Fig. 131.
Fig. 132.
Fig. 133.
All steam piped rooms should be frequently dusted, cleaned and kept free from accumulation of inflammable material.
The use of the air valve is as follows: In generating steam from cold water all the free air is liberated and driven off into the pipe, with the air left in them, all of which is forced up to the highest point of the coils or radiators, and compressed equal to the steam pressure following it. Now, by placing a valve or vent at the return end of the pieces to be heated, the air will be driven out by the compression. Why the vent is placed at the return is, that the momentum of the steam, it being the lightest body, will pass in the direction of it, falling down into the return as it condenses, thus liberating the air. Otherwise, should the vent not work, and the air is left in the radiator, it will act as an air spring, and the contents of the pipes left stationary will be the result; no circulation, no heat; and the greater steam pressure put on, the greater the chances are of not getting any heat; and thus a little device, with an opening no larger than a fine needle, will start what a ton of pressure would not do in its absence.
If the drip and supply pipes are large there is very little danger of freezing, provided suitable precautions are taken to leave the pipes clear. They should be blown through, when left, and the steam valve should be closed. There should also be a free chance for air to escape in all systems of piping.
No rule can be given relating to capacity for heating pipes and radiators which do not require to be largely modified by surroundings.