Choosing the right Sewage Ejector pump can seem overwhelming, given the variety of options available and the potential costs involved. However, by focusing on a few key factors, you can make an informed decision that balances performance, durability, and cost.
Understanding Your Application
First, one should consider what wastewater sources are leading to the pump station. Will this pump be solely responsible for the transportation of raw sewage, or will the sewage be diluted by lines of grey water coming from a local sink, for example? The critical factor in selecting a sewage ejector pump that will optimize performance and longevity is understanding the solids content and volume of wastewater in the application. “Solids content”, in this context, is not limited to the volume of fecal matter in the wastewater stream, but also includes toilet paper, wet wipes, and a laundry list of other items that are commonly found in our local wastewater streams. As the Leader in Wastewater Innovation, Crane Pumps and Systems is committed to providing solutions for applications with higher levels of solids.
Material and Build Considerations
The pump market is saturated with a wide variety of sewage ejector pump options that appear to be interchangeable on the surface. However, behind the shiny coat of paint, we unveil more about the quality of product we are being offered. Sewage ejector pumps are typically comprised of 7 key components: cord(s), motor, motor housing, volute, impeller, bearings, and seals. The competitive nature of the market has led many brands to find alternative solutions for these components. What does this mean for the end user? Understanding the materials and construction of your pump can enable the customer to choose a product that optimizes reliability and life expectancy.
Cords- Its common to find in catalogs and service manuals lengthy acronyms for cords like SJTOW, SOOW, SJOOW, SEOOW. Under common operating conditions, most options are acceptable for residential and light commercial applications. If the application dictates premium cord protection, use the below guide when selecting the necessary cord type.
S- Service Cord
OO – Oil resistant outer jacket and insulation
W- Weather and water resistant
O- oil-resistant outer jacket
E- Elastomer
T- Thermoplastic
J- Junior service (up to 300V)
Motor
For single phase sewage ejectors, there are primary motors types, capacitor start/ capacitor run and permanent split capacitor motors. Depending on the application, both options have their benefits and tradeoffs. Without going into too much detail on the different technologies, the permanent split capacitor (PSC) option is preferred in most residential applications due to having lower starting currents, quieter operation and higher life expectancy. Capacitor start/ Capacitor run motors in most cases come at a higher price, but provides a higher starting torque and efficiency than PSC motors.
Volute
Your sewage ejector’s volute is the curve-shaped casing that redirects the flow of fluid generated from the impeller towards the discharge of the pump. Volutes come in a variety of shapes in sizes and has a huge impact on the pump’s performance, price, reliability, and cost. It is not uncommon for these volutes to be made of a thermoplastic material, while the majority are made of different grades of cast iron. Plastic volutes may reduce the upfront cost for customers but are more susceptible to discoloration and ultimately fracturing over time. In most cases, a cast iron pump with outlive several generations comparable models with plastic, saving money for the end user in the long run.
Impellers
Like the pump volute, most sewage pump products will have an impeller either made from a thermoplastic or cast iron. This detail is not known until the pump fails or we look at the engineering specifications for the product. However, the same rule applies to impellers. Cast iron will outlast plastic impellers in most applications. The impeller is one of the only dynamic components of the pump that comes into direct contact with the wastewater. Having the increase durability of a cast iron impeller will increase the overall lifespan of the pump.
Bearings
Bearings are used in sewage pumps to reduce the friction between the motor shaft and stationary components housing the pump motor. Both ball bearings and sleeve bearings can be found in many sewage ejector pumps. These two designs also have a cost-reliability tradeoff. Ball bearings will come at a higher price but reduce friction resulting in quieter, more efficient operation. Lower horsepower sewage ejectors can be found with 2 ball bearings, 1 ball bearing with 1 sleeve bearing, and certain models with the motor fully supported with two sleeve bearings.
Seals
Seals are the last line of defense protecting the electric motor from water damage. Common seal types include mechanical, cartridge, and lip seals. Mechanical and cartridge seals are similar in design and provide similar levels of protection as one another. Cartridge seals are preassembled packages whereas mechanical seals require the spring tension to be applied separately. These seals contain both a stationary and rotary face that are in direct contact with one another when the pump is in operation. These faces are typically made of either carbon ceramic or silicon carbide. Silicon carbide is a harder material making it more resistant to corrosive materials, while carbon ceramic is a viable option in most applications, if the pump station is exposed to corrosive or abrasive substance like sand, silicon carbide seals will be the preferred option. Lip seals provide less protection directly to the motor and are best utilized as a secondary seal preventing debris coming in contact with a mechanical or cartridge seal.
