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Solids and fibres raise the power drawn by the pump in an unpredictable way: rags, wet wipes or sand wrapped around the impeller cause sudden load surges during operation and, in the worst case, jamming. For this reason the motor is assessed not only against the duty point on the clean-water curve, but also against the load during partial clogging and the need to restart.
How clogging shows up at the motor
As ragging builds up, friction between the impeller and the casing increases, current rises and speed drops. When the pump stops and is restarted, the deposit inside the impeller makes starting harder. Overload protection saves the motor in this situation but does not solve the root cause; the protection concept is explained in the article on overload protection methods, while the settings are a matter for qualified electrical personnel.
Distinction by pump arrangement
| Arrangement | Motor situation |
|---|---|
| Submersible wastewater pump | The motor is integrated with the pump and immersed in the liquid; this type of motor is not part of DRG's standard range. |
| Horizontal or vertical pump in a dry well | A standard IEC three-phase motor can be considered among the options. |
| Belt-driven sludge pump | Assessed together with the pulley ratio; the motor is foot-mounted. |
Ambient conditions
In lift stations, humidity and sewer gases corrode metal surfaces. IP55 protection covers water jets and dust, not submersion. If the area is classified because of an explosive gas risk, a certified product is required; such motors are not in the DRG range, and an assessment by the person responsible for the site is essential.
Data to collect before selection
- Shaft power and impeller type (vortex, channel, cutter) stated by the pump manufacturer
- Solids content of the fluid and the largest particle size
- Number of starts per day and how the well level is controlled
With this data you can review the application notes on the wastewater treatment plant motors page and compare models suited to a dry-well layout in the online motor list.