Sluice valves in water distribution mains — purpose and siting Which statements correctly describe the use and placement of sluice valves on main water pipelines?

Introduction / Context:
Sluice valves (gate valves) are isolation devices on water mains. They allow sections to be shut for repair, tie-ins, or operational control. Their correct spacing and location differ from that of air valves and washouts.

Given Data / Assumptions:

• Trunk main and distribution network for potable water.
• Standard practice for long pipelines and urban grids.

Concept / Approach:
Sluice valves control or isolate flow. Spacing depends on network topology, consumer nodes, and the need to minimize service disruption; typical guidance may be a few kilometers on trunk mains, but exact spacing is not always fixed at 5 km. Placement at summits is characteristic of air valves, not sluice valves; washouts (blow-offs) go at low points.

Step-by-Step Solution:
Identify primary function → isolation/regulation → (a) true.Evaluate spacing → (b) is not a universal rule; spacing is context-specific.Check siting → (c) is incorrect; summits require air valves, not sluice valves by default.Therefore, only statement (a) stands universally correct.

Verification / Alternative check:
Design manuals show valve clusters at junctions, branches, and boundary points to sectionalize networks efficiently rather than strictly by a fixed kilometer spacing.

Why Other Options Are Wrong:

• (b) Over-specific; not a standard invariant distance.
• (c) Misattributes summit placement (that is for air valves).
• (d) Cannot be correct since (b) and (c) are incorrect.

Common Pitfalls:
Confusing roles of sluice valves, air valves (summits), and washouts (low points). Over-spacing valves can lead to large outage areas during maintenance.

Final Answer:
They are used to regulate or isolate the flow of water in pipes