7. Decide whether the following statements are true or false according to text b.

1. Pumps can be categorized into six techniques.

2. Momentum transfer pumps are also called molecular pumps.

3. Cryopums belong to the entrapment pumps.

4. Positive displacement pumps are not effective for low vacuums.

5. The momentum transfer and the positive displacement pumps are the most common to achieve high vacuums.

6. The entrapment pumps never saturate.

7. Pumps differ in details like manufacturing tolerances, pressure.

8. Momentum transfer pumping is only possible below pressures of about 1 kPa.

9. Molecular pumps sweep out a smaller area than mechanical pumps.

10. The two main types of molecular pumps are the diffusion pump and the turbo-molecular pump.

8. Answer the questions to text b.

1. Are pumps categorized into three or six techniques?

2. What is another name for the momentum transfer pumps?

3. The Entrapment pumps include cryopumps, getters, and ion pumps, don’t they?

4. What pumps are the most effective for low vacuums? Why?

5. What type of pump can help to reach ultrahigh vacuums?

6. What is the disadvantage of the entrapment pumps?

7. In what details do pumps differ?

8. Do mechanical pumps or molecular pumps sweep out the large area?

9. What are the two main types of molecular pumps?

10. What pumping systems are the most reliable?

11. What pumps are portable?

12. At what circumstances do the turbo-molecular and diffusion pumps can stall?

Comprehension Check – 2

9. Make sure you know the meanings of these words. Match the words with their definitions.

a) absorb; b) contract; c) momentum; d) portable; e) rotary; f) saturate

1) make or become smaller or shorter, tighter or narrower;

2) moving round a central point;

3) quantity of motion of a moving body (the product of its mass and velocity);

4) take in or suck in;

5) make thoroughly wet, soak with moisture;

6) that can be carried about

10. Match the words with the synonyms.

1) absorb 5) portable a) efficacious e) comprise

2) effective 6) prevent b) diminish f) permeate

3) evacuate 7) reduce c) empty g) removable

4) include 8) saturate d) obviate h) imbibe

11. Match the same words with the antonyms.

1) absorb 5) portable a) inefficient e) exclude

2) effective 6) prevent b) enlarge f) suck dry

3) evacuate 7) reduce c) inflate g) stationary

4) include 8) saturate d) facilitate h) eject

12. Fill in the correct prepositions.

1. Vacuum pump is the device __ reducing the pressure of a gas.

2. Otto von Guericke demonstrated the properties of vacuum __ a practical way.

3. The horses could not pull the hemispheres __.

4. Blood enters the heart __ a set of one-way inlet valves.

5. Force pumps __ many types are used…vacuum pumps.

6. In the 21^st century the vacuum pump has become a major necessity __ the progressive lifestyle.

7. Pumps can be categorized __ three techniques.

8. Positive displacement pumps are the most effective __ low vacuums.

9. Entrapment pumps have a maximum operational time __ they do not exhaust materials.

10. In a momentum transfer pump, gas molecules are accelerated __ the vacuum side __ the exhaust side.