164. New buildings are piped while the work of construction proceeds, as soon as the walls are up, and the roof is on. On large jobs, the risers are usually put up first, then the horizontal branches are constructed, proceeding always from the riser back towards the radiators, and lastly the mains are put in place. The returns are constructed at the same time, and in a similar manner.

In many cases, however, particularly in small buildings, the mains are run in first, then the risers, and finally the radiator connections. This latter method avoids the use of right and left fittings, or unions, between the risers and the mains.

All radiator connections should be promptly capped as soon as erected, and all openings in T's and other fittings should be plugged at once, so that no dirt may get into the pipes.

165. During erection, the matter of expansion must be carefully considered. The best point for fastening each principal pipe, so that its expansion will cause the least disturbance, should be determined by close examination. Care must be taken to have every such pipe free at its ends, and to see that its connections or branches are not bound or rendered immovable by plaster, brick, wood, or iron beams or columns.

166. The piping should be tested for tightness, before it is covered by plaster or flooring, so that if any defective fittings or split pipes are discovered, they may be replaced without trouble. The testing is done by filling the system full of water, every opening being tightly closed, and then applying pressure by means of a force pump. The pressure is increased until the gauge shows from 100 to 150 pounds per square inch. Another test should be made, with steam, before the pipes are covered up, if possible. This will determine whether the expansion is properly provided for, and whether the system is in working order. The steam pressure used should not greatly exceed the proposed working pressure.

167. All steam pipes should be kept out of contact with woodwork or other combustible materials. A clearance of at least two inches should be maintained at all points, and where this cannot be had, special protection should be provided. Return pipes are liable to be full of hot steam at times, therefore they must be guarded the same as steam-supply pipes.

Fig. 62.

Fig. 62 shows the manner of using floor and ceiling flanges to protect the woodwork where a steam pipe passes through an ordinary floor. When the ceiling flange e is secured to the pipe by a setscrew, as shown, allowance must be made in setting it for the vertical expansion of the pipe, otherwise it will be liable to break the plaster forming the ceiling. A better construction is to connect the upper and lower flanges by a nipple, a size or two larger than the riser, and have a current of air flowing through the spaces between the pipes and any combustible material.