Wikipedia has an excellent entry discussing the flows through an orifice plate. Included in the entry is the equation for calculating the permanent pressure loss across the plate.
Q.E.D. Environmental Systems, Inc., a manufacturer of environmental products and subsidiary of Graco Inc., announces the release of its newly-redesigned Quick-Change Orifice Plate Wellhead for ...
Office of NEPA Policy and Compliance CX-022989: Install Orifice Plates, Flammable Gas Cylinders in 773-A Section C Labs Installation of flow restricting orifices on flammable gas cylinder ...