877,605. Fluid-flow meters. BENDIX CORPORATION. May 23, 1960 [May 28, 1959], No. 18144/60. Class 69 (1). A fluid-flow meter comprises a powerrotated driver element 44, 46 connected by elastic couplings to a first impeller element 22 which accelerates fluid tangentially and to a second impeller element 32 which is accelerated when traversed by the rotating fluid, each of the impellers being angularly displaceable with respect to the driver element and means being provided to measure displacement between any two of the said three elements to indicate rate of mass flow. An electric motor 90 rotates a ring magnet 96 which couples through the non-magnetic casing 10 to rotate another ring magnet 97 fixed on the driver. Between the ports 46 and 44 of the driver is a drive-disc 42 which is coupled to the impellers through coil springs 82 and 86. The driver, the two impellers and the drive-disc are mounted coaxially to rotate independently of each other. Radial vanes (not shown) in conduit 18 align the flow of fluid entering the vanes 30 of impeller 22. The fluid, now rotating, passes thence through holes 80 in the disc 42 and passes through the vanes 38 of impeller 32 which it rotates in the same direction as the driver element. It then passes out through flow-rectifying vanes at 56 into conduit 20. In consequence of the passage of the fluid the impeller 22 tends to lag behind the driver element and the impeller 32 to lead on it, the relative motives taking place against the force of the springs 82 and 86. The lag or lead is measured against a time bore by magnetic pick-ups 98, 100 and 102 in cooperation with magnets 104, 106 and 108 on the driver and on the two impellers respectively. Stop-pins-112 and 116 co-operate with a stop 110 on the drive disc to cause one or other of the impellers to be coupled at will for direct rotation by the drive disc, thereby rendering either or both of the torsion springs inoperative, thus altering the sensitivity rate. The flow meter can be used to measure flow in either direction. Specification 857,052 is referred to.