问题 问答题 简答题

油控跳闸阀作用?

答案

参考答案:

再热主汽门系一90°转角的摇板全开、全关式阀门,其转轴外露,为防止蒸汽沿转轴外漏,转轴结构上采取了金属密封,即转轴上凸肩对管道上凹槽,正常运行中蒸汽作用在凸肩上,压紧防止蒸汽外漏。机组从开机越接近正常运行状态,金属密封越紧。但发生脱扣停机,此蒸汽的压紧作用力即阻碍中主门的关闭。为此设置一油压操纵的遮断引预启阀,用以当再热主汽门关闭时泄放作用于轴内部端面不平衡的蒸汽力。

该阀由一操作阀和油动机组成。油动机连接到液压系统,因而当AST危急遮断阀和OPC超速遮断阀关闭时,再热主汽门将处于开启状态而油控跳闸阀则处于关闭状态。当危急遮断机构动作时,遮断引预启阀将打开,以使轴端部腔室与一低压区(凝汽器)相通,从而减小作用于轴端的蒸汽压力,以致可以用最小的作用力关闭再热主汽门。

单项选择题

The sun rose upon a tranquil world, and beamed down upon the peaceful village like a benediction. Breakfast over, Aunt Polly had family worship: It began with a prayer built from the ground up of solid courses of Scriptural quotations, welded together with a thin mortar of originality; and from the summit of this she delivered a grim chapter of the Mosaic Law, as from Sinai.
Then Tom girded up his loins, so to speak, and went to work to "get his verses." Sid had learned his lesson days before. Tom bent all his energies to the memorizing of five verses, and he chose part of the Sermon on the Mount, because he could find no verses that were shorter. At the end of half an hour Tom had a vague general idea of his lesson, but no more, for his mind was traversing the whole field of human thought, and his hands were busy with distracting recreations. Mary took his book to hear him recite, and he tried to find his way through the fog:
"Blessed are the—a—a—"
"Poor"—"Yes—poor; blessed are the poor—a—a—"
"In spirit—"
"In spirit; blessed are the poor in spirit, for they—they—"
"THEIRS—"
"For THEIRS. Blessed are the poor in spirit, for theirs is the kingdom of heaven. Blessed are they that mourn, for they—they—"
"Sh—"
"For they—a—"
"S, H, A—"
"For they S, H—Oh, I don’t know what it is!"
"SHALL!"
"Oh, SHALL! for they shall—for they shall—a—a—shall mourn—a—a—blessed are they that shall—they that—a—they that shall mourn, for they shall—a—shall WHAT Why don’t you tell me, Mary—what do you want to be so mean for"
"Oh, Tom, you poor thick-headed thing, I’m not teasing you. I wouldn’t do that. You must go and learn it again. Don’t you be discouraged, Tom, you’ll manage it—and if you do, I’ll give you something ever so nice. There, now, that’s a good boy. "
"All right! What is it, Mary, tell me what it is. "
"Never you mind, Tom. You know if I say it’s nice, it is nice."
"You bet you that’s so, Mary. All right, I’ll tackle it again."
And he did "tackle it again"—and under the double pressure of curiosity and prospective gain he did it with such spirit that he accomplished a shining success. Mary gave him a brand-new "Barlow" knife worth twelve and a half cents; and the convulsion of delight that swept his system shook him to his foundations. True, the knife would not cut anything, but it was a "sure-enough" Barlow, and there was inconceivable grandeur in that—though where the Western boys ever got the idea that such a weapon could possibly be counterfeited to its injury is an imposing mystery and will always remain so, perhaps. Tom contrived to scarify the cupboard with it, and was arranging to begin on the bureau, when he was called off to dress for Sunday-school.

When Tom was reciting the verses, ______.

A.Mary discouraged him constantly

B.it was foggy outside

C.he couldn’t focus his attention all the time

D.he tried very hard to please the grownups

单项选择题