II. Make up questions concerning the content of the text.
Positive displacement pumps (II)
Lobe pumps resemble external gear pumps, but have rotors with two, three, or four lobes in place of gears; the two rotors are both driven. Lobe pumps have a more pulsating output than external gear pumps and are less subject to wear. Lobe-type compressors are also used to pump gases; each rotor has two lobes. In a screw pump, a helical screw rotor revolves in a fixed casing that is shaped so that cavities formed at the intake move toward the discharge as the screw rotates. As a cavity forms, a partial vacuum is created, which draws fluid into the pump. This fluid is then transferred to the other side of the pump inside the progressing cavity. The shape of the fixed casing is such that at the discharge end of the pump the cavity closes, generating an increase in pressure that forces the fluid into the outlet line. Screw pumps can pump liquids containing vapours or solid particles. They deliver a steady output with negligible pulsations for a given rotor speed. Since screw pumps do not need inlet and outlet check valves, they can be used to pump very viscous liquids. Although screw pumps are bulky, heavy, and expensive, they are robust, slow to wear, and have an exceptionally long life. In a sliding vane pump the rotor is mounted off-centre. Rectangular vanes are positioned at regular intervals around the curved surface of the rotor. Each vane is free to move in a slot. The centrifugal force from rotation throws the vanes outward to form a seal against the fixed casing. As the rotor revolves, a partial vacuum is created at the suction side of the pump, drawing in fluid. This fluid is then transferred to the other side of the pump in the space between the rotor and the fixed casing. At the discharge side, the available volume is decreased, and the resultant increase in pressure forces the fluid into the outlet line; the pumping rate can be varied by changing the degree of eccentricity of the rotor. Vane pumps do not need inlet and outlet check valves; they can pump liquids containing vapours or gases but are not suitable for pumping liquids containing solid particles. Vane-type compressors are used to pump gases. Vane pumps deliver a constant output with negligible pulsations for a given rotor speed. They are robust, and their vanes, easily replaced, are self-compensating for wear. Pumping capacity is not affected until the vanes are badly worn.
Essential vocabulary (II):
1. to resemble – напоминать, иметь сходство 2. external - внешний 3. helical – спиральный, винтовой 4. to revolve - вращаться 5. to shape – придавать форму, формировать 6. cavity - полость 7. bulky - громоздкий 8. robust – прочный, живучий 9. to mount – устанавливать, прикреплять 10. to wear – изнашивать, носить 11. rectangular vane- прямоугольная лопасть 12. curved – искривленный, загнутый 13. resultant - равнодействующий 14. fixed casing – зафиксированный корпус
Water-supply system (I)
Water supply system is an arrangement for transporting water from areas of abundance to an area of shortage. This includes works for the collection, transmission, treatment, storage, and distribution of water for homes, commercial establishments, industry, and irrigation, as well as for such public needs as fire fighting and street flushing. There is much archaeological evidence to indicate that ancient peoples were concerned with their water supply. Wells were sufficient for small communities, and rivers provided enough water for civilizations along the Tigris and Euphrates, the Nile, and the Indus rivers; but as populations grew, wells had to be dug deeper, and water had to be brought in from more distant sources. These ancient systems included storage reservoirs at water sources, canals and aqueducts for water conveyance to points of use, and water-distribution systems. Highly advanced systems appeared about 2500 BC and reached their peak in the system supplying ancient Rome. The outstanding features of this system were the 11 aqueducts totaling 359 miles (578 kilometres) in length—of which 30 miles were supported on stone arches—that delivered some 50,000,000 gallons (189,000,000 litres) of water to the city daily. The water was distributed from large storage cisterns to public fountains and baths by an elaborate system of lead pipes. During the Middle Ages, water supplies were largely neglected, and epidemics caused by waterborne organisms were common. In the 17th and 18th centuries, distribution systems utilizing cast-iron pipes, aqueducts, and pumps were installed in London and Paris. During the 19th century the pollution of most water supplies became so serious that slow-sand filtration was initiated; and by the end of the century the realization that diseases could be transmitted by water led to the use of sterilizing chemicals, usually chlorine compounds. Water sources for modern supply systems include wells, rivers, lakes, and man-made reservoirs. When points of use are near sources, direct intake can be used. Offshore intakes are sometimes built in lakes to obtain water of better quality and to avoid freezing problems in winter. Reservoirs are formed usually by constructing dams near the collection point of mountain-water runoff or across rivers. Dams provide a way of regulating water collection and flow so that the supply remains constant.
Essential vocabulary: 1. arrangement - размещение 2. abundance - избыток 3. shortage - нехватка 4. treatment - обработка 5. distribution – распределение 6. transmission - передача 7. flushing - промывание 8. establishment - создание 9. evidence - подтверждение 10. to indicate - указывать 11. to concern with smth./smb. – касаться чего-либо/кого-либо 12. well - колодец 13. sufficient - достаточный 14. dug – (от dig 1) копать, рыть 15. ancient - древний 16. conveyance – перевозка, передача 17. outstanding features - 18. elaborate – 1)разработанный, 2) сложный 19. lead - свинец 20. to neglect – пренебрегать, отвергать 21. to utilize - использовать 22. cast-iron pipes – чугунные трубы 23. pollution - загрязнение 24. to initiate - вводить 25. disease - болезнь 26. offshore - прибрежный 27. runoff - сток
I. Answer the following questions: 1. What is water supply system? 2. What does indicate that ancient peoples were concerned with the water supply? 3. What did the ancient water systems include? 4. What distribution systems were popular in the 17th /18th centuries? 5. How was water filtrated in the 19th century? Why? 6. What do usual water sources for modern supply system contain?
II. Find the English equivalents of the following phrases in the text: - система доставки воды - общественные нужды - копать глубже - достигнуть пика (верхней точки) - акведук для подачи воды - резервуары для хранения воды - организмы (бактерии), появившиеся в воде - загрязнение воды - использование (применение) чугунных труб - болезни, переносимые водой - постройка дамб через реку - поставка остается постоянной
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