Above ground pump stations: reducing wear and tear on equipment and minimising breakdowns

Rich MacGregor looks at a grit removal system which captures ultra-fine grit particles down to 75 microns, offering unmatched performance across all flow conditions

The growing trend towards above ground pump stations is transforming wastewater collection systems, empowering operators to rise above the challenges of conventional submersible pumps. 

It is common sense that relocating pumps above ground, away from constant exposure to corrosive and hazardous sewage, safeguards the mechanical and electrical components of the pumps, as well as the workers who handle them.

This strategic move simplifies maintenance by making the equipment more accessible and eliminates the need for workers to enter dangerous, confined spaces, thus improving safety. 

Additionally, it reduces wear and tear on equipment and minimises breakdowns. By dramatically improving reliability, pump efficiency and longevity, the increasing adoption of above ground systems aligns with sustainability goals by eliminating the costly problems of frequent stocking, replacement and disposal of submersible pumps. 

The longevity of above ground pump stations is evident in their decades-long lifespan, markedly outperforming the brief lifespan of a few years typical of submersible pumps. The longer service life and easier maintenance add up to a significantly lower total cost of ownership.

Reliability, energy efficiency and operator safety 

Let us explore the vital role of pump stations and their key requirements. Wastewater pump stations are crucial in residential, commercial, and industrial settings for effective wastewater management and to prevent sewage backups and overflows. Throughout the United States, countless pump stations perform an essential role: they pump wastewater from lower to higher elevations in situations where gravity flow is impractical. 

Pump Station facilities comprise a receiving well (wet-well) that is equipped with pumps, pipes, valves, power supply, and control systems and may include a screen or other specialised components designed to mitigate against heavy clogging materials along with systems for odour control and ventilation. Typically, pump stations employ at least two pumps for redundancy, alternating between the lead and lag roles to ensure both efficiency and reliability.

Reliability. The reliability of wastewater lift stations is vital for public health and environmental protection. A failure can result in sewage backups, untreated wastewater overflow, and severe flooding, leading to odour issues, health risks, environmental harm, and property damage. Considering the potentially severe consequences that can arise from pump station failures, it is imperative that these systems be designed with a focus on robustness to guarantee their long-term reliability and efficiency. Pump stations must also be designed for easy access, facilitating regular inspection and maintenance to prevent failures and performance degradation and to prolong system life

Energy Efficiency. Maintaining operational efficiency is crucial because pump stations consume a significant amount of electricity. Ensuring they continually operate at peak performance is therefore not only an environmental necessity but also a financial one. 

Prior to installation, optimising pump performance begins with pump selection based on the pump station’s flow and head conditions. Pump manufacturers publish pump curves demonstrating the range of pump efficiencies that a particular pump model will achieve, assuming proper care. Selecting a pump that optimises the pump’s efficiency — and ultimately the pump station’s wire-to-water efficiency — translates into lower power consumption and lower utility costs. 

Of course, it follows that pumps with more robust internal construction generally feature higher pumping efficiencies. Yet, dry-pit solids-handling wastewater pumps tend to be more efficient than typical wet-pit or submersible pumps. The latter’s design must account for full submergence in the sewage to prevent seepage into the motor, which can lead to pump failure. As a result, submersibles tend to be less efficient compared to dry-pit pumps.

Operator Safety. Ensuring the reliability and performance of pump station operations necessitates regular maintenance, underscoring the critical need for pump operators to conduct these tasks in a safe and efficient manner. Conventional submersible lift station designs present significant safety hazards, complicating maintenance procedures.

Confined Spaces. Lift stations that require access to the wet wells and any associated valve vaults will often be classified as confined spaces by municipal utilities and industrial end-users per OSHA guidelines. These sub-surface spaces pose significant safety challenges because operators must enter these spaces to perform routine maintenance or emergency repairs. Operators are exposed to risks like toxic gasses and contact with sewage. Ensuring safety requires strict and costly protocols such as permitting, multiple personnel, proper ventilation, gas monitoring, harnesses, and protective gear, along with thorough training for adherence to OSHA standards and other Class 1 Div. 1 requirements.

