Bruce Hardboss, PE
Sewage pump stations which can be utilized in sewage collection methods, also known as lift stations, are frequently made to handle raw sewage
that’s supplied through subterranean gravity-given pipelines (piping that happens to be laid in a location to make sure that a liquid can easily flow one path subjected to gravity). Sewage is given directly into and saved within below grade tank, generally referred to as a wet well. The well is usually equipped by having electro-mechanical instrumentation to measure the amount of sewage available. Whenever the sewage level goes up to some predetermined point, a pump motor will be began to raise up the sewage ” up ” by means of a pressurized conduit system termed as a sewer pressure main or maybe rising primary in which the sewage is discharged right into a gravity manhole. Then the pattern commences all over again before the sewage reaches its destination – often a treatment plant. With this method, lift stations are utilized to move waste to greater elevations. Within the situation of high sewage flows in to the well (for instance throughout peak flow periods and wet weather) additional pumps are generally used. If this sounds like inadequate, or perhaps in the situation of failure from the moving station, the sewer system can back up, resulting in a sanitary sewer overflow – the release of raw sewage in to the environment. Most facilities are quite concerned about the hazards of raw sewage releases. For example, in San Diego, CA, the beaches were shut down following most major rainfall events due to sewage releases. The bad press over many years prompted San Diego to build it’s new Point Loma facility.
Sewage pumping stations are usually designed to ensure that one pump or multiple pumps will handle normal peak flow conditions. Redundancy built into the system to ensure that when anyone pump has run out of service, the rest of the pump or pumps will handle the designed flow. Present day designs include lots of electronic remotes on the market designed specifically with this application. The storage amount of the wet well between your ‘pump on’ and ‘pump off’ configurations are designed to minimize pump on-off cycles, however is not such a long enough retention time to promote septic conditions in the tank wet well. If the sewage remains static for too long a period of time, then ecessive corrosion and/or explosive conditions can occur. Also, some regulatory bodies require a minimum height to cross-sectional area requirement to minimize these effects.
Sewage pumps are nearly always centrifugal pumps with open impellers and therefore are specifically fashioned with a sizable open passage in order to avoid blocking with debris or winding debris around the impeller. A 4-pole or 6-pole AC induction motor normally drives the pump. Some pumps do not rely the ability to pass large solids, and typically more compact sewage pumps, macerate any solids inside the sewage breaking them into more smaller parts which can easily pass through the impeller.
The inside of the sewage pump station is an extremely hazardous. Poisonous gases, for example methane and hydrogen sulfide, build up within the wet well an ill-outfitted person entering the well could be rendered unconcous very rapidly. Any entry in to the wet well necessitates the correct limited space entry of a hazardous atmosphere. To reduce the requirement for entry, the wet wells are generally located outside, which minimizes some confined space entry concerns.
Traditional sewage lift stations incorporate both a wet well along with a ‘dry well’. Frequently fundamental essentials same structure separated by an interior divide. Within this configuration pumps are installed on the bottom of the dry well to ensure that their basins are below level of pump start, priming the pump as well as increasing the accessible NPSH. Although nominally isolated in the sewage within the wet well, dry wells are subterranean, confined spaces and require appropriate safeguards for entry. Further, any failure or leakage from the pumps or pipe-work can discharge sewage into the dry well with complete flooding. Consequently, the electrical motors are usually mounted over the overflow, top level from the wet well, usually above walk out, and drive the sewage pumps with an extended vertical shaft. To safeguard the above mentioned ground motors from weather, small pump houses are usually built, that also incorporate the electrical switch-gear and control electronics. Fundamental essentials visible areas of a conventional sewage moving station even though they are usually more compact compared to subterranean wet and dry wells.
More contemporary sewage pumping stations don’t require a dry well or pump house in most cases comprise merely a wet well. Within this configuration, submersible sewage pumps with a combined motor unit are mounted inside the wet well itself, immersed inside the sewage. Submersible pumps are installed on two vertical guide rails and seal onto a permanently fixed ‘duckfoot’, which forms both a mount in addition to a vertical bend for the discharge pipe. Maintenance is performed by elevating the submersible pumps with a chain from the duckfoot, or they are extracted by guide rails to the maintenance (normally at the ground surface) level. The pumps are re-installed by simply reversing this procedure. Because the motors are sealed and weather isn’t a concern, no above ground structures are needed, except a control panel which contains the electrical switch-gear and control systems. In the past 20-years or so, pump materials have allowed us to design sealed submersible-pumps that can withstand being submerged in relatively caustic conditions. In the 1960′s and earlier, few true submersible pumps were available, therefore pump stations that contain large dry-wells were predominant. Modern sewage lift stations rely almost exclusively on submersible pumps.
When we balance safety and reliablility concerns, and require more compact footprint and visibility, submersible pump sewage pumping stations have almost completely replaced traditional sewage lift stations. Further, a refit of the traditional pumping station usually involves transforming it right into a modern lift station by setting up submersible pumps within the wet well, destroying the pump house. Wet well designs, utilizing submersible pumps are the future of wastewater lift stations.
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