问题 问答题 简答题

离心泵为什么应在空负荷下启动?

答案

参考答案:

离心式泵的轴功率随流量增大而增大,在空负荷时,轴功率最小,为了减少启动功率,以免启动时跳闸甚至烧坏电机,应当在空负荷时启动。对于离心式泵,启动时应将出口门关闭;但应注意在出口门关闭时泵运转不宜超过2~3分钟,以防水泵产生汽化。

单项选择题
阅读理解

阅读理解。

     Is there anything more important than health? I don't think so. "Health is the greatest wealth (财富),"

wise people say. You can't be good at your studies or work well when you are ill. If you have a headache,

toothache, backache, earache or bad pain in the stomach, if you complain of a bad cough, if you run a high

temperature and have a bad cold, or if you suffer from high or low blood pressure, I think you should go to

the doctor. The doctor will examine your throat, feel your pulse, test your blood pressure, take your

temperature, sound your heart and lungs, test your eyes, check your teeth or have your chest X-rayed. After

that he will advise some treatment, or some medicine. The only thing you have to do is follow his advice.

     Speaking about doctor's advice, I can't help telling you a funny story.

     An old gentleman came to see the doctor. The man was very ill. He told the doctor about his weakness,

memory loss and serious problems with his heart and lungs. The doctor examined him and said there was

no medicine for his disease. He told his patient to go to a quiet place for a month and have a good rest. He

also advised him to eat a lot of meat, drink two glasses of red wine every day and take long walks. In other

words, the doctor advised him to follow the rule:"Eat at pleasure, drink with measure and enjoy life as it is."

The doctor also said that if the man wanted to be well again, he shouldn't smoke more than one cigarette a

day.

     A month later the gentleman came into the doctor's office. He looked cheerful and happy. He thanked the

doctor and said that he had never felt a healthier man.

     "But you know, doctor," he said, "it's not easy to begin smoking at my age."

1. The doctor usually tells his patient what to do _____. [ ]

A. without examining the patient

B. after he has examined the patient

C. if the patient doesn't take medicine

D. unless the patient feels pain

2. The writer thinks that _____. [ ]

A. health is more important than wealth

B. work is as important as studies

C. medicine is more important than pleasure

D. nothing is more important than money

3. The underlined part means "_____". [ ]

A. he was feeling better than ever

B. he wasn't a healthy man

C. he was feeling worse than before

D. he will be well again

4. From the last sentence of the passage, we learn the man _____ before the doctor told him not to smoke

    more than one cigarette a day. [ ]

A. was a heavy smoker

B. didn't smoke so much

C. didn't smoke

D. began to learn to smoke

5. Which of the following is NOT true?[ ]

A. The doctor usually tests his/her blood pressure when a person is ill.

B. The man told the doctor he couldn't remember things.

C. The man thanked the doctor.

D. The man didn't follow the doctor's advice.