Hazardous Materials. Exposure to raw sewage, commonly referred to as ‘black water’, is hazardous. This term encompasses any waste contaminated with human faeces and other liquid waste, including discharges from urinals and toilets. Additionally, sewage presents chemical dangers, including the presence of ammonium compounds, formaldehyde, chlorine-based products, sodium hydroxide, and enzymes used in odour control and sewage decomposition. It also contains sanitisers, biocides, agents for cleaning or bleaching, pharmaceuticals, hormones, and heavy metals. The pandemic has heightened awareness of the risks that operators face, especially the increased risk of waterborne diseases. 

Enhancing job safety and reducing unpleasant aspects are crucial for minimising accidents and health risks, as well as boosting worker morale and satisfaction. This is becoming increasingly vital in the wastewater sector as it seeks to recruit and retain its workforce. With a significant number of employees nearing retirement—statistics indicate that up to 30% of the current wastewater operations workforce in some areas may retire within the next five to ten years—addressing these issues is essential for ensuring a skilled and motivated workforce.

Pump station progression

A century ago, the original design of pump stations organised the placement of the pumps in a dry location. This led to the adoption of a ‘dry-well’ or ‘dry-pit’ arrangement, where the pumps were located in a separate chamber, adjacent to and isolated from, the wet well that collected the wastewater.

These pump stations were custom designed, constructed and assembled onsite, much like any traditional construction project. This process involved the contractor being responsible for procuring all necessary components to build the pump station at the location. Components such as pumps, valves, pipes, and control systems were sourced from specialised suppliers. This process was susceptible to delays due to supply chain issues and adverse weather conditions. 

The first major innovation in pump stations occurred in the late 1940s when Smith & Loveless introduced complete prefabricated pump stations. This packaged solution streamlined construction and operation, with the vendor assuming single-source responsibility and support throughout the product’s lifespan. 

These prefabricated systems featured a steel structure, designed for continuous human occupancy, encompassing all the required components such as pumps, controls, valves, and piping. This integration significantly expedited the installation process for contractors. Additionally, factory-built and factory-tested solutions reduced project costs and timeframes by eliminating the need for designing and constructing subterranean spaces or basements. The pump station was shipped virtually complete and dropped into place and piped up. 

Submersibles

Later submersible wastewater pumps, initially developed in Europe, were introduced into the US in the 1960s and began achieving widespread adoption in the 1980s with the development and refinement of guide rail systems. 

Submersible lift stations employ sealed pumps that operate while fully submerged in the wet well. These pumps are periodically lifted to the surface for maintenance and reinstallation via guide rails and a hoist.

While submersible lift stations require only a single underground chamber to house the pumps, which minimises excavation and construction costs, they still require a separate valve vault, usually placed a few feet away from the wet well. These sub-surface spaces are smaller and much shallower than an underground pump room chamber, but they are not always ‘designed for continuous human occupancy’. This phrasing is a key aspect of determining whether entry into a given work area may be deemed a confined space per OSHA guidelines. These valve vaults can lessen the need for operators to have to access the wet well, the potential of H2S gasses and flooding create hazards that can classify them a confined space. Inside the wet well, the submersible pump components, including the motor and electrical connections, must be sealed to protect them from moisture penetration and corrosion.

Not only are the pumps constantly exposed to the raw sewage, but so too are operators when they perform inspections and maintenance. Paradoxically, while submerging pumps in wastewater increases the necessity for physical inspections, it simultaneously makes the inspection process more difficult and onerous. Handling equipment covered in raw sewage is not a pleasant or safe task! 

The EPA advises that submersible pumps undergo inspections at least four times a year. This recommendation stems from the fact that sand, grit, and other abrasive and corrosive materials can wear down the pumps, creating gaps between the impeller and wear ring, significantly diminishing their performance.

The third and final significant advancement in lift station design emerged when Smith & Loveless tackled the limitations associated with submersible pumps by pioneering the development of the above ground Wet Well Mounted Pump Station. This configuration strategically positioned all the mechanical equipment of the pump station outside and above the wet well, usually at ground level. 

