ver 07-Jan-2019
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Full Port Ball Valves vs Standard Port
The difference is the relative size of the flow path through the valve body
Bore Size
The difference between a standard ball valve and a full-port ball valve is in the size of the ball and
bore in relation to the nominal pipe size of the valve. For example, the bore size in a 3/4-inch full-
port ball valve is 3/4-inch in diameter, while the bore diameter in a standard ball valve is 1/2-inch
in diameter. Ball sizes are in proportion to bore sizes. The 1/2-inch diameter is the nominal size of
the next smaller pipe. This is typical. Full-port bore size equals pipe size; standard-port bore size
is the next smaller pipe size.
Nominal pipe size (NPS) is the approximate internal diameter of standard pipe based on its wall
thickness, its Schedule. For example, take a piece of North American standard 2-inch steel pipe. It will
probably be referred to as 2-inch nominal steel pipe, Schedule 40. This standard pipe will have an inside
diameter of about 2-1/8 inches and an outside diameter of about 2-5/8 inches. Learn more about
nominal pipe size at Werner Sölken's Explore the World of Piping website.
Flow Coefficient
The flow coefficient is a measure of the resistance to flow of a given part of a fluid system. It is
used to calculate the length of straight pipe equivalent to an elbow or valve or anything else that
affects the flow. The flow coefficient for a full-port ball valve is almost as low as that of straight
pipe so it provides minimal resistance to flow and thus creates only a small pressure drop. The
standard-port ball valve has a higher flow coefficient and thus causes a larger pressure drop for a
given flow.
Wikipedia has a concise but dense explanation of flow coefficient. As a plus, it includes information
on the metric system version called flow factor. The more technically minded of us here at ISM are
partial towards The Engineering ToolBox version because it includes online flow calculators for air,
gases and classes of steam.
Get more insights into the differences between full port and standard port ball valves.