Which option best describes the relationship between a ball valve and flow resistance?

Which option best describes the relationship between a ball valve and flow resistance?

• A. Ball valve permits full flow with minimal friction loss
• B. Ball valve reduces flow by half
• C. Ball valve causes significant pressure drop
• D. Ball valve increases friction loss

Answer: (A)

When the ball valve is fully open, it behaves like a straight section of pipe, so flow resistance is minimal. A full-port ball valve has a bore that matches the pipe diameter, letting fluid pass with only small losses from the valve surfaces. The pressure drop across a fully open valve is therefore tiny compared with the drops caused by the pipe itself. Only when the valve is throttled or a standard-port design is used does the bore become smaller and the resistance and pressure drop increase. So, the best description is that a ball valve permits near full flow with minimal friction loss.

When the ball valve is fully open, it behaves like a straight section of pipe, so flow resistance is minimal. A full-port ball valve has a bore that matches the pipe diameter, letting fluid pass with only small losses from the valve surfaces. The pressure drop across a fully open valve is therefore tiny compared with the drops caused by the pipe itself. Only when the valve is throttled or a standard-port design is used does the bore become smaller and the resistance and pressure drop increase. So, the best description is that a ball valve permits near full flow with minimal friction loss.