Orifice Plate

Orifice plate is a restriction formed in the flow by placing a plate in the pipe at the position where flow needs to be measured. The orifice plate has a opening smaller than the diameter of the pipe. Through this opening the fluid is made to flow. The pressure difference across the plate is proportional to the velocity of fluid flowing through the pipe. The image below shows the installation of orifice plate.

 Image Source:By fpunktz (http://www.ilkdresden.de/iso5167/index.html) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

The material of construction of orifice plates is generally Nickel, Phosphor or Bronze.
Their thickness typically varies from 3mm to 12 mm, although plates of larger thickness can also be used.

Types of Orifice plates

There are three types of orifice plates classified on the basis of the position and type of opening. Each type has its own significance and problems which have been discussed below:

  1. Concentric Type
    It has a circular opening with its center located at the axial center of the pipe.
  2. Eccentric Type
    It also has a circular opening similar to concentric type. However its center is located just below the axial center of the pipe. Only a small part of the plate needs to be present between the opening and the pipe. Eccentric type of orifice is preferred for fluids containing dissolved gases in large quantity.
  3. Segmental Type
    Its opening is not completely circular; but a segment of the circle. Its center is concentric with the axial center of the pipe. This type of orifice plate is used for fluids which contain solid particles or dirt.
A concentric type of orifice plate is shown in the image below. The smaller image besides it shows a Differential pressure transmitter (DPT) installed across the orifice plates.

Image Source: By Alfaomega at German Wikipedia (Own work) [CC-BY-SA-3.0-de (http://creativecommons.org/licenses/by-sa/3.0/de/deed.en)], via Wikimedia Commons