Orifice Plate Bore Size Calculation:-The orifice flow meter is used to determine the liquid or gas flow rate by measuring the differential pressure (P1 – P2) in the orifice plate. Two standard pressure tapping arrangements for small bore holes are shown in the figure; the location of the pressure tap affects the discharge coefficient to some extent. The flange pressure tap enters the flange and is at a standard distance of 1 inch (2.54 cm) from either side of the orifice. For corner taps, the tapping occurs just above the hole.

The smallest diameter orifice calculation is valid for holes installed in pipes with pipe diameters between 1 cm and 5 cm (2 in), and the pipe Reynolds number greater than 1000.

Equations for Small Bore Orifice Plate

The calculations on this page are for orifices carrying a liquid as described in ASME (2001).

w is the static pressure loss occurring from a distance of approximately D upstream of the orifice to a distance of approximately 6D downstream of the orifice. It is not the same as differential pressure. Differential pressure is measured at the exact locations specified in ASME (2001) (shown in the above figures). K_{m} is computed to allow you to design pipe systems with orifices and incorporate their overall pressure loss, w.

Discharge Coefficients for Orifice Plate Bore Size Calculation Small Bore Orifice for Liquids (ASME, 2001)

To calculate Bore size of orifice plate. first of all orifice tapping should be segregated , that are flolowing-

Discharge CoefficientsCorner Taps:

Discharge Coefficients Flange Taps:

Where,

D is in inches

d/D and Re_{D}are dimensionless.

C is dimensionless.

Applicability:

Pipe Diameter, D :- Calculation requires 1 cm < D < 5.1 cm for both corner and flange taps.
ASME (2001) suggests 1.2 cm ≤ D ≤ 4 cm for corner taps and 2.5 ≤ D ≤ 4 cm for flange taps.

Diameter ratio, d/D:- ASME (2001) require 0.1 ≤ d/D ≤ 0.8 for corner taps and 0.15 ≤ d/D ≤ 0.7 for flange taps.

Reynolds number based on pipe diameter, Re_{D :- }ASME (2001) require Re_{D} > 1000.