Design Considerations for Pump Discharge Goosenecks in Pressurized Water Systems (AWWA-Based) The U-bend (gooseneck) on a pump discharge is a de...
Published on by Hossein Ataei Far, Ambassador for Sustainability | Water & Energy PPP Finance Facilitator
The U-bend (gooseneck) on a pump discharge is a deliberate engineering feature that serves both mechanical protection and hydraulic functionality. Its primary role is to act as an expansion loop, providing flexibility to absorb thermal expansion and reduce pipe stresses and pump nozzle loads, thereby protecting pump alignment, bearings, and mechanical seals.
This approach is consistent with AWWA Manual M11, which states that pipe offsets, loops, and changes in direction may be used to provide flexibility and to control longitudinal stresses resulting from temperature, pressure, and support conditions (AWWA M11, Chapter 13 – Flexibility and Expansion).
The symmetrical geometry of the gooseneck also helps attenuate vibration transmission from rotating equipment into the piping system, thereby reducing fatigue loading on welds, flanges, and pipe supports. AWWA M11 further emphasizes that excessive restraint at pump connections should be avoided to limit equipment nozzle loads and vibration transfer (AWWA M11, Chapter 7 – Design Considerations for Appurtenances and Connections).
From a hydraulic and operational perspective, a gooseneck inherently creates a high point in the discharge line. AWWA Manual M51 – Air-Release, Air/Vacuum, and Combination Air Valves explicitly notes that air accumulates at system high points and locations of vertical profile change and must be released to prevent flow restriction, vibration, and energy loss (AWWA M51, Chapter 2 – Air in Pressurized Pipelines). Accordingly, AWWA M51, Chapter 4 – Location of Air Valves, recommends that air-release or combination air/vacuum valves be installed at all summits, including those formed by discharge piping loops or goosenecks.
Entrapped air at such locations can significantly worsen transient behavior. AWWA Manual M32 – Distribution Network Analysis explains that air pockets can intensify pressure fluctuations and contribute to column separation during pump shutdown or rapid valve closure (AWWA M32, Chapter 9 – Transient Analysis). While the U-bend introduces limited elasticity and additional volume that may marginally soften surge effects, AWWA guidance does not recognize expansion loops as surge control devices; dedicated transient mitigation measures therefore remain necessary.
Summary (AWWA Best Practice)
The gooseneck is a valid solution for thermal flexibility, pump nozzle load reduction, vibration control, and routing (AWWA M11).
Any gooseneck that forms a hydraulic high point must include appropriate air-release provisions (AWWA M51).
Surge behavior must be evaluated independently through transient analysis and addressed using appropriate protection systems (AWWA M32).
References
[1] Manual M11 – Steel Pipe: A Guide for Design and Installation.
AWWA.
[2] Manual M51 – Air-Release, Air/Vacuum, and Combination Air Valves.
AWWA.
[3] Manual M32 – Distribution Network Analysis. AWWA.
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