Washouts and drainage of water mains Valves installed at low points of pipelines to quickly drain water by gravity are called:

Introduction / Context:
Pipeline networks need provisions for emptying lines for maintenance, flushing sediments, and protecting against freezing. Special valves are located at low points to discharge water safely to drains or sewers.

Given Data / Assumptions:

• Potable-water distribution or transmission main.
• Valve positioned at local low point.
• Discharge routed to a safe outfall.

Concept / Approach:
These valves are commonly called blow-off or washout valves. They open to allow gravity drainage and high-velocity flushing to remove deposits. While one might informally say “drain valve,” the technical term in waterworks is blow-off/washout.

Step-by-Step Solution:
Identify the function: fast gravity drainage and flushing at low points.Match to standard nomenclature → blow-off (washout) valve.

Verification / Alternative check:
Distribution standards show blow-offs at dead ends and low points sized to achieve scouring velocities while draining the main.

Why Other Options Are Wrong:

• “Drain valves” is generic and not the standard waterworks term used in design drawings/specs.
• “Sewer valves” are unrelated to potable water mains.
• “All the above” is incorrect because not all listed choices are proper terms for this application.

Common Pitfalls:
Undersizing blow-offs, leading to slow drain-down and ineffective flushing; not providing adequate erosion protection at the outfall.

Final Answer:
Blow-off valves (washout valves)