How do i draw trunion ball valve?

Check out some tutorials on making ball valves, or any kind of valve: https://grabcad.com/tutorials?query=ball+valve&sort=most-liked
The skills learned can easily be applied to other types of valves.

Then check the library for some already made SW valves. Look at how other people made their valves, and learn some more skills by copying what they did: https://grabcad.com/library?page=1&time=all_time&sort=recent&softwares=solidworks&query=valve

Then, if you have some specific questions, ask them here, and upload your 3D models. You'll receive much more help with specific questions, especially if you demonstrate what you've already worked on.