3.Active vocabulary:

4.Answer the questions:

1.What is the minimum size of a soil drain? 2. Why should the drains be laid to the correct fall? 3. What happens if the drain is too steep? too shallow? 4. The invert of a 45 metre long 100 mm drain is 875 mm below the datum at the higher end. What is the depth of the invert at the lower end?

Text 3 (2200)

1.Study the meanings of the following misleading words:

list – перечень, список;

clay – глина;

normally – обычно;

commercial – промышленный

2.Read and translate the text: Types of drainpipe

Drainpipes can be made from a variety of materi­als. Your choice of drainpipe will depend on avail­ability, price and suitability for the purpose. This list describes some of the most common materials for drainpipes:

1. vitrified clay, which is clay that was fired at a very high temperature to make it waterproof;

2. cast iron, which is a very hard metal alloy. This material is quite expensive and normally only used for commercial buildings;

3. concrete, which is cast using the methods of production for concrete;

4. plastic, which is polyvinyl chloride (PVC). This is a popular material because it comes in long lengths, is light and it makes joints easily.

Methods of joining drains. The method that you use to join drains depends on whether you are using:

• rigid pipes with rigid joints;

• rigid pipes with flexible joints;

• flexible pipes with flexible joints.

Rigid pipes with rigid joints. Rigid pipes made from clay, concrete or cast iron need rigid joints with socket ends that are wide enough to insert pipes with straight ends, called spigots. There should be enough space around the spigots to put the jointing material.

You make a joint for a clay pipe by wrapping rope or yarn around the spigot and pushing the pipe into the socket of the adjoining pipe so that it fits tightly. Then fill the socket with a 3:1 cement mortar mix and finish it off neatly, joints for con­crete pipes are made in the same way as clay pipes.

Cast iron joints are formed by wrapping yarn around the spigot and filling the space between the spigot and socket with molten lead.

Rigid pipes with flexible joints. Recent developments in pipe technology have made it possible to use rigid pipes with jointing methods that allow some flexibility. This is useful because rigid joints may crack with slight movement.

There are two types of flexible joint:

1. spigot and socket combinations, which are fitted with plastic pieces which have

grooves for rubber rings;

2. polypropylene sleeves, which are fitted with rubber rings to grip the pipes instead of spigot and socket joints.

These combinations can be used to make flexible joints for concrete pipes.

Flexible pipes with flexible joints. Flexible pipes distort under loads. This distortion should be limited to 5 per cent of the pipe’s diameter to maintain the flow of water. Similarly, the flexibility of the joint should only take up slight movement so that the pipe maintains the correct falls.

PVC pipes are made with socket and spigot ends. They can be jointed by using a solvent to weld the pipes to­gether so that one pipe sits tightly inside the other or by inserting rubber rings in the grooves of the sockets and spigots.