For any machine, achieving high efficiency levels is of the utmost importance. Improving efficiency doesn’t just reduce your facility’s energy usage; it can also determine your ability to achieve desired results and reduce the need for system repairs. When it comes to getting the best centrifugal water pump efficiency, even small steps towards improving efficiency can lead to big financial benefits for your company.
Unfortunately, because centrifugal water pump efficiency involves mechanical, hydraulic, and volumetric energy, there is ample opportunity for lost efficiency. While hydraulic issues such as liquid friction tend to have the biggest impact on centrifugal water pump efficiency, vane clearances and other factors can also reduce efficiency.
With several different centrifugal water pumps on the market, it can sometimes be difficult to determine how to achieve the highest efficiency. However, the following centrifugal water pump features have been found to have a positive impact for several businesses:
Variable Speed Drives
Also referred to as variable frequency drives, variable speed drives have been found to significantly reduce energy costs in proportion with speed reduction. These drives serve as a highly effective method of controlling flow and pressure in high usage centrifugal pump systems that experience high flow variations and friction losses.
A key advantage of a variable speed drive is that it lowers the centrifugal pump’s operating speed and even allows facilities to “soft start” their system. This greatly reduces wear and tear on the pump, motor, coupling, and other important areas, which in turn can reduce the need for expensive repairs and maintenance work. Installing a variable speed drive also eliminates the need for a standard control valve, a piece that often has a sizeable energy expense.
While variable speed drives can be a great way to improve a system’s efficiency, they may not always be the best fit for centrifugal water pump systems that don’t experience flow variation or frequent use. For these less-demanding systems, a discharge control valve can serve as a more cost-effective option.
Volute Design and the Impeller
The right volute design -- particularly of the throat and tongue areas -- can also have a big impact on a centrifugal pump system’s energy efficiency. Pump volutes should have a circular design to avoid abrupt changes in direction that would disrupt the flow.
Even more important is creating the right amount of space between the system impeller and the tongue. With too much space, water escapes the throat and cycles back into the volute case. Create too little space, however, and pressure pulsations occur that can also reduce efficiency. In general, keeping the impeller radius between five and 10% has been found to produce the best results. For best results, purchase centrifugal water pumps that adhere to these measurements.
Another efficiency-improving method employed by facilities that experience significant flow demand fluctuations is the parallel operation of multiple centrifugal water pumps. This is typically done to improve flow control in individual pumps while simultaneously providing an emergency backup system.
In general, these systems operate by activating more pumps as demand increases, and deactivating pumps as demand slows. For example, during a period of very low flow demand, only one pump might be activated. This ensures that the pump that is active will be operating at a higher efficiency rate. As demand increases, additional pumps are activated as needed. Each of these pumps discharges into the same header to ensure the best results.
While a parallel system can be an effective method for improving efficiency, choosing the right pumps is essential for reaping these benefits. Low-quality pump selections can ultimately hurt the reliability and efficiency of the entire system, resulting in some costly maintenance headaches. On the other hand, choosing quality pumps (and even taking the extra step of installing variable speed drives) can result in a highly efficient operation.