The orifice plate is the most popular primary device (Flow Measurement).
Orifice plates are applicable to all clean fluids.
Orifice plates are not good for the measurement of fluid containing solids in suspension (Dirty Fluids).
Construction Of Orifice Plate
A conventional orifice plate consist of a thin circular plate containing a hole.
Construction Material -
The plate is usually made of Stainless Steel.
Other materials are occasionally used. Monel,Nickel,hastelloy,steel,glass and plastic.
Different types of Orifice plates are available.
2. Sharp edge
The most popular orifice plate is sharp edge.The upstream face of the plate usually is polished and the downstream side is often counterbored to prevent any interface with flowing fluid.
The eccentric plate has a hole that is bored off-center,usually a tangent to the bottom of flow line.
The segmental orifice plate has a segment removed from the lower half of the orifice plate.
The eccentric and segmental orifice plates are designed to accommodate limited amount of suspended solids.
Quadrant edged is designed to minimize the effect of low reynolds number.Quadrant edged orifice has the ability to perform well at lower velocities.
Orifice plate comparing to other primary devices operate most satisfactorily at higher flow rate.
Orifice plates that are to handle liquids containing small amount of dissolved air should contain a small vent hole bored at the top to permit the air to pass through the plate.
Plates for use with steam should have a similar hole drilled at the bottom to drain condensation to drain.