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The simple impulse turbine consists of one or more fixed nozzles discharging steam against a single row of blades mounted on the periphery of a wheel or a rotor. The steam expands from the initial high pressure to the final lower pressure in a single set of nozzles. A steam jet issuing from the nozzle acquires very high velocity and is then directed against the blades of the turbine wheel. Velocity of flow depending upon the difference in pressure between high and low pressure regions creates impulse of the steam jet. This impulse produces rotation of the turbine wheel. High steam and blade velocities produce high speed of rotation.

Very high velocity of the steam jet occurs due to the relatively great ratio of expansion of the steam in the nozzles. Steam issues from the nozzle outlet with velocity, e. g. about 3.500 feet per second. The velocity of the blades for good economy should be about one-half of the steam velocity, at about 1.700 feet per second. The exit velocity involves loss of energy, a small final velocity is necessary in order that the steam may escape from the turbine into the condenser. The principal example of this turbine is a well-known de Laval Turbine.

Упражнение 1. Найдите эквиваленты английских глаголов:

1. discharge a) иметь место, происходить

2. issue b) производить, создавать

3. acquire c) выпускать

4. produce d) приводить к, вызывать, влечь за собой

5. create e) приобретать

6. occur f) создавать

7. involve g) выпускать, подавать, нагнетать (пар)

8. deliver h) предотвращать

9. attach i) покидать

10. prevent j) прикреплять, присоединять

11. escape k) доставлять, снабжать

12. enclose l) распределять

13. surround m) наклонять

14. distribute n) окружать

15. bevel o) вмещать, помещать (в корпус)

The De Laval Turbine

Слова и словосочетания к тексту.

circumference	—	окружность, длина окружности
rigidly adv	—	жестко, неподвижно
a steam chamber	—	паровая камера
uniformly adv	—	равномерно

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This turbine was introduced in 1888 by Dr. De Laval of Stockholm, Sweden. This is a single stage turbine of impulse type. It has a single wheel with one row of radial blades. Steam is delivered to the blades in jets from nozzles placed at intervals round the circumference of the wheel. They deliver steam at the highest possible velocity. The turbine wheel is rigidly attached to the shaft, the outer ends of the blades form a rim to prevent the steam from escaping a radial direction. The turbine wheel is enclosed in a casing surrounded by a steam chamber from which the steam enters nozzles and expands as it passes through them. The nozzles are placed around the wheel to distribute the steam uniformly. They are beveled at the ends nearest to the wheel, so as to fit closely to it and deliver the steam to the blades without waste. The total expansion of the steam occurs in the nozzles and at the points where the jets strike the blades the steam pressure is equal to the pressure of the exhaust.

In other words this is a turbine where a high-pressure steam jet is issued from a nozzle and passing through it the steam expands and increases in volume. A high velocity steam jet strikes the blades set around the circumference of the wheel. The blades are curved as to deflect the steam in backward direction.

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