I want to start studying selection of manual valves and flow criteria inside valves, so I need a guidance like some books or softawre for fluid simulation?
In addition: Use the net actively. Search this forum and the net generally (especially for suppliers and producerssuppliers information) both for specific questions and general selection. Many larger well-renownn producers have updated selection guides depending on flow, media and detailed flow characteristics.
Remember that the situation seldom is static over a longer perode in a valve: it will always vary and be dependent on what you let in and take out of your system, and what happens elswehere in the system.
Everybody helps a lot here. Just the very fact that all these people take their time to read posts and type answers, is an effort which should be appreciated. Depending how detailed is your question and how much input data is provided, you are likely to receive more and good quality answers.