Follow These 10 Tips for Better Pump Efficiency
Proper sizing of systems, utilizing well-trained operators and performing routine maintenance can help overcome day-to-day challenges.
By Bill Davis and Gregg Rivoir, ABEL Pumps
Perpetual motion is a concept that has captured the imagination of many an inventor. The success of creating such a device would not only reap the obvious financial returns, but would solve a myriad of world problems including at the very least, clean water and world hunger. Many have tried but failed. From the theoretical "Maxwell's Demon" to the elegant "drinking bird", it appears that the laws of thermodynamics foil all attempts to violate its principles. But as stubborn as those laws may be, there are still those inventors and engineers, who diligently chip away the old barriers to reveal maybe not quite perpetual motion, but at least a more efficient means of motion.
The best mechanical systems are designed when engineers focus on efficiency; that is to say, a task accomplished by the least amount of steps and with the least possible amount of energy and effort. Furthermore, parasitic losses in any mechanical system must be kept to a minimum if one desires to maintain an edge over the competition, keep pace with ever-increasing environmental regulations or meet sustainability goals.
Perhaps nowhere else in industry today can efficiency be more appreciated than in pumping systems. Here are 10 tips to aid in improving pump efficiency.
Conduct an energy audit and life-cycle cost estimate of new or existing systems. Before replacing that worn-out thickener underflow pump or that consistently troubling absorber recycle pump with the exact make and model, perform an energy audit that can reveal the true cost associated with the ownership and operation of the device. If saving time and money is important to your bottom line, do not be afraid to explore and consider the use of new and alternate technologies. Though many new technologies may require higher initial capital investment, the final life-cycle cost may prove more beneficial to your cost center.
For example, many air-operated pumps are being replaced with more energy-efficient ABEL EM series electric diaphragm or electromechanical membrane type pumps. These newer pumps are not only great energy savers; they also are controllable and provide regulated flow not possible with air-type pumps. A good guideline to remember: Greater energy efficiency, less downtime, less maintenance and lower operating costs all make their way to the balance sheet. In the end, your diligence will pay off.
Use gauges to monitor pump performance. Gauges can be used in both the suction and discharge side of the pump. These gauges serve as the best early warning of pump wear or poor performance caused by blockage or system anomalies. A low discharge pressure could signify wear on internal pump components, leading to reduced efficiency. It is not enough to just install the gauges. The gauges must be monitored and trigger maintenance or other remedial action when readings trend beyond the established control limits.
Know the limits of the pump and materials of construction. Abrasive wear of internal components such as valve seats, check balls, impellers, gears and pistons should be minimized by choosing the correct materials. When these internal components wear, efficiency is lost and, as is the case with some pump types, their operating point on a pump curve changes and does not necessarily match the optimal system curve.
Properly size the pump for the application. Avoid oversizing. When faced with a new or unique application, it is often difficult to resist overdesign. No one wants to be the supplier that underperforms in a system. The tendency is to overdesign—for example, a little extra horsepower or a larger-than-necessary discharge pipe spool can create waste and inefficiency. Instead, look into pipe modeling software to help determine required flow rate and discharge pressure. Use traditional hand calculations to validate the more sophisticated computer output.
Properly size the piping. In addition to keeping costs at a minimum, proper pipe diameter can prevent sedimentation or settling when pumping slurries. The velocity of the pumped medium depends on density, solids content and grain size of the particulate. For most sewage applications, a velocity of 1.8 meters per second (m/s) is sufficient to prevent sedimentation. Sludge with higher content of solids requires higher velocity to prevent sedimentation. The velocity can be influenced by changing the flow rate or selecting a different pipe inside diameter. An optimally sized discharge line would be one that is large enough to control excess backpressure but small enough to prevent sedimentation in the pipeline (see Equations 1 and 2).
Velocity can be influenced by changing the flow rate (Q) or by selecting a different pipeline inside diameter (Di), as shown in Equation 1.
To prevent sedimentation, velocity must be higher than the settling velocity (VL) which is defined in Durand's formula (see Equation 2).
||= Durand factor based on particle size and volume concentration
||= 1.3 x Cv^0.125 x (1-e-6.9 x d50)
||= percent concentration by volume
||= Average particle size (mm)
||= Acceleration due to gravity = 9.81 m/s2
||= Density of dry matter (t / m3)
||= Density of mix medium (t / m3)
If velocity is too low, particles from the slurry may set up and block the pipeline.
Properly design the suction piping. Feed lines should be connected to the pump in a manner that prevents force from being applied to the pump. Use supports, hangers or other means to carry the pipe's weight. Use connections that can accommodate expansion forces or other forces created by minor misalignment. Use strainers to catch large particulate matter. Avoid air locks (air pockets) in the suction line created by elevation changes. Use a single diameter suction piping to promote stable fluid flow. Lay out the suction piping in such a way that minimizes the amount of 90-degree bends and allows for the shortest line possible. This will increase the net positive suction head available (NPSHA) and improve pump system efficiency.