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Recent Improvements to Trench-Type, Self-Cleaning Wet Wells
Author: Garr M. Jones, George E. Hecker, Robert L. Sanks, Arnold Sdano, Theodore T. Williams
Date: 9/102
DEMLOW, Thomas C.,

In trench-type wet wells, pump intakes are in a deep, narrow trench, below and in line with the influent conduit. The walls slope outward above the trench. The result is a small, compact wet well. Between 1960 and 1990, over 40 such wet wells have been constructed and operated with success and client satisfaction. Since the almost simultaneous publication in 1998 of American National Standard for Pump Intake Design, ANSI/HI 9.8-1998 and Pumping Station Design, 2cd Ed., many trench-type wet wells have been built in sizes ranging from 0.13 to over 4.3 m3/s (3 to over 100 million gallons/d). They are especially popular with many engineering firms and utilities for wastewater, because they can be self-cleaned in a few minutes simply by overriding the water level controls and operating the pumps at full speed. As the water level falls, the influent liquid flows down a curved ramp, gains high velocity, and sweeps solids along the floor to the last pump for ejection. Some utilities now require trench-type wet wells for their wastewater service. A number of improvements to reduce swirling and vortexing and improve the pump intake environment have been developed following publication of the above works. The purpose of this paper is to describe these improvements so that designers can produce ever better products for their clients.