问题 问答题 简答题

什么是闭死容积?有什么危害?

答案

参考答案:

由于齿轮传动的重叠系数大于1,这样在两对齿轮之间形成一个与吸、排液腔均不相通的密闭空间,这个空间称为闭死容积。

当容积增大时,容易引起气穴和气蚀现象;当容积增小时,不但使轴及轴承承受很大的冲击载荷、降低了泵的效率,而且还使液体发热并产生噪音和振动。

阅读理解

Last Monday we did a survey about how often the students do the housework in Shiyan High School. Here are the results.

Most students do the housework twice or three times a week. They often clean their rooms. Some students do the housework five times a week. They often clean the floor. Some students help their parents on the farm. They think their parents are too busy, so they help them.

The results for “wash clothes” are interesting. Some students wash clothes once or twice a week. They often wash clothes on Saturdays or Sundays. Some students wash clothes three or four times a week. They only wash their own clothes. But most students wash their clothes once a week. And they wash clothes on Sundays.

Liu Ying, a girl in Class 4, Grade 8, has lots of housework to do. She washes the dishes and cleans the floor every day. She often cooks, sometimes three times a day. She says, “My mother isn’t healthy. My father works in another city. So I have to do most of the housework at home.”

根据短文内容,选择正确答案(10分)

小题1:From the results we know      students do the housework five times a week.

A、all                  B、most             C、some

小题2:Some students help their parents on the farm because        .

A、they think they are old enough              

B、they think their parents are too busy

C、they don’t have too much homework

小题3:How often do most students wash their clothes?

A、Once a week.         B、Twice a week.        C、Three times a week.

小题4:From the passage we know that       .

A、Liu Ying is an unhealthy student

B、Liu Ying is good at homework

C、Liu Ying has to do much housework

小题5:Which of the following is NOT true?

A、They did the survery last Monday.

B、Most students don’t do the housework.

C、Liu Ying is a student from Class 4, Grade 8.

选择题