EXPERIMENTAL INVESTIGATIONS OF CAVITATION EFFECTS ON FLOW CHARACTERISTICS OF SMALL ORIFICES AND VALVES IN WATER HYDRAULICS

The flow characteristics and cavitation effects of water passing throughsmall sharp-edged cylindrical orifices and valves of different shapes in water hydraulics areinvestigated. The test results using orifices with different aspect ratios and different diametersshow that the flow coefficients in the case of non-cavitating flow are larger than that of flow inthe case of cavitation occurrence. The flow coefficients of flow with cavitation initially decreaseas Reynolds number increases and ultimately tend to be of constant values close to contractioncoefficient. Large aspect ratio has an effect of suppressing cavitation. The experimental resultsabout disc valves illustrate that the valves with sharp edge at large opening are less affected bycavitation than that at small opening. Throttle with triangle notch has better anti-cavitationability than that with square notch. The flowrate of the throttle with square notch is significantlyaffected by the flow direction or the flow passage shape.

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNG k-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43 000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result.

Simulation investigation on fluid characteristics of jet pipe water hydraulic servo valve based on CFD

Simulation investigation on fluid characteristics of the water hydraulic jet pipe servo valve （WHJPSV） is conducted through a commercial computational fluid dynamics （CFD） software package FLUENT. In particular, the factors to fluid characteristics of WHJPSV are addressed, which include diameter combination of jet pipe and receiver pipe, jet pipe nozzle clearance, angle between two jet receiver pipes and deflection angle of the jet pipe. It is concluded from the results that： （i） Structural parameters have great influences on fluid characteristics of WHJPSV, when d1 = d2 = 0.3 mm, α= 45 , b = 0.5 mm, and the simulation exhibits better fluid characteristics; （ii） The magnitude of the recovery pressure and flow velocity increase almost linearly with the deflection angle of jet pipe. The research work in this paper is important for determining and optimizing the structural parameters of the jet pipe and jet receiver. The relevant conclusions could be extended to the study of other water hydraulic servo control components.

Water Hydraulic 2/2 Directional Valve with Plane Piston Structure

Due to the fire resistance and environmental compatibility, using water as the working fluid in hydraulic circuits is receiving an increasing attention by both manufactures and users. This hydraulic directional valve is developed. When new water hydraulic directional valve is designed and manufactured, this paper introduces a water hydraulic 2/2 directional valve and its principle. The valve is composed of a hydraulically operated seat valve and a magnetic 3/2 direction valve. Aimed at the serious leakage and impact generating easily in reversing suddenly, an improved structure of water space seal is changed to direct seal, compaction force between main valve spool and main valve pocket was logically designed and damper in pilot valve port is matched with sensitive cavity in main valve. From the view of flow control, the methods of cavitation resistanee of the directional water hydraulic valve are investigated. The computational fluid dynamics approaches are applied to obtain static pressure distributions and cavitation images in the channel of the main stage of the valve with two kinds of structure. The results show that the method of optimized spout can effectively restrain cavitation. The work provides some useful reference for developing water hydraulic control valve with the lower noise and lower vibration. Meantime, the structural parameters are optimized on the basis of information obtained from simulation. Static test, dynamic test and life test are accomplished, and the results show that the water hydraulic directional valve possesses good property, its pressure loss is 1.1 MPa lower, switching time is shorter than 0.025 s, and its strike crest is 0.8 MPa lower. The valve possess fine dynamic performance with the characteristic rapidly action and lower implusion.

Flow and cavitation characteristics of water hydraulic poppet valves

Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were considered. Cavitation inception was detected by the appearance and rapid growth of a particular low frequency component of the outlet pressure fluctuation of valve when cavitation occurs. Experimental results show cavitation, back pressure, valve opening and its geometrical shape have significant effects on the flow characteristics of valve. The flow coefficient of throttle with water used as working medium is 0 85～0 95 when there is no cavitation. The pressure drop of flow saturation decreases with the increasing of poppet lift. The sharp-edged throttle has stronger anti-cavitation ability than the chamfered one.

