Red Seal Steamfitter/Pipefitter Practice Exam

What mechanism is used by a ball valve to control flow?

1. Piston movement

2. Rotating ball

3. Sliding gate

4. Spool valve

The correct answer is: Rotating ball

A ball valve controls flow through the use of a rotating ball. This ball is designed with a hole or port in the center, allowing fluid to flow through when aligned with the piping. When the valve handle is turned, the ball rotates either to open or close the flow path. In the open position, the hole in the ball aligns with the inlet and outlet, permitting unrestricted flow. Conversely, when the ball is rotated 90 degrees to the closed position, the solid part of the ball blocks the flow path, stopping the fluid from moving through the valve. This mechanism allows for quick operation, as just a quarter-turn is necessary to completely shut off or allow flow, making ball valves particularly effective for applications requiring tight sealing and reliable operation.