There is actually no process system that can do without valves.
They ensure that a flow is guided through a piping system in a controlled manner. With a valve you can start, stop and throttle a flow; each type of valve has its own specialty.
Here you will find a large collection of standardized valves as 3D CAD models. They are available in the step (.stp) format, you can open them in almost any 3D solid modeling program and then save them in your native software file format.
This way you can build your own 3D CAD library and fill it with the files you use regularly.