When creating a piping system, it's important to know how large your restrictive device, or orifice, should be because it determines the appropriate pressure level and flow rate of the system. There are a few reasons why you might want to install an orifice, which include increasing the line pressure and decreasing the flow through the line. You can calculate the orifice size using a formula, but you will need to know a few key numbers before you begin.

Write down the flow of the liquid that will be going through the piping system in cubic feet per second. For example, the flow of the liquid in a system might be 8 cubic feet per second.

Write down the velocity of the liquid flowing through the piping system in feet per second. The velocity of the liquid in the system described in Step 1 might be 2 feet per second, for example.

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Divide the flow of the liquid by the velocity of the liquid to determine the area of the orifice in square feet. In the above example, you would divide 8 by 2. The total area of the orifice would be 4 square feet.