About Orifice Plate Assembly

For many years differential pressure types of flowmeters have been the most widely applied flow rate measuring device for fluid flows in pipes that require accurate measurement at reasonable cost. Although a number of different types of flow rate-measuring devices are now available, the differential pressure type of flowmeter still makes up the largest segment of the total flow measurement market.
This type of device has a flow restriction in the line that causes a differential pressure or "head" to be developed between the two measure-ment locations. Differential pressure flowmeters are also known as head meters, and, of all the head meters, the orifice flowmeter is the most widely applied device. Italian physicist Giovanni B. Venturi (1746-1822) in 1797 performed the first recorded work that used orifices for the measurement of fluid flows.

About Orifice Plate
Orifice Plate is the heart of the Orifice Meter. It restricts the flow and develops the Differential Pressure which is proportional to the square of the flow rate. The flow measuring accuracy entirely depends upon the quality of Orifice plate, its installation and maintains.
When measuring wet gas or saturated steam a weep hole is drilled in a concentrically bored orifice plate. This is a small hole drilled on the orifice plate such that its location is exactly on ID of the main pipe.The Orifice plates are manufactured as per ISA / AGA/ API / ANSI standards and in various materials such as SS304 /SS316 / SS316L /Hestoly C / Monel / PTFE coated. Various bores are used for various applications.
Orifice Plate is categories in two types :
Paddle Type, Universal Palate

Operating Principle

Differential pressure flowmeters have a change in flow cross section that can be described as a restriction placed in the flow line that causes the velocity of the flowing fluid to change. The difference in pressures between the two measure­ment locations of the flowmeter is the result of the change in the flow velocities. The volume flow rate through the cross-sectional area is given by,
.................................................... Q = A x v

..................................Q = the volumetric flow rate
..................................A = flow in the cross-sectional area
..................................v = the average fluid velocity



  The most commonly applied orifice is a thin, concentric, and flat metal plate with an opening in the plate, installed perpendicular to the flowing stream in a circular conduit or pipe. In most applications, a sharp edged hole is bored in the center of the orifice plate. As the flowing fluid passes through the orifice, the restriction causes an increase in velocity. A concurrent decrease in pressure occurs as potential energy (static pressure) is converted into kinetic ener­gy (velocity). As the fluid leaves the orifice, its velocity decreases and its pres­sure increases as kinetic energy is converted back into potential energy according to the laws of conservation of energy. However, there is always some permanent pressure loss due to friction, and the loss is a function of the ratio of the diameter of the orifice bore (d) to the pipe diameter (D). This ratio (d/D) is known as beta ratio.

For dirty fluid applications, a concentric orifice plate will eventually have impaired performance due to dirt buildup at the plate. Instead, eccentric or segmental orifice plates are often used. Measurements are typically less ac­curate than those obtained from the concentric orifice plate. Eccentric or segmen­tal orifices are rarely applied in current practice.


Despite various advances in flow measurement, Orifice Assembly remains one of the most used flow element.This is because it gives accuracy within +/-1% .It is Robust, Simple and Proven Design. It is suitable for Almost All Types of Fluids. It works on First Principle which never fails. It is Suitable for All Pipe Sizes from 1/2" to 36".The cost is very nominal and needs no maintenance. Being stationary device frequent calibration is not required.

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