When a pump is properly protected, the energy savings that results can be quite significant, enough to pay the bills for the drive or even the entire system.
It’s as simple as that, according to ABB Business Development Manager Torben Poulsen. “With the energy savings, you are paying less for your electricity bill and that is paying for the all the other benefits that comes with it,” he says.
Well, perhaps it’s not that simple. “First, you must understand the problem and the application,” Poulsen explains. “That’s the key to protecting the pump.”
Common Pump Problems and Solutions
When protecting pumps for the Water, Wastewater, and HVAC industries, the focus lies on cavitation detection and control, dry run protection, intelligent controls, pressure and flow monitoring, pump clean and quick ramps to protect bearings. This article explores each problem and solution in detail.
Cavitation Detection and Control
Cavitation in centrifugal pumps occurs when vapor bubbles form and collapse inside a liquid, generating shockwaves that can cause significant damage to pump components. This phenomenon often arises from low inlet pressure, which can result from a low liquid level in the supply tank or leakage in the pipes. Pressure drops reduce the local pressure below the liquid’s vapor pressure, leading to the formation of vapor bubbles. These bubbles are not caused by a temperature increase but by localized pressure decreases, often due to obstructions in the system. Cavitation is common in applications like water and wastewater treatment or food and beverage processing.
When the vapor bubbles move into areas of normal pressure, they implode, releasing energy that can erode impeller blades or pump housing, leading to noise, vibrations, and reduced pump efficiency. This damage can escalate to severe pitting and equipment failure, often resulting in unplanned maintenance or costly replacements. Recognizing symptoms like noise and vibration early is critical to preventing cavitation and maintaining pump performance.
The inlet pressure is important for a pump to work in the right way. The required head at the inlet is known as NPSH, and it is flow dependent. A pump impeller creates vacuum on the suction side/inlet. If the vacuum gets too large, the water starts to boil— water goes from liquid to vapor(steam). When the steam bubbles collapse to liquid again, cavitation occurs.
“The trick is to avoid that the suction pressure goes so low that we get the transformation from liquid to vapor,” Poulsen explains. “This can be done by making sure that there is sufficient pressure in front of the pump or by controlling the speed of the pump according to the pre-pressure. Decreasing the speed will move the pump curve toward a lower flow, requiring lower pre-pressure.”
There is a high risk of cavitation in emptying a tank or in applications where the pump is supplied from a tank.
ACQ580 drives for water and wastewater applications feature an ABB exclusive, patented algorithm with user-configurable reactions to cavitation detection. A system can return to normal operation when cavitation is no longer detected. These sophisticated drives prevent impeller failure or loss of efficiency due to the pitting damage caused by collapsing bubbles. The drives require no additional hardware—only a simple autotune of the system upon activation of the function.
Dry Pump Run Protection
The danger of a pump running dry lies in the absence of the liquid needed to cool and lubricate its internal components, which can lead to severe damage. Centrifugal pumps, for instance, rely on the liquid being pumped to dissipate heat generated during operation. When a pump runs dry, heat builds up rapidly, causing components like seals and bearings to overheat and potentially warp or fail.
In addition to heat-related damage, a dry-running pump can experience increased friction and wear, leading to mechanical failure. For pumps with mechanical seals, running dry can cause seal faces to overheat and crack, resulting in leaks. If not addressed quickly, dry running can lead to costly repairs, unplanned downtime, or even the complete replacement of the pump. Preventative measures, such as installing dry-run protection systems, are critical to avoiding these risks.
ABB’s ACQ580 drives for water and wastewater applications prevent the pump from running dry by warning or faulting the drive. They use underload monitoring, digital inputs from low/high level mechanical switches, or its supervision function based on pressure sensors.
These drives protect the pump’s bearings and shaft seal from damage when there is no water in the pump. The water pump shaft and impeller rotate at fast rates. If there is no water in the system, the energy is released as heat and damages the bearings and shaft seals, limiting the lifetime.
