液压与气动系统外文翻译

液压与气动系统

仅有以下三种基本方法传递动力：电气、机械和流体。大多数应用系统实际上是将三种方法组合起来而得到最有效地

最全面的系统。为了合理地确定采取哪种方法，重要的是了解各种方法的显著特征。例如液压系统在长距离上比机械系统更能经济地传递动力。然而液压系统与电气系统相比，传递动力的距离较短。

液压动力传递系统涉及电动机、调节装置和压力，流量控制，总的来说，该系统包括：

l 泵：将原动机的能力转换成作用在执行部件上的液压能。

2 阀：控制泵产生流体的运动方向、产生的功率的大小，以及到达执行部件液体的流量。功率大小取决于对流量和压力大小的控制。

3 执行部件：将液压能转换成可用的机械能。

4 介质即油液：可进行无压缩传递和控制，同时可以润滑部件，使阀体密封和系统冷却。

5联接件：联接各个系统部件，为压力流体提供功率传输通路，将液体返回邮箱。

6 油液贮存和调节装置：用来确保提供足够质景和数量并冷却的液体。

液压系统在工业中应用广泛，例如冲压，钢类工件的磨削及一般加工业、农业、矿业、航大技术、深海勘探、运输、海洋技术，近海天然气和石油勘探等行业，简而言之，在日常生活中很少有人不从液压技术中得到某种益处。

液压系统成功而又广泛使用的秘密在与它的通用性和

易操作性。液压动力传递不会像机械系统那样受到机器几何形体的制约，另外，液压系统不会像电气系统那样受到钢的磁饱和极限的限制，相反，液压系统的功率仅仅受材料强度的限制。

企业为了提高生产率将越来越依靠自动化，这包括远程和直接控制生产操作、加工过程和材料处理等。液压动力之所以成为自动化的重要组成部分，是因为它有如下主要的四

种优点：

1 控制方便精确通过操作一个简单的操作杆和按钮，液压系统的操作者便

能立即起动、停止、加减速和能提供任意功率、位置精度为万分之一英寸的位置控制力。

2 增力一个液压系统（没有使用笨重的齿轮、滑轮和杠杆）能简单有效地将不到一盎司的力放大产生几百吨力的输出。

3 恒力或恒扭只有液压系统能提供不随速度变化而变化的

恒力或恒扭矩，它可以驱动对象从每小时移动几英寸到每分钟几百英寸，从每小时几转到每分钟几千转。

4 简便、安全、经济总的来说，液压系统比机械或电气系统使用更少的运动部件，因此，它们运行与维护简便。这使得系统结构紧凑，安全可靠。例如一种用于车辆上的新型动力转向控制装置己淘汰其他类型的转向动力装置，该转向部件中包含有人力操纵方向控制阀和分配器。因为转向部件是全液压的，没有万向节、轴承、减速器齿轮等机械连接，这使得系统简单紧凑．

另外，只需输入很小的扭知就能产生满足极恶劣工作条件所需的控制力，这对于因操作空间限制而需要小方向盘的场合很重要，这也是减轻司机疲劳度所必需的。

液压系统的其他优点包括双向运动、过载保护和无极变速控制，在己有的任何动力系统中液压系统亦具有最大的单位质量功率比。

尽管液压系统具有如此高性能，但它不是可以解决所有动力传递问题的灵丹妙药。液压系统也有些缺点，液压油油污染，并且泄漏不可能完全避免，另外如果油液渗漏发生在灼热设备附近，大多数液压油能引起火灾。

下面以一具体实例― -液压站来介绍液压系统的优越性。

液压站又称液压泵站，是独立的液压装置。

它按逐级要求供油。并控制液压油流的方向、压力和流量，适用于主机与液压装置可分离的各种液压机械上。

用户购后只要将液凡站与主机上的执行机构（油缸或油

马达）用油管相连，液压机械即可实现各种规定的动作和工作循环。

液压站是由泵装置、集成块或阀组合、由箱、电气盒组合而成。各部件功能为：

泵装置--上装有电机和油泵，是液压站的动力源，将机械能转化为液压油的压力能。

集成块--由液压阀及通道体组装而成。对液压油实行方向、压力和流量调节。

阀组合--板式阀装在立板上，板后管连接，与集成块功能相同。

油箱--板焊的半封闭容器，上还装有滤油网、空气滤清器等，用来储油、油的冷却及过滤。

电气盒--分两种型式。一种设置外接引线的端子板：一种配置了全套控制电器。

液压站的工作原理：电机带动油泵转动，泵从油箱中吸油供油，将机械能转化为液压站的压力能，液压油通过集成块（或阀组合）实现了方向、压力、流最调节后经外接管路并至液压机械的油缸或油马达中，从而控制液动机方向的变换、力量的大小及速度的快慢，推动各种液压机械做功。

