Hidrostal – axial pump – column and vertical turbine pump for high water flow rates (Axial Diffuser)
The Hidrostal axial-flow pump is an axial-flow pump designed for pumping large volumes of water at a low head. The Axial Diffuser Pumps group comprises two designs: the axial column pump and the vertical turbine pump. The manufacturer is Hidrostal Holding AG, Neunkirch, Switzerland. General information about the technology and the company can be found on the brand page Hidrostal.
What is a Hidrostal axial pump and how is it designed?
The axial column pump uses the same screw-centrifugal impeller as Hidrostal volute pumps, but the volute casing is replaced by an axial-discharge casing. As a result, the pump is installed in a vertical pipe or concrete chamber rather than on a foundation with a side discharge pipe.
The unit is assembled on the basis of the standard range of Hidrostal submersible motors. The motor is cooled by the pumped liquid.
The head characteristic is steep and stable, and the power consumption curve is flat across the entire operating range. Because of this, the motor does not overload when the operating mode changes.
The single-channel screw-centrifugal impeller provides a large free passage, meaning the hydraulics are largely resistant to clogging. This same passage makes the pump suitable for fish-friendly pumping.
What are the technical specifications of the Hidrostal axial pump?
| Parameter | Value |
|---|---|
| Capacity | 6–1500 l/s (21.6–5400 m³/h) |
| Pressure | up to 20 m |
| Diameter of the tube chamber | 400–1500 mm (16–60 inches) |
| Shaft power | 1.5–250 kW |
| Shaft speed | 375–1500 rpm |
| Power supply | 50 Hz, 60 Hz or frequency inverter |
| Hydraulic efficiency | over 82% |
| Shaft seal | dual mechanical seal, tandem, with barrier fluid |
| Impeller | mixed-flow, axial direction of flow |
| Pump materials | cast iron, spheroidal graphite cast iron, Hidrohard, stainless steel, duplex steel |
| Engine materials | cast iron, stainless steel, duplex steel |
The introductory description on the manufacturer's website gives a narrower range