【正文】 cing its volume as described by the perfect gas systems normally use a large centralized air pressor which is considered to be an infinite air source similar to an electrical system where you merely plug into an electrical outlut for electricity. In this way, pressurized air can be piped from one source to various locations throughout an entire industrial plant. The air then flows through a pressue regulator which redeces the pressure to the desired level for the particular circuit application. Because air is not a good lubircant（ contains about 20% oxygen） , pneumatics systems required a lubricator to inject a very fine mist of oil into the air discharging from the pressure regulator. This prevents wear of the closely fitting moving parts of pneumatic ponents. Free air from the atmosphere contains varying amounts of moisure. This moisure can be harmful in that it can wash away lubricants and thus cause excessive wear and corrosion. Hence ,in some applications ,air driers are needed to remove this undesirable moisture. Since pneumatics systems exhaust directly into the atmosphere, they are capable of generating excessive noise. Therefore, mufflers are mounted on exhaust ports of air valves and actuators to reduce noise and prevent operating personnel from injury resulting not only from exposure to noise but also from highspeed airborne particles. There are several reasons for considering the use of pneumatic systems instead of hydraulic systems. Liquids exhibit greater inertia than do gases. Therefore, in hydraulic systems the weight of oil is a potential problem when accelerating and decelerating actuators and when suddenly opening and closing valves. Due to Newton’s law of motion(force equals mass multiplied by acceleration), the force required to accelerate oil is many times greater than that required to accelerate an equal volume of air. Liquids also exhibit greater viscosity than do gases. This results in larger frictional pressure and power losses. Also ,since hydraulic systems use a fluid foreign to the atmosphere, they require special reservoirs and noleak system designs. Pneumatic system use air which is exhausted directly back into the surrounding environment. Generally speaking, pneumatic systems are less expensive than hydraulic systems. However, because of the pressibility of air, it is impossible to obtain precise controlled actuator velocities with pneumatic systems. Also, precise positioning control is not obtainable. While pneumatics pressures are quite low due to pressor design limitations(less than 250 psi), hydraulic pressures can be as high as 10000 psi. Thus, hydraulics can be highpower systems, whereas pneumatics are confined to lowpower applications. Industrial applications of pneumatics systems are growing at a rapid pace. Typical examples include stamping, drilling, hoist, punching, clamping, assembling, riveting, materials handling, and logic controlling operations. 翻譯： 流體和液壓系統(tǒng) 水力的歷史由來已久，始于人類為利用它周圍的能源而做出的努力。容易利用的能源就是水和風(fēng) —— 兩種自由的流動流體。 第一臺液力裝置水車是最早的發(fā)明。從 15 世紀早期，水車圖畫就出現(xiàn)在大宮殿的 馬賽克上。磨粉機由羅馬人發(fā)明，而水磨機的歷史更早，可以追溯到大約公元前 100 年。當(dāng)一些上進的農(nóng)場主厭惡由手工沖擊、研磨谷物時，谷物的家庭養(yǎng)殖已開始 5000 多年。也許，真正的發(fā)明家是那些農(nóng)場主的妻子，因為她們經(jīng)常要干重的農(nóng)活。 流體是可以流動的物體，與就是說，構(gòu)成物質(zhì)的粒子可以連續(xù)地改變它們之間的相對位置，而且，它提供流體層間流動非連續(xù)的阻力。這意味著流體在靜止時，在其內(nèi)部沒有剪切力（作用表面切向方向的受力）存在。 流體可以分為牛頓流體或非牛頓流體。在牛頓流體中，流體層間作用的剪切力和角度變形總量的大小成線性 關(guān)系。在非牛頓流體中，流體層間作用的剪切力和角度變形總