1.发展历程

我国液压（含液力，下同）、气动和密封件工业发展历程，大致可分为三个阶段，即：20 世纪50 年代初到60 年代初为起步阶段：60 -70 年代为专业化生产体系成长阶段；80-9 0年代为快速发展阶段。其中，液压工业于50 年代初从机床行业生产仿苏的磨床、拉床、仿形车床等液压传动起步，液压元件由机床厂的液压车间生产，自产自用．进入60 年代后，液压技术的应用从机床逐渐推广到农业机械和工程机械等领域，原来附属于主机厂的液压车间有的独立出来，成为液压件专业生产厂。到了60 年代末、70 年代初，随着生产机械化的发展，特别是在为第二汽车制造厂等提供高效、自动化设备的带动下，液工压元件制造业出现了迅速发展的局面，一批中小企业也成为液压件专业制造厂。1968 年中

国液压元件年产景已接近20 万件：1973 年在机床、农机、工程机械等行业，生产液抓件的专业厂己发展到100 余家，年产量超过100 万件，一个独立的液压制造业己初步形成。这时，液压件产品已从仿苏产品发展为引进技术与自行设计相结合的产品，压力向中、高压发展，并开发了电液伺服阀及系统，液压应用领域进一步扩大。气动工业的起步比液压稍晚儿年，到1967 年开始建立气动元件专业厂，气动元件才作为商品生产和销售。含橡塑密封、机械密封和柔性石墨密封的密封件工业，50 年代初从生产普通0 型圈、油封等挤压橡塑密封和石棉密封制品起步，到60 年代初，开始研制生产机械密封和柔性石墨密封等制品。70 年代，在原燃化部、一机部、农机部所属系统内，一批专业生产厂相继成立，并正式形成行业，为密封件工业的发展成长奠定了墓础。进入80 年代，在国家改革开放的方针指引下，随着机械工业的发展，基础件滞后于主机的矛盾日益突出，并引起各有关部门的重视。为此，原一机部于1982 年组建一通用基础件工业局，将原有分散在机床、农业机械、工程机械等行业归口的液压、气动和密封件专业厂，统一划归通用基础件局管理，从而使该行业在规划、投资、引进技术和科研开发等方面得到基础件局的指导和支持。从此进入了快速发展期，先后引进了60 余项国外先进技术，其中液压40 余项、气动7 项，经消化吸收和技术改造，现均己批量生产，并成为行业的主导产品。近年来，行业加大了技术改造力度，1991 -1998年国家、地方和企业自筹资金总投入共约20 多亿元，其中液压16 亿多元。经过技术改造和技术攻关，一批主要企业技术水平进一步提高，工艺装备得到很大改善，为形成高起点、专业化、批量生产打下了良好墓础。近几年，在国家多种所有制共同发展的方针指引下，不同所有制的中小企业迅猛崛起，呈现出勃勃生机。随着国家进一步开放，三资企业迅速发展，对提高行业水平和扩大出口起着重要作用。目前我国己和美国、日本、德国等国家著名厂商合资或由外国厂商独资建立了柱塞泵／马达、行星减速机、转向器、液压控制阀、液压系统、静液压传动装置、液压件铸造、气动

控制阀、气缸、气源处理三联件、机械密封、橡塑密封等类产品生产企业50 多家，引进外资2 亿多美元。

二、日前状况

( 1 ）基本概况

经过40 多年的努力，我国液压、气动和密封件行业已形成了一个门类比较齐全，有一定生产能力和技术水平的工业体系。据1995 年全国第三次工业普查统计，我国液压、气动和密封件工业乡及乡以上年销售收入在100 万元以上的国营、村办、私营、合作经营、个体、“三资”等企业共有1300 余家，其中液压约700 家，气动和密封件各约300 余家。按1996 年国际同行业统计，我国液压行业总产位23 . 48 亿元，占世界第6 位：气动行业总产值4 . 19 亿元，，占世界第10 位。

