Pneumatic Temperature Regulation.
—Pneumatic temperature regulation is very generally used in large and complicated heating systems, because of its positive action and completeness of heat control. This method of heat regulation utilizes the energy of compressed air, with which to open and close the valves of the radiators. It may be adapted to any mode of heating and can be used with any size of plant, but is particularly suited to extended systems. The radiators, providing heat for any particular space, are under control of separate thermostats, which by means of motor valves admit heat only as required. A motor, operated by compressed air, is attached directly to each radiator valve. Any change in temperature of the room causes the thermostat to correct in the radiator the required amount of heat.
With this method of regulation the temperature-controlling element of the thermostat, like that of the electro-thermostatic system, is a sensitive part, which by expanding and contracting with the heat and cold directly controls the heat in any part of the building. The motive power for opening and closing the valves of steam or hot-water radiators or for operating the dampers in a hot-air system is supplied by compressed air. The air supply is furnished by an air compressor which automatically stores air under pressure in a pressure tank, from which is drawn the necessary energy, as occasion demands. The air is conducted to the motors through small pipes which are connected with the regulating elements and also with the motors. The function of the thermostat is to so govern the air which enters the motor as to correct any change in the temperature of the rooms. This it does by opening and closing the valves as occasion demands.
In Fig. 166 is shown the arrangement of the thermostat T as it appears on the wall. Air from the supply tank is conveyed by the pipe A through the thermostat T to the motor valve V attached to the radiator. The function of the thermostat is that of so controlling the radiator valve by means of the motor V that the radiator will give out just sufficient heat to keep the room at the desired temperature. A closer view of the thermostat is given in Fig. 167.
Fig. 167.—Outside view of thermostat as it appears in use.
The thermostat illustrated in Fig. 167 is that employed by the National Regulator Co. The drawing shows the exterior and interior construction of the parts enclosed in the previous illustration. The pipe C at the right and opening P at the left are the same as A in Fig. 169; likewise, the pipe D connects at the opening M of the motor valve in Fig. 169.
Referring again to Fig. 168, the sensitive part consists of a tube A of vulcanized rubber. It is the dark-shaded part in the left-hand drawing. Any change in the air temperature influences the length of this tube. The changing length of the tube effects the air supply to close the radiator valve when the temperature rises above the desired amount and to reopen it when more heat is required. A finely threaded screw passes through the plug H at the top and to this is secured the indicating disc X. The bottom of this screw is cupped to receive the point of the rod K, which connects with the piece L. Any change in length of the sensitive tube moves the valve lever O, and thus opens or closes the air port G.
Fig. 168.—Internal construction of the National Regulator Co.’s thermostatic regulator.