The Cone Venturi is a differential pressure type flow meter primary device.
It operates on the same principle as other differential pressure producing flow meters, suing the theorem for the conservation of the energy in fluid flow through a pipe.
A cone, positioned in the corner of the precision meter tube, interacts with the flowing fluid, reshaping the fluid’s velocity profile and creating a region of the lower pressure immediately downstream of itself.
This pressure difference, between the static line pressure and the lower pressure created just the cone, can be measured via two pressure sensing taps, one placed slightly upstream of the cone and the other in the downstream face of the cone itself.
The pressure difference can then be incorporated into a derivation of the Bernoulli equation to determent the fluid flow rate.