Check (non-return) valves in water systems: Where should they be installed to prevent reverse flow and cross-contamination?

Introduction / Context:
Check valves (non-return valves) are one-way devices that stop reverse flow. They are vital for protecting pumps and safeguarding potable networks from backflow that could introduce contamination.

Given Data / Assumptions:

• Pumping systems discharge to pressurized mains.
• Potential interconnections exist between safe (potable) and compromised (polluted or process) lines.
• Objective is to prevent reverse flow and back-siphonage.

Concept / Approach:

On pump delivery lines, a check valve prevents the pumped column from returning through the pump during shutdown, protecting equipment and avoiding water hammer effects. At interconnections, check/backflow prevention assemblies stop contaminated water from flowing into the potable system due to pressure drops or siphonage.

Step-by-Step Solution:

Verification / Alternative check:

Codes and best practices require backflow prevention for cross-connections and recommend check valves on pump discharge to avoid reversal and surges.

Why Other Options Are Wrong:

• Only suction side: does not protect against reverse flow from the main.
• Neither location: ignores basic hydraulic safety.

Common Pitfalls:

• Placing the check valve too far from the pump, increasing column reversal and surge.
• Using incorrect type (swing vs. spring) without considering headloss and response time.

Final Answer:

Both (a) and (b).