Air release and vacuum breaking in water distribution: At which locations on distribution mains should air valves be provided to discharge accumulated air effectively?

Introduction / Context:
Entrained air collects at high points in pressurized pipelines, causing air pockets that reduce carrying capacity, increase headloss, and risk flow interruptions or water hammer. Air valves (air-release and vacuum-break types) are installed to manage this trapped air and to admit air during draining to prevent collapse.

Given Data / Assumptions:

• Closed-conduit pressurized water distribution main with undulating profile.
• Air enters during filling, from dissolved air release, or via pump suction.
• Objective is to expel accumulated air and prevent vacuum conditions.

Concept / Approach:
Since air rises to the highest elevations, strategic placement is at summits (local high points). Automatic air-release valves discharge small pockets under pressure; vacuum-breakers admit air during draining or sudden negative pressure events. Locating them at summits ensures the trapped air is vented promptly.

Step-by-Step Solution:
Map pipeline profile and identify summits.Install suitable air valves at these high points and, as needed, near pump discharges and dead ends.Confirm connectivity of valve chambers for maintenance access and drainage.

Verification / Alternative check:
Hydraulic transient analyses and operational experience show headloss spikes and flow instabilities where air pockets persist at high points; properly sited air valves mitigate these issues.

Why Other Options Are Wrong:

• Lower points: air does not accumulate there; scour valves are located at low points for drainage.
• Junctions only: air can accumulate between junctions at summits.
• Anywhere: indiscriminate placement is inefficient; profile-driven siting is required.
• Immediately after every valve: unnecessary and costly unless a summit coincides.

Common Pitfalls:

• Failing to consider undulating terrain profiles.
• Using only manual air cocks where automatic release is needed.

Final Answer:
Higher points (summits) of the profile