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Flowmeters - How They Work

1. Fuel first enters the hydraulic driver, which provides the torque to rotate the shaft, drum and impeller.


2. The fuel then passes through a stationary straightener and into the impeller.


3. The mass of fuel flowing through the rotating impeller causes it to deflect proportionally against the spring.


4. Impeller deflection relative to the drum is measured by pulses generated by magnets (attached to the drum and the impeller) rotating past two pickoff coils.


5. The time between start and stop pulses, caused by the angular displacement of the impeller relative to the drum, is directly proportional to the mass flow rate of the fuel.


Theory of Operation