Investigation of Valve Plate in Water Hydraulic Axial Piston Motor

This paper has introduced the developments of water hydraulic axial piston equipments. According to the effects of physicochemical properties of water on water hydraulic components, a novel valve plate for water hydraulic axial motor has been put forward, whose moment exerted by the fluid field between valve plate and bearing plate is balanced entirely. The material screening experiment of valve plate is done on the test rig. Through numerical simulation the effects of some geometry parameters on the performance of water hydraulic motor have been studied. The silencing grooves on the valve plate in water hydraulic motor can reduce the pressure shock and the occurrence of cavitation effectively. It is evident that the appropriate structure should change the wear status between matching pairs and reduces the wear and specific pressure of the matching pairs. The specimen with the new type valve plate is used in a tool system.

Dynamic characteristics of the high-flow water three-way valve

Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated numerically by software Fluent, and its dynamic characteristics were analyzed during the work process such as raising leg, loading and overflow, the influence of the related parameters on high-flow water three-way valve was determined. The results as follows： during the raising leg stage and early raising leg stage, when the damping ratio increases, the overshoot of system decreases and the setting time reduces, and the dynamic response performance has a significant improvement. During the loading stage and the overflow stage, the pressure in plunger chamber of single hydraulic prop, the output flow and the displacement of the high-flow water three-way valve decrease with the decreasing of the external load. The spring stiffness of the safety valve directs the flow and the spool＇s displacement of the safety valve, and it can be used to control the high-flow three-way valve＇s sensitivity.

浅水受限区水下油气田开发方案

针对国内浅水油气资源开发环境影响及空间受限等问题,本文提出了国产浅水水下生产系统的总体设计方案。通过对浅水水下生产系统关键设备结构进行分析,提出了一种满足受限区海域开发要求的环境友好型设计思路。结果表明:通过系统和总体布置的设计,国产浅水水下生产系统与深水相比在单体重量、作业方式、维护检修方面更加经济。

低速大扭矩水液压马达的深海性能迁移特性

为实现深海水液压机械手回转关节的稳定输出,研制了一种新型阀配流低速大扭矩水液压马达。搭建了其数学及物理模型,完成了马达与机械手腕部关节的集成设计,通过马达的AMESim仿真模型分析了深海环境对马达输出性能的影响。研究发现:随着海深的增加,马达的输出扭矩显著降低,输出转速也出现一定变化,环境压力从0 MPa增加至120 MPa的过程中,马达的输出扭矩累计降低了34%,最大稳定转速却较陆上工况增加了13%。此研究为马达的结构优化与深海作业控制提供了理论依据。

真空破坏阀对虹吸断流管道的水锤防护效果

针对虹吸断流结构管线水锤防护问题,运用Bentley Hammer软件进行水力过渡过程分析,提出了泵后液控蝶阀与真空破坏阀联合防护方案.结合管道压力控制标准,分析对比了在水泵事故停泵工况下真空破坏阀对虹吸结构处水锤的防护效果,同时对真空破坏阀在不同进口直径和不同整定值下的水锤防护效果进行了探讨分析.计算结果表明,增设真空破坏阀极大改善了虹吸处水锤负压,最低水锤负压为-3.69 m;真空破坏阀直径越大防护效果越好,最佳直径设置为管道直径1/3处;真空破坏阀整定值越大对水锤防护的效果越弱,整定值设为-3.80 m时管道水锤负压最小,整定值小于管道最小压力时阀不动作.该分析结果给真空破坏阀的选择提供了一定的参考,对虹吸断流结构输水工程水锤防护具有重要的意义.

油压锥阀与水压锥阀空化特性的对比分析

油压锥阀与水压锥阀在空化特性方面有较大差异,其流场机制尚未明确。为此,利用VOF空化两相流数值模拟算法在OpenFOAM开源平台上开展流场模拟,研究水压锥阀与油压锥阀空化特性。结果表明,水压锥阀及油压锥阀的空化分布较为一致,集中在自由剪切层、壁面剪切层及阀芯后沿等位置,同时各区域的空化诱发机制相同。油压锥阀的近壁面漩涡空化呈现径向链状特征,而水压锥阀则为分散性的片状结构,不同的空化形态主要源于转捩过程的差异。另外,在高强度空化流动条件下,直角型油压锥阀的整体空化强度相对水压锥阀较大,而倒角型锥阀则相反。水压锥阀比油压锥阀更容易发生空化初生。研究分析了水压锥阀与油压锥阀的空化特性差异及相关机制,可为不同介质的液压阀设计提供理论参考。

