The purpose of a lift station is to receive, store temporarily as needed, and move wastewater and/or storm water through a collection system.
Submersible pump stations come in sizes: very small, small, medium, and large stations, each with its own design parameters. Submersible system components include the fiberglass basin, the pump-motor, piping, valves, float controls, control panel and access hatch covers. Stainless steel guide rail systems can be useful in the deeper stations. Special submersibles, called grinder pumps, are suitable for pressurized sewage system applications.
The two generic types of lift station designs are wet well and wet well/dry well. The wet well/dry well type uses a wet well or pit to collect wastewater and a companion dry well which contains the pumps, controls, and related equipment.
The submersible wet well lift station has become the norm and is preferred in present day applications. It uses only one well as opposed to two, with a submersible solids-handing pump which is designed to operate under water with an opening submerged inlet. All system components are installed in or contiguous to the single wet well.
More and more, submersible solids-handling pumps and grinder pumps are being specified by design engineers. They are used for wet well sewage lift stations and industrial sump effluent applications. Large and small units are used in a variety of ways in home, hotel, school marine, commercial building, and industrial plant, and municipal sewage and storm water systems.
Submersible pumps have proven effective since their introduction, refuting those skeptics who originally wondered how an electric pump motor “could run under water.” Originally developed in Europe, they are now used throughout the world to pump clear water, raw water, and wastewater. Millions are in continuous use daily.
The submersible wastewater pump came to the United States about 1955. It became popular in the early 1960s, when a pump release idea was developed to allow the pump to be disconnected easily from the piping and be lifted out of the well for service. Currently this feature is referred to as Guide Rails, is used on the deeper stations and is constructed of stainless steel. This ended the dirty and sometimes dangerous task of sending personnel into the station to disconnect and then reconnect the pump.
Submersible wastewater pumping stations are usually classified by size in GPM (Gallons Per Minute).
This type of station usually serves an individual dwelling or several isolated buildings. Diameter of the unit is normally 24" or 36" with the depth being at least 3' below the sewage inlet. Simplex pumps may be permitted for private installations; however, duplex units are recommended for service ability. If one pump needs service the other pump is already in place and the utility is not interrupted. Most individual units are package units consisting of a fiberglass basin, pump, piping and controls from one supplier.
Duplex stations are specified almost exclusively with each pump sized to handle the peak flow. Provision may be made for future growth by selecting venders who have the same pump models available over a range of impeller or horsepower sizes. Diameter of the unit is normally 48" and larger to accommodate 2 pumps, and it may or may not have guide rails depending on budget and wet well depth. If the unit has guide rails, assembly is offered by most reputable venders thus lowering the cost of on-site installation and labor of the installing contractor. Check valves and gate valves may also be installed inside the wet well in most private applications. In public applications fiberglass valve boxes are available and attached to the wet well.
Generally, duplex pump stations are used. The physical size of the wet well itself is based on both the current flow and projected future needs. Depth of the station is partly dictated by the levels of the intake and discharge lines. Diameter is reflective of the pump run time needed and retention time. Guide rails are another option that is commonly used since the pumps are larger/ heavier to lift out. In this size pump station a valve vault or box is normally used and can be attached to the wet well or separate and close to the wet well. The wet well itself may be RCP, but FRP (fiberglass) is more frequently specified.
The large wastewater lift station only differs from the medium size in the fact that the pumps are larger horse powers and transport more gallons per minute.