Intelligent (Process) Pump Control
Intelligent pump control becomes especially important in HVAC applications. For example, in a hotel. an excessive amount of water is used in the mornings while not as much is needed in the afternoon. In the mornings, multiple pumps may be running to accommodate the demand. To control this, drive software controls the number of pumps running simultaneously. When more pumps are needed, the system will automatically start the pumps. When there is not as much need for water, the pumps are automatically paused.
This kind of intelligent control technology is also useful in a redundant system. When one pump goes down, the backup pump can be automatically triggered to turn on and begin running without interrupting the flow. Intelligent controls can also provide a schedule of “shifts” for each pump to run so that one of them doesn’t get overworked. This is especially essential in HVAC applications in which heating and cooling consistently are important.
ACQ580 drives from ABB control up to eight drives/pumps in a pumping system. A moving lead strategy can be implemented that shares process information and configuration through a dedicated VFD-to-VFD link. Automatic parameter synchronization between drives can be enabled during set up. These drives allow pump redundancy to avoid unplanned downtime and balances operation times to increase the time between repairs. Energy usage is optimized on process demand with smooth transitions that reduce pressure surges and hammer. The synchronization across pumps ensures parameter consistency and saves significant commissioning time.
Pressure and Flow Monitoring (Sensorless Flow Calculations)
Pressure and flow monitoring in water and wastewater pumping applications presents several challenges due to the demanding and variable nature of these environments. Accurate monitoring is crucial to ensure the efficiency, reliability, and safety of pumping systems, but achieving it can be complicated by factors such as fluctuating operating conditions, the presence of debris or solids, and the need for system longevity.
To overcome these challenges, operators often rely on advanced monitoring technologies, such as non-contact flow sensors, self-cleaning devices, and smart systems with remote monitoring capabilities. These solutions provide the durability, accuracy, and efficiency needed for effective management of water and wastewater pumping applications.
For flow protection, ABB ACQ580 drives utilize user configurable limits to set warning and/or fault protection levels the input can come from a flow sensor or by using the sensorless flow calculation included as a feature in the drive. The sensorless flow calculation is based on information from the pump performance curve QH or from the power curve of the pump (QP curve). The information combined with advanced math, makes it possible to estimate the actual flow, and this estimation can be used as input for flow protection.
For pressure protection, ABB ACQ580 drives utilize individual configurable limits to set warning and/or fault protection levels for inlet and outlet pressures with a configurable delay to eliminate nuisance warnings during pump starts. The inlet provides minimum pressure protection with early indication that can be used to prevent cavitation. The outlet minimum pressure protection indicates a rupture or leakage, while the outlet maximum pressure protection indicates a blockage or closed valve.w
Pump Clean
Cleaning pumps in wastewater applications is a significant challenge due to the complex and demanding nature of the operating environment. Wastewater often contains a mix of solid debris, grease, sludge, and fibrous materials, all of which can accumulate and impair pump performance.
Wastewater pumps frequently handle materials like rags, wipes, and other fibrous debris, including corrosive and abrasive fluids, and grease and sludge accumulation that can entangle around impellers or block passages. This leads to reduced efficiency, increased energy consumption, and potential pump failure. Cleaning clogged pumps can be time-consuming and hazardous for maintenance personnel.
Pumps in wastewater systems are often located in confined spaces, submerged in wet wells, or placed in hard-to-reach locations. Cleaning generally requires the pump to be taken offline, leading to downtime and potential disruptions in system operation.
Addressing these challenges requires a combination of advanced pump technology, proper maintenance practices, and system optimization to ensure efficient, reliable operation.
Based on a programmable sequence of rapid impeller rotations, ABB’s ACQ580 drives force obstructions away (forward only, or forward/reverse). They can detect under/overload, start the cycle when detected, and can be scheduled to clean without interrupting normal duty: manually, timed intervals, fieldbus or every start/stop.