长距离负扬程加压泵站调水工程水力控制方式探讨

事故掉电引发的停泵水锤是泵站调水工程安全运行最主要的威胁之一,而对于下游水位低于上游水位的长距离负扬程加压泵站调水工程而言,事故停泵易造成管道拉空,负水锤防护难度较大,因此,针对其停泵工况的水力控制研究十分重要。以某长距离负扬程泵站调水工程为例,模拟计算了事故停泵、阀门拒动这一控制性工况下的水力过渡过程,并对比分析了空气罐、空气阀与空气阀联合空气阀调压室3种水力控制方案的水锤防护效果。结果表明:对于长距离负扬程加压泵站调水系统而言,当采用空气罐的水力控制方式时,所需的空气罐体积较大,投资高昂;当单纯采用空气阀的水力控制方式时,难以有效解决管道局部高点处负压较大的问题,仍可能诱发弥合性水锤;当将部分空气阀附加一根短管组合成空气阀调压室后,能够有效控制管内负压。空气阀与空气阀调压室联合防护是一种十分经济且有效的水锤防护方案,可为这类负扬程加压调水工程的水力控制方式选取提供参考。

泵站停泵水锤事故溯源分析及防护

为研究两阶段缓闭止回阀关阀时间及类型对停泵水锤的影响,以蓝山县高塘坪分置式抽水蓄能工程中的泵站为例,基于两阶段缓闭止回阀工作原理,采用数值模拟方法溯源分析停泵水锤事故产生原因,并对比不同工况下液控蝶阀及多功能水泵控制阀在相同总关阀时间下的停泵水锤防护效果。结果表明,液控蝶阀关阀规律不合理是导致停泵水锤事故的主要原因;与液控蝶阀相比,多功能水泵控制阀在不同工况下的一阶段零流速的自适应关阀方式,可显著降低停泵工况下的水锤峰;经现场实测获取更换多功能水泵控制阀后的停泵水锤曲线,多功能水泵控制阀有效地解决了泵站水锤防护问题,提升了泵站的安全韧性。

事故停泵工况下蝶阀关闭规律对并联大型离心泵组的水锤影响研究

泵后蝶阀是泵站水锤防护的重要装置,采取合适的关阀规律是降低事故停泵时水泵最大反转转速和管线最大压力,保证水泵安全运行的关键,本文以犬木塘输水工程为研究对象,利用一维特征线法对事故停机水锤进行数值模拟计算,分析了液控蝶阀线性关闭规律与两阶段关闭规律对并联大型离心泵组的影响。采取控制变量法,分别以快关时间、慢关时间、快关阀门关闭量作为变量着重分析了两阶段关闭规律下供水系统最大压力和水泵最大反转转速的变化,通过比较2泵同停和1泵运行1泵停止工况下停泵水锤,得到了最佳的关阀规律。结果表明:相比于线性关闭规律,合适的两阶段关闭规律能显著降低管线最大压力,减少水泵最大反转转速,影响水泵最大反转转速的主要因素为快关阀门关闭量,次要因素为阀门快关时间和阀门慢关时间;在合适的阈值内快关阀门关闭量越大、阀门快关时间越短、阀门慢关时间越短为最佳的两阶段阀门关闭规律。

井下清洁施工系统的研发与应用

针对临盘油田液压封隔器坐封过程中容易出现液压通道堵塞的问题,研发了清洁施工系统。该系统主要包括液压封隔器沉淀过滤装置和防堵型油套平衡阀两部分,具有结构简单、成本低廉、可靠耐用、适用性强、可重复使用、极易推广等特点。自2012年在临盘油田投入实际使用至今,平均每年应用80口井左右,均无液压通道堵塞问题。该系统已成为临盘油田Y445型液压封隔器封层施工必备辅助工具,并形成规范化的施工流程,带来了丰富的成果应用效益,可以在全国各油田液压封隔器施工中推广使用,具有广阔的应用前景。

