Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
2001-08-03
2004-08-10
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Including geographic feature
C210S798000, C210S806000, C210S170050, C210S256000, C210S299000, C210S411000, C210S532200
Reexamination Certificate
active
06773606
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to treatment of septic tank effluent before it is discharged to a drain field, and more particularly it relates to systems and apparatus for straining the effluent.
BACKGROUND OF THE INVENTION
Certain wastes introduced into a septic tank tend to separate into distinct layers: a bottom sludge layer, a top scum layer, and a noticeably distinct intermediate liquid layer that is to a large extent free of scum and sludge. As waste accumulates, liquid is periodically pumped out of the tank as effluent that is discharged to a drain field. An electric-operated pump is typically used for pumping, and it is desirable to communicate the suction inlet of the pump to the intermediate layer because that layer is generally freer of solids and particulate matter than are the scum and sludge layers.
To avoid the entry of undesired particulate matter into the pump, a stationary screen may be used to screen the liquid before it enters the pump. The particle size that can be effectively strained is determined by the screen mesh. Generally speaking, the finer the mesh, the smaller the particle that can be screened; however, the finer the mesh, the greater the tendency for the screen to clog. Actual screen mesh size may be a compromise based on conflicting factors. Because a screen is typically disposed within a tank or within a vault that is disposed within a tank, it may be inconvenient to regularly clean. Because a homeowner may not maintain a septic tank at the intervals recommended by a manufacturer, a manufacturer may decide that the mesh of a strainer screen may be deliberately sized more coarsely to guard against clogging due to lack of homeowner maintenance. This means that larger particulate material may enter the pump, and while this may be undesirable as far as the pump is concerned, it may be deemed preferable to the risk of screen clogging.
Commonly assigned U.S. Pat. No. 6,231,764 of Charles A. Wilkins discloses a pump arrangement, including a self-cleaning rotary strainer that is effective in straining liquid that is pumped out of a septic tank as effluent to a drain field.
The exemplary pump arrangement disclosed in that patent comprises an electric-motor-operated effluent pump disposed generally upright, and coaxially within, an upright main tube that extends downward from a top wall of a septic tank to a location at or near a bottom wall of the tank. The tube passes through the top scum layer, through the intermediate liquid layer, and into the bottom sludge layer. Sensors, or switches, that sense the level of waste in the tank control operation of the pump. When the level rises beyond an upper limit, the pump operates to pump fluid out of the tank until the level drops to a lower limit at which the pump shuts off.
A strainer strains liquid entering the main upright tube from the intermediate layer, and includes a cylindrical filter screen disposed coaxial with the tube to constrain the effluent to flow radially through the filter screen and into the interior of the strainer. An electric pump unit is disposed coaxially within the tube and comprises an inlet port which is disposed downstream of the strainer along the direction of effluent flow through the system. The effluent provides some cooling of the motor as it flows along the motor exterior toward the inlet port where it enters the pump unit. An outlet pipe that is communicated to an outlet port at which pumped effluent exits the pump unit conveys pumped effluent out of the septic tank.
A nozzle is communicated to the pump unit outlet port and arranged to emit some of the pumped effluent toward the cylindrical filter screen opposite the effluent flow through the filter screen so as to cause the filter screen to be acted upon by both radial and circumferential flow components. A journal mounts one of the screen and the nozzle for rotation relative to the other such that effluent emitted from the nozzle is effective both to turn the screen and nozzle relative to each other and to dislodge debris from the filter screen.
In some embodiments, the nozzle is disposed within the interior of the strainer and arranged to emit effluent in a radially outward direction, and the flow of effluent through the filter screen is radially inward toward the interior of the strainer. In others, the nozzle is disposed in the exterior of the strainer and arranged to direct effluent radially inward toward the interior of the strainer, and the flow of effluent through the filter screen is radially outward toward the exterior of the strainer.
It is believed that the self-cleaning action enables the screen to have a finer mesh, yet avoid clogging, when the septic system is used in compliance with manufacturer recommendations. In a septic system where strainer clogging may be a limiting factor, the system disclosed in the Wilkins patent can offer the potential for extending the length of time between maintenance intervals.
SUMMARY OF THE INVENTION
The present invention relates to further improvements in self-cleaning septic tank strainers. Various embodiments of improvements are disclosed, and each possesses certain unique features within generic aspects of the present invention. The strainers use materials that are suited to provide long service life, but when needed, service may be conveniently accomplished. The inventive strainers are adapted for retrofitting existing septic systems, as well as for installation as original equipment in new septic systems.
Moreover, various embodiments make the inventive strainer suitable for use in various types of septic systems. Certain embodiments are suited for use with electric-motor-operated effluent pumps of the type described at length above with reference to the Wilkins patent. Certain embodiments are suited for use with other types of septic tank pumps that comprise electric-operated pumps housed within pump vaults that are disposed within septic tanks. Certain embodiments are intended for integrated assembly with a pump to form a pump/strainer unit that can be installed within a septic tank. Certain embodiments can provide for the strainer to be remotely located from the pump. Strainers that embody principles of the invention can be used in single and multiple septic tank systems.
A general aspect of the invention relates to a system for straining liquid pumped as effluent from a septic tank to a drain field. The apparatus comprises a strainer for straining liquid that is being pumped out of a septic tank by a pump before the liquid enters the pump. The strainer comprises a straining screen through which the pump draws the liquid. Solid material that is sucked against a face of the screen by pump suction is dislodged from the screen by returning some of the pumped effluent to a nozzle that is aimed toward the screen. The effluent emitted from the nozzle can act on a limited area of the screen while liquid is drawn through the remaining screen area. The screen and nozzle move relative to one another so that the area of the screen being acted on by the effluent from the nozzle is continually changing. This relative motion eventually enables the full extent of the screen to be cleaned, with the cleaning being repeated as long as the pump continues to operate.
The various embodiment of the invention provide for different types of relative motion and different screen and nozzle geometries. The nozzle may be stationary while the screen moves, or alternatively the screen may be stationary while the nozzle moves. The nozzle may execute either rotary motion or oscillatory motion. The screen may have a circular annular shape that extends 360° about an axis. The screen may be mounted on a wall in covering relation to a hole in the wall, and as such may be either flat or curved.
Because a septic tank that comprises a self-cleaning strainer embodying principles of the present invention allows the screen to have a finer mesh, yet avoid clogging, any particles that pass through the screen will have a smaller size. The pump is therefore not taxed by larger size part
Stoneburner James O.
Wilkins Charles A.
Boller George L.
Perfection Sprinkler Co.
Upton Christopher
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