What is an Orifice Plate? A Complete Guide to Flow Measurement
What is an orifice plate?
An orifice plate is a precision-machined metal disc with a calibrated opening, the bore, at its centre. The disc is installed between two flanges within a pipeline. By restricting the flow path, the orifice plate creates a measurable pressure difference on either side of the disc. That pressure differential is directly related to the flow velocity and volumetric flow rate of the medium passing through the pipe.
Because the bore diameter is a fixed, exact measurement, flow calculations can be performed with a high degree of accuracy. This makes the orifice plate a reliable measurement instrument with no moving parts and no complex electronics.
How does the differential pressure principle work?
The operating principle of an orifice plate is based on Bernoulli's theorem: when a fluid or gas passes through a restriction, its velocity increases and its pressure decreases. By measuring the pressure difference upstream and downstream of the orifice plate using a differential pressure transmitter, the flow rate can be accurately calculated.
The principle is straightforward, but accuracy depends heavily on the precision of the bore. Small deviations in diameter or surface finish can introduce measurement errors, which is why orifice plates must always be custom-manufactured to strict standards.
Types of orifice plates and bore configurations
Not every application calls for the same bore design. There are four common bore types:
Fig 1 – Concentric bore: the most widely used design, suitable for homogeneous liquids and gases. The opening is positioned precisely at the centre of the disc.
Fig 2 – Eccentric bore: the opening is offset from the centre. This type is used for media containing solids or entrained gas that might otherwise accumulate around a central bore.
Fig 3 – Segmental bore: the opening is shaped as a segment (semi-circle). Suitable for media containing sludge or two-phase flows.
Fig 4 – Quarter-circle bore: a rounded inlet edge that is less sensitive to variations in Reynolds number. Used for viscous fluids or low-velocity flow conditions.
Industrial applications
Orifice plates are widely used across industries where precise flow measurement is essential:
- Oil and gas: measurement of production streams and pipeline volumes
- Petrochemical: process control and safety monitoring
- Power generation: steam measurement in turbine systems
- Water treatment: flow control in treatment facilities
- Pharmaceutical: accurate dosing of liquids and gases
Beyond flow measurement, orifice plates are also used in pressure testing, strength tests and pressure reduction within pipeline systems.
DIN or ANSI?
Orifice plates are manufactured to two international standards: DIN (Deutsches Institut für Normung) and ANSI (American National Standards Institute). The choice depends on the piping system in which the orifice plate will be installed. European installations typically follow DIN standards with pressure ratings such as PN10, PN16 or PN40. American and international systems generally use ANSI pressure classes.
Custom orifice plates from Steekflens
At Steekflens, we manufacture orifice plates fully to specification; in accordance with both DIN and ANSI standards. Whether you require standard materials such as 316 stainless steel or a specific alloy for aggressive media, every detail is tailored to your installation: bore type, bore diameter, pressure class and facing type.
Have a specific application in mind or unsure about the right configuration? Get in touch with our team. We're happy to help.