Answer the following questions.

1) What meters are used to measure the flow in open channels?

2) What are the types of weirs?

3) What is necessary for weirs to give accurate water discharge?

4) What may alter the weir coefficient?

5) Is accurate flow measurement possible?

6) What is the head on the weir usually measured with?

7) What provides sizable error in measurements?

8) What happens if water contains suspended particles?

9) What difficulties are partially overcome by use of venture-type flumes?

10) Where must venture-flumes be installed for obtaining the best results?

11) What are venture-flumes made of?

Make a short summary of the text.

Find the synonyms of the following words in the text.

Find the opposites of the following words in the text.

Fill in the correct prepositions where necessary then choose any three items and make sentences.

1) to result ___ sth.; 2) to be ___ right angle; 3)___ addition; 4) to measure ___ sth. ___ sth; 5) to be made ___ iron; 6) to be installed ___ the straight section; 7) to provide ___ an error ___ measurements.

Translate the following words into English using the vocabulary of the text.

Измерительный прибор, использовать треугольный водослив Томсона, водослив с острым прямоугольным гребнем, трубка Вентури, поддерживать напор воды, прямой подводящий канал, неизменные условия, изменять коэффициент водослива, измерять при помощи водомерной рейки в водобойном колодце, потеря давления, неточное определение напора, частично преодолевать, атмосферное давление.

Find the translation of the following terms and memorize their meaning.

Read the text to get the gist of it. Answer the following questions.

a) When is a pressure conduit used?

b) What is the synonym to the term “inverted siphon”?

Text C                                                      Pressure Conduits

A pressure conduit is a conduit which is flowing full. Such conduits are often less costly than canals or flumes. If water is scarce, pressure conduits may be used to avoid loss of water by seepage and evaporation which might occur in open channels. Pressure conduits are preferable for public water supplies because of the reduced opportunity for pollution. Pipes must be designed to withstand stresses created by internal and external pressures, external loads and temperature changes and to satisfy the hydraulic requirements of the project. The internal pressure within a conduit is caused by static pressure and water hammer.

When a liquid flowing in a pipe is abruptly stopped by the closing of a valve, dynamic energy is converted to elastic energy and a series of waves travel back and forth in the pipe until they are damped out by friction. This phenomenon is known as water hammer. Water-hammer pressures can be greatly reduced by use of slow-closing valves, automatic relief valves, air chambers and surge tanks. The principal pipe materials are steel, cast iron, concrete, wood, asbestos-cement and vitrified clay. Other materials used for pipes include copper, wrought iron, plastics, asphaltic fiber and brick. Copper and wrought iron are used for small diameter pressure pipe. Copper is quite expensive but may be advantageous in situations where corrosion is likely to occur. Plastic pipes are corrosion free and light in weight, but their low strength, however, precludes them from being used in large sizes. Asphaltic fiber pipes are inexpensive but they are not often used. Brick was formerly used for sewers but nowadays is rarely used.

A large number of different types of valves are required for the proper functioning of a pipeline. Gate valves are used to regulate the flow in the pipe. These valves are similar to the gate valves used in dams but not so large. Check valves permit flow in one direction only. They are required at interconnections between a polluted water system and a portable water system to prevent entry of pollution into the pure water. Drain or blow off valves are necessary at the low points of a pipeline to permit the pipe to be trained for inspection and repair. Water-hammer pressures in a pipe can be minimized by use of pressure-relief valves, adjusted to open automatically at a predetermined pressure.

Surge tanks are installed on large pipelines to relieve excess pressure caused by water hammer and to provide a supply of water if a valve is suddenly opened. A simple surge tank is a vertical standpipe connected to a pipeline. Surge tanks are usually open at the top and of sufficient height so that they will not overflow. In some cases overflow is permitted if the flow can be disposed of without damage.

The bottom of the surge tank must be far enough below reservoir level so that the tank contains water at all times to prevent air from entering the pipe. Surge tanks are often built partially or wholly underground. Exposed surge tanks are usually built of steel or reinforced concrete. Surge chambers for tunnels may be excavated in the rock above the tunnel if geologic conditions are favorable. In cold climates a surge tank must be protected from freezing. Electric heating units have been used successfully for this purpose.

The term "inverted siphon" is applied to a pressure pipe. Actually no siphon action exists and the term "sag pipe" would be more descriptive and more accurate. Flow in a sag pipe is under pressure and follows the principles of flow in pressure conduits. If the water contains suspended solids, the minimum velocity in the sag pipe should be great enough to prevent deposition of these solids at the bottom of the sag. This usually requires a minimum velocity of about 3 ft/sec.