The Impeller

Hidrostal Impeller

The patented single screw centrifugal impeller was invented by Hidrostal’s founder Martin Stähle in 1960. The impeller was originally designed to handle fish and was developed as a means of unloading fresh fish, damage free, from a trawler, therefore guaranteeing the quality and the appearance of the fish for market.

Its gentle handling characteristics combined with exceptionally large free passages led to the Hidrostal pumps being applied to a much wider range of applications. Each pump in the Hidrostal range uses a variation of the impeller to solve specific pumping problems.

The large free passage with excellent solids handling capability is derived from the unique impeller geometry. This makes its ability to pump raw unscreened sewage second to none. The pump is also able to comfortably handle sludges and slurries.

Extremely versatile in its application, the impeller provides efficient handling of a range of liquids, often highly abrasive or corrosive in nature. It is ideal for Solids Handling, Pumping Viscous Sludges and Handling Delicate or Low Shear Products. Unique to all Hidrostal pumps is the ability to handle each of these in combination.

Many applications too arduous for other types of centrifugal pumps can be handled by the Hidrostal screw centrifugal impeller. The impeller comprises a single spiral vane, with large open passages, which makes a long slow turn from the axial inlet to the radial outlet. The design provides optimum hydraulic performance giving:

The Impeller
The Impeller
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Waste Water

Free ball passage has always been the traditional measure of a pumps ability to handle solids without blocking.  Despite recent trends and “innovative” designs, this concept remains the most vital component of a non-clog pump.

A large free ball passage in the impeller will trap less rag or fibre and pass large objects with ease.  The consistency of sewage can be infinitely variable and hard to predict, but free passage will ensure that whether the blockage is hard or soft it will not clog.  

Measuring the proportion of space through which solids can pass, relative to the discharge size of a pump, (referred to as the Free Passage Index) will guide a prospective buyer through the differing range of pumps in the market place.

A Hidrostal hydraulic guarantees the highest average Free Passage Index (FPI) at 0.88 on pumps between 80-200mm discharge size (a totally unimpinged passage would carry an index of 1).   On pumps above 200mm discharge the Hidrostal FPI widens evens further compared to other centrifugal solid handling designs.  Moreover this is coupled with an excellent efficiency of up to 84%.   The only other type of pump which could achieve a similar FPI index is the Vortex design, but this would be at a very poor efficiency.


The Hidrostal family of pumps are ideally suited for all industrial applications; water and wastewater schemes are just the beginning.  

From diesel driven pumpsets for fire-fighting and irrigation, to pumps that can handle the more challenging properties of paint, crystals or oily water.  The low shear, gentle handling characteristics of the impeller are ideally suited to handling liquids where emulsification is not desirable.  

Hidrostal are renowned in their field for designing and delivering innovative solutions for challenging applications and the Hidrostal screw centrifugal impeller with its low shear properties can pass an infinite variety of fluids and materials.


From its successful origins in pumping fish, Hidrostal has diversified on to a wider range of applications that also benefit from the pumps delicate handling properties.

The F type pump from Hidrostal incorporating the unique single vane centrifugal impeller with a shroud are ideal for handling raw produce, offering more versatile piped transfer routes compared to conveyors, elevators or containers.  

The enclosed pipework system has the benefit of being hygienic and cleaner as it is protected from any surrounding potential pollutants. 

In addition to the gentle handling requirements at the start of raw produce processing, the Hidrostal range is also suited to the energy efficient circulation and removal of the washwater used to clean raw produce. This often contains grit, sand, peelings and vegetable lumps. Hidrostal hydraulic parts built from hard materials and with a large free ball passage offer a robust and reliable solution.

Hidrostal Waste Water
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