Describe the procedure of sizing the By Pass Pipe/Valve for Variable Speed system (CHWS)?

The bypass pipe or valve are usually of same sizebut sometimes the valve is one size different than pipe it depends on friction rate and flow rate. Any how the size mostly depends on the flow in bypass line @4 to6 ft per sec. If the by pass pipe is designed to accomodate maximum of200 gpm then deisgn it for max6 ft per sec and min4 ft per sec