Rule of Thumb for Valve Size Compared With Line Sized

It is good practice to have the valve not less than half line size. If the valve size is very small compared to the line size, too much stress may be created on the valve neck, which can be caused by twisting of the pipes, misalignment of the drilled holes and thermal expansion of the pipe.

In addition, there will be some pressure loss within the system due to pipe reducers.