Introduction
Clean water is a cornerstone of public health, environmental integrity, and economic stability and is also essential in manufacturing processes in many industrial sectors. Ensuring a well-functioning and uninterrupted water supply is, therefore, highly critical. Condition monitoring provides insights into the condition of critical equipment and predictive alerts as to when and where maintenance is needed.
This case study from the German waterworks Mülheim Styrum-East involves the detection of a structural resonance issue in the electric motor of a drinking water pump.
RWW, Rheinisch-Westfälische Wasserwerksgesellschaft mbH, is one of Germany’s biggest water supply companies. It supplies around 70 million cubic meters of drinking and service water to about 900,000 people, industry, and commerce annually. The Mülheim Styrum-East waterworks is one of three on the river Rhur.
Conclusion and summary
After installing online monitoring on all drinking water feed pumps in the Mülheim Styrum-East waterworks, abnormalities were found in the VEL vibration values on the Oberhausen 3 feed pump relating to the electric motor’s A and B sides. After spectrum analysis and follow-up measurements with portable instrumentation on the foundation confirmed high amplitude vibration at the resonance frequency, it was concluded that the motor frame was too weak. To resolve the issue, the frame was stiffened by fitting cross braces.
System configuration
For continuous monitoring of the twelve drinking water feed pumps in the Mülheim Styrum-East waterworks, two 32-channel Intellinova Parallel EN online system units and four DuoTech SLC144 accelerometers per machine are used.
Figure 1 Flowchart of the waterworks. Image: RWW
As of 2024, RWW Styrum-East waterworks uses a total of nine Intellinova Parallel EN online system units with DuoTech SLC144 accelerometers to monitor critical equipment across its seven waterworks. Forty-two feed pumps in three waterworks and three turbines in a hydroelectric power plant are monitored online. Sixty-eight pumps are monitored through route-based measurement with two Leonova Emerald handheld devices.
Image 1 Intellinova system units and the Styrum-East waterworks
Objectives
The objectives of the online monitoring are:
• Changing the maintenance strategy from run-to-breakdown/reactive and preventive maintenance to condition-based and proactive maintenance
• Use the online systems to alert the control room in the event of poor operating condition and damage.
• Increased continuity of supply.
Application description
The application is a horizontally installed spiral casing pump with a double-suction impeller and a water-cooled frequency-controlled electric motor. The double-suction design balances the axial forces on the impeller, thus causing less wear and tear on the bearings. This pump design also allows higher flow rates.
Image 2 The motor non-drive side
Image 3 The motor-pump assembly.
System configuration
The machine is equipped with four DuoTech accelerometers SLC144TB-M8. The system unit is a 32- channel Intellinova Parallel EN online system. To determine the rotatinal speed, an inductive sensor M18x1 with LED is used.
Figure 2 Measuring point locations on the motor and pump A and B sides.
In the Condmaster analysis and diagnostics software, four measuring points are configured (Motor – A and B sides, Pump – A and B sides); each with the SPM HD shock pulse measurement technology 100 orders, 1600 lines, and vibration measurement 50 orders, 1600 lines. The measurement interval is 5 minutes with forced storage of every six results.
The short measurement interval results in large amounts of measurement data, but it was chosen to enable quick alarms in the control room. As long as the measured values are stable, the filtering keeps the amount of data down.
Image 4 Screenshot of measuring points in Condmaster.
Image 5 SPM HD measuring assignment configuration.
Image 6 Velocity measurement configuration.
Case description
After the installation of the online monitoring system and the collection of sufficient measuring results, a noticeable fluctuation (between 1.3 mm/s and 5.8 mm/s) of the measured VEL values occurred on the electric motor of the Oberhausen 3 drinking water pump at both measuring points.
Image 7 Fluctuating vibration velocity readings on the motor’s A side.
Image 8 Fluctuating vibration velocity readings also on the B side.
The spectrum was examined, and a high amplitude was found at the 1st order. Due to the last revision, increased machine imbalance could be ruled out.
Image 9 Spectrum and time signal from the B side, showing high values at 1X.
As a result, control measurements were carried out with the handheld measuring device on the supposedly fixed frame. These measurements also showed an increased vibration speed in the horizontal direction.
The motor frame was then provisionally fitted with several cross braces for reinforcement.
Image 10 Before (left) and after (right) corrective measures to reinforce the frame.
The online readings recorded after this corrective measure showed significant improvement in the vibration values.
Image 11 Vibration readings showed less fluctuation after the frame was reinforced with cross braces.
