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森林工程专业英语考核 压力之源泵和压缩机原文名称：压力之源泵和压缩机姓名：学号：专业班级：指导老师：电子邮箱：日期：内容提要从原理上讲，大多数适合于泵送流体的泵都可以泵送空气或气体，尽管大多数油泵几乎不会作为空气压缩机来用，而某些压缩机未作调整也不可以输送非压缩性流体。泵和压缩机有共同之处，亦有不同之处。关键词：泵 压缩机 流体 压力压力之源泵和压缩机从原理上讲，大多数适合于泵送流体的泵都可以泵送空气或气体，尽管大多数油泵几乎不会作为空气压缩机来用，而某些压缩机未作调整也不可以输送非压缩性流体。从总的原则来考虑，一台可以提供足够大压力来实际使用的液压泵，保证其能力的主要要求是：a. 应采取控制流体泄漏的措施。应当采用特殊密封，或者减小工作间隙。b. 要完全均匀而不是脉冲式地输送流体。c. 在运行过程中，流体不能存在空穴现象，因为实际使用的流体都是非压缩性的。 d. 机械平衡达到足够的程度，使泵能尽可能快地旋转，以减小保证输出一定功率时的泵的体积。e. 由于泵内有内压力，要采取适当的措施，最大限度地减小工作零件或泵壳等部件变形的影响。f. 间隙量要小，以便在泵起动时能很快转动起来，对空气流体，泵就像压缩机那样，把空气通过输送管排出，而不是让它滞留在泵中。g. 配置适当的进油阀或配流装置，已便提高泵的吸油能力，在高空飞行的飞机液压装置上或使用较高粘度的液体作为液压油时，更应采取这些措施。应该注意的是入口阀或油门开启的时间，这几乎和油口尺寸一样的重要。 对一台良好的压缩机的主要要求是：a) 与机械间隙相适应的尽可能小的间隙容积。这是因为在间隙容积中被压缩的任何气体都将会再次膨胀而不是被排放掉。因此，不仅将影响泵的输出，而且影响可能产生的最高压力。b) 除了低压泵外，在两个或更多的压缩阶段之间，尽量布置中间冷却。由于气体是进行绝热式压缩的，而不是等温压缩的，因此，首先希望减少作功和功率的损失；其次，由于间隙容积的原因，会减少总体的输出损失。c) 泵中空气的预压缩压力应升高到输送管中的压力。尽管标准往复泵因具有自动阀或受压弹簧阀能保证这点，但某些旋转式压缩机则必须配专用气阀来配流，以便获得预压缩，而另一些泵则全然不可能做到。泵内无预压力，一旦排气阀口打开，管道中的气体会膨胀而回到泵内，整个泵内的流体会再次被压缩。具有预压缩装置的旋转压缩机不可能输送液体油。d) 缸体的气冷或水冷措施，使得压缩机中气体温度尽可能保持等温状态，而被输送的气体体积相应增加。这是液压泵在正常情况下所不需要的特性。e) 在压缩过程中，控制气体泄漏的措施，是靠往复运动式压缩机的活塞上的密封环，或靠旋转式压缩机上的微小间隙。f) 配置足够的进气阀面积，以防止进来的气体在节流过程中所产生的容积效率损失。各种主要类型的泵和压缩机，都采用了活塞、互相啮合的齿轮或旋转的叶轮，这些类型的泵和压缩机已经证明能够提供高压和良好性能。其他类型的泵，例如离心泵或者涡轮压缩机，是不用于压力系统的，因为它们不能产生足够高的有用的压力。 Sources of Pressure - Pumps and CompressorsFundamentally most pumps suitable for pumping hydraulic fluid will operate with air or gas, although most oil pumps make poor air compressors, and some compressors will not operate with incompressible fluid without modification.General considerations. The main requirements of a hydraulic pump capable of delivering sufficiently great a pressure to be of practical use, are:a. Means for controlling fluid leakage either by special seals or close working clearances.b. A substantially uniform, non-pulsating delivery.c. The absence of trapping of fluid during rotation, since the fluid is for all practical purpose incompressible.d. Mechanical balance to a sufficient degree to enable the pump to be run as fast as possible, to reduce bulk for a given output.e. Adequate provision for minimizing the effect of distortion of the working parts, casings, ect.,due to the internal pressure in the pump.f. Low clearance volumes so that the pump will act momentarily during priming, or with aerated fluid, as a compressor, to discharge the air through the delivery line, instead of leaving it trailed in the pump. g. Adequate inlet valve or port provision to enable the pump to create a good suction, or alternatively, as in the case of aircraft, to operate at high altitude, and with relatively thick fluids. It should be noted that the time of opening of the inlet valve or port is almost as important as the size of the port.The main requirements of a good compressor are:a. the smallest possible clearance volume compatible with mechanical clearance; this is because any gas compressed in the clearance volume will expand again instead of being discharged, and will thus adversely affect not only the output of the pump, but the maximum pressure that can be achieved.b. Except on low-pressure pumps, two or more stages of compression with as much intercooling between stages as possible. This is desirable, firstly, to reduce the wastage of work and output due to the gas being compressed adiabatically instead of isothermally, and, secondly, to reduce the overall loss of output due to clearance volume.c. Pre-compression of the air in the pump up to the pressure of the delivery line. Although the normal reciprocating pump with an automatic or spring-load delivery valve will ensure this, some of the rotary compressors have to be ported specially to obtain pre-compression, and with some it is not possible at all. Without pre-compression, as soon as the delivery port opens, the gas in the delivery pipe expands back into the pump, and the whole volume has again to be compressed. A rotary compressor with pre-compression cannot be operated with hydraulic fluid.d. Provision for air or water cooling of the cylinder so that the temperature of the air in the compressor may be kept as near isothermal as possible, and the volume of air being delivered correspondingly increased. This is a feature not normally necessary on a hydraulic pump.e. Means for controlling gas leakages during compression either by piston rings on a reciprocating piston compressor, or fine clearances on the rotary types.f. Adequate inlet valve area to prevent throttling of the incoming air, with the consequent loss of volumetric efficiency.The main types of pump and compressor use pistons, meshing gears or