This innovation eliminates the need for a separate valve vault used in submersible lift stations, lessening excavation further while enhancing safety by eliminating the necessity of workers entering confined spaces. 

Moreover, it overcomes the drawbacks of submersible pumps by situating the pumps in a dry environment. Positioning the pumps in a dry and safe location significantly increases their reliability and longevity and simplifies inspection and maintenance processes. 

Pumps in state-of-the-art above ground lift stations operate reliably for more than 20–30 years, with basic maintenance. This durability stands in stark contrast to the typical lifespan of submersible pumps, which ranges from three to seven years. 

Operations and maintenance are also radically streamlined. After opening the enclosure, a single operator can visually inspect pumps, valves, and other mechanical components in seconds and can access the impeller or mechanical seal in a few minutes, without the need to clean sewage off the equipment. And because of the vertical construction, there are no sewage spills when the pump is opened because the wastewater falls straight back into the volute and into the wet well.  

More economical 

Above ground packaged lift stations have proven to be more economical than submersible pump systems because of lower installation costs, reduced operation and maintenance expenses, and a longer system lifespan. 

Installation costs. Consider the full scope of installation expenses. Unlike submersibles, above ground pump stations are fully pre-assembled and rigorously tested as complete systems before shipment. This advantage significantly cuts down on the time and labor required for on-site piping, electrical work, and testing.

Furthermore, procurement expenses are notably lower with packaged systems, as they come equipped with many components that would otherwise have to be acquired separately. In contrast, submersible pump systems necessitate additional elements such as a guide rail assembly, pump lifting gantry, lifting chains or cables, suction pipes, power cables, control panel, and the wet well cover. Moreover, the installation of discharge piping and valves, not to mention a valve vault and its cover to encase them, further escalates the costs.

Operations and Maintenance Costs. The full life-cycle expenses of lift stations encompass time and materials for maintenance and repairs, energy efficiency, downtime impact, externally contracted services, and depreciation based on the anticipated lifespan of the equipment. Routine tasks like pulling a pump to change a seal or impeller can be completed in minutes by a single operator, without the use of multiple operators, outside contractors or pricey pump maintenance centres. This contributes significantly to lower parts and O&M costs when compared to submersibles.

A published, comprehensive 12-year side-by-side study by one municipal-county utility demonstrated the life-cycle cost advantages of above ground lift stations compared to their submersible pump counterparts. Utilising asset management software, the study meticulously recorded all maintenance and repair expenses for 53 duplex pump stations within Wyandotte County’s (Kan.) wastewater collection system. This enabled a comprehensive analysis of the operational and maintenance costs between 21 submersible pump stations and 32 above ground packaged systems from Smith & Loveless, all functioning under similar conditions and applications.

The findings revealed that the above ground systems yielded nearly 56% in total cost savings. This translated to an average annual saving of over $2,700 per station, culminating in almost $400,000 in savings for the city during the span of the study. Perhaps the single most dramatic part of the study’s findings revealed that in the 12-year period, not one pump of the 32 above ground pump stations  required replacement, whereas 40 pumps needed replacement in the county’s 21 submersible stations during the same time period. 

Above ground lift stations are a sensible choice for many small and medium-sized pump station applications. These systems position the pump in a conveniently accessible and dry area to simplify design, prolong lifespan, and ease inspection and maintenance. By using a pre-assembled, factory-tested solution, above ground lift stations also guarantee straightforward, economical installation. Moreover, the single chamber design ensures a compact footprint, minimising excavation costs, and the above ground stations remove the risks and inefficiencies associated with entering confined spaces for inspection and maintenance.

By improving the accessibility of equipment, significant safety challenges are eliminated, and costs are drastically reduced without compromising the integrity of the pump system. Increased reliability, efficiency, and longevity provided by above ground systems guarantee improved performance and operator safety, and reduced financial spending.

Rich MacGregor is a technical writer with Smith & Loveless Inc.