The original practice of U.S. manufacturers was to make the face-to-face dimensions of flanged ball valves to the nearest valve standard, which gave minimum material content. This happened to be the gate valve standard. But the face-to-face dimensions of class 150 and of sizes DN 200 (NPS 8) through DN 300 (NPS 12) of class 300 permitted only reduced-bore construction.
In 1961, when UK manufacturers also introduced the flanged ball valve, there was an additional demand for full-bore ball valves. When it was impossible to accommodate the full-bore ball valve in the confines of the face-to-face dimensions of gate valves, the face-to-face dimensions of regular-pattern plug valves were adopted.
Thus, there is a short and a long series of ball valves for class 150,
and in sizes DN 200 (NPS 8) through DN 300 (NPS 12), and for class
300—one for reduced-bore and one for full-bore ball valves, respectively.
In the case of the higher-pressure ratings, the face-to-face dimensions of gate valves accommodate both reduced-bore and full-bore ball valves throughout.
The master standard for face-to-face dimensions is ISO 5752. This
standard includes all the recognized dimensions worldwide that are used in the piping industry. However, ISO 5752 does not try to define reduced bore or full-bore except for sizes DN 200 (NPS 8) through DN 300 (NPS 12) of class 300.