US Patent 6912919 Restriction flowmeter

A restriction flowmeter including a cylinder through whose interior a fluid to be measured flows and a pipe for forming a restriction structure penetrating the cylinder in a direction perpendicular to the central axis of the cylinder, the pipe having a diameter smaller than the inner diameter of the cylinder, characterized in that a first pressure measuring hole is formed on the most restricted cross section perpendicular to the flow direction and a second pressure measuring hole is formed on a wall of the cylinder located upstream which is away from the most restricted cross section by ½ or more of the inner diameter of the cylinder.