Pressure-relief/pressure-reducing provisions on water mains: For controlling excessive pressures and water-hammer risk, pressure relief (or reducing) valves are provided with attention to which of the following placements/functions?

Introduction / Context:
Water mains experience elevated static pressures at low elevations and transient surges during rapid valve or pump operations. Pressure-reducing/relief valves (PRVs) are vital hydraulic control devices that protect pipelines, appurtenances, and customer plumbing from overstress and nuisance leakage.

Given Data / Assumptions:

• Pressurized distribution main traversing varied topography.
• System includes isolation (sluice) valves and other fittings.
• Objective is to limit both steady and transient over-pressures.

Concept / Approach:
PRVs reduce high upstream pressures to a setpoint suitable for the downstream zone. Relief valves open when pressure rises above a threshold, discharging flow to limit peak pressures. Placement often targets low points (highest static head) and locations where operational changes (near large valves/pumps) may create damaging surges.

Step-by-Step Solution:
Function: reduce/relieve excessive pressure to a safe level.Siting: at low points or boundaries between pressure zones.Protection: upstream of critical valves to mitigate surge during closures/openings.

Verification / Alternative check:
Transient modeling with water-hammer software demonstrates reduced surge amplitudes when PRVs/relief valves are optimally located and sized.

Why Other Options Are Wrong:

• “Only at high points for air removal” confuses PRVs with air valves; air valves handle trapped air, not pressure control.
• Choosing a single siting principle neglects system-wide pressure management.

Common Pitfalls:

• Setting PRVs without considering fire flow; ensure setpoints maintain adequate residual pressure.
• Ignoring maintenance access and drainage for relief discharges.

Final Answer:
all the above