火电厂循泵出口蝶阀热工常见故障分析

循环水泵作为电力生产系统的重要辅机,对火电厂的安全稳定运行有至关重要的作用。对循泵出口蝶阀的液压系统原理、操作方法进行了介绍,总结了循泵出口蝶阀热工常见故障问题以及解决方案,并根据实例逐步解析、拆检和修复、更换失效部件,为后续检修工作提供技术经验支撑,提升设备的运行稳定性。

多排阀口水液压安全阀动态开启与气蚀特性研究

煤矿高压大流量水液压安全阀阀芯采用多排阀口设计,具有体积小、结构紧凑等优点,利用数值模拟方法,在3种不同开启次序下,对4排阀口安全阀的动态响应与气蚀特性进行研究。通过瞬态仿真,分析3种开启次序下阀芯位移和速度变化以及阀腔内气蚀分布特性。结果表明:阀芯采用3步和4步次序开启时,首排阀口完全开启用时短,响应速度更快;不同开启次序下,阀腔内气蚀产生位置一致,均发生在阀芯左端入口台阶和各阀口靠近阀芯入口侧位置;在阀腔中心截面,2步次序降气蚀效果最优,4步次之;采用4步次序能够有效降低各排阀口内壁面的气蚀强度。阀芯的4排阀口单排依次开启方案,有利于安全阀面在高压时快速响应,并能降低阀口壁面气蚀伤害。

液控缓闭蝶阀运行中存在的问题及解决方案

文章以长距离输水工程运行为例,介绍了缓闭蝶阀在输水泵站中的应用,阐述了蓄能罐式液控缓闭蝶阀结构和工作原理,分析了其在工程实际应用中的优缺点,并提出改进方案。通过增加液压伺服闭环系统,充分发挥电、液两类伺服的优点,使泵站及输水管线运行更加平稳安全,对高扬程输水管线水锤危害及水泵的倒转现象起到了很好的抑制作用,其改进措施可供其他同类型输水工程借鉴参考。

轴流式止回阀与水击泄放阀组合的水锤防护系统研究

【目的】研究减小长距离高扬程输水工程中水锤作用对建筑物安全运行的不利影响,保障管道等建筑物安全。【方法】基于瞬变流理论及特征线法结合水柱分离数学模型的方法,并考虑水锤防护设备的边界条件,运用水锤仿真计算软件对系统停泵水锤进行数值计算。对传统的“单向调压塔+空气阀”和“水击泄放阀+轴流止回阀+空气阀”2种水锤防护措施进行比较,验证轴流止回阀与水击泄放阀组合的水锤防护系统防护效果。【结果】经过计算及后期实际工程多年运行验证后表明在长距离高扬程输水工程中:2种水锤防护方案对事故停泵下管线高压及负压水锤均有一定的防护效果。“单向调压塔+空气阀”的防护措施能使管道内负压由汽化负压-8.4 m降到了-6.9 m水头压力,管道正压最大值由3.04 Mpa降低至2.98 Mpa,但若要继续降低管线负压则需再增加调压塔数量,增加工程投资,经济性上并无优势;“水击泄放阀+轴流止回阀+空气阀”的水锤防护措施,能够有效防护因停泵引起的高低压水锤及水泵倒流倒转等问题,管道内负压由已汽化负压降到了-5 m水头压力,使其系统内最高压力由3.04 Mpa降低至3.0 Mpa,管道最大压力控制在稳态压力的1.2倍之内。【结论】工程竣工多年运行验证,此水锤防护系统只需在输水系统中设1处水击泄放阀和轴流止回阀即可实现有效的防护因停泵引起的高低压水锤及水泵倒流倒转等问题,具有相同的可靠性和更高的经济性,可为类似工程防水锤设计提供依据。

长输热水管网水锤防治措施分析

根据对水锤压力公式各项含义的分析,阐述了管道内水锤形成的基本原因及对水锤产生影响的基本因素。根据分析结果,提出了在长输供热管网及系统中,减少或避免水锤的一般性建议。同时,以某长输供热管网实际工程为例,进一步解释水锤成因的各项因素在实际工程中的影响情况,具体为对该实际工程进行动态水力分析,针对该工程中阀门关闭、水泵故障、事故断电等多种工况进行分析并对比,提出了在此类工程中保证供热系统安全运行的措施。