimal residual oil content;
• rotary screw compressors are more economical, energy consumption is lower (see above);
• possibility of continuous running 24 hours per day;
• much longer (2-3 times) operation life period.
The main advantage of rotary screw compressors is economy: investigations show that only 50-80% of compressor’s capacity is used at manufactures. In such cases standard rotary screw compressor works in the regime «load- idling», and old piston-type compressor throws excess air through the valve into atmosphere, i.å. money paid for spent electric energy goes bust…
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