【正文】 of the pistons to move reciprocating. The pistons’ reciprocating motion converts into crankshaft rotation through the crank and connecting rod mechanism. The crankshaft then drives the distribution valve which fixed on it to move simultaneously, causing the pressed air to enter different cylinders according to the angle change of distribution valve. The pistons move in turn to develop a continuous crankshaft rotation. At the same time, the cylinder opposite to the inlet cylinders is connected to the atmosphere and the high pressure air is released. The soft feature of the powerspeed and the torquespeed characteristic curves of piston motors under different working pressures are also very evident. (3)Diaphragm motors: Diaphragm motors are basically an application of diaphragm cylinders. The cylinder’s reciprocating motion converts into the ratchet wheel’s intermittent rotary output pressibility, . the output torque falls off with the increase of intermittent transmission speed under the constant working pressure. 大連交通大學(xué)信息工程 學(xué)院 2020 屆本科生畢業(yè)設(shè)計(jì)（論文）外文翻譯 7 Selection and application of air motors (1)Air motors’ selection: The selection of air motors is mainly base on its loaded conditions. In variable load occasions, the speed range and the torque needed to meet working conditions are principally considered. Working speed is also an important factor for constant load occasions. Other factors must be considered except for the above performancerelated factors, such as working pressure, gas consumption installation type, etc. (2)Air motors’ application: Air motors find more and more applications as the developing of the productivity. They can be used in all walks of life, particularly applicable for the occasions which require safetyneeded, stepless speed changing, frequent direction changing for startup, resistant exploding, and load startup and that easy to be overloaded. They are equally suitable the harsh environment with moisture, high temperature, vibration or that inconvenient to operate directly, such as mine, car manufacturing. (3)Air motors’ lubricating: The working medium of air cannot provide lubrication itself, so additional lubricants are needed in air motors. Proper used and nice lubricating will extend air motors’ use life, with the second repair time of 2500 3000h or longer. The mon way to lubricate is to set an oil mist lubricator before the control valve in the air motor and supply oil in time。 the lubricant will enter the system with the pressed air to acplish lubricating purposed. Pneumatic control elements An important item in a pressed air layout is a regulating valve which ensures the desired pressure, flow rate and direction in the system. The first important function of these valves is for safety。 the second function is to provide for a part of the system to operate at a lower pressure than the main supply. There are various types of regulating valves。 generally they can be divided into three main categories defined by the functions they perform: pressure control, flow control and directional control The pneumatic fixed value switching regulating valves are similar to hydraulic regulating valves。 there are also pneumatic proportional regulating valves and pneumatic servocontrol valves. The recentlydeveloped valve terminal has the advantages of concise construction, easy to install and maintain, high degree of modularization, and can achieve centralized control in medium or small pneumatic systems. Pneumatic attachments Mufflers Unlike hydraulic circuits, there are no return pipelines in pneumatic circuits. The pressed air exhausts to the atmospheric directly after having been used. The air will sharply expend due to high pressure difference and produce serious exhausting noise. Usually 大連交通大學(xué)信息工程 學(xué)院 2020 屆本科生畢業(yè)設(shè)計(jì)（論文）外文翻譯 8 a muffler is set at the discharge port to reduce the velocity and power of the jet noise by means of damp or increasing exhausting area. Three types of muffler are available: absorptive mufflers, expansive mufflers, expansive and absorptive mufflers. This is an absorptive muffler structure. The muffler body is made of multihole absorptive material, sintered by copper or polystyrene bean. Today absorptive mufflers are also most wildly used. Pipeline connectors Pipeline connectors incorporate tubes and pipe fittings. There are rigid tubes and hose tubes. Pipe couplings include bite type tube fittings, flared type tube fittings, corpling of borsing and quick release fittings. 大連交通大學(xué)信息工程 學(xué)院 2020 屆本科生畢業(yè)設(shè)計(jì)（論文）外文翻譯 9 氣壓傳動(dòng) 類似與液壓傳動(dòng)，氣壓傳動(dòng)通過(guò)介質(zhì)的流量來(lái)執(zhí)行能量傳遞和控制的功能。在工作原理、組成結(jié)構(gòu)、系統(tǒng)組成及圖形符號(hào)等方面，他們有許多共同之處。讀者應(yīng)該注意到他們的不同之處。氣動(dòng)系統(tǒng)包含以下組件和設(shè)備： (1) 氣壓發(fā)生裝置：他們包括壓力產(chǎn)生設(shè)備、空氣再生和儲(chǔ)存設(shè)備， FRL（空氣過(guò) 濾器、減壓閥和油霧潤(rùn)滑）組件，等等。它為氣動(dòng)系統(tǒng)提供合格的壓縮氣體。 (2) 執(zhí)行元件：他們把壓縮空氣的壓力能轉(zhuǎn)變?yōu)闄C(jī)械能，例如 氣動(dòng)缸和氣動(dòng)馬達(dá)。 (3) 控制元件：他們是被用來(lái)控制壓縮氣體壓力、流速、和流動(dòng)方向，是執(zhí)行機(jī)構(gòu)按要求工作，如氣動(dòng)閥。 (4) 氣動(dòng)輔件：氣動(dòng)輔件包含使壓縮空氣冷卻、消聲、凈化和潤(rùn)滑以及用于連接各元件所需要的一些裝置。 氣壓發(fā)生裝置 氣壓發(fā)生裝置是用來(lái)為氣動(dòng)系統(tǒng)提供壓縮氣體的。一套氣體發(fā)生裝置是氣動(dòng)系統(tǒng)的重要組成部分之一，為氣動(dòng)系統(tǒng)提供合格的壓縮空氣（具有一定的壓力、流量和凈化過(guò)的）。一般來(lái)說(shuō)，對(duì)于流量超過(guò)或等于 6～ 12 min3m ，空氣壓縮站是必須具備