问题 问答题 简答题

汽封的作用是什么?轴封的作用是什么?

答案

参考答案:

为了避免动、静部件之间的碰撞,必须留有适当的间隙,这些间隙的存在势必导致漏汽,为此必须加装密封装置----汽封。根据汽封在汽轮机中所处位置可分为:轴端汽封(简称轴封)、隔板汽封和围带汽封(通流部分汽封)三类。

轴封是汽封的一种。汽轮机轴封的作用是阻止汽缸内的蒸汽向外漏泄,低压缸排汽侧轴封是防止外界空气漏入汽缸。

阅读理解

阅读理解。

     Tom arrived at the bus station quite early for Paris. The bus for Paris would not leave until five to

twelve. He saw a lot of people waiting at the station. Some were standing in line, others were walking

around. A teacher was trying to keep a group of schoolgirls in line. Tom looked around but there was

no place for him to sit.

     He walked into the station cafe. He looked up at the clock there. It was only twenty to twelve. He

found a seat and sat down before a large mirror(镜子) on the wall. Just then, Peter, one of Tom's

workmates came in and sat with Tom. "What time is your bus?" asked Peter. "There is a lot of time yet."

answered Tom. "Well, I'll get you some more tea then." They talked while drinking. Then Tom looked at

the clock again. "Oh! It's going backward(反方向的)!" he cried. "A few minutes ago it was twenty to

twelve and now it's half past eleven." "You are looking at the clock in the mirror." said Peter. Tom was

so sad. The next bus was not to leave for another hour. Since then Tom has never liked mirrors.

1. Tom went into the station caf? because _____.

A. Peter asked him to have a cup of tea

B. it was quite early and he could find a seat there

C. he didn't like to stay with the schoolgirls

D. he wanted to have a drink with his workmate there

2. What time was it in fact when Tom looked at the clock in the mirror the last time?

A. Half past twelve

B. Twenty to twelve

C. Half past eleven

D. Half past one

3. From the story we know that when we look at a clock in a mirror, we will find _____.

A. the time is right

B. it's going slower

C. it's going backward

D. it's going faster

4. Which of the following is true?

A. Tom arrived in Paris on time

B. The next bus would leave in half an hour

C. After that Tom didn't like clocks any longer

D. Tom looked at the clock in the mirror only once

5. Which of the following is the best title for the story?

A. The Mirror of the Station

B. Not a Careful Man

C. Missing a bus

D. The Man and the Mirror

单项选择题