往复式压缩机培训精讲.ppt

进气容积效率：进气阀启闭过程占总行程的百分比； 排气容积效率：排气阀启闭过程占总行程的百分比。 By viewing the P.V. card, we can get an indication of cylinder efficiency and horsepower. Let’s first discuss the efficiency: The volumetric efficiency of a cylinder is a useful function for determining the ability of a compressor cylinder to fill up with gas (inlet volumetric efficiency) or empty of gas (discharge volumetric efficiency). The capacity of a compressor cylinder is calculated by using the volumetric efficiency. The portion of the stroke during which the valves are open, compared to the total length of the stroke, is known as the volumetric efficiency, and is usually expressed as a percentage of the stroke of the end of the cylinder being considered. That is (in this example), the gas at discharge pressure, is being discharged during 45% of the discharge stroke. Likewise, gas pressure within the compression chamber is sufficiently low to permit inlet gas into the compression chamber for 85% of the inlet stroke. As mentioned earlier, when the piston reaches the end of its stroke on the delivery cycle, a portion of the gas (at discharge pressure) remains within volumes of the cylinder which are unswept by the piston. The volumes of the cylinder which contain the undisplaced gas are referred to as fixed clearance. When the cylinder is configured with minimal fixed clearance, the cylinder is considered to be at base clearance. The fixed clearance is expressed as a percentage of the total displacement volume of the cylinder. Also, as mentioned previously, the gas in these volumes must be expanded so the pressure can reduce enough to let new gas into the cylinder. In this P.V. card, the area inside of the rectangle on the P.V. card represents the total cylinder volume including the fixed clearance volumes. The area within the curve (1-2-3-4) represents the displacement volume, which is the volume displaced by the piston movement. If we subtract the displacement volume from the total cylinder volume, we w