Ansi Hi 9.8 Rotodynamic Pumps For Pump Intake Design ((better)) Jun 2026

| Type | Name | Description | Acceptability | | :--- | :--- | :--- | :--- | | | Surface dimple | A shallow depression, no rotation | Acceptable | | 2 | Surface swirl | Rotating string, extends < 50% to bell | Marginal | | 3 | Swirl with dye trail | Dye streak visible, no air core | Not acceptable for critical service | | 4 | Funnel vortex | Air core reaches bell but not pump | Unacceptable | | 5 | Air-entraining vortex | Air enters the pump | Prohibited | | 6 | Full air core | Continuous air column | Prohibited |

The standard’s recommended dimensions (e.g., sump length, bell submergence) are intentionally conservative. For space-constrained projects (e.g., barge-mounted pumps, retrofits in existing plants), strict adherence may force uneconomical or infeasible designs. In such cases, model testing or CFD is required to justify deviations. ansi hi 9.8 rotodynamic pumps for pump intake design

Understanding why ANSI/HI 9.8 enforces strict limits requires looking at the mechanics of vortex formation. When a fluid rotates as it is drawn into a localized low-pressure zone (the pump inlet), it creates a vortex core. Q=A⋅Vcap Q equals cap A center dot cap V If the approach velocity ( | Type | Name | Description | Acceptability

The standard also specifies minimum clearances between adjacent pumps and between pumps and basin walls. Minimum clearance between pump volutes (C_b) is 0.25 times the volute diameter, with an absolute minimum of 4 inches (approximately 100 mm). Minimum wall clearance (C_w) is similarly 0.25 times the volute diameter, also not less than 4 inches. Understanding why ANSI/HI 9

Common remedial measures addressed by the standard include installing flow straighteners or baffles, adding splitter plates on the sump floor to control submerged vortices, modifying the approach channel geometry, adjusting pump placement within the wet well, and installing anti‑vortex devices (AVD) as outlined in ANSI/HI 9.8.

Common for wet pits, with or without flow-straightening devices. Circular Sumps: Often used in industrial applications.