本科生毕业设计 (论文)外 文 翻 译原 文 标 题Oil pressure pump cover译 文 标 题油压泵简介作者所在系别机械工程系作者所在专业机械设计制造及其自动化作者所在班级机本1007作 者 姓 名龙张平作 者 学 号10201420739指导教师姓名范志明指导教师职称副教授完 成 时 间2014年5月20译文标题油压泵原文标题Oil pressure pump cover 作 者 译 名国 籍原文出处http:/www.freepatentsonline.com原文A hydraulic pump is a mechanical device which converts mechanical energy into hydraulic energy.More specifically ,a pump converts the kinetic(moving) energy of a rotating shaft into the kinetic energy of fluid flow. The fluid flow also has potential energy that allows it to overcome the resistance of the system to fluid flow .Remember that a pump provides the force produce flow and transmit power . Hydraulic pressure is caused by the load on the system and by the resistance of the hydraulic system to fluid flow.When operating , a hydraulic pump performs two functions. First, it creates a partial vacuum at its inlet ,permitting the atmospheric pressure in the fluid reservoir to push the hydraulic fluid through the inlet strainer and line into the pump .Second, its mechanical action delivers the fluid to its outlet and into the hydraulic systems, as shown in Fig.5-1. As the fluid leaves the pump, it encounters the working pressure in the system. This pressure is produced by the pressure regulating valve, the system work load ,and flow losses in the hydraulic tubingA pump is classified on the basis of the physical arrangement of its pumping mechanism and its basic principle of operating. Pumps classified by principle of operation include positive displacement and nonpositive-displacement types. Positive-displacement pumps are equipped with a mechanical separation(gears,vanes,or impellers) between the inlet and outlet, which minimizes internal leakage or slippage. Therefore,the output of positive-displacement pumps is almost unaffected by variations in system pressureNopositive-displacement pumps(such as centrifugal pumps) do not have a positive internal separation against leakage or slippage. Because of this slippage,the delivery of these pump is reduced as the working pressure of a system is increased. However, nonpositive-displacement pumps deliver a continuous flow, while positive-displacement pumps deliver an intermittent(pulsating) flow. These pulsations are small and can be smooth out by the accumulator or the system piping. Most hydraulic pumps are positive-displacement pumps of the rotary type.Positive-displacement pumps have either a fixed or variable displacement. The volume of delivery ,or gpm, of a fixed-displacement pump can be changed only by changing the speed of the pump, because the physical arrangement of the pumping mechanism cannot be changed, (This does not mean that the flow in other portions of the system cannot be adjusted by valves.)The flow of a variable-displacement pump can be changed by changing the physical arrangement of the pumping mechanism with a built-in controlling device. This device often functions in response to system pressure or other signals. Variable-displacement pumps are more complex than fixed-displacement pumps and,therefore,cost more. In addition, the efficiency of a variable-displacement pump is lower than that of a fixed-displacement pump. This is offset somewhat by the higher overall efficiency of a system powered by a variable-displacement pump.Most positive-displacement pumps are classified as rotary pumps. This is because the assembly that transfers the fluid from the pump inlet to the pump outlet has a rotating motion. Rotary pumps are further classified according to the mechanism that transfers the fluid-such as gears,vanes,or screws.A different kind of positive-displacement pump is piston pump. This pump uses a reciprocating (back-and-forth) motion of the piston, alternately to receive fluid on the inlet side, and to discharge fluid on the outlet side. A radial-piston pump has a revolving assembly with several piston assemblies built into it, and can be classified as a rotary pump. Several types of piston pumps will be discussed later in this chapter.The performance of different pumps is evaluated on the basis of many factors, inculding physical characteristics, operating characteristics,and cost. When selecting a pump, the follow pump rating and selection factors are considered;CapacityPressureEnergy consumptionDrive speedEfficiencyReliabilityFluid characteristicsSize and weightControl adaptabilityService lifeInstallation and maintenance costsSome of the performance characteristics of different pumps are given in Table 5-1.Each of these selection factors is described briefly in the following paragraph.The primary rating of a pump is its capacity. This is also called the delivery rate ,flow rate, or volumetric output. The capacity usually is given in gallons per minute (gpm), cubic inches per minute() ,or cubic inches per revolution at specified