Plumbing valves: gate, ball, globe, check, vacuum breaker, butterfly

One-line orientation

Each valve type has a specific purpose and typical location — the exam tests which valve prevents backflow, which handles frequent operation, and which is for maintenance isolation only.

Key points

• Gate valve
  • Requires many turns to fully open or close.
  • Designed for maintenance isolation — fully open (no restriction) or fully closed.
  • Not intended for daily use or flow throttling.
  • Now largely replaced by ball valves in modern practice.
• Ball valve
  • Uses a rotating ball with a hole through its center — quarter-turn (90°) to open or close.
  • Replaces gate valves as the preferred isolation valve; easier and faster to operate.
• Globe valve
  • Used in faucets and applications requiring frequent operation.
  • Globe valves suit frequent or precise throttling. Gate valves should not throttle; ball valves are generally used for on/off isolation but can throttle in some applications.
• Check valve
  • Allows flow in one direction only; automatically closes if flow reverses.
  • Typically installed where the main water supply enters the building to prevent backflow into the municipal system.
• Vacuum breaker
  • Prevents back-siphonage — admits air into the supply line so atmospheric pressure cannot pull contaminated water backward.
  • Used at hose bibs, irrigation systems, and fixture connections where a physical air gap is impractical.
• Butterfly valve
  • A disc rotates 90° — parallel to flow (open) or perpendicular (closed).
  • Compact and cost-effective; quick operation.
  • Common in water systems, HVAC, and industrial processes where large-diameter lines need a compact shutoff.

Confusions / comparison

Valve	Mechanism	Operation	Primary use	Backflow protection?
Gate	Rising wedge disc	Many turns	Maintenance isolation	–
Ball	Rotating ball (bore hole)	Quarter-turn (90°)	General isolation	–
Globe	Disc moves into seat	Multi-turn	Throttling / frequent use	–
Check	Swing flap / spring disc	Automatic (flow-driven)	Prevent backflow (pressure)	●
Vacuum breaker	Air-admit port opens on vacuum	Automatic (pressure-driven)	Prevent back-siphonage	●
Butterfly	Disc rotates 90° in pipe	Quarter-turn	Large-diameter shutoff	–

Related

→ Plumbing: water pressure & supply (air gap + vacuum breaker as backflow devices) · DWV traps & vents (separation of supply and drainage) · piping materials (copper supply lines where ball/globe valves are installed).