Abstract: A flow measuring apparatus having increased sensitivity is disclosed for measuring the flow of gas, particularly through a confined passage. The flow measuring apparatus comprises a tube having a constant or tapered orifice section followed by an abrupt expansion of the orifice; a total pressure sensing probe is located preferably in the section of the tube with the constant or tapered orifice, the total sensing probe having an opening parallel to the flow of gas and facing upstream; and a static pressure sensing probe is located in the walls of the tube in the expanded orifice section immediately after the abrupt expansion, the static pressure probe having an opening either parallel to the flow of gas and facing downstream or perpendicular to the flow of gas. The sensing probes may be connected to a measuring device that provides a readout of the sensed pressures or pressure differential or to a control unit that is responsive to the sensed pressures or pressure differential.

Abstract: A flow sensing apparatus having increased sensitivity is disclosed for sensing the flow of gas, particularly through a confined passage such as the ducts in heating, ventilating and air conditioning systems. The flow sensing apparatus comprises a tube divided by a wall into an upstream chamber and a downstream chamber. The upstream chamber can have a constant orifice but preferably the walls of the tube in the upstream end are tapered to form a tapered chamber section. A total pressure sensing probe is located in the center of the tube and has its opening in the upstream chamber of the tube. The total sensing probe has its opening parallel to the flow of gas and facing upstream, the opening of the total pressure sensing probe preferably being in the wall dividing the tube into the upstream and downstream chambers. A static pressure sensing probe is located in the downstream chamber. The static pressure probe may be located in the walls of the tube and have its opening perpendicular to the flow of gas.

Abstract: An improved variable volume control assembly for conditioned air systems having an improved air flow amplifying sensing means that amplifies the difference between the total pressure and the static pressure and is sensitive at low pressures, an improved air flow collector-straightener, a critical ratio of the area of the inlet to the area of the expansion chamber, and a vortex filter strategically located within the assembly for maximum reduction of turbulence and noise.

Abstract: An improved variable volume control assembly for conditioned air systems having an improved air flow amplifying measuring means that amplifies the difference between the total pressure and the static pressure and is sensitive at low pressures, an improved air flow collector-straightener, a critical ratio of the area of the inlet to the area of the expansion chamber, and a vortex filter strategically located within the assembly for maximum reduction of turbulence and noise.