问题 问答题 简答题

分析并说明直动式和先导式溢流阀中阻尼孔作用有何不同,当溢流阀的阻尼孔堵塞时,直动式和先导式溢流阀各会出现什么现象。

答案

参考答案:

直动式溢流阀中的阻尼孔的作用是对阀芯运动形成阻尼,避免阀芯产生振动使阀工作平稳。

先导式溢流阀中的阻尼孔的阻尼的作用是使油液流过时产生压降,使阀芯顶端油液的压力小于其底端油液的压力,通过这个压差作用使阀芯开启,使主阀弹簧刚度降低。溢流阀在溢流量变化时,溢流阀控制压力变化较小。

若直动式溢流阀阻尼孔堵赛,该阀就失去调压作用。主阀芯始终关闭不会溢流,将产生超压事故。若先导式溢流阀阻尼孔堵塞,先导阀就失去对主阀的压力调压作用。当进油压力很低时,就能将主阀打开溢流,由于主阀弹簧力很小,因此系统建立不起压力。

填空题
单项选择题

She’s cute, no question. Symmetrical features, flawless skin, looks to be 22 years old-entering any meat-market bar, a woman lucky enough to have this face would turn enough heads to stir a breeze. But when Victor Johnston points and clicks, the face on his computer screen changes into a state of superheated, crystallized beauty. "You can see it. It’s just so extraordinary," says Johnston, a professor of biopsychology at New Mexico State University who sounds a little in love with his creation.
The transformation from pretty woman to knee-weakening babe is all the more amazing because the changes wrought by Johnston’s software are, objectively speaking, quite subtle. He created the original face by digitally averaging 16 randomly selected female Caucasian faces. The changing pro-gram then exaggerated the ways in which female faces differ from male faces, creating, in human-beauty-science field, a "hyper-female". The eyes grew a bit larger, the nose narrowed slightly and the lips plumped. These are shifts of just a few millimeters, but experiments in this country and Scotland are suggesting that both males and females find "feminized" versions of averaged faces more beautiful.
Johnston hatched this little movie as part of his ongoing study into why human beings find some people attractive and others homely. He may not have any rock-solid answers yet, but he is far from alone in attempting to apply scientific inquiry to so ambiguous a subject. Around the world, re-searchers are marching into territory formerly staked out by poets and painters to uncover the underpinnings of human attractiveness.
The research results so far are surprising and humbling. Numerous studies indicate that human beauty may not be simply in the eye of the beholder or an arbitrary cultural artifact. It may be ancient and universal, wrought through ages of evolution that rewarded reproductive winners and killed off losers. If beauty is not truth, it may be health and fertility: Halle Berry’s flawless skin may fascinate moviegoers because, at some deep level, it persuades us that she is parasite-free.
Human attractiveness research is a relatively young and certainly contentious field-the allure of hyper—females, for example, is still hotly debated—but those on its front lines agree on one point: We won’t conquer "looks—ism" until we understand its source. As psychologist Nancy Etcoff puts it: "The idea that beauty is unimportant or a cultural construct is the real beauty myth. We have to understand beauty, or we will always be enslaved by it. \

Victor Johnston synthesized a new face by combining the features of 16 ______.

A.beautiful European women

B.different women around the world

C.casually chosen white women

D.ordinary western women