The distance from the bottom edge of the bell to the sump floor.
This is the distance from the water surface to the top of the bell inlet.
ANSI/HI 9.8 (Hydraulic Institute Standard for Rotodynamic Pumps for Pump Intake Design) is the definitive industry guideline for designing pump sumps, wet wells, and suction piping. Its primary goal is to ensure uniform, swirl-free flow entering the pump impeller. Poor intake design is a leading cause of hydraulic performance problems, yet it is frequently overlooked.
If you’d like, I can also summarize a specific section of HI 9.8 (e.g., submergence formulas, bell design, or model testing criteria).
The ANSI/HI 9.8-2024 standard, titled Rotodynamic Pumps for Pump Intake Design, is the definitive American National Standard for engineering efficient, reliable pump stations. Developed by the Hydraulic Institute (HI), this standard provides the technical framework for designing new intakes and modifying existing ones to ensure optimal hydraulic performance. Core Objectives of ANSI/HI 9.8
The fundamental goal of the standard is to ensure that flow reaching the pump impeller is uniform, steady, and free from swirl or entrained air. Poorly designed intakes often lead to:
Reduced Efficiency: Non-uniform velocity distributions at the pump suction can significantly lower hydraulic performance. ansi hi 9.8 rotodynamic pumps for pump intake design
Mechanical Damage: Problems like cavitation, high vibration, and noise can cause premature mechanical seal and bearing failures.
Operational Issues: Formation of surface or submerged vortices and excessive pre-swirl can lead to air entrainment and performance drop-off. Standard Intake Configurations
ANSI/HI 9.8 defines specific geometries for several common intake types. Adhering to these "standard" designs often eliminates the need for expensive physical testing. ANSI/HI 9.8-2018 - Rotodynamic Pumps for Pump Intake Design
ANSI/HI 9.8 standard, titled "Rotodynamic Pumps for Pump Intake Design,"
is the definitive American national guideline for designing and evaluating pump station intake structures. Published by the Hydraulic Institute (HI)
, it provides normative criteria to ensure that the flow entering a pump is uniform, steady, and free from harmful phenomena like vortices or excessive swirl. Core Design Objectives The distance from the bottom edge of the
The primary goal of the standard is to optimize the hydraulic environment at the pump inlet to prevent reliability issues such as cavitation, vibration, and reduced hydraulic efficiency. Key objectives include: Uniform Flow Velocity:
Ensuring the velocity profile at the pump's impeller eye is consistent to prevent side-loading and uneven bearing wear. Vortex Suppression:
Minimizing free-surface and sub-surface vortices that can entrain air or cause pressure pulsations. Swirl Minimization:
Controlling the rotation of the fluid before it enters the pump. Solids Handling:
For wastewater applications, designs must prevent the buildup of solids and allow for easy removal of settled or floating debris. Intake Types Covered
The standard provides specific dimensional guidelines for various intake configurations: Pipes, Pumps & Valves Africa Jan-Feb 2023 - Issuu If you’d like, I can also summarize a
The gold standard. Scale at least 1:4 (prefer 1:2). Froude number scaling is mandatory for free-surface effects.
HI 9.8 statement: “Physical modeling is recommended for flow rates exceeding 10,000 gpm (2,300 m³/h) or where NPSHa margin is less than 50%.”
Standard NPSHa calculations assume steady, uniform flow. However, vortices and swirl reduce NPSHa dynamically.
HI 9.8 introduces the concept of Vortex-Induced NPSH Penalty. If a Type 3 vortex (see Part 4) is present, the effective NPSHa can drop by 20–30% due to localized pressure depression.
The standard’s requirement:
NPSHa must exceed NPSHr by the margin specified in HI 9.6.1 plus an additional 1.5 ft (0.45 m) for every vortex type above Type 2.
In practice, most engineers using HI 9.8 design for NPSHa ≥ 1.2 x NPSHr, with a minimum absolute margin of 3 ft (0.9 m).