Why are there ball checks on sight glass valves?

• A. To regulate flow if pressure changes
• B. To stop the flow if there are leaks or if the sight glass breaks
• C. To filter debris from the fluid
• D. To measure temperature of the fluid

Answer: (B)

Ball checks on sight glass valves act as a one-way safeguard to prevent backflow and isolate a damaged sight glass. In normal operation the valve allows forward flow, but if the sight glass leaks or breaks, the ball seats and stops flow in that direction, preventing hot fluid or steam from escaping into the surrounding area or the rest of the line. This keeps the system safe and contained. The other choices aren’t the function of a ball check here: it doesn’t regulate flow with changing pressure, it doesn’t filter debris, and it isn’t a temperature sensor.