ANSI HI-9.8-1998 pdf download Pump Intake Design
9.8.2.1.1 Approach flow patterns The characteristics of the flow approaching an intake structure is one of the most critical considerations for the designer, When determining direction and distribu- tion of flow at the entrance to a pump intake structure, the following must be considered:
● The orientation of the structure relative to the body of supply liquid
● Whether the structure is recessed from, flush with, or protrudes beyond the boundaries of the body of supply liquid
● Strength of currents in the body of supply liquid perpendicular to the direction of approach to the pumps The number of pumps required and their antici- pated operating combinations The ideal conditions, and the assumptions upon which the geometry and dimensions recommended for rec- tangular intake structures are based, are that the structure draws flow so that there are no cross-flows in the vicinity of the intake structure that create asymmetric flow patterns approaching any of the pumps, and the structure is oriented so that the supply boundary is symmetrical with respect to the centerline of the struc- ture. As a general guide, cross-flow velocities are sig- nificant if they exceed 50% of the pump bay entrance velocity, Section 9.8.5 provides recommendations for analyzing departures from this ideal condition based upon a physical hydraulic model study.
9.8.2.1.2 Open vs. partitioned structures If multiple pumps are installed in a single intake struc- ture, dividing walls placed between the pumps result in more favorable flow conditions than found in open sumps. Adverse flow patterns can frequently occur if dividing walls are not used. For pumps with design flows greater than 315 I/s (5,000 gpm) dividing walls between pumps are required.
9.8.2.1.3 Trash racks and screens Partially clogged trash racks or screens can create severely skewed flow patterns. If the application is such that screens or trash racks are susceptible to clogging, they must be inspected and cleaned as frequently as necessary to prevent adverse effects on flow patterns. Any screen-support structure that disrupts flow, such as dual-flow traveling screens, otherwise known as double-entry single-exit screens, can create a high- velocity jet and severe instability near the pumps. A physical hydraulic model study must be performed in every such case. The screen exit should be placed a minimum distance of six bell diameters, 6D, (see Sec- tion 9.8.6) from the pumps. However, this distance should be used only as a general guideline for initial layouts of structures, with final design developed with the aid of a physical model study. The recommendations in this standard should be followed if suction bell strainers are used.
9.8.2.1.4 Recommendations for dimensioning rectangular intake structures