Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

—The damper regulator used on a steam boiler is a simple device that automatically controls the draft dampers by reason of the changing pressures of the steam. The object of the damper regulator is to prevent the generation of steam in the boiler beyond a certain pressure at which the valve is set. This point is usually 3 or 4 pounds below the pressure at which the safety valve would act. If in proper working order the damper regulator will so control the dampers that the boiler will always contain a supply of steam, but the pressure will not reach a point requiring the action of the safety valve. Fig. 51 illustrates its connections with the furnace dampers. In Fig. 18 the regulator appears at D. In external appearance and in operation of the dampers, it is the same as the regulator for a hot-water boiler but its internal construction is simpler. Fig. 50 shows its construction. It is attached to the steam space of the boiler at E. The steam pressure acts directly on the flexible metallic diaphragm B. As the pressure of the steam approaches the desired amount the diaphragm is raised and with it the lever V. A chain D, attached to the end of the lever, opens the check draft, and another at C closes the draft damper. When the steam pressure falls, the diaphragm lowers the lever and the dampers are restored to their original position. The same movements are repeated with each rise and fall of the steam pressure.

Fig. 52.—Damper regulator for hot-water boiler.

Damper Regulators for Hot-water Furnaces.

—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.