Among butterfly,ball,needle and gate valves which is used mostly in pneumatic system?
It depends on what sort of system you are operating. Most butterfly valves leak, a few don't. Ball valves are instant operation, and don't normally leak. Needle valves are used for fine control of the flow rate. Gate valves are quick to operate, and don't normally leak. On aircraft pneumatic systems, butterfly valves are common, where a leak is permissable. Where no leak is permissable, slide valves are used, which have rubber seals.
I don't agree that gate valves operate quickly and that they usually don't leak. Gate valves are slow to operate specially in large sizes and they all tend to leak unless they have a soft seat and there are very few of these type of gate valves. In larger piping systems globe valves are used to throttle air but not usually as a on/off valve. Probably the best on/off valve is the soft seated ball valve. They work well regardless of size with very little if any leakage. You can get some butterfly valves with soft seats that are really designed to operate much like a ball valve but are only economic in large sizes. The disc in these valves is essentially a wafer out of the sphere and that is why they do so well.
