What type of valves are typically used on a sight glass to direct flow?

• A. 3 way valves
• B. Ball valves
• C. Globe valves
• D. Check valves

Answer: (A)

Directing flow through a sight glass requires a valve arrangement that can switch between two flow paths. A three-port valve provides a common port connected to either of the other two ports, letting you route all flow through the sight glass to observe the liquid or bypass the sight glass when observation isn’t needed. This single valve setup simplifies the circuit and reduces the number of components compared to using separate isolation and bypass valves.

Two-port ball valves can isolate or allow flow but can’t switch paths on their own without extra valves. Globe valves can be multi-port, but they introduce more pressure drop and complexity for this purpose, making a dedicated three-way valve the more practical choice. Check valves restrict flow to one direction and don’t offer the path-switching capability needed for directing flow through or around the sight glass.