Читать книгу Mechanics of the Household - E. S. Keene - Страница 49

—It is evident that, in heating a house by steam, the damper regulator governs only the steam pressure of the boiler. In the use of a thermostat alone, the regulation is that of the temperature of the rooms only, and has nothing to do with the steam pressure. As an example: Suppose that in cold weather the house is cold and that the gage of the steam boiler shows no pressure. The desire is to get up steam as soon as possible. In so doing a hot fire is made with a large amount of fuel. As soon as the steam begins to form, the pressure rises rapidly. When the radiators have become hot and the steam is no longer taken away as fast as it is formed, the pressure of the steam in the boiler keeps on rising. The thermostat will not close the furnace dampers until the temperature of the rooms is normal. This may require so great a length of time as to produce a great excess of steam that cannot be used at the time and the pressure will be relieved by the safety valve. This may not be dangerous but it is disagreeable. To prevent the safety valve from blowing except in case of emergency, a combined thermostat and draft regulator is used. In such a combination, the draft regulator closes the draft as soon as the pressure reaches the desired point, after which the thermostat does the regulating according to suit the temperature of the house.

In Fig. 2 is shown such a combination attached to a boiler. The cord from the regulator, instead of extending directly to the direct-draft damper, passes over the pulley P and connects to the thermostat cord. The regulator may now close the damper to suit the steam pressure, but after the temperature in the rooms is normal, the amount of heat necessary to maintain the desired degree is regulated entirely by the thermostat which opens and closes the dampers regardless of the position of the damper regulator.

If occasion should require but a very slight amount of steam to keep the house at the desired temperature, the thermostat will govern the drafts aright. If the steam pressure is in danger of becoming excessive, the damper regulator will govern the drafts.

Fig. 56.—Automatic switch which opens the battery circuit when the thermostat motor weight, reaches its limit.