Text 11

A low-pressure hot-water system

Words and word-combinations to be remembered:

low-pressure hot-water system – система водяного опалення низького тиску

dense – щільний

to sink – опускати, осідати

convection – конвекція

to rise – підніматися

primary flow – прямий стояк

storage cylinder – акумуляційний циліндр

to descend – опускатися

primary return – зворотній стояк

draw-off point – зливний кран

feed tank – витратний бак

to dissolve – випаровуватися

to release – випускати

vent pipe – вентиляційний канал

air lock – повітряна пробка

to drain – спускати воду

Read and translate the text:

A low-pressure hot-water system

A low-pressure hot-water system is described below. Water in the boiler is heated, and consequently becomes less dense than the cold water in the higher parts of the system. The denser cold water sinks to displace the heated water, which is forced to rise. In this way, a circulation of water is set up-the process known as convection. The water rises up the primary flow (PF) into the hot-water storage cylinder, or tank, and is replaced by water descending the primary return (PR). If a temperature difference is maintained between the water in the primary flow and that in the primary return, then the process will continue. This is called the primary circulation and it is made more effective by connecting the primary flow to the upper region of both the boiler and the cylinder, and the primary return to the lower region of each. If a draw-off point is opened, water will be forced from it because of the height of the water in the feed tank (often this tank is also the building's main cold-water storage cistern). The hot-water supply is drawn from the top of the storage cylinder, where it collects because its density is lower than that of the colder water.

Heating water causes the dissolved air contained in cold water to be released. Consequently, a vent pipe has to be taken from the top of the storage cylinder and carried up above the level of the water in the feed tank. The pipe allows air to escape from the system and, as a result, prevents the formation of air locks.

A safety valve, set to operate at a certain pressure, is fitted to the system. Also, a draw-off point is fitted at the lowest part of the system so that it can be drained.

Exercise 1.

What’s the English for:

система водяного опалення низького тиску

щільний

опускати, осідати

конвекція

підніматися

прямий стояк

акумуляційний циліндр

опускатися

зворотній стояк

зливний кран

витратний бак

випаровуватися

випускати

вентиляційний канал

повітряна пробка

спускати воду

Exercise 2

Give the Ukrainian equivalents for the following English word–combinations:

a circulation of water, escape from the system, primary flow, becomes less dense, if a draw – off point is opened, cold water sinks, above the level of water, connect the primary flow to the upper region, in this way, heating water causes, prevents the formation of air locks, a safety valve.

Exercise 3.

What do the following abbreviations mean?

PR, PF, SV, W.C., H.W., B, C.W.

Exercise 4.

Answer the questions in English:

1. What is the function of the cold-water cistern?

2. Where on the cylinder is the primary flow connected? Why is it connected there?

3. How does heating affect cold water?

4. How can you stop the process of convection?

5. What causes water to be forced out of a draw-off point?

6. What is the most important function of the vent pipe?

7. If a safety valve is not fitted to the system, what might be the result?

Exercise 5.

Complete these sentences which describe how the low-pressure hot-water system works:

1. Water in the boiler is heated with the result that…

2. …is caused by the dense cold water sinking.

3. As a result of…water rises up the primary flow and is replaced by water descending the primary return.

4. …thereby continuing the process of convection.

5. The pressure at a draw-off point is due to…

6. Hot water has a lower density than cold water. Consequently …

7. The formation of air locks in the system is prevented by…

8. The operation of the safety valve results in…

9. …the system will drain.