Standard orifice plate pressure tapping method

Read ISO5167; it explains it there.

A throttling device is a flow device used when fluid filling a pipe flows through it; the flow stream undergoes local contraction at the throttling point, which increases the flow velocity and reduces the static pressure, thereby creating a difference in static pressure before and after the throttling element. The throttling device consists of a throttle element, a pressure tapping device, and straight pipe sections at the front and rear. The pressure tapping methods for throttle devices include corner tapping, flange tapping, pitch tapping, theoretical tapping, and pipe tapping. 1. Corner tapping: The distance between the axis of each tapping hole on the upstream and downstream sides and the front and rear end faces of the orifice plate is equal to half the diameter of the tapping hole, or equal to half the width of the tapping gap; as a result, the point where the tapping hole penetrates is exactly at the same level as the end face of the orifice plate. Corner tapping includes tapping from within the annular chamber and tapping through separate holes ； 2. Flange pressure tapping: The distance from the center of the pressure tapping holes on the upstream and downstream sides to the front and rear surfaces of the orifice plate is (25.4 ± 0.8) mm ； 3. Radial distance for pressure measurement: The distance from the center of the pressure measurement hole on the upstream side to the front surface of the orifice plate is 1D, while the distance from the center of the pressure measurement hole on the downstream side to the back surface of the orifice plate is 1/2D ； 4. Theoretical pressure tapping: The distance from the center of the pressure tap on the upstream side to the front surface of the orifice plate is 1D ± 0.1D, while the distance from the center line of the pressure tap on the downstream side to the back surface of the orifice plate varies depending on the value of β = d/D ； 5. Pressure tapping for pipes: The centerline of the pressure tapping hole on the upstream side is 2.5D away from the front surface of the orifice plate, while the centerline of the pressure tapping hole on the downstream side is 8D away from the rear surface of the orifice plate ； Among the above five pressure tapping methods, the corner connection method is the most commonly used, followed by the flange pressure tapping method. The pressure measurement locations for media that are primarily gases, liquids, or vapors differ fundamentally.