At Barnes, we offer a range of high-quality Sewage Ejector pumps built with robust materials designed to handle even the most demanding environments. Our pumps feature advanced designs such as oil-lubricated bearings for quieter operation and longer life, as well as cast iron construction that enhances durability.
Solids Handling and Efficiency
Another key consideration is the pump’s ability to handle solids. A submersible centrifugal pump hydraulic typically consists of only an impeller and volute that come in a variety of configurations that are suitable for different applications. The physics behind hydraulic design gives rise to a trade off between its ability to handle solids and the efficiency in which it converts mechanical energy from the motor to flow through the system. For example, a hydraulic that provides optimal efficiency will, in most cases, not be the most clog-resistant solution.
There are 3 common hydraulic technologies found in the sewage ejector market including vortex, semi-open, and fully eclosed. These hydraulics share many characteristics but will provide different results depending on the application. Vortex designs operate just as it sounds, generating a vortex of fluid within the pump volute before being transported though the system piping. This design is often chosen in some of the harshest conditions as a minimal amount of solids come into contact with the impeller during operation. This ideal non-clog capability, however, comes at the expense of the pumps overall efficiency. A fully enclosed impeller comes with an upper and lower shroud, fully encasing the impeller vanes. These impellers are designed to minimize hydraulic performance but is more susceptible to clogs when comparing to alternative solutions. The Semi-Open impeller is a hybrid of the two technologies, with taller vanes than a vortex but no outer shroud that is found on fully enclosed design. Semi-Open impellers are a popular design in the market due to this balance of performance and their ability to prevent clogging.
Vortex sewage ejectors are a common and appropriate choice for most residential and light commercial applications. Most fractional HP units will utilize this design as the system requirements are often less demanding. However, in systems that are redistributing wastewater from public facilities will often see more volume in a day requiring larger HP products and more efficient hydraulics. These public stations will often see a higher volume of non-sewage solids as users that are contributing sewage to the system are not liable to maintain the system. These public stations include local parks, schools, gas stations, senior healthcare facilities and many others that have public bathrooms all leading to onsite stations that can provide a variety of challenges. Understanding what solids these stations may see is critical to selecting the best sewage ejector pump.
System Head Requirements
One of the most technical aspects of selecting a Sewage Ejector pump is understanding the system head requirements, which refers to the total height the pump needs to lift the wastewater. This is critical because a pump must be capable of meeting the head requirements of your system to function effectively. System head is a common term that’s commonly used in the industry, but its important to understand the nuances that make up total head when designing or operating a pump system. Total head (system) is comprised on three elements: elevation head, pressure head, and friction head.
Elevation or “static” head simply refers to the height difference in which the pump must transfer the fluid. If a sewage ejector is installed in a basement that is 10’ below the gravity fed sewer line, this would result in an elevation head of 10’.
Pressure head is the difference in pressure from the station that the pump is located to the destination pressure. For example, if sewage line leads to a public force main sewage line, the pump will have generate enough head pressure to feed into the line.
Friction head consists of all the pressure losses due to various aspects of the system. Friction head losses are a function of the liquid velocity or flow rate squared and is depending on the size of piping in the systems, as well as the number of fittings, valves and other equipment present in the system.
Once these three elements are calculated, you can then plot a system curve. As mentioned previously, friction losses are calculated as a function of flow, the system curve will show how the losses (head requirement) is increased that the flow is increased. This system curve, along with the published pump curve will show us where the pump will operate in that system. Many manufacturers will publish what the preferred operating region (POR) or allowable operating region (AOR) which outlines which operating regions along the performance curve will optimize the life expectancy of the pump. Most hydraulic designs will operate most efficiently and for the longest life towards the center of their performance curves.
Fortunately for those who are looking to buy a sewage ejector, the Barnes brand is experienced in the sewage ejector market and has a product portfolio that can meet the needs of any application and are design with the expertise on common system head requirements so that are customers can be confident they Barnes product will meet the requirements of their system.
Conclusion
In conclusion, selecting the right sewage ejector pump requires a comprehensive understanding of your specific application needs, including wastewater sources, solids content, and system head requirements. By carefully considering the material and build quality, motor type, volute design, impeller configuration, and the pump’s ability to handle solids, you can ensure long-term reliability and efficiency. Barnes offers a range of high-quality sewage ejector pumps engineered to meet diverse application demands, providing a balanced solution between performance, durability, and cost, making them an excellent choice for both residential and commercial installations.