Abstract: A volumetric water meter of the type having an eccentric piston oscillating in a cylindrical chamber has a drive peg (64) on the piston engaging a rotor arm (50) which rotates about the chamber axis to drive an external register or the like. The drive peg is offset from the piston axis by that amount necessary to compensate for the periodic variation in angular velocity of the piston. The likelihood of the peg becoming disengaged from the rotor arm is thus considerably reduced.

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.