( 2 ）当前供需概况

通过技术引进，自主开发和技术改造，高抓柱塞泵、齿轮泵、叶片泵、通用液压阀门、油缸、无油润滑气动件和各类密封件等一大批产品的技术水平有来了明显的提高，并可稳定的批量生产，为各类主机提高产品水平提供了保证。另外，在液压气动元件和系统的CAD、污染控制、比例伺服技术等方面也取得一定成果，并已用于生产。目前，液压、气动和密封件产品总计约有3000 个品种、23000 多个规格。其中，液压有1200 个品种、10000 多个规格（含液力产品60 个品种、500 个规格）；气动有1350 个品种、8000 多个规格：橡塑密封有350 个品种、5000 多个规格，已基木能适应各类主机产品的一般需要，为重大成套装备的各种配套率也可达6 0％以上，并开始有少量出口。

1998 年国产液压件产量480 万件，销售额约28 亿元（其中机械系统约占 70 % ) ：气动件产量360 万件，销售额约5 . 5 亿元（其中机械系统约占6 0%）；密封件产最约8 亿件，销售额约10 亿元（其中机械系统约占50%）。据中国液压气动密封件工业协会1998 年年报统计，液压产品产销率为97 . 5 % （液力为101 % ) , 气动为95 . 9 % ，密封为98.7 ％。这充分反映了产销基本衔接。

我国液压、气动和密封工业虽取得了很大的进步，但与主机发展需求，以及和世界先进水平相比，还存在不少差距，主要反映在产品品种、性能和可靠性等方面。以液压产品为例，产品品种只有国外的1 / 3 ，寿命为国外的1 / 2 。为了满足重点主机、进口主机以及重大技术装备的需要，每年都有大量的液压、气动和密封产品进口。据海关统计及有关资料分析，1998年液压、气动和密封件产品的进口额约2 亿美元，其中液压约1 . 4 亿美元，气动近0 . 3 亿美元，密封约0 . 3 亿美元，比1997 年稍有下降。按金额计，目前进口产品的国内市场占有率约为30 ％。1998 年国内市场液压件需求总量约600 万件，销售总额近40 亿元：气动件需求总量约500 万件，销售总额7 亿多元：密封件需求总量约11 亿件，销售总额约13 亿元。

三、今后发展走势

1 、影响发展的主要因素

（1)企业产品开发能力不强，技术开发的水平和速度不能完全满足先进主机产品、重大技术装备和进口设备的配套和维修需要：

（2）不少企业的制造工艺、装备水平和处理水平都较落后，加上质量意识不强，导致产品性能水平低、质量不稳定、可靠性差，服务不及时，缺乏使用户满意和信赖的名牌产品；

（3）行业内生产专业化程度低，力最分散，低水平承狂严承，地区和企业之间产品趋同，盲目竞争，相互压价，使企业效益下降，资金缺乏、周转困难，产品开发和技术改造投入不足，严重地制约了行业整体水平的提高以及竞争实力的增强：

(4）国内市场国际化程度日益提高，国外公司纷纷进入中国市场参与竞争，加上国内私营、合作经营、个体、三资等企业的崛起，给国有企业造成愈来愈大的冲击。

2 、发展走势

随着社会主义市场经济的不断深化，液压、气动和密封产品

的市场供求关系发生较大变化，长期来以“短缺”为特征的卖方市场已基本成为以“结构性过剩”为特征的买方市场所取代。从总体能力看，已处于供大于求的态势，特别是一般低档次液压、气动和密封件，普遍供过于求：而主机急需的技术含量高的高参数、高附加值的高档产品，又不能满足市场需要，只能依赖上进口。在我国加入WTO 后，其冲击有可能更大。因此，“十五”期间行业产值的增长，决不能依赖于量的增长，而应针对行业自身的结构性矛盾，加大力度，调整产业结构和产品结构，也就是应依靠质的提高，促进产品技术升级，以适应和拉动市场需求，求得更大的发展。

气压系统

气压系统是用压力气体传递和控制动力，正如名称所表明的那样，气压系统通常用空气（不用其他气体）作为流体介质，囚为空气是安全、成本低而又随处可得的流体，在系统部件中产生电弧有可能点燃泄漏物的场合下（使用空气作为介质）尤其安全。

在气压系统中，压缩机用来压缩并供应所需的空气。压缩机一般有活塞式、叶片式和螺旋式等类型。压缩机基本上是根据理想气体法则，通过减小气体体积来增加气体压力的。气压系统通常考虑采用大的中央空气压缩机作为一个无限量

