What Is an Orifice Plate?
An orifice plate is a thin metal plate with a perforation (hole) process that controls fluid flow and pressure when installed in a pipe.
There are four major types of orifice plates; concentric orifice, eccentric orifice, four-part circular orifice, and restricted orifice plates.
Concentric orifice plates are used in aperture flowmeters such as general differential pressure flowmeters.
Quadrant orifice plates are used when the flow rate in the piping is low and the Reynolds number is small. A Reynolds number is a dimensionless number that is the ratio of inertia force to viscous force.
Eccentric orifice plates are used when the fluid contains slurry (a mixture of solid particles and liquid). The slurry can flow easily by installing an orifice hole on the lower side of the pipe. The use of a deflection orifice plate is the same as that of an eccentric orifice plate.
When an orifice plate is installed in piping it is sandwiched between flanges and used as an assembly. Sometimes, like shock absorbers, orifice plates are used pre-assembled into products.
Applications of Orifice Plates
Orifice plates are used in a variety of flow and pressure control applications in industrial applications and industrial piping. As an example of differential pressure flowmeter use, an orifice plate is used to measure the flow rate of a fluid in a pipe as a differential pressure flowmeter. Fluid is extracted from the flanges before and after the orifice plate, and the differential pressure is converted into a flow rate and displayed on the indicator.
Orifice Plate Uses
For the regulations when an orifice plate is used for flow measurement in this manner, refer to JIS Z 8762-2, methods of flow measurement by an orifice mechanism in a circular pipeline. Shock absorbers take advantage of the high pressure drop across the orifice plate. The smaller the orifice hole diameter, the higher the fluid pressure drop and the greater the damping force of the shock absorber. Conversely, a larger hole diameter results in a smaller damping force.
Principle of Orifice Plates
To briefly explain the orifice plate principle, the fluid pressure is lower downstream of the orifice than upstream of the orifice based on Bernoulli’s theorem because the orifice hole’s inner diameter is smaller than the pipe’s inner diameter where the orifice plate is installed. Bernoulli’s theorem is a law of conservation of energy in fluid flow. When a fluid passes through a small hole in an orifice, a pressure difference occurs before and after the orifice in the pipe. This is due to Bernoulli’s law, which states that pressure energy, velocity energy, and potential energy are always constant in a pipe.
The fluid immediately after passing through the orifice plate has a higher velocity and the velocity energy increases. If the potential energy is the same, then the pressure energy decreases by the same amount as the velocity energy increases. By measuring this difference in pressure before and after the orifice plate, the flow rate of the fluid can be calculated. When an orifice plate is used to regulate flow or pressure, the flow rate downstream of the orifice plate can be determined based on the following equation: