S-tube by Grundfos

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Grundfos S-tube

The S-tube is the only impeller available in the wastewater market that does not compromise hydraulic efficiency or free passage through the pump.

The key to the design is simplicity, with no cutting or moving functions that can get worn over time and hereby ensuring a constant, superior efficiency over time. The S-tube impeller is a tube-shaped impeller placed in a pump housing that matches the smooth tube shape through the entire pump with no obstructions or dead zones through the hydraulic.


The S-tube impeller and the new tube design through the pump provide:

  • World-class hydraulic efficiency up to 84% without compromising free passage.
  • Spherical free passage up to 160mm, meaning better solids handling and greater non-clogging capabilities.
  • A design as simple and robust as a tube results in longer lifetime and lower maintenance costs.


The difficulties in designing high-efficiency impellers have traditionally been challenges with sealing against backflow, vibrations, abrasive wear and clogging. The Grundfos S-tube impeller meets and surpasses all these challenges.

Furthermore, we have tested the S-tube in the field in many hundreds of wastewater installations worldwide prior to release with very good results. What our customers experienced was substantially lower noise and vibration levels, reduced maintenance, and far better non-clogging capabilities than ever experienced previously.



At Grundfos, we do not compromise in our wastewater product development. Our dedication to improving hydraulic, electrical and mechanical efficiencies is made possible by our focus on the technology areas that resolve very real issues for our customers.

Read more about  NO COMPROMISE


Our commitment is to introduce breakthrough technologies to the market - S-tube is one of them.

Read more about our other technologies here:





- between high efficiency and free passage.


Read more here

A history of wastewater

Traditionally, wastewater pump owners have faced a trade-off between larger free passage and high hydraulic efficiency. If optimised for free passage for trouble-free operation, the efficiency of the pumps has had to be compromised. Or if optimised for efficiency to lower energy consumption, it has been necessary to narrow the free passage in the pump hydraulics.

Many attempts have been made to increase the reliability level of wastewater pumps, some more successful than others. Various kinds of impellers have been developed over the years, such as vortex, semi-open to single- and multi-channel impellers, and other more sophisticated creations.

Furthermore, these pumps have often been fitted with advanced and costly add-on assemblies that in a static or an adaptive way are designed to lead, cut or treat the wastewater as it passes through the pump. To this we can add the fact that the very nature of wastewater is challenging, with dry solids content varying over time. Water use has not remained static either.

All of these hydraulic layouts have been designed in good faith – but have they resolved the fundamental trade-off facing pump owners?

The answer must be ‘no’. With the S-tube impeller we have resolved these issues:

  • We have resolved sealing issues:
    The unique and patented sealing system provides the highest possible reliability, as the hydraulic parts are kept clean during operation.


  • We keep vibration levels as low as possible:
    A new and unique static and dynamic balancing of S-tube impellers provides the lowest possible vibration level. Compared to earlier pump generations, the vibrations are now reduced to less than half. This means less noise and longer lifetime for bearings and shaft seals, helping reduce maintenance costs.


  • Abrasive wear is considerably lower:
    The smooth design of the S-tube impeller with no sharp edges and bends gives the most optimised flow and the lowest abrasive wear.


  • Non-clogging capabilities:
    The large free passage combined with the smooth design of the channel in the S-tube impeller ensures clogging-free operation in the most demanding applications.


With hydraulic efficiency up to 84% and spherical free passage up to 160mm for small and medium sized pumps, the S-tube is rewriting the history of wastewater!

SE & SL wastewater pumps

The SE and SL ranges of wastewater pumps with S-tube provide the highest total efficiency currently available.

Read more about the SE & SL wastewater range here

View Grundfos pumps with S-tube

SL 0.9 -11 kW wastewater pumps

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SL wastewater pumps

The SL range is created to optimise performance in your system; minimising known risk factors and reducing maintenance requirements. Remarkably durable, the SL range offers long lasting, service-friendly submersible wastewater pumping.

SL 1.1-11 kW wastewater pumps

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SE wastewater pumps

The SE range of pumps is built for years of trouble-free operation. The SE range can operate submerged or dry-installed without motor cooling, and is extremely reliable and very easy to service.

Breakthrough technologies to the water utility market

At Grundfos, our commitment is to introduce breakthrough technologies, raising the bar and setting new standards for water utility pump systems and solutions.


More about Grundfos SMARTDESIGN


Grundfos SMARTDESIGN represents the best from Grundfos within functionality and usability and is part of how we set the standard.


More about Grundfos iSOLUTIONS


Grundfos iSOLUTIONS is a holistic systems approach and part of how we set the standard for optimal performance, total energy efficiency, and ultimate reliability.

Technical Articles

Click on the technical articles below to read why it is important to ensure free passage and optimum efficiency to maintain low Lifecycle Costs and high reliability.



How Grundfos talk lifecycle costs for wastewater pumps

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Lifecycle costs for wastewater pumps

Lifecycle cost calculations in wastewater installations can realise huge savings over time for the wastewater company. The lifecycle costs summarise the total cost of a wastewater installation – and in this regard the pump system plays a major role.

How greater free passage ensures reliability and lower LCC

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Reliability and lower LCC

A reliable pump operation is a must when dealing with wastewater and this reliability must remain at the same level year-by-year.

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