的气源，这类似于电力系统中只要将插头扬入插座便可获得电能。用这种方法，压力气体可以从气源输送到整个工厂的各个角落，压力气体可通过空气滤清器除去污物，这些污物可能会损坏气体组件的精密配合部件如阀和气缸等，随后输送到各个回路中，接着空气流经减压阀以减小气压值适合某一回路使用。因为空气不是好的润滑剂（包括20 ％的氧气），气压系统需要一个油雾器将细小的油雾注射到经过减压阀

减压的空气中，这有助于减小气动组件精密配合运动件的磨损。

由于来自大气中的空气含不同数量的水分，这些水分是有害的，它可以带走润滑剂引起过分磨损和腐蚀。因此，在一些使用场合中，要用空气干燥器来除去这些有害的水分。

由于气压系统直接向大气排气，会产生过大噪声，因此可在气阀和执行组件排气口安装消声器来降低噪声，以防止操作人员因接触噪声及高速空气粒子有可能引发的伤害。

用气动系统代替液压系统有以下几条理由：液体的惯性远比气体大，因此，在液抓系统中，当执行组件加速减速和阀突然开启关闭时，油液的质量便是一个潜在的问题，根据牛顿运动定律（力等于质量乘以加速度），产生加速运动油液所需的力要比加速同等体积空气所需的力高出许多倍。

液体比气体具有更大的粘性，这会因为内冷擦而引起更大的压力和功率损失：另外，由于液压系统使用的液体要与大气隔绝，故它们需要特殊的邮箱和无泄漏系统设计。气压系统使用可以直接排到周围环境中的空气，一般来说气压系统没有液体系统昂贵。然而，由于空气的可压缩性，使得气庄系统执行组件不可能得到精确地速度控制和位置控制。气压系统由于压缩机局限，其系统压力相当低（低于25Opsi ) , 而液压力可达10000psi之高，因此液压系统可以是大功率系统，而气动系统仅用于小功率系统，典型例子有冲压、钻孔、提升、冲孔、夹紧、组装、铆接、材料处理和逻辑控制操作等。

Hydraulic System

There are only three basic methods of transmitting power ：electrical，mechanical ,and fluid power.Most applications actually use a combination of the three methods to obtain

the most efficient overall system. To properly determine which principle method to use, it isimportant to know the salient features of each type. For example，fluid systems can transmit power more economically over greater distances than can mechanical types. However,fluid systems are restricted to shorter distances than are electrical systems. Hydraulic power transmission system are concerned with the generation, modulation,and control ofptrssutr and flow, and in general such systems include:

l. Pumps which convert available power from the prime mover to hydraulic power at the actuator.

2.Valves which control the direction of pump-flow.the level of power produced,and the amount of fluid-flow to the actuators. The power level is determined by controlling both the flow and pressure level.

3.Actuators which convert hydraulic power to usable mechanical power output at the point required.

4.The medium which is a liquid, provides rigid transmission and control as well as lubrication of compments, sealing in valves, and cooling of the system.

5.Connectors which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank（reservoir).

6.Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid.

Hydraulic systems are used in industrial applications such as stamping presses, steelmills，and general manufacturing, agricultural machines, mining industry, aviation. spacetechnology,deep-sea exploration, transportation,rnarine technology, and offshore gas and petroleum exploration. In short, very few people get through a day of their lives without somehow benefitiong from the technology of hydraulics.

The secret of hydraulic system?ˉs success and widespread use is its versatility and manageability. Fluid power is not hindered by the geometry of the machine as is the case in mechanical systems. Also,power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example .the performance of an electromangnet is limited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material.

Industry is going to depend more and more on automation in order to increase productivity.This includes remote and direct control of production poerations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories.

1 Ease and accuracy of control. By the use of simple levers and push buttons, the poerator of a fluid power system can readily start , stop ,speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one ten-thousandth of au inch.

2Multiplication of force. A fluid power system (without using cumbersomegears, pulleys, and levers) can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output.

3 Constant force or torque.Only fluid power systems are capable of providing constant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches per minute, a few revolutions per hour, or thousands of revolutions per minute.

