What can an air pocket in a water main cause?

• A. Restricted flow
• B. Water hammer
• C. Air lock
• D. Loss of pressure

Answer: (A)

Trapped air in a water main takes up space that water would normally occupy, reducing the pipe’s effective cross-sectional area for flow. That directly leads to restricted flow downstream, since less water can pass through the same pipe diameter.

Water hammer involves pressure surges from rapid changes in velocity, such as valve closures, and isn’t caused by a simple air pocket on its own, though air can influence transients. Air lock describes a condition where air prevents flow, which is related but is not the most immediate, everyday consequence in a distribution main. Loss of pressure can occur if flow is severely impeded, but the primary effect of an air pocket is the reduced flow rate due to the reduced open area.