Air under pressure is supplied by the pipe C, connected to the air supply, flowing into the thermostat through the filter P, the restriction S, the passage T, and the port G. The adjustment of the thermostat for different temperatures is provided for by the screw J through the top plug H, and the indicating disc X. The screw R in the connector Q at the base of the thermostat is a needle valve which opens or closes the connection with the air supply, and is used as an air shut-off valve when it is desired to remove the thermostat. The screw S is a restriction valve which controls the supply of air to the thermostat, and this screw is set so as to allow the air to pass in a restricted quantity.
When the temperature of the apartment has risen so as to expand the thermostatic element A, the pressure on K and L is relieved and the spring N closes the port G. The air admitted through the restriction screw S, since it cannot escape through the port G, accumulates in the passage Y and pipe D, filling the diaphragm and moving the valve into the position to decrease the supply of heat. When the temperature of the apartment has decreased so as to produce pressure on the connecting rod K, through the contraction of the thermostatic element A, the port G will be opened by the valve lever O, allowing the air in the pipe D, together with that which flows through the restriction S, to escape through the passage W to the atmosphere, allowing no air to accumulate in the pipe D, and thus permitting the spring at the diaphragm to actuate the damper or valve for more heat. The amount of air released through the port G by the valve lever O varies the pressure accumulated in the pipe D and produces the graduated or intermediate action desired.
Fig. 169.—Cross-section of pneumatic radiator valve showing its internal construction.
Fig. 170.—Pneumatic motor valve for automatic control of dampers, etc.
A further application of air pressure in temperature regulation is that of the type of motor shown in Fig. 170. This device is intended to open and close dampers such as are used in the automatic regulation of temperature where heated air is used to warm the buildings. The operation of the motor is the same as that which controls the steam valve. The pressure exerted by the diaphragm is applied at A and the attachment to the damper is made at B. The motors indicated at V and N in Fig. 174 and D in Fig. 175 are examples of its application.
Mechanical Ventilation.
—Draft ventilation produced by open windows, flues and chimneys is influenced by extremes of temperature and by the force and changing direction of the wind; it is, therefore, but imperfectly controlled. The superiority of mechanical ventilation is generally recognized because the amount of entering air may be regulated to suit any circumstance and its temperature and humidity varied to conform to any desired atmospheric conditions. Mechanical ventilating plants are seldom employed in any but the more pretentious dwellings, but their use has extended to a degree that they are occasionally installed in apartment buildings and their further application is likely to grow. Neither the cost of installation nor the expense of operation is prohibitive in dwellings of the better types. Mechanical ventilation is quite generally employed in school buildings, auditoriums, hospitals, public buildings and others where means will permit, and there is a universal recognition of the effects of the agreeably conditioned air.
Mechanical ventilation may be accomplished by power-driven fans, either by exhausting the air from the building or by forcing air into it, and under some conditions a combination of the two methods is used.