Steam Boilers and Connections

It is necessary, for soft coal boilers, that the flues and smoke-pipe be larger than for hard coal heaters, in order to provide for the more rapid accumulation of soot. Soft coal boilers are also built on the down-draft principle, the air being drawn down through the fire in stead of passing upward in the usual manner.

Coke Boilers. Coke is a popular fuel in some parts of the coun try; and certain makers are putting out specially designed boilers for this service, having a very deep fire-box.

Boiler Setting and Foundations. Brick setting of boilers, as in the case of furnaces, has been quite generally discarded, except in cases where the space around and above the boiler is used as a cen tral heating chamber for indirect systems, the radiators being placed above the heater (see Fig. 6). The pipes lead off as in furnace heating. The ash-pits under most boilers are rather shallow; therefore it is a good plan to excavate and build a pit not less than 4 to 6 inches below the floor, to give additional space for the collection of hot ashes, thus avoiding the burning-out of grates. Such pits should be built preferably of brick, and the bottom should be paved with bricks on edge, to prevent their being easily dislodged. Fig. 7 shows the general rangement of an ash-pit built as described.

Boiler Connections. Small jobs frequently have no stop valves at the boiler. In the case of larger ones, or where there are two boilers, valves in the supply mains must al ways be accompanied with check valves in the returns; otherwise, in case a stop valve in the main steam line is closed, the water will be backed out of the main returns at the boiler, by the pressure. Should the water partially leave the boiler in this manner and then suddenly return, the water coming in contact with the heated sections will crack them.

A stop valve should be placed between the boiler and the check valve in the return. A typical arrangement of return, etc., is shown in Fig. 8. It is convenient to have an independent drain connection from the returns to provide for drawing off the water in the system without emptying the water from the boiler. The latter, of course, has its independent blow-off cock. The water supply to the boiler should be controlled by a lock-shield valve or a cock that cannot be tampered with by any person not in charge. Boilers having eight sections or more, as a rule, have two or more steam outlets, thus re ducing the likelihood of the boiler priming or making wet steam, since, with a single outlet, the velocity of steam through it may be so great that the water is picked up and carried into the piping system.

When two boilers are to be connected, especial care must be taken to make them maintain an even water line when working together. Fig. 9 shows a method of making these connections that is simple and effective. The valved connection between the two boilers, below the water, gives free communication between them, making them work as one and preventing a difference in the water level in the two boilers. The equalizing pipe is often omitted, the header being made about twice the diameter of the pipes leading to it from the boilers.

The returns are connected with the twin boilers practically as shown in Fig. 8, the check valve being placed between the stop valve of each boiler and the main return.

Boiler Fittings or Trimmings.

It is important to have a reliable safety-valve, preferably one of the "pop" type specially designed for steam heating systems.

The damper regulators used are of the ordinary diaphragm pat tern, and should be connected by chains with both the lower draft door below the grate, and with the cold-air check in the smoke connection.

The steam gauge with siphon, the water column, water gauge, gauge cocks, etc., require no special description.

Capacity of Boilers.

Boiler capacities are commonly expressed in the number of square feet of direct radiating surface they will supply without undue forcing. Mains and risers should, of course, be added to the actual amount of surface in the radiators and coils. Even if the pipes are covered, a small allowance should be added to the com bined surface of the radiators. Not less than 50 per cent, and pre ferably 60 per cent, must be added to indirect radiation, to reduce it to equivalent direct radiation; and not less than 25 to 30 per cent to di rect-indirect radiation, to get its equivalent in direct surface. Another point to be kept in mind in selecting a boiler for heating rooms to be kept at different temperatures, is that more heat is given off per square foot of radiation in a room at 50°, for example, than in a room kept at 70°, the amount given off being approximately proportional to the difference in temperature between the steam and the air. With steam at, say, 220°, corresponding to a trifle over 2 pounds' pressure, the difference, in the case assumed, would be 220°-50°m 170°, and 220° 70° — 150°. That is, the actual amount of radiation in the rooms to be kept at 50° should be multiplied by to ascertain the amount of radiation in a 70° room that would give off the same amount of heat.