共查询到20条相似文献，搜索用时 156 毫秒
1.
左倩 《扬州职业大学学报》1998,(2):24-27
液压卡紧现象会使液压系统中的滑阀动作困难,严重时可造成事故。本文从分析阀孔与阀芯间液流的压力分布特性入手,阐述了造成液压卡紧现象的原因及解决方法。 相似文献
2.
在工程机械、矿山机械、机械加工等设备中广泛使用液压传动，而液压在动力传动中都要产生压力损失。本文就液体在油管内流动时的压力损失计算方法进行了分析和研究，提出了正确计算公式，以免在液压传动系统设计与计算时产生错误和误差，保证其计算准确与可靠性。 相似文献
3.
关于油缸差动连接时压力损失的计算 总被引：1，自引：0，他引：1
在职业高师、中专和技工学校等院校机械专业均开设液压传动理论课程,主要讲授液压传动的基本知识与原理、典型回路和实际应用,以使学生学会分析各类机械液压系统的工作原理,并能掌握从简单到复杂的有关回路各参数计算方法,从中接受并加强必要的基本技能训练。在各层次教材中,对油缸非差动连接回路系统压力损失的计算都有明确而详细的论述。然而对油缸差动连接时压力损失的计算论述得不够充分。因此,容易引起学生在概念上的模糊。为了在计算压力损失时使学生建立明确清楚的概念和方法,本文从推导公式入手,并通过实例分析其计算过程、方法及结果。 相似文献
4.
《实验室研究与探索》2015,(10):51-54
针对目前液压电梯定压式节流调速系统在低负载时高能耗的问题,开发了液压电梯系统实验平台系统。将压力流量复合阀作为液压电梯上行控制的主控阀,电梯下行由比例调速阀进行速度控制,对液压电梯的液压系统进行了重新设计。运用AMESim软件对所设计的液压电梯系统进行了低负载上行的仿真实验分析。仿真结果表明,在低负载上行时采用复合阀的液压系统可以降低泵的输出功率,减小了溢流损失,与定压式节流调速系统相比具有节能的效果。 相似文献
5.
液压系统泄漏的原因及对策 总被引：1，自引：0，他引：1
液压系统泄漏是机电产品漏油和产生故障的重要原因之一。液压系统泄漏不仅造成油液资源浪费和污染环境,同时还造成停机损失、系统效率下降、火灾隐患、污染设备和制品等问题。液压系统泄漏不仅影响了液压系统与电气传动的竞争力,还影响到在其他领域的应用。为此,世界各国都非常重视这个问题。 相似文献
6.
《实验室研究与探索》2020,(4):1-5
针对轮毂液驱系统在工作过程中可能出现压力饱和、油温过高等极限状态,提出了一种极限状态泵排量控制策略,分别对泵排量进行温度限制控制和压力限制控制。通过Matlab/Simulink和AMESim联合仿真平台,在极限状态下对该控制策略进行仿真验证。结果表明,泵排量控制策略在保证系统性能的前提下,使液压系统油温尽快回归正常工作范围,系统流量损失显著降低。本研究增强了轮毂液驱车辆在极限状态下的应对能力,提高了液压系统能量利用率,减小了系统发生故障的可能,对轮毂液驱车辆的实际开发具有指导意义。 相似文献
7.
在节流闲出口节流调速系统中,负载的变化特别是阶跃变化,液压缸两腔压力会发生动态变化,使活塞(杆)的速度产生波动,甚至引起系统中波压元件损坏,影响液压系统的正常工作.以负载作为输入,液压缸有杆腔和无杆腔压力作为输出分别建立系统的数学模型,得到了液压缸两腔压力超调量的变化规律,并利用压力传感器测量了压力超调量的变化,通过试验对理论分析进行了验证,试验数据与理论分析相吻合,利用系统液压缸两腔压力动态变化规律,修正了液压元件主参数(额定压力)选择的计算公式,为系统设计以及元件参数选择提供依据. 相似文献
9.
在液压实验中,经常会碰到液压系统运行过程中液压泵连续吸进空气,使液压系统压力不能提升,执行部件工作不稳定乃至爬行和冲击,系统噪声增大,严重影响液压设备的正常工作。分析液压泵连续吸进空气的现象及排除方法。 相似文献
10.
单向阀在液压系统和气压系统中非常广泛,其作用是保证通过阀的液流或气流只向一个方向流动而不能反方向流动,一般由阀体、阀芯和弹簧等零件构成。我们常见的自行车轮胎的气门芯是最简单的单向阀。单向阀虽然简单,但单向阀经排列、组合及变形后则作用非凡。下面举例说明单向阀在液压系统中的常见应用。一、说单向阀的排列1.一个单向阀在图1中只能让油液从油泵向上流,反向流则被单向阀截止,油液流不通。 相似文献
11.
In this paper,a new pressure reducing valve(PRV) with an orifice plate is proposed.The main objective is to explain the mechanisms of pressure reduction and energy conversion in the new PRV.A numerical simulation method was used to investigate the PRV internal flow field and to analyze the throttling effects of the orifice plate and the transform of thermal parameters as outlet pressure,outlet temperature,velocity,and superheat.A structure improvement method for the valve body and orifice plate is put forward to reduce energy loss.The governing equations for internal flow numerical simulation are composed of the continuity,momentum,energy and k-ε transport equations,based on isotropic eddy viscosity theory.Different valve plug displacement models were built to describe the double throttling process.Our analysis shows that the steam pressure drops twice and the degree of superheat increases.There are also lots of eddies which clog the flow channel and disturb the steam flow in the valve cavity after the valve plug and the outlet cavity.After modifying the structure,the numerical results show a better performance of steam flow. 相似文献
12.
