The orifice meter is a flat plate with a circular hole that has pressure taps up and downstream form the orifice plate. There are in general four(4) methods of placing the taps. The coefficient of the meter depends upon the position of taps.
The discharge coefficient – Cd: This varies considerably with changes in area ratio and the Reynolds number. A discharge coefficient, Cd-0.60 may be taken as standard, but the value varies noticeably at low values of the Reynolds number Pressure recovery of an orifice plate is very much limited and permanent pressure loss is primarily affected by the area ratio. For an area ratio of 0.5, the head loss is about 70-75% of the orifice differential.
The restriction orifices are used for reducing fluid pressure are designed somewhat different form the orifice plates that are used for measuring flow rates.
There are some types of restriction orifice:
- Single plate with a single hole without bevelled 45º angle for pressure recovery.
- Multiple orifice(SMO-s). also know as Multi stage restriction orifice for high-pressure drops.
- Multi Hole type(SMO-H).