Pipeline appurtenances — location of air valves: In pressure pipelines of a water-supply system, where are air valves generally installed to ensure safe and efficient operation?

Introduction / Context:
Air valves (air release and vacuum break valves) are essential for long pressure mains. Trapped air can reduce capacity, cause inaccurate flow measurements, induce water hammer, and accelerate corrosion. Proper siting of these valves is a core part of transmission main design.

Given Data / Assumptions:

• Closed-conduit, pressurized flow.
• Topography with rises and falls (undulating profile).
• Desire to avoid air pockets and vacuum conditions.

Concept / Approach:
Air naturally migrates to high points. At summits, air pockets collect and constrict the cross-section, increasing headloss and potentially causing vapor pockets. Air valves release accumulated air during operation and admit air rapidly during sudden draining or column separation, preventing excessive negative pressure.

Step-by-Step Solution:

Verification / Alternative check:
Surge analysis confirms that properly located air valves limit transient pressures. Constructability checks ensure accessibility at summits.

Why Other Options Are Wrong:

• Pipe junctions and service connections: not systematic locations for trapped air.
• Low points: suited for scour/sluice valves to remove sediment, not for air release.
• Pump discharge only: insufficient for long undulating mains.

Common Pitfalls:
Undersizing or omitting vacuum-breaking capacity; installing at low points where air will not accumulate.

Final Answer:
At summits (high points)