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

1. Reciprocating compressors don’t use pistons driven by a crankshaft.

2. Reciprocating compressors can be either stationary or stationery.

3. Rotary screw compressors may be either stationary or portable.

4. Axial-flow compressors are almost always multi-staged.

5. Many large snow-making operations (like ski resorts) use centrifugal compressors.

6. Diagonal compressor is completely different from a centrifugal compressor.

7. Scroll compressor includes two interleaved spiral-shaped scrolls to compress the gas.

8. The reliability of scroll compressors is debatable.

9. Diaphragm Compressor is used for hydrogen.

10. There are oil-lubricated and oil-free compressors.

11. Oil-free compressors are not needed anymore.

12. In a diving-air compressor even minimal oil may be unacceptable.

8. Answer the questions to text b.

1. Are reciprocating compressors stationary or portable?

2. How can reciprocating compressors be driven?

3. Are reciprocating compressors in great demand?

4. Are rotary screw compressors used for continuous operation?

5. What is the function of axial-flow compressors?

6. When can centrifugal compressor achieve extremely high output pressures?

7. Where are centrifugal compressors used?

8. What is the function of the diffuser and where is it used?

9. Has scroll technology been adopted to vacuum use?

10. What is the Archimedean Screw?

11. Is scroll compressor widely used?

12. Why are oil-free compressors desirable?

Comprehension Check – 2

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

a) to wobble; b) scroll; c) stationary ; d) recovery; e); f) stationery; f) screw

1) returning to a proper state of strength, ability

2) materials for writing: paper, pens, pencils, etc.

3) curved, spiral or coiled form

4) to move unsteadily from side to side, shake

5) propeller

6) standing still, not moving

10. Match the words with the synonyms.

1) include 5) common a) by means of e) intermediate

2) moderate 6) decline b) novelty f) general

3) function 7) medium c) economical g) diminish

4) via 8) innovation d) purpose h) comprise

11. Match the words with the antonyms.

1) continuous 5) inexpensive a) initial e) incompressible

2) compressible 6) conventional b) indisputable f) multi-stage

3) final 7) disputable c) maximum g) unusual

4) single 8) minimal d) constant h) expensive

12. Fill in the correct prepositions.

1. Compressors are similar __ pumps

2. The term pump is generally used __ liquid-handling or hand-operated devices.

3. In centrifugal pumps and compressors, the vanes of the impeller, or rotor take fluid __ __ the axis.

4. Centrifugal pumps and compressors can handle __ moderate flow rates and pressure increases.

5. Axial-flow compressors consist __ a number of stages,

6. They are typically used __ vacuum pumps but can also be used __ gas compressors

7. This liquid ring creates a series __ seals in the space __ the impeller vanes.

8. The eccentricity __the impeller rotating axis and the casing geometric axis results … a cyclic variation of the volume.

9. Typically a multi-stage pump will have __ to two compression stages __ a common shaft.

10. Oil-free compressors are desirable because __ proper consideration (additional parts) oil can make its way __ the air stream.