压缩机Compressors

压缩机Compressors(中文4900字,英文2800字)
泵和压缩机主要区别是：流体被压缩机传送—气体—在它被传送的同时被压缩并处于压力之下，即使系统在没有载荷的情况下。大多数用于空气压缩的装置原理上非常相似--甚至在零部件上-如液压泵，考虑和选择是相同的。
它们本质上唯一的不同是大多数的液压系统由单一泵供给能量，并且泵实际上是系统的一部分，而大多数的气动动力系统往往由单一压缩机供给能量，像厂区内的水、电力服务一样它几乎是厂区“公共设施”。不过有许多小型压缩机用于特殊、不连续的工作场合。他们通常是可移动型压缩机。动力型的或非移动型压缩机通常是大型的单元设备。
压缩机装置比较简单，如果纳入适当的气动系统则使压缩机能长期维持运转，由于在系统设计中忽视了明显的注意事项导致了压缩机一次又一次的前期故障。只要适度的努力遵循四项基本规则可大大提高压缩机设计寿命：
•    泵和压缩机应该以最低压力和流量来分级，最好在10至25%以上；
•    应选择过滤器来保护泵单元，并且有时也保护下游产品和部件；
•    应选择安全阀来保持压力或真空度在适当的水平；
•    泵单元应安放在一个干净、通风、干燥的环境。

Compressors
The main difference between pumps and compressors is that the fluid delivered by compressors -- air -- is compressed and under pressure at the time it is delivered, even if there is no load on the system. Most devices used to compress air are very similar in concept and -- perhaps even in hardware -- to hydraulic pumps, and selection considerations are similar.
The only other substantive difference is that most hydraulic systems are powered by a single pump that is actually a part of the system, whereas a host of pneumatic systems are often powered by a single compressor, which is almost a "utility" in the plant like water or electric service. Nevertheless, many small compressors are available for specific, discrete jobs; typically they are positive-displacement compressors. Dynamic, or nonpositive-displacement compressors are typically larger, facility-type units.
Compressors are fairly simple devices, capable of long periods of maintenance-free operation if properly integrated into pneumatic systems. Yet time and again they suffer from early failures because obvious precautions were ignored during system design. Four basic rules can provide substantial improvement in compressor life with only moderate design effort:
•    Pumps and compressors should be sized to provide at least the required pressure and flow, and preferably 10 to 25% more.
•    Filters should be selected to protect the pumping unit, and sometimes to protect downstream components or products as well.
•    Relief valves should be selected to keep pressure or vacuum at appropriate levels.
•    Pumping units should be placed in a clean, cool, dry environment.