A centrifugal pump is one of the most widely used pumps suited to many applications. The simplicity of design makes this pump popular, and it’s commonly used in wastewater applications to transfer sewage and treated effluent. Centrifugal pumps are mainly used for large-volume pumping in wastewater operations. These pumps can also be operated for a short period with the discharge valve closed.
How centrifugal pumps work
A centrifugal pump is a type of rotary machine that uses centrifugal force to generate energy and pressure that pushes fluids from the centre to move long distances and against great pressure. These pumps have an impeller or a rotary element that increases the fluid speed and pressure, while the impeller casing will direct the fluid towards the discharge port and control the flow on release.
Types of centrifugal wastewater pumps
- Single-stage pumps – consists of a single impeller rotating on a shaft encased within a pump casing. There are many variations of the single-stage pump depending on the application, the impeller design and seal types. These pumps can be used for clean or dirty water, or water laden with solids. Single-stage centrifugal pumps include close-coupled, long-coupled, and vertical-inline pumps.
- Multi-stage pumps – have multiple liquid chambers (stages) that are connected in a series and the pumps can generate higher pressures. As fluids pass through the different stages in a multi-stage pump, the pressure and flow rate increases. The combined pressure generated by all the impellers in the different stages ensures that the fluid is discharged at the required discharge pressure.
- Submersible pumps – also known as stormwater pumps, sewage pumps or septic tank pumps. Submersible pumps operate while submerged in water and push water out using the rotation energy generated by the impeller inside the sealed pump. The fluid floods the hydraulic parts in these pumps, which are usually not fitted with suction lines.
- Self-priming pumps – handle a variety of fluids and can be used for a variety of applications including sewage, construction sites and industrial processing. A self-priming pump uses air-water mixture to be fully primed for function, requiring the pump casing to be filled with fluid to operate properly. This type of pump is useful in lifting fluids where the pump is located above the fluid level.
- Grinder pumps – handle wastewater with high volumes of solids and fibrous content which can clog other types of pumps. A grinder pump has a grinding mechanism built into it, which is often a rotating cutter or shredder to cut down the solids in the wastewater, making it easier for the impeller to move the fluids forward. The high pressures generated enable wastewater to be transported over long distances and even uphill.
Factors to consider when choosing a centrifugal wastewater pump
The right centrifugal wastewater pump can make a difference in pump efficiency and operating cost. Here are some factors to consider before buying:
Pump capacity and discharge size
It’s important to determine the pump capacity required for the application. Therefore, consider that hydraulic characteristics of the application and match it to the pumping system. Some key factors to consider for this are the flow rate (capacity), pipe size, amount of resistance and the system curve.
Total dynamic head (TDH)
Determine the vertical distance the pump must carry the wastewater, accounting for friction losses in the pipe as a result. This is expressed as the total dynamic head (TDH) which is the work to be done by the pump for a specific flow rate requirement.
Type of wastewater handled
Evaluate the characteristics of the wastewater and the size and concentrations of solids and other debris that needs to be handled by the pump. Select a pump that can handle the size and concentration of these solids to prevent any clogging and breakdown issues.
Efficiency and power consumption
Choose pumps that are efficient for the application, giving you optimal performance. One method is to look at the best efficiency point (BEP) which is usually provided by the pump manufacturers. A centrifugal pump should be operated at, or close to, the BEP for long-term performance. Efficient pumps will reduce power consumption and lower operating costs.
Installation and maintenance considerations
Consider the ease of installation when choosing pumps. Pumps that are easier to install save time and costs. You should also determine and account for other requirements necessary for pump installation. Ease of service and routine maintenance also reduce costs and increase the lifecycle of the pump.
Matching pump types to pumping station requirements
There are various factors to consider when matching pump types to pumping station requirements:
- Consider station size and calculate the flow rates of wastewater to be pumped.
- Determine the depth of the pumping station (distance between the pump’s inlet and wastewater storage) and the inclination of the discharge pipes as these affect the TDH.
- Determine the distance wastewater has to travel from the pumping station to the discharge point, including the vertical distance it needs to travel as these factors will affect pressure, flow rate and pump efficiency.
Tips for evaluating pump manufacturers and suppliers
Looking for the right centrifugal pump can be stressful, but not when you have found the right pump manufacturer or supplier. Working with trusted suppliers and manufacturers can ensure good quality pumps and good after-sales support, giving you peace of mind.
Consider the following factors when choosing a pump supplier:
- Experience and reputation of the manufacturer or supplier.
- Quality and reliability of products.
- Ease of support and service.
- Proven record of timely delivery.
- Availability of customisation options
- Comprehensive pump warranties offered.
- Important certifications like ISO 9001.
Making the right choice for your centrifugal wastewater pump
There are several types of centrifugal pumps to consider for wastewater management systems. By evaluating factors such as flow rate, pressure, resistance, type of wastewater and other environmental aspects that impact pumps and wastewater management systems, you can choose the right pump that ensures reliability, operating efficiency, and cost-effectiveness.
With over 50 years of service and experience in wastewater management products, we can help you with information on wastewater pumps and pumping stations. Contact us here.