The cleaning cycle counter may help detect failing pumps or screens and prevents pump clogging (also known as anti-jam or de-ragging). These intelligent drives improve operational efficiency by reducing downtime and reduces the cost of having to lift and clean pumps. This further reduces worker exposure to wastewater and decreases sedimentation in pipes to improve flow/efficiency.
Quick Ramps to Protect Submersible Pump Bearings
“Variable speed pumping requires that the correct ramps are being used for different pumps,” Poulsen explains. “Normally, a maximum time is defined for reaching the minimum speed from 0Hz. This time is typically rather short for multistage pumps and slightly longer for single stage pumps.”
The same rules typically apply during stop (rom minimum speed to 0Hz).
There are two main issues for defining a maximum ramp time to the minimum speed.
- The shaft seals need lubrication from the liquid in the pump. Running too slow will not create the lubrication needed.
- The second part can be linked to bearings and friction loss, in which a certain speed is needed to overcome friction loss for certain pump types.
There is no specific requirement for operation in the range from minimum to maximum speed. Using a drive to start a pump provides soft start compared to direct online start. The pressure is built up slowly and the stress on pipes and valves are reduced. The first ramp is used to bring the pump from stand still to the minimum speed.
The second ramp is used to reduce turbidity in deep-well pumping. To even further reduce the stress, the pipe filling function can be used for filling vertical pipes. Just remember to keep the requirement for meeting the minimum speed within the maximum starting time.
Stopping the pump can be done in two ways, either as ramp to stop (soft stop), where the drive keeps control of the stopping sequence by ramping to stop, or coast to stop, where the pump is free running to stop from the time the stop command is given
Ramp to stop is likely the most used stop sequence on multistage pumps where the impeller inertia is low. Coast to stop is used more commonly in single stage pumps. The inertia of such a system is high. Coast to stop is used in applications where the pump is forced by the media to keep spinning (low speed) either due to pre-pressure or due to uncontrolled backflow. It can be required to have a start delay from the stop command to next start in case of using coast to stop to make sure that the pump has stopped or used to catch a spinning motor.
ACQ580 drives from ABB use dedicated ramp sets to quickly accelerate or decelerate the pump at dictateable rates. The first ramp allows immediate water flow to lubricate and cool the pump bearings and reach the minimum speed. The second ramp is used to reduce turbidity as the pump is not producing any flow in this region.
When a pump starts as slow as possible, it creates the lowest turbidity values for the water being moved. Submersible pumps need immediate water flow. By combining quick ramps with long normal ramps, the drive will ensure proper lubrication, efficient ramping in the no-flow zone, and slow ramping after that to ensure minimal turbidity.
Understand the Application to Properly Protect Your Pump
Proper pump protection is essential for achieving long-term reliability, energy efficiency, and reduced maintenance costs in water, wastewater, and HVAC applications. By addressing common challenges like cavitation, dry running, intelligent control, pressure and flow monitoring, and cleaning, operators can significantly enhance pump performance and extend equipment lifespan.
Advanced technologies, such as ABB’s ACQ580 drives, play a critical role in mitigating risks, optimizing processes, and ensuring smooth operations through features like cavitation detection, dry-run protection, and intelligent ramping.
Understanding the specific requirements of each application is key to implementing effective solutions. By leveraging innovative tools and best practices, operators can reduce downtime, improve operational efficiency, and maximize the return on investment in their pumping systems. As demand grows for sustainable and efficient pumping solutions, integrating smart technologies will remain crucial to meeting these challenges head-on.
Michelle Segrest is President of Navigate Content, Inc., and has been reporting on the industrial processing industries since 2008. Torben Poulsen is ABB’s Business Development Manager for pump applications and holds a degree in Electronic Engineering and a degree in Business development/innovation from universities in Denmark. He has worked in the drives industry since 1993.
