The Two Pipe System Part 4 82

Fig. 50.

In this country the one-pipe system is not used largely when there are radiators on one or more floors above the ground floor, but there is no reason why the system should not be adopted in such cases, if the general conditions make it desirable. In America the two-pipe system is almost unknown, and when the overhead method is not resorted to the one-pipe circuits have pairs of "risers" - rising branches - such as are shown in Fig. 50, to serve whatever upper floors need warming. There are no objections to this, - in fact, it works quite satisfactorily if the apparatus is properly proportioned, the mains in particular being of full size, as this helps to hasten the arrival of the hot water at the distant risers and to keep them well supplied.

The cold-supply service is arranged and connected as with the two-pipe system, and further description is therefore unnecessary.

The particular good features claimed for the one-pipe system are, firstly, that "short-circuit" is not possible. This term has been used when heated water circulates up to a certain point in a long run of pipes, and returns from this point to the boiler, leaving the water in the more distant parts of the run undisturbed and cold. This is considered to be possible with the two-pipe system, as each branch provides a means for the heated current to get from the main flow to the main return and so back to the boiler. It is a fact, too, that short-circuit has been experienced with two-pipe work, but only when the parts have been badly proportioned or the runs arranged without regard to correct practice. In other words, it is quite true that the one-pipe system prevents short-circuit, but it is quite preventable in any other system. A second advantage claimed is the reduced cost, this being based on the fact that one main pipe serves where two might otherwise have to be used. The two-pipe system certainly requires two main pipes to be run, close together, in whatever direction the radiators may be ; and this entails extra expense compared to one-pipe work, when the radiators all lie round the outer wall of a building. At other times, however, such as when the radiators lie in a nearly straight line, the two-pipe system is the cheaper, as there must be two main pipes carried whatever the system, and with two-pipe work the pipes can be reduced in size as the work is passed, while the one-pipe system must have full sized mains all the way. It may be said that each is the cheaper under certain ■conditions, but the one-pipe system most often.

Sizes Of Main And Branch Circulating Pipes, One-Pipe System Of Low-Pressure Hot- Water Apparatus

Sizes of Pipes.

Area of radiating or heat-losing Surface.

4

inches . . .

1300

sq. feet.

3

"

750

"

2 1/2

"

500

"

2

"

250

"

1 1/2

"

150

"

1 1/4

"

75

"

I

"

45

"

3/4

"

20

"