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* 压缩机有常用的RWBII、RWF、RXF等；H为高压级、B为低压级。 * * * Perhaps the most important reason for using anti-friction bearings in a screw compressor is that they have less internal clearance than sleeve bearings. This allows tighter rotor to rotor positioning. Any gas compressed to high pressure in a screw will try to leak back to suction through any available leakage path. The most difficult leakage path to control is the path down the center directly between the two rotors. A 3 inch diameter journal bearing will require approximately 0.003 inch internal clearance in order to build an oil film. A cylindrical roller sized to handle the same load will have roughly half the internal clearance. With half the radial motion possible on each rotor this gives one quarter of the leakage path down the center and yields significantly better efficiency at high compression ratios. * The oil separator performs three basic functions. Removing oil from the refrigerant is obvious. Typically the separator will discharge gas with no more than 2 to 5 ppm of oil in the discharge gas stream. The separator also gives time for the oil to sit and allow refrigerant to boil out. This is particularly important on liquid injection cooled screws where some time is needed for the liquid to absorb heat from the oil and gas. This is referred to as the dwell time. The separator also allows an oil sump to store the oil before reinjection back to the compressor. * This schematic shows the general function of a horizontal oil separator. The oil is injected into the gas stream as it passes through the compressor. The gas/oil mixture travels down the discharge line and it blasted against the wet head of the oil separator. This gives a direction change and a large velocity drop which knocks out most of the oil. The gas then travels the length of the oil separator where time and gravity pulls all of the remaining larger oil particle down into the oil sump. By the time the gas gets to the coalescing filters