4 Simplicity, safety, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This , in turn, maximizes safety, compactness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on

many off-highway

vehicles. The steering unit consists of a manually poerated directional control valve and meter in a single body. Because the steering unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears ,etc. arecliminated. This provides a simple, compact system. In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control space require a small steering wheel and it becomes necessary to reduce operator fatigue. Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads ,and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems .Hydraulic, systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to completely eliminate. Also, most hydraulic oils can cause tires if an oil leak occurs in an area of hot equipment.

Now, below a concrete example - hydraulic stations to introduce the advantages of the hydraulic system.

Hydraulic Station and the development of hydraulic componenis Profiles

Hydraulic Pump Station also known as the stations are independent hydraulicdevice.

It requested by the oil gradually. And controlling the hydraulic oil flow direction, pressure and flow rate, applied to the mainframe and hy- draulic devices separability of hydraulic machinery.

Users will be provided after the purchase hydraulic station and host of implementing agencies (motor oil or fuel tanks) connected with tubing, Hydraulic machinery can be realized from these movements and the work cycle.

Hydraulic pump station is installed, Manifold or valve combination, t-anks, a combination of electrical boxes.

Functional components

Pump device -- is equipped with motors and pumps. hydraulic station is the source of power. to mechanical energy into hydraulic oil pressure can be.

Manifold -- from hydraulic valve body and channel assembled. Right direction for implementation of hydraulic oil, pressure and flow control.

Valve portfolio -- plate valve is installed in up board after board connects with the same functional IC.

Tank -- plate welding semi-closed containers, also loaded with oil filtering network, air filters, used oil, oil filters and cooling.

Electrical boxes -- at the two patterns. A set of external fuse terminal plate:

distribution of a full range of electrical control.

Hydraulic Station principle : motor driven pump rotation, which pump oil absorption from the oil tank. to mechanical energy into hydraulic pressure to the station, hydraulic oil through Manifold (or valve combinations) realized the direction, pressure, After adjusting flow pipe and external to the cylinder hydraulic machinery or motor oil, so as to control the direction of the motive fluid transformation force the size and speed the pace of promoting the various acting hydraulic machinery.

A development course

China Hydraulic (including hydraulic, the same below), pneumatic and seals industrial development process can be broadly divided into three phases, namely : 20 early 1950s to the early 1960s, the initial stage: 60`s and 70 for specialized production system :80-90`s growth stage for the rapid development stage. Which, hydraulic industry in the early 1950s from the machine tool industry production of fake Su-grinder.broaching machine, copying lathe, and other hydraulic drive started. Hydraulic Components from the plant

hydraulic machine shop. self-occupied. After entering the l960s, the application of hydraulic technology from the machine gradually extended to the agricultural machinery and mechanical engineering fields, attached to the original velocity of hydraulic shop some stand out as pieces of hydraulic professional production. To the late 1960s, early 1970s, with the development of mechanized production, especially in the second automobile factory in providing efficient. automatedequiment. along with the Hydraulic Components manufacturing has experienced rapid development of the situation, a group of SMEs have become professional hydraulic parts factory. 1968 China?ˉs annual output of hydraulic components have nearly 200.000 in 1973, machine tools, agricultural machinery, mechanical engineering industries, the production of hydraulic parts factory has been the professional development of more than 100 and an annual output more than one million, an independent hydraulic manufacturing industry has begun to take shape. Then, hydraulic pieces of fake products from the Soviet Union for the introduction of the product development and technical design combining the products to the pressure, Hypertension and the development of the electro-hydraulic servo valves and systems, hydraulic application areas further expanded. Aerodynamic than the start of the industrial hydraulic years later, in 1967 began to establish professional pneumatic components factory, Pneumatic Components only as commodity production and sales. Sealed with rubber and plastics, mechanical seals and sealing flexible graphite sealing industry, the early 1950s from the production ordinary 0-rings, rubber and plastics extrusion, such as oil seal sealing and seal asbestos products start to the early 1960s, begun production of mechanical seals and flexible graphite sealing products. 1970s, the burning of the former Ministry, a Ministry, the Ministry of Agricultural Mechanization System, a group of professional production plants have been established, and the official establishment of industries to seal industrial development has laid the foundation for growth.

