【正文】 uding 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。s 6。 Seals total demand of about billion. total sales of about billion. the development trend of the future affect the development of the main factors (1) product development ability, and the level of technological development and speed can not pletely meet the advanced mainframe products, major equipment and technology imported equipment and maintenance support。ity in modular machine tool fay means of the method of power bond graph and state space analysis. The dynamic mathematical model of selfadjusting back pressure speed control system used to drive slide unit is established. Main reasons and affect172。s feeding. The supply pressure of the pump is approximately constant under the action of pressure relief valve, the oil through the control valve and pressure pensate。 and the host of urgent hightech highparameter, high valueadded highend 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.2 The application of hydraulic power sliding stage Power sliding Taiwan introducedThis paper deals with the investigation for slide unit39。s 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 onethird, 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 . dollars, Hydraulic which about billion dollars, aerodynamic nearly 030 million . dollars, sealed about 030 million . dollars. pared 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 for hydraulic total of about six million, the total sales of nearly 40 billion。s reform and opening up policy guidelines, with the development of the machinery industry, based mainframe pieces behind the conflicts have bee increasingly prominent and attracted the attention of the relevant departments. To this end, the Ministry of the original one in 1982, formed the basis of mon 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 mon 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 industryleading products. In recent years, the industry increased the technological transformation efforts, in 1991, Local enterprises and the selffinancing total input of about 20 billion yuan, of which more than 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 mon ownership guidelines, under different ownership SMEs rapid rise showing great vitality. With the further opening up, threefunded 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 whollyowned 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 . dollars. the current situation Profiles After 40 years of efforts, China hydraulic, pneumatic and sealing industry has formed a relatively plete 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 ine of 100 million yuan in stateowned, villagerun, private and cooperative enterprises, individual, 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 China39。2008 楊曙東 何存興主編[2] 現(xiàn)代工程圖學[M].湖南科學技術出版社。系統(tǒng)設有過載保護和吸空補油回路，很好的保護了系統(tǒng)中的各元件。為保證穩(wěn)定性，＜=＜，采用兩端固定。查表得其許用切應力===855。額定開度計算 （514）式中： ——額定壓力（）； ——閥芯直徑（）； ——油液密度； ——閥口流量系數(shù)，=。即 ==取 =16閥芯的直徑：按經(jīng)驗取 ～）