why does the DAB NKV multistage pump stop and how to fix it
The multi-stage pump NKV from the brand DAB is a reliable solution for heating and technical water, but its shutdown in operation often requires quick diagnostics. This article will show you how to identify the causes of failure and how to gradually repair the system to avoid costly repairs or unnecessary replacement of the entire unit.
Critical reasons for the stoppage of the multi-stage pump
The most common reason for the sudden stoppage of the NKV type pump is dry running caused by a drop in the level in the tank or clogging of the suction pipe, which leads to motor overheating and activation of thermal protection. Another common cause is mechanical load on the shaft, which occurs when bearings are damaged or when foreign objects are present in the impeller, preventing the motor from starting even under voltage.
Diagnosis of electrical and mechanical faults
Before any disassembly, it is necessary to check the supply voltage and the status of the thermal protection, which may be inactive due to a relay failure or incorrect setting of the current limiter. If the motor is warm and not moving, use a multimeter to measure the resistance of the windings and check whether the starting capacitor is damaged, which is critical for the start-up of three-phase motors.
- Measure the insulation resistance between the winding and the motor housing (the value should be >1 MΩ).
- Open the cover and visually check the condition of the capacitor to see if it is swollen or leaking.
- Check whether the shaft turns freely by hand when the voltage is disconnected, which rules out mechanical jamming.
Disassembly and replacement of seals
Regular maintenance of bronze impellers and replacement of seals are key to the long life of the pump, especially in operation with hard water or in systems without water treatment. During disassembly, consider that double flanged versions, such as model DKLP 40-1800 M Dry-running pump - double flanged, have a specific design that requires precise adherence to the tightening torque of the screws during reassembly.
Solving problems with suction pipe and air venting
If the pump is running but does not reach the required pressure or regularly turns off, it is often due to air pockets in the system, which disrupt the hydraulic balance and cause cavitation. In such cases, it is essential to install or check the functionality of air venting set 6/4", which ensures smooth air removal and prevents damage to the impeller.
For larger systems where the risk of sedimentation is higher, the installation of submersible sewage pumps designed to work with impurities, such as FEKA FXV 20.07 M-NA submersible sewage pump, is recommended. However, for clean heating water, the NKV remains the optimal solution with proper filtration.
When replacement or professional service inspection is necessary
If the pump still does not work properly after performing basic steps such as cleaning the filter and replacing the seals, it may be due to internal bearing wear or winding damage, which requires professional intervention. In such a case, it is often more economical to replace the entire pump with a new one, for example NKV 1/14 S T Multi-stage centrifugal pump, rather than investing in the repair of an old unit with an unknown history.
Exploring hydraulic losses and their impact on operation
Multi-stage pumps NKV are designed for a specific performance curve that requires precise system setup. If the pump stops or frequently cycles, it is often due to excessively high hydraulic load, which occurs with a poorly dimensioned piping system or clogged valves. In such a case, the motor operates outside its optimal range and the thermal protection reacts to the overload.
Analysis of the characteristic and operating point
The key to understanding the problem is comparing the pump characteristic with the piping system characteristic. If the system is too "closed" (for example, partially closed valves or narrow pipes), the pump reaches a point where it exceeds the maximum pressure, leading to a sharp drop in flow to zero. This is called the "operating point at the end of the curve" and is the most dangerous for the motor's lifespan.
The importance of correct NPSH calculation and cavitation phenomena
One of the less obvious, yet technically critical causes of shutdown is cavitation caused by insufficient suction pressure (NPSH - Net Positive Suction Head). If the pressure at the pump inlet is lower than the vapor pressure of the water, bubbles form and implode upon impact with the impeller. This implosion damages materials and causes strong vibrations, which can trigger vibration protection or mechanical damage to the shaft.
- Low suction pressure: A long suction pipe with a large number of bends increases losses and reduces NPSH.
- High water temperature: In heating systems above 80 °C, the difference between available NPSH and required NPSH decreases, significantly increasing the risk of cavitation.
- Tanks without air pockets: If the tank is not properly equipped with an air compressor, pressure may collapse when the pump starts.
Maintenance and diagnostics of electronic control
Modern versions of NKV pumps may be equipped with frequency converters or automatic regulators, which have their own error codes. A shutdown is not always caused by a mechanical failure, but can be a protection against motor overheating or current spikes during startup.
Overview of common error codes and their meanings
| Error code | Cause | Solution |
|---|---|---|
| E-01 | Incorrect power phase | Check the direction of rotation and phase connections. |
| E-02 | Motor temperature exceeded | Cool down the motor and check the ventilation. |
| E-03 | Rotation sensor error | Check the sensor connection and shaft. |
| E-04 | Low pressure at the inlet | Check the suction pipe and filters. |
Repair strategy and preventive measures
Repairing a multistage pump requires a systematic approach. After identifying the cause of the shutdown, it is necessary to proceed according to a plan to avoid further damage. The most important part of the repair is not only eliminating the fault, but also setting the parameters so that a similar situation does not recur.
Step by step: From disconnection to testing
- Disconnect from the network: Always ensure complete disconnection from the power supply before any manipulation.
- Drain the water: Open the drain valves and disconnect the pump from the piping to eliminate pressure inside.
- Disassembly and inspection: Disassemble the pump and visually inspect the condition of the bearings, seals, and impellers. If you find corrosion or wear, immediately replace the damaged parts.
- Cleaning and lubrication: Clean all components and lubricate the bearings with a suitable lubricant recommended by the manufacturer.
- Reassembly and sealing: Use new seals and tighten the bolts according to the torque specified by the manufacturer (usually 5-10 Nm for small bolts).
- Test operation: Start the pump without load and monitor the current and vibrations. If everything is normal, reconnect it to the system and check its performance under full load.
Regular inspection and following these steps will ensure long and reliable operation of your NKV pump. If you have doubts about the properties of the system or need expert advice on sizing, do not hesitate to contact our technicians, who will help you find the optimal solution for your specific needs.
Frequently asked questions
Can I start the NKV pump after a long break?
Yes, but only after a thorough check of the power supply and manual rotation of the shaft to ensure that it has not seized or corroded during the break.
Is it possible to use the NKV pump for pumping sewage water?
No, multistage pumps are designed for clean water; for sewage water, it is advisable to use a specialized submersible pump, for example FEKA 600 T-NA 10H07 submersible sewage pump; 10m cable.
How often should the seals on a multistage pump be replaced?
Seals should be checked at least once a year or during each major service, and their replacement should be carried out immediately at the first sign of water leakage.
Proper diagnosis and timely maintenance of the multistage NKV pump extend its lifespan and prevent unplanned outages in heating, which is crucial for the comfort of both households and industrial facilities.
Do you have a question about this topic?
Not sure or dealing with a specific situation in your home? Write to us - we are happy to help.