"We don't believe things because they are true, things are true because we believe them."
"Small people talk about others, average people talk about things, smart people talk about ideas and legends never talk."
The best place to start is to obtain a copy of the book "The Design of Valves and Fittings" by G. H. Pearson. It was published about 50 years ago, but it is still on the shelf of nearly every valve designer. It is out of print, but can usually be found at
If you are designing a ball valve, "The Valve Book", published by Neles-Jamesbury can be helpful as well. In addition you will need a copy of ANSI/ASME B16.34 to obtain pressure temperature ratings for the materials you choose for the valve shell.