Why control valve is sized 1 size less than actual line size?

 

> Why control valve is sized 1 size less than actual line size? <


because at higher differential pressure the line sized valve will have too much capacity for a good control.

 

As Suvo pointed out it's to give good control.

Another way is to use line size valves with reduced trim. It's a more expensive valve but you save on piping reducers, welding etc.

Roy

 

can it is proved by formula?