Up to 12 inches , the entire venturi is machined from a single solid bar-stock . Above 12 inches the venture is fabricated from sheet. Rectangular type venture used in ductwork are also fabricated from sheet. Many times the piping geometry does not allow full length of the Venturi Tube. In such case, ‘Truncated' classical Venturi Tube can be offered wherein the divergent section can be truncated down by about 35% of its length without modifying the divergent angle. The outer diameter of the divergent section is less than the inside diameter D of the pipe. The throat restricts the fluid flow resulting in a pressure drop. This differential pressure relates to the flow rate by applying Bernoulli's equation. The angled inlet and outlet cones help control the pressure recovery, making the Venturi the most efficient of all the differential meters available. This results in lower permanent pressure loss and greater capacity than other differential meters of the same size. Permanent pressure loss is generally 5% to 20% of the differential pressure, depending on the bore size selected.