Fig. 11.

Remedy for hammering.

Fig. 12.

Where a steam-heating system has been laid out with insufficient care, so that it gives annoyance by hammering, relief-pipes can often be added in this way, so as to cure the trouble, without any great expense; and, where this is impracticable, something may often be gained by covering the long, vertical steam-pipes with felt, so as to diminish the condensation in them.

In managing steam radiators with two pipes, it should be remembered that the smaller, or return-pipe, communicates, in most cases, with the water of the boiler; and if it is left open, when the steam-valve is shut, the vacuum left in the radiator by the condensation of the steam remaining in it will draw up water from the boiler into the radiator, nearly or quite filling it. With small house-heating boilers the water may be drawn dangerously low by being sucked up into the radiators in this way, and the two valves of radiators fitted up on the two-pipe system should always be opened or closed together. In a single-pipe system the radiators have but one valve, which shuts off or opens both steam and return at once. Where the radiators to be cared for are those of an indirect steam-heating system, it is still more necessary to remember to shut off the steam and return together, as a radiator which has been allowed to fill with water through neglect to close the return is likely to freeze and burst where exposed to the cold air which passes through the fresh-air conduits of an indirect system. The radiators of a direct-indirect system are also liable to freezing in the same way, if allowed to fill from an open return. In any case, if a return-valve has been left open when the steam-valve is closed, so as to allow the radiator to fill, the water may be easily expelled by opening the steam-valve. The pressure of the steam soon forces out the water through the open return-valve, and when the gurgling noise incident to this process has ceased, and the radiator is warm in all portions, both valves may be closed.

Freezing.

As the radiators of a hot-water system cannot be emptied separately of water, they are always in some danger of freezing in cold weather; but a small fire in the boiler will be sufficient to keep the water in them warm, where a steam radiator, owing to the lack of pressure enough to force steam into it, would be cold, and, if full of water, would freeze. As the freezing of a hot-water radiator is a serious matter, care should be taken, in very cold weather, to see that none of the radiators are shut off, by closing the valve, which, in the case of a hot-water system, leaves the radiator full of water. Any pipes or radiators that are liable to become "air-bound " should also be tried, and air-valves opened, or relief given in other ways, so that the circulation may be free throughout the system while the cold weather lasts.

Freezing of hot-water radiators.

Many people, including some dealers in heating apparatus for houses, advise drawing all the water out of a steam or hot-water heating system at least once a year, and refilling with fresh water. This may be advisable where the steam is used to drive an engine, as the oil from the cylinder of the engine finds its way into the return water, and accumulates in the boiler; but in the case of heating systems it is injudicious, as every addition of fresh water causes rust in the pipes and other apparatus. It should be kept in mind that water containing dissolved air and carbonic acid acts upon iron, while water that has been heated, and is, therefore, free from dissolved gases, does not act upon it. After the apparatus, therefore, has once been filled with reasonably pure water, and the water heated, no further serious rusting will take place inside the pipes and boiler, even in many years, so long as they remain filled with the same water; while, if the boiled water is drawn off, and fresh water put in, rusting will immediately begin again. Both in hot-water and steam systems there will be some loss, owing to evaporation from the expansion-tank in a hot-water system, and to leakage from valves in a steam apparatus; and it is occasionally necessary, where the water contains much sediment, to draw off the sediment at the lowest part of the system, to prevent clogging. Losses of this kind must be made up with fresh water, which is added to a hot-water system by pouring it into the expansion-tank, and to a steam-boiler for house heating, usually, by turning it on from the street-supply until the water gauge shows the boiler to be sufficiently filled; but unnecessary addition of fresh water to a system of either kind should be avoided.

Fresh water.