Of several formulas for calculating bursting pressure of mild steel vessel, the Faupel formula is the most famous one. In fact, Faupel formula is conservative in calculating mild steel pressure. Based on hundreds of bursting experiments on mild steel pressure vessels such as Q235(Gr.D), 20R(1020) and, after statistically analyzing data on bursting pressure, it was found that the Faupel formula had some errors in calculation. The authors derived a more approximate modified formula from the data, which proved more general after examining the data on other mild steel pressure vessels with different diameters and shell thickness. 相似文献
13.
曲恒绪 《佳木斯教育学院学报》2012,(5):417-418
对水泥筒仓在减压锥高度范围内的贮料压力进行了分析,证明在实际使用过程中锥体所受的荷载明显大于设计承载力,而按锥底深度计算出来的贮料压力是最大的。 相似文献
14.
《Child abuse & neglect》2014,38(11):1747-1754
Adverse childhood experiences are associated with hypertension in older adults. This study assessed whether an association between child maltreatment and blood pressure is detectable in young adults and whether any association differs by sex or is modified by genetic polymorphisms known to be involved in stress sensitivity. We examined these patterns in a sample of 12,420 young adults ages 24–32 years who participated in Wave IV of the National Longitudinal Study of Adolescent Health. Participants retrospectively reported history of physical, emotional, or sexual abuse before age 18 years. Participants with a systolic blood pressure (SBP) ≥140 mmHg or a diastolic blood pressure (DBP) ≥90 mmHg were classified as hypertensive. We used sex-stratified linear and logistic regression models to assess associations between each type of childhood maltreatment and SBP, DBP, and hypertension. We created interaction terms to assess for effect modification of any relationship between maltreatment and blood pressure by sex or SLC64A genotype. Fifteen percent of females and 31.5% of males were hypertensive. Frequent physical abuse in childhood was reported by 5%, frequent emotional abuse by 12%, and any sexual abuse by 5%. No association was observed between abuse history and blood pressure in either males or females, nor was effect modification present by SLC64A genotype. Child maltreatment exposure was not associated with blood pressure or hypertension in young adults in this study. Future studies should investigate additional critical windows for the effect of child maltreatment on cardiovascular health. 相似文献
15.
In this part of the article, various experimental techniques for investigating materials under high pressure are discussed.
The effect of pressure on the behaviour of materials is discussed with suitable examples.
P Ch Sahu (left) is at the Materials Science Division of Indira Gandhi Centre for Atomic Research, Kalpakkam. He is a specialist
in the field of high pressure science and is presently heading this activity at his institute.
N V Chandra Shekar (right) is a Senior Scientist at the Materials Science Division of Indira Gandhi Centre for Atomic Research,
Kalpakkam. His primary research areas are in high pressure phase transitions and in synthesis and study of novel materials
under extreme pressure and temperature conditions. 相似文献
16.
In this article, different methods for generating and measuring high pressure are described. Empirical equations of state
(EOS) are illustrated for some standard materials.
P Ch Sahu (left) is at the Materials Science Division of Indira Gandhi Centre for Atomic Research, Kalpakkam. He is a specialist
in the field of high pressure science and is presently heading this activity at his institute.
His primary research areas are in high pressure phase transitions and in synthesis and study of novel materials under extreme
pressure and temperature conditions. 相似文献
17.
实验室利用差压传感器测量空气相对压力系数时,真空泵的抽真空度对于实验结果有很大的影响。实验采用控制变量法,对真空泵抽真空度这一影响因素进行了研究。结果表明,真空泵抽真空程度越高,测量所得空气相对压力系数值越小,并且越接近其真实值,空气相对压力系数测量值的改变量随真空度的增大而不断减小,二者之间呈现出一条斜率渐渐减小的曲线关系。真空泵无法完全抽真空时,可以通过将最终测得的空气相对压力系数值乘以其对应真空度值的方法对实验结果进行修正。 相似文献
18.
特区高职院校新生心理压力探析 总被引：4，自引：0，他引：4
李志德 《深圳职业技术学院学报》2004,3(1):89-91
运用问卷调查表对特区某高职院校新生心理压力的主要来源及其特点进行调查研究，结果表明：人际交往、学业成就与前途以及生活环境的改变与适应等是大学生心理压力的主要来源；亲人、好友发生突发变故(如父母患急、重病或父母离异等)对学生带来的心理压力相当大；男女大学生的心理压力存在一些性别上的差异。 相似文献
19.
Russell Tytler 《International Journal of Science Education》2013,35(8):929-958
Children's responses to a series of air pressure activities were tracked in detail during group discussion and interview, and again in interview six months later. Results for different age cohorts have yielded insights into age‐related knowledge components framing children's conceptions of air pressure phenomena. Case studies of individuals have been constructed to explore the way conceptions change over time, and the difficulties presented by the concept of atmospheric pressure. These are used to evaluate different structural theories of conceptual change. The findings point to the complexity of children's conceptions, the stability and extension over time of productive conceptions, and the critical role of contextual features of phenomena in the conceptual change process. Although structural aspects of changes in concepts related to air pressure are identified, the difficulty of accessing the atmospheric pressure conception is argued to have more to do with presupposition based in perceptual features of air, and with difficulties associated with the application to particular phenomena. 相似文献