Читать книгу Mechanics of the Household - E. S. Keene - Страница 47

—The damper regulator for a hot-water boiler automatically controls the dampers of the furnace so as to keep the water of the boiler approximately at a constant temperature. The regulator is shown in Fig. 52. The ends of the lever are connected to the direct-draft and check-draft dampers, as in the case of the damper regulator for the steam plant. A cross-section of the working parts shows the details of construction. The lever d is operated by a diaphragm g, which tightly covers a brass bowl, containing a mixture of alcohol and water, of such proportions as will produce a vapor pressure at the desired temperature, say 200°. The hot water from the boiler passes through the valve, entering at a and leaving at b. When the water reaches the desired temperature, the contained liquid vaporizes and a pressure is produced that is sufficient to lift the diaphragm and the lever. The chain attached to the right-hand end closes the direct-draft damper; at the same time the other end of the lever opens the check draft, and the supply of air to the furnace fire is entirely cut off. As soon as the water has cooled sufficiently, the vapor pressure in the bowl is reduced, allowing the weight W to depress the diaphragm and the lever is restored to its first position. The weight W is for adjusting the valve to the desired temperature. The plug f tightly closes the orifice through which the liquid is introduced into the bowl.

The object of the damper regulator on a hot-water boiler is to govern the fire of the furnace so as to keep the water in the boiler at the desired temperature. In case there is a demand for heat at any part of the house, a supply of hot water will always be on hand. It has nothing to do with the regulation of the temperature of the house. The control of the house temperature is the office of the thermostat.

The thermostat is a mechanical device for automatically regulating temperature. It may be arranged to operate the valve of a single radiator or register and so control the temperature of a room, or as commonly used in the average dwelling, the controller may be placed to govern the temperature of the living room and in so doing keep the furnace in condition to satisfactorily heat the remainder of the house.

Thermostats are made in a variety of forms by different manufacturers but they may be divided into two general classes: the electric, and the pneumatic types. The electric thermostat depends on an electric current as a means of controlling the action of the motor which in turn operates the furnace dampers so as to maintain a constant heat supply. The pneumatic thermostat regulates the supply of heat by means of pneumatic valves. It will be considered later in discussing mechanical ventilation. This type of temperature regulation is particularly adapted to large buildings.

Fig. 53 illustrates one style of electric thermostat that is very generally used for temperature regulation in the average dwelling. It consists of three distinct parts—the controller, the electric battery and the motor. In the drawing the motor is shown connected with a steam valve, such as may be used for furnishing steam for a series of radiators. It may with equal facility be attached to the dampers of a furnace or other heating apparatus.

The controller occupies a place on the wall of the room to be heated and makes electric connections between the battery and the motor. Whenever the temperature varies from the required degree, a change of electric contact in the controller starts the motor, and the radiator valve or the furnace drafts are opened or closed as occasion requires.

The controller appears in Fig. 54 as commonly seen in use. The upper part carries a thermometer and the pointer A indicates the temperature to be maintained in the room. The middle division indicates 70°F. Each division to the right of the middle point raises the temperature 5°. Each division to the left lowers the temperature a like amount.

In addition to the ordinary type this controller is furnished with a time attachment by means of which the controller may permit the temperature of the room to fall to any desired degree at night and raise it again in the morning at the time for which it is set.

This is accomplished by a little alarm clock shown at the bottom of the controller in Fig. 54. The indicator B is arranged to correspond with the indicator A; the middle point representing 70°F. To set the time attachment, the alarm is wound and set as in any alarm clock,½ hour earlier than the desired time for rising. The indicator B is set for the day temperature and A is set for the temperature desired during the night. At the appointed time the alarm moves the indicator A to the desired point for the day and the controller raises the temperature accordingly.

Fig. 55 shows the mechanism that is exposed to view when the cover of the controller is removed. The bent strip C is the part that is influenced by the change of temperature. It is made of two thin strips of metal, one of brass and the other of steel. The two strips are soldered firmly together. Any change in temperature will affect the strip and cause it to bend and touch the contact point—K or J. The bending of the strip is due to the unequal expansion of the brass and steel due to the change of temperature. Brass expands 2.4 times as much as steel with the same change of temperature. The amount of bending is sufficient to make an appreciable movement in a small fraction of a degree change. The brass part of C is on the left and since it expands the greater amount, a rising temperature causes C to come into contact with the point J. When this happens the motor is started and makes one-half cycle. In so doing it shuts off the air supply of the furnace, opens the check draft and at the same time the motor changes the electric contact from J to K. When the temperature begins to fall, the brass contracts in the same ratio to the steel as it expands during the rising temperature and as a consequence the bar bends to the left. When the strip touches the point K the motor again makes one-half circle, admitting air once more to the furnace, closes the check draft and shifts the electric contact back to K. When properly started the thermostat will regulate the temperature within a degree of temperature.