Reducing Pump Submergence with Formed Suction Inlets

The use of formed suction inlets on large vertical pumps has been utilized in the flood control field for many years. While a variety of different configurations exist, the US Army Corps of Engineers Type 10 inlet is a common example that has been used extensively throughout the south eastern United States for flood control as well as on numerous projects as part of the broader Everglades Restoration Project. Utilizing formed suction inlets offers several advantages such as improved approach flow hydraulics in high cross flow conditions and also excellent sub-surface vortex suppression. However, an often debated characteristic of this type of inlet is the submergence requirement. Conflicting design guidance for formed inlets exists which on one hand suggests significantly lower submergence requirements than for a typical wet pit suction bell while on the other hand does not suggest a significant advantage. This paper reviews the results of several different physical model studies of varying formed suction inlets under a variety of approach flow conditions. The studies were reviewed to evaluate surface vortex intensity versus different submergence levels and then compare the results to published US Army Corps of Engineer and Hydraulic Institute submergence guidelines.