Abstract: A fluid flow meter of the type having a vaned rotor mounted in a measuring chamber is provided with a series of inlet apertures arranged around the chamber with each aperture having one face (84) which extends sufficiently in the circumferential direction as to meet the opposite face (90) of the adjacent aperture. Since almost the entire periphery of the chamber wall is formed by apertures the collection of inflowing fluid is maximized while the apertures serve to direct at the rotor vanes (66) jets of fluid which are placed for maximum efficiency.

Abstract: A flowmeter having a flow passageway with co-axial inlet and outlet openings at its opposite ends and a vaned flow measuring rotor between the openings. The rotor is mounted in low friction bearings and yet the meter is operable within the normal accuracy specification for a conventional high-friction meter as a result of the presence of a constriction in the passageway upstream of the rotor. The passageway and constriction are of circular cross section and the constriction has a main portion which opens directly at the downstream end near the rotor, and a tapering upstream portion connecting with the passageway. The constriction affects flow at the rotor at turbulent but not at laminar velocities.