In a distribution network, at which locations should drain (scour) valves be provided on water-supply pipelines to facilitate complete emptying and flushing?

Introduction / Context:
Drain (scour) valves enable flushing sediments and fully emptying pipelines for maintenance. Correct placement ensures gravity drainage and prevents stagnant pockets when lines are dewatered.

Given Data / Assumptions:

• Pressurized distribution pipelines traverse varying elevations.
• Goal: complete drainage and effective flushing.

Concept / Approach:
Water drains by gravity toward local low points. Sediments settle at sags; placing scour valves at these low points allows high-velocity discharge to remove settled solids and to empty the main efficiently.

Step-by-Step Solution:
Identify sags/valleys (lowest elevations) along the alignment. Provide drain valves at these low points to ensure gravity outflow. Complement with air valves at summits for admitting air during drainage to avoid vacuum.

Verification / Alternative check:
Operational practice shows that drains at high points cannot empty sags; conversely, low-point drains plus summit air release enable rapid, safe dewatering.

Why Other Options Are Wrong:

• Higher points: Needed for air valves, not drains.
• Junctions irrespective of elevation: Hydraulic profile, not node type, dictates drain placement.
• Anywhere: Ineffective; may leave undrained pockets.

Common Pitfalls:

• Omitting air admittance at high points during draining, leading to damaging vacuums.

Final Answer:
At lower points of the pipeline profile.