Steam Piping

One-Pipe System.

The one-pipe up-feed system is most com monly used in connection with relatively small heating plants. It has the advantage of simplicity, there being but a single valve to operate. In tall buildings with the up-feed system, the risers must be objection ably large to provide for the pas sage of steam up, and water of condensation down, the s am e pipe. With the overhead sys tem, the risers may be made con siderably smaller, since the water is not hindered in its passage by a flow of steam in the opposite Erection. With this one-pipe iystem, the radiator connections ihoul d be short and pitched lownward toward the risers to avoid pockets. When used in high buildings with the overhead sys tem, the lower portion of the risers must be liberally proportioned, Jtherwise the steam will become too wet.

The Two-Pipe System.

This system is commonly used where the -adiator connections must be long and where it would be impossible to secure a proper pitch to insure good drainage with one-pipe ra diator connections. Coils are nearly always made up with two pipe connections. In high build ings, where a large amount of radiation m u s t be carried by each riser, they may be made smaller if two-pipe connections are made with the radiators. This is often a decided advan tage, especially if the risers are to be concealed.

Draining Mains and Risers.

With long mains, it frequently is the case that if given a continuous pitch they would be too low at the extreme ends; and it is therefore customary to rise and drip at intervals, as shown in Figs. 23 and 24.

The siphon trap (Fig. 23) prevents a greater pressure being in troduced along the overhead return than occurs at the extreme end, since any excess in pressure at an intermediate point merely forces down the water in the inlet leg of the siphon trap to a point where the difference in pressure in the two mains is equalized by the higher level of water maintained in the outlet pipe of the syphon trap.

With indirect systems, the mains are frequently drained through the benches or stacks of radiators, the connections being taken from the bottom of the main. It is assumed that all the indirects will not be shut off at the same time (see Fig. 25).

Mains and risers are monly drained as shown in Fig. 20, connections being taken from the bottom of the main and the heel of the riser. Risers are not frequently drained to the main, which in turn is drained at the end (see Fig. 26). This arrangement requires less fitting than when the risers are relieved at the base, as shown in Fig. 20. If the mains are long, they should be dripped at intervals of 50 to 75 feet.

Overhead-feed mains on a down-feed system are nearly always dripped from the bottom to the various risers, as previously stated.

Artificial Water Line.

It is sometimes necessary, when a boiler is set very low with reference to the returns, and it is desired to use a wet return system, to seal the relief pipes by means of an artificial water line established as shown in Fig. 27. The equalizing pipe is to be connected with a steam main.

When the discharge from the system leads to an open return, a trap must be used. One of

the type shown in Fig. 28, arranged with an equalizing pipe and set at the proper level, will hold the water line in the system, no stand pipe being required.

Pipe

Sizes.—Mains.

The capacities of pipes to supply heating surface in crease more rapidly than their sectional areas; that is, a 6-inch pipe, with about four times the area of a 3 inch pipe, will supply nearly six times as much surface.

Table III shows the amounts of radiating surface in gravity return systems which main pipes 100 feet long, of different diameters, may be safely counted on to supply with low-pressure steam (say, 3 to 5 lbs.).

In case the radiating surface is located some distance above the water line in the boiler, the carrying capacity of the pipes may be increased as much as 50 per cent, owing to the greater drop in pressure that may be allowed without interfering with the return of water to the boiler.

Mains are frequently made much larger than necessary, simply because the fact has been overlooked that the radiators are located well above the boiler, and that a drop in pressure between the boiler and the end of the main of } lb., or even more, would be permissible.

The greater the drop in pressure allowed the smaller may be the pipe for a given capacity.

Pipe Sizes.—One-Pipe Risers. Riser capacities are given in Table IV.

The capacities of the I-inch and I If-inch pipes for up-feed are somewhat greater than those stated; but they are given as above, since these figures correspond closely to stand ard radiator tapping, and it is advisable to make the pipes of the same size as the tapped openings.

In high buildings with the down-feed system, the lower half of the risers should be based on not much more than half the capacities stated in the right-hand column, in order that the pipes may be of ample size to carry off the great amount of condensation from the radiators above, without making the steam too wet for use in the radiators below. The pipe to the lowest radiator connection should be not less than 2-inch.

Pipe Sizes.—Two-Pipe Risers. With the two-pipe system, the capacity of the risers is of course, considerably greater than with the one-pipe system, since the condensation is carried off through a sepa rate system of returns.

Table V gives the approximate capacities of risers for the two pipe system.

Pipe Sizes, Indirect. Supply connections with indirect radia tors must be larger for a given surface than for direct radiators. The following table gives ample sizes when the radiators are but little above the water line of the boiler. When this distance is con siderable, the pipes may be safely rated to supply one-third more face; for a greater drop in pressure may be allowed between the supply and the return mains, and drop in pressure means a greater velocity in the pipes, and consequently a greater flow of steam to the radiators.

Indirect radiators are seldom tapped larger than 2 inches; there fore radiators that require larger connections should be subdivided in groups.