Flowmeter with pressure taps located at 1D upstream and D/2 downstream of the measuring element
According to ISO 5167, flowmeters with orifice plates and nozzles (long radius) can benefit from D - D/2 mounting. This corresponds to a positioning of the upstream tap at a distance of 1D (D, internal diameter of the pipework) from the upstream of the orifice plate and the downstream tap at a distance of 1/2D from the downstream of the plate.
This type of assembly has the advantage of not requiring orifice flanges (more expensive than standard flanges): you simply prepare bosses on the piping upstream and downstream of the measurement to position the pressure taps. It is widely used for large pipe diameters.