Abstract: A liquid volumetric flow measuring apparatus is disclosed wherein a turbine or vane, flow straighteners therefor, and a rotating shaft mounted therewith, and a magnetic sender are all mounted as an integral unit in a U-shaped pipe trap, and a volumetric calculator is mounted in conjunction therewith. By a specific mounting of the turbine in the trap there is a dampening action causing the calculator to cease recording the flow immediately upon this stopping of the motion of the liquid through the trap. This construction provides a guard against any air which is pumped through the pipe being recorded as liquid in contradistinction to a gaseous fluid. The magnetic sender has a reed switch and a magnet which are specifically mounted so as to provide low angular momentum and reliability, at both high and low flow rates.