The structure and craftwork of gear pump is the most simple among the other hydraulic pump , and the aspects of its price , dependability , life - span , anti - contaminativity , self - absorb ability have more strong advantage too , so gear pump are used widely in fluid drive and cybernetic technology , such as lathe machine , light industry , agriculture , metallurgy , mining , building , ships , airplanes , cars , petrochemical machine and soon on . but gear pump also have some defects , the strong flow and press pulse , the low of dynamic capability , the high noise , the unchangeable output 齿轮泵的结构和工艺在各类液压泵中最简单，并在价格、可靠性、寿命、抗污染以及自吸能力等方面都有很强的优势，因此在液压传动与控制技术中，齿轮泵的应用占很大的比重，它广泛应用于机床、轻工、农林、冶金、矿山、建筑、船舶、飞机、汽车、石化机械等机械产品的液压系统中。但齿轮泵也有不少缺点，主要是流量和压力脉动较大，动态性能差，噪声较大，排量不可变，高温效率较低。
On base of the cases above , how to reduce the flow pulse of gear pump and preserve its good characters are presented in the paper . the primary method to solve the problem is to replace the spur gear with helical gear in the pump , which is base on the theory that the swing of a periodical cure will decrease on the case of the add of the same cure with some phase difference 如何减小齿轮泵的脉动，已成为各国学者深入研究的课题。本论文针对如何降低齿轮泵的输出流量脉动并力求在保持直齿轮泵的结构和工艺在各类液压泵中最简单，在价格、可靠性、寿命、抗污染和自吸能力强的优势上开展了对低脉动齿轮泵的机理分析与研究。
While a major purpose of the beach water quality monitoring programme is to chart long - term trends and changes in water quality , there are times when the programme alerts the government and the public to sudden and unexpected deterioration due to pollution incidents . in such cases , the epd in collaboration with other government departments brings into operation its beach pollution response plan , which is designed to call a series of anti - pollution measures into play quickly and effectively 环保署推行泳滩水质监测计划，主要目的是评估水质的长期趋势和变化，此外如发生个别不可预计的污染事故导致水质恶化，我们亦会立即知会相关单位和公众，并与其它有关部门协力执行泳滩污染应变计划，迅速而有效地实施各种抗污染措施。
Yet , most existing high speed on / off valves use electromagnet as their electicity - mechanism conversion element , and good performant electromagnets have to be imported from other countries , in such situation , it is difficity to make excelent high speed electromagnet valve made in our country , even if we can make good performant high speed electromagnet valve in our country , it still has the shortcoming of not high enough respond speed , too small placket and big volumeo in this thesis , a new high speed on / off valve is developed based on two types of existing valves , this new valve has higher respond speed , a little big placket and little volume o for the new valve , several main task was made out as below : a ) several types of high speed on / off were first analyzed , then the basic performance of the actuator of the new valve was analyzed 高速开关阀是20世纪80年代发展起来的一种具有响应速度快、抗污染能力强、与电子电路配合好等特点的一个良好的动力放大元件。但是现有的高速开关阀基本上采用电磁铁为电?机转换元件，高性能的电磁铁又基本为进口，难以满足高性能高速开关阀国产化的要求，即使是高性能的电磁铁式高速开关阀，仍存在着响应速度不够大、开口过小、体积较大的缺点。本文在现有两种高速开关阀的基础上，设计了一种新颖的高速开关阀，在提高其动态性能的同时，增大了阀的开口，减小了阀的体积。
This paper supplied a new way through variable frequency variable speed ( vfvs ) to change its output flow rate and adding a constant - pressure - drop valve , which could solve the defects in hydraulic pressure servo control system , such as low efficiency in control system , short life , poor ability in resisting pollution , low efficiency in driving system and flow rate , pressure pulse . and this way was proved to be effective 本论文针对传统伺服控制系统效率不高、元件寿命短、抗污染能力差、驱动系统效率低、存在流量及压力脉动等缺陷，利用先进的交流变频调速技术改变液压泵转速的容积调速新方法，提出了在液压系统中加一个定差减压阀的新思路，较好地解决了液压伺服系统存在的上述问题。
