英文翻译外文文献翻译404硬齿面齿轮减速器的价格现状及分析.docxVIP

（二）Hardened gear reducer prices and AnalysisThe purpose of the pump ,to give pressure to the oil ; in other words, to give power to the machine .The purpose of the valves is to control the flow of oil and to apply the power when and where it may be needed .To illustrate as simply as possible how this is accomplished in a “circuit”, that is , in the run of oil from the reservoir ,through the pump , the valves , the driven unit , and back to the reservoir, references are made to the diagrams shown in Figs,11.1 and 11.2.Every fluid-power system used one or more pumps to pressurize the hydraulic fluid the fluid under pressure, in turn, performs work in the output section of the fluid-power system. Thus, the pressurized fluid may be used to move a piston in a in a cylinder or to turn the shaft of a hydraulic motor.So we find that find that every modern fluid –power system used at least one pump to pressurize the fluid.TYPES OF PUMPSThree types pumps find use in fluid-power systems: rotary , reciprocating, and centrifugal pumps .Simples hydraulic systems may use but one type of pump, The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In matching the characteristics of the pump to the requirements of the hydraulic system, it is not unusual to find two types of pumps in series . For example , a centrifugal pump may be may be used to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for the controls associated with a reversing variable-displacement reciprocating pump .ROTARY PUMPSThese are built in many different designs and are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur gear , internal-gear , generated rotor , sliding-vane , and screw pump . Each type has advantages that make it most suitable for a given application.Spur-Gear Pumps. These pumps (Fig.11.3) have two mating gears are turned in a closely fitted casing. Rotation