1. Field of the Invention
This invention relates to wet wells and sump basins which are used in a variety of industries and settings to remove fluid from a defined area, and specifically relates to precast basins.
2. Statement of the Art
Wet wells are commonly used in a variety of industries including, for example, mining, oil drilling, core drilling, sewage collection, industrial sites, municipal waste systems and water run-off from collection areas to concentrate unwanted fluid in a defined area and pump it away from that defined area. Wet wells typically include an enclosed area which is positioned below ground level and is structured to receive a fluid therein. A sump basin is positioned at the bottom of the enclosed area. A pump or pump system is positioned in or near the sump basin to pump fluid out of the wet well. A discharge pipe is usually connected to the pump to carry the pumped fluid out of and away from the defined area.
A wet well may also comprise a prerotation basin into which the inlet of the pump is positioned. A weir surrounds the prerotation basin and a fluid channel is formed tangentially to the prerotation basin to introduce fluid into the prerotation basin and the pump at an angle. Under high fluid inflow into the wet well (i.e., when the level of fluid in the wet well is higher than the weir of the wet well), the pump operates in a conventional manner to pump water out of the wet well. However, when the fluid level is low, the weir directs the fluid into a forebay which is positioned at the entrance to the fluid channel. The forebay and fluid channel direct the fluid into the prerotation basin at an angle which modifies the performance of the pump, resulting in a lower head capacity and reduced energy consumption by the pump. As a result, the pump may operate without complicated speed controls, and fluid inflow is matched to fluid outflow through the pump.
Most prerotation wet wells are formed by one of two methods. In one method, a hole or cavity is formed, or excavated, below ground and concrete is poured into the hole or cavity to form the sump basin, the weir, the fluid channel and the forebay. In the other method, concrete is poured into the excavated hole or cavity, but a void is left in the concrete for placement of a sump basin. A prefabricated sump basin having a partial weir is then lowered into the concrete formation and is grouted into place.
Several disadvantages are inherent in either means of forming a prerotation wet well. Both methods require that the hole or cavity be completely dry before the concrete can be poured, a pre-condition which is very difficult to achieve in many settings. Both methods require one or more workmen to enter the cavity after the concrete is poured to form certain elements of the prerotation wet well, including the fluid channel, the weir and the forebay. There are critical factors which impact the optimal operation of the prerotation wet well, including the angle, depth, width and side wall slope of the fluid channel, the height of the weirs, the depth and diameter of the prerotation basin and the placement of the forebay, all of which demand that the workmen exercise particular skill while working below ground in a relatively dark and confined space. Numerous and significant errors may occur as a result. Even with a prefabricated basin as previously described, a workman must enter the concrete enclosure of the prerotation wet well to grout in the prefabricated basin.
Once the concrete prerotation wet well of prior art systems is formed, it may be discovered that the void left for the prefabricated basin was improperly positioned or sized, and ameliorative steps must be taken to correct the situation. Also, the pump and fast out (the equipment used to raise the pump out of the hole) may often be positioned relative to the prerotation wet well prior to the concrete being poured, and the pump is later discovered to be misaligned with the sump basin, or vice versa. It may also be discovered that the fast out anchors (usually holes drilled in the concrete) formed near the basin are incorrectly placed or incorrectly positioned in height relative to the prerotation basin so that the pump is positioned too high in the basin.
These and other disadvantages of conventional prerotation wet well construction are overcome in the present invention.