Abstract: In a pneumatic variable air volume controller, a linear relationship is achieved between the actual air velocity in a duct carrying conditioned air to a defined area and a pneumatic pressure signal representing the temperature in that area; and this linear relationship is used to vary the volume of air flowing in the duct. This is achieved by comparing a pneumatic pressure control signal which is a linear representation of the velocity pressure in the duct to a pneumatic pressure control signal which varies as the square of a thermostat pneumatic pressure signal which itself varies in a linear manner with respect to the temperature in the controlled area.

Abstract: A multi-stage pressure-to-electric switch assembly includes a top casing provided with a pressure receiving chamber, a bottom casing integrally secured to the top casing in closing relation to the pressure receiving chamber, and a diaphragm clamped between the top casing and the bottom casing to be in sealing, closing relation to the pressure receiving chamber. This diaphragm is provided with three spaced-apart pressure response switch control portions, each portion including a switch control button. Three two-position electrical switches are fixedly supported with respect to the bottom casing. Three hollow, externally threaded switch control sleeves are aligned between the diaphragm control buttons and the switches. A switch operating control nut is threadably mounted on each of the switch control sleeves, and a switch operating plunger extends through each control sleeve between the diaphragm button and a switch.

Abstract: A rotary actuator for a damper shaft controls the angular position of the damper shaft in accordance with variations in fluid pressure inside of the actuator. The actuator includes a housing, a flexible diaphragm within the housing separating it into a fluid-tight compartment and a second compartment open to the atmosphere. The fluid-tight compartment is provided with a fluid pressure receving port open to a control source of variable pressure. The piston and piston rod are slidably mounted in the second compartment in contact with the diaphragm. The piston rod includes a longitudinally extending rack, and a crank arm rotatably mounted in the housing has a gear segment in meshing relationship with the rack. The actuator shaft to be controlled extends through the housing and is mounted in the crank arm to support the rotary actuator, and the rotary actuator is clipped to an air conditioning duct to prevent it from rotating on the damper actuator shaft axis.