Lift stations generally employ centrifugal pumps, pneumatic ejectors or screw type pumps, (centrifugal pumps are the most common).
The wet well can be constructed of pre-cast concrete rings (similar to manhole rings), poured in place concrete, fiberglass or metal. It should be designed to withstand characteristics common in the wastewater it will pump. The wet well should be sized so that the pumps will not have to cycle too often, which can cause unnecessary wear, yet not so large that the wastewater becomes septic due to excessive holding times. (This can also be altered to some extend by changing the operating levels by adjusting the pump controls).
The hardware uses in lift stations should be either high-grade aluminum or stainless steel to prevent corrosion.
It is often desirable to include a bar rack at the inlet to the wet well of a lift station to catch large objects and rags before they enter and damage the pumps. If bar racks are included they must be made of the appropriate material (aluminum or SS) and they must be easily cleaned without entry into the wet well.
Dry well structures commonly have two or more floor levels. Pumps and valving are located on the lowest level while electrical controls and motors are often located on
an upper level. A sump pump is provided to removed seal water or any water that leaks into the dry well. Ventilation and atmospheric monitoring are provided to prevent dangerous conditions from developing.
Valves are of critical importance to lift station O & M but they are frequently neglected, abused, misused and installed at improper locations. The major valves found in wastewater lift stations are:
* Pump suction and discharge isolation valves (gate valve, plug valve or knife valve). Isolation valves are used to section off the pump when service is required. These valves should not be used to throttle (control) the flow into or out of the pump because the valve and pump could be damaged.
* Discharge check valves, (swing check or ball check valves). Check valves prevent water from flowing backward through the pump when the pump shuts off. Hard closing or noisy check valves indicate that something is wrong, such as air trapped in the force main.
* Cross connection control valves.
All but the smallest lift stations are provided 3-phase electrical service so that the system will work efficiently and for practicality. Many lift stations have emergency back-up generators to maintain pumping during power outages. If a generator is not provided a transfer switch should be included so that a portable generator could be rapidly hooked up to maintain pumping during times of loss of power.