Valve flow area and velocity, flow rate is directly related to, flow velocity and flow rate are two interdependent. But when the flow, flow, flow, flow area can be smaller, velocity is small, flow area can be capitalized. Conversely, large walking area, small flow, flow area is small, air flow velocity. Medium flow rates, valve statistics can be smaller, but the resistance is very large, so that the valve is problematic. Velocity is large, prone to static electricity, easy medium for flammable pipes cause great danger, flow rates small, so time is running out, is not the economy. For those who have a viscosity or flammable media, to channel a small valve.