The Thermostat Motor.

—The thermostat motor automatically opens and closes the furnace dampers or the valve that admits steam to the radiators as heat is demanded by the controller.

The motor, as shown in Fig. 53, consists of a system of gears and a brake S, which regulates the speed, a cam M, and armature I, for starting and stopping the motor, and the electromagnet H-H which operates the bar I. Two lever arms L, one in front and the other at the back of the motor furnish means for attachment to the valve or furnace dampers. An emergency switch at D is shown in detail in Fig. 56. The battery B furnishes the current which energizes the magnets and an iron weight supplies the motive power for the motor.

The description of the operation of the motor applies to the steam valve shown in Fig. 53. The same motor might be used for opening and closing of the dampers of the furnace in any kind of heat supply. The method of communicating the motion of the motor arms to the dampers of the furnace will be described later. The connections with the furnace drafts are shown in Figs. 3, 6, 8, 34, etc.

Suppose that the valve for admitting steam to the radiators, as that in Fig. 53, is closed and that the temperature of the house is falling. The strip C of the thermostat controller is moving toward J. When contact is made, the current from the battery B energizes the magnets H-H and the bar I is lifted. As the bar I is raised the catch J is released and permits the motor to start. The bar I is held suspended by the cam M until the arm L has made one-half revolution, when the lug K drops into the depression in the cam made to receive it and the catch J engages with the brake and stops the motor.

During this movement the arm L has lifted the valve arm N and the valve admits steam to the radiators, at the same time the contact M has been shifted from the right-hand contact to the left, and the electric circuit is ready to be made in the controller at the point K. When the temperature has fallen a sufficient amount the controller bar C will make contact at K and the motor will again make a half cycle, changing the valve back to its original position. This process will be kept up so long as the motor is wound and there is sufficient fuel in the furnace to raise the temperature.

Fig. 55 shows the method of connecting the electric wires from the battery to the controller. A three-wire cable connects the battery, and makes contacts as indicated at H, K and J. The wires are shown attached to the motor as in Fig. 55. A wire is taken from either pole of the battery and attached to one of the ends of the magnet coil. Passing through the magnet the wire is attached to the frame of the motor. This makes the cam M a part of the electric circuit. The other two wires are attached to the brass strips on each side of the arm L. The strips are insulated from the frame. The electric circuit through the magnet is made alternately by contact with the strips at right and left of the arm L.

In case the motor, through neglect, runs down, a safety switch at D (Fig. 53) disconnects the battery and keeps it from being discharged. This switch is shown in detail in Fig. 56. When the weight has reached its limit, the piece C on the chain comes into contact with D and lifting it out of contact, breaks the circuit. When the motor is again wound, C engages with E and restores the contact. The switch is so arranged that when open, the valve will always be closed.