Hydraulic compressors are usually divided in four main groups: piston compressors, rotary vane compressors, rotary screw compressors and gear compressors. The piston-models are the most suitable for basic need for compressed air such as energizing small handtools or airflushing of small quarry drills. Rotary vane-models include also a cooled lubrication system, oil separator, relief valve on the air intake and automatic rotation speed valve. Rotary vane-models are the most suitable for installation on different excavators, mining and other machines.
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Hydraulic compressor Wikipedia(Text) CC BY-SA