Fig. 134.
It is important to protect all wood work or other inflammable material around steam pipes from immediate contact with them, especially where pipes pass through floors and partitions. A metal thimble should be placed around the steam pipe, and firmly fastened on both sides of the floor, in such a way as to leave an air space around the steam pipe.
For indirect radiating surfaces, the box coils are the forms most used. The chambers or casings for containing them are made either of brickwork, or often of galvanized sheet-iron of No. 26 gauge, with folded joints. The coils are suspended freely within the chambers, which are themselves attached to the walls containing the air inlet flues. Besides coils of wrought iron tubes, cast-iron tablets or hollow slabs, having vertical surfaces with projecting studs or ribs, have been extensively used for the radiating surfaces.
As the amount of heat given off from the radiator cannot be satisfactorily controlled by throttling the steam supply, it is usual to divide all radiators into sections, each of which can be shut off from the supply and return mains, separately from the rest of the sections. This method of regulation applies to radiators for indirect heating as well as for direct.
Vertical pipe coils, constitute a distinctive form of radiator now largely used. In these a number of short upright 1-inch tubes, from two feet 8 inches to 2 feet 10 inches long, are screwed into a hollow cast iron base or box; and are either connected together in pairs by return-bends at their upper ends, or else each tube stands singly with its upper end closed, and having a hoop iron partition extending up inside it from the bottom to nearly the top. The supply of steam is admitted into the bottom casting; and the steam on entering, being lighter than the air, ascends through one leg of each siphon pipe and descends through the other, while the condensed water trickles down either leg, and with it the displaced air sinks also into the bottom box. For getting rid of the air, a trap is provided, having an outlet controlled by metallic rods; as soon as all the air has escaped and the rods become heated by the presence of unmixed steam, their expansion closes the outlet.
A thorough drainage of steam pipes will effectually prevent cracking and pounding noises.
The windward side of buildings require more radiating surface than does the sheltered side.
When floor radiators are used, their location should be determined by circumstances; the best situations are usually near the walls of the room, in front of the windows. The cold air, which always creates an indraft around the window frames, is thus, to some extent, warmed as it passes over the the radiators, and also assists in the general circulation.
Water of condensation will freeze quicker than water that has not been evaporated, for the reason that it has parted with all its air and is therefore solid.
Whatever the size of the circulating pipes, the supply and drip pipes should be large, to insure good circulation; the drip pipes especially so. This is also the more necessary when the pipes are exposed, or when there is danger of freezing after the steam is shut off.