Since the l980s, in the country`s reform and opening up policy guidelines, with the development of the machinery industry, based mainframe pieces behind the conflicts have become increasingly prominent and attracted the attention of the relevant departments. To this end, the Ministry of the original one the 1982, formed the basis of common pieces of Industry, will be scattered in the original machine tools, agricultural machinery, mechanical engineering industries centralized hydraulic, pneumatic and seals specialized factories, placing them under common management infrastructure pieces Bureau, so that the industry in the planning, investment, technology and scientific research and development in areas such as infrastructure pieces Bureau of guidance and support. Since then entered a phase of rapid development, has introduced more than 60 items of advanced technology from abroad, including more than 40 items of hydraulic, pneumatic 7. After digestion and absorption and transformation,now have mass production, and

industry-leading products. In recent years, the industry increased the technological transformation efforts, in 1991, Local enterprises and the self-Financing total input of about 20 billion yuan, of which more than I .6 billion yuan Hydraulic. Through technological transformation and technology research, and a number of major enterprises to further improve the level of technology, technique and equipment to be greatly improved. In order to form a higher Starting point, specialization, and run production has laid a good Foundation. In recent years, many countries in the development of common ownership guidelines, under different ownership SMEs rapid rise showing great vitality. With the further opening up, three-funded enterprises rapid development of industry standards for improving and expanding exports play an important role. Today, China has and the United States, Japan, Germany and other countries famous manufacturers joint ventures or wholly-owned by foreign manufacturers to establish a piston pump / motor, planetary reduction gears, steering gear, hydraulic control valve,

hydraulic system. hydrostatic transmission, hydraulic Casting, pneumatic control valve, cylinder, gas processing triple pieces, mechanical seals, rubber and seal products more than 50 production enterprises, attracting foreign investment over 200 million U.S. dollars. Second, the current situation

(1) Basic Profiles

After 40 years of efforts, China hydraulic, pneumatic and sealing industry has formed a relatively complete categories, a certain level of technical capacity and the industrial system. According to the 1995 Third National Industrial Census statistics, hydraulic, Pneumatic seals and industrial 370,000 annual sales income of 100 million yuan in

state-owned, village-run, private and cooperative enterprises, indi vidual, “three capital”enterprises with a total of more than 1,300. of which about 700 hydraulic, Pneumatic seals and the approximately 300 thousand. By 1996 with the international trade statistics, the total output value of China`s industry hydraulic 2.348 billion yuan, accounting for the world`s 6;Pneumatic industry output 419 million yuan, accounting for world No. 10.

(2) The current supply and demand profiles

Through the introduction of technology, independent development and technolo2ical innovation, and high-pressure piston pump, gear pumps, vane pump. General Motors hydraulic valves, tanks, Non-lubricated aerodynamic pieces and various seals of the first large technology products has increased noticeably, stability of the mass production may, for various mainframe products provide a level of assurance. In addition, hydraulic and pneumatic components of the CAD system, pollution control, proportional servo technology has scored some achievements, and is already in production. Currently, hydraulic, pneumatic and seals products total about 3,000 species, more than 23.000 specifications. Among them, there are 1,200 hydraulic varieties, more than I 0,000 specifications (including hydraulic products 60 varieties 500 specifications): Pneumatic are 1 .350 varieties, more than 8,000 specifications: Rubber seal 350 species more than 5,000 specifications have been basically cater to the different types of mainframe products to the general needs, complete sets of equipment for major varieties of matching rate was over 60%, and started a small amount of exports.

1998 pieces of homemade hydraulic output 4.8 million, sales of about 28 billion (of which about 70% mechanical systems); aerodynamic pieces yield 3.6 million. Sales of about 5.5 billion (of which about 60% of mechanical systems);Seals output of about 800 million, sales of about 10 billion (of which about 50% mechanical systems). According to the China Hydraulic Pneumatic Seals Industry Association 1998 annual report.hydraulic product sales rate of 97. 5% (101% for hydraulic), pneumatic 95.9%, 98.7% sealed. This fully reflects the basic marketing convergence.

My hydraulic, pneumatic and sealing industry has attained a great deal of progress, but with mainframe development needs, and the world?ˉs advanced level, there are still many gaps, mainly reflected in the product variety, performance and reliability, and so on. Hydraulic products as an example, products abroad only one-third.life for half abroad. In order to meet key mainframe, and mainframe imports of major technology and equipment needs, every year a large number of hydraulic, pneumatic and sealing Products imports. According to customs statistics and the analysis of data, in 1998 hydraulic, pneumatic and seals in the import about 200 million U.S. dollars, Hydraulic which about 1.4 billion dollars, aerodynamic nearly 030 million U.S. dollars, sealed about 030 million U.S. dollars. compared with a slight decline in 1997. By sums, currently imported products on the domestic market share of about 30%. 1998 pieces of the domestic market demand the hydraulic total of about six million, the total sales of nearly 40 billion: aerodynamic pieces of the total demand of about 5 million, with sales more than 7(X) million yuan: Seals total

demand of about 1.1 billion, total sales of about 1.3 billion.

Third, the development trend of the future

1. Affect the development of the main factors

(1) product development ability, and the level of technological development and speed can not completely meet the advanced mainframe products. major equipment and technology imported equipment and maintenance support:

(2) the number of enterprises manufacturing technology, the level of equipment and management standards are comparatively backward, coupled with a strong sense of quality, resulting in low levels of product performance quality, Reliability poor services in

a timely manner, lack of user satisfaction and trust of the brand-name products:

(3) industry specialization of production low, scattered strength, low repeat serious, between regions and enterprises of convergence products, blindly compete with each other. driving down prices, the decline of enterprise returns, lack of funds, liquidity difficulties, product development and technological transformation is inadequate and seriously restricted the industry to improve the overall level of

competition and the increase of strength:

(4) The internationalization of the domestic market and the increasing degree of foreign companies have entered the Chinese market and participate in competition with the domestic private and cooperative enterprises, individuals, foreign-funded enterprises, such as the rise of state-owned enterprises due to the growing impact.

2, the development trend

As the socialist market economy continues to deepen. hydraulic, pneumatic and sealing products in the market supply and demand and there is a greater change, long ago to

a“shortage” of the seller`s market has basically become a “struct ural surplus” of the characteristics of the buyer`s market place . Overall capacity, is already in oversupply situation, in particular the general low level of hydraulic, pneumatic and seals, the general oversupply: and the host of urgent high-tech high-parameter，high value-added high-end products, and they do not satisfy the market needs, only dependent on imports. China joins the WTO, its impact may be even greater. Therefore，the “15”during the growth of the output value of industry, must not depend on volume growth and the industry should address the structural problems of their own, increase the intensity of the adjustment of the industrial structure and product mix, is, we should rely on the improvement of quality, and promote technical upgrading of products to meet market demand and stimulating, seek greater development.

Pneumatic System

Pneumatic systems use pressurized gases to transmit and control power. As the name implies, pneumatic systems typically use air(rather than some other gas) as the fluid medium because air is a safe，low-cast，and readily available fluid. It is particularly safe in environments where an electrical spark could ignite leaks from system components.

In pneumatic systems, compressors are used to compress and supply the necessary quantities of air. Compressors are typically of the piston, vane or screw type. Basically a compressor increases the pressure of a gas by reducing its volume as described by the perfect gas law.

Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite air source similar to an electrical system where you merely plug into an electrical outlet for electricity. In this way, pressurized air can be piped from one source t various locations throughout an entire industrial plant. The compressed air is piped to each circuit through an air filter to remove contaminants which might harm the closely fitting parts of pneumatic components such as valve and cylinders. The air then flows through a pressure regulator which reduces the pressure to the desired level for the particular circuit

application. Because air is not a good lubricant (contains about 20% oxygen)，pneumatics systems required a lubricator to inject a very tine mist of oil into the air discharging from the pressure regulator. This pervents wear of the closely fitting moving parts of pneumatic components.

Free air from the atmosphere contains varying amounts of moisture. This moisture can be harmful in that it can wash away lubricants and thus cause excessive wear and corrosion. Hence, in some appplications, air driers are needed to remove this undesirable moisture. Since pneumatic systems exhaust directly into the atmosphere, they are capable of generating excessive noise .Therefore, mufflers are mounted on exhaust of air valves and actuators to reduce noise and prevent operating personnel from possible injury resulting not only from exposure to noise but also from high-speed 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 vales. Due to newtong`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 systems 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 compressibility of air, it is impossible to obtain precise controlled actuator velocities with pneumatic systems. Also, precise positioning control is not obtainable. While pneumatic pressures are quite low due to compressor design limitations(less than 250 psi),hydraulic pressures can be as high as l0.000psi. Thus, hydraulics can be high-power systems, whereas pneumatics are confined to low-power applications. Industrial applications of pneumatic systems are growing at a rapid pace. Typical examples include stamping, drilling, hoist, punching, clamping, assembling, riveting, materials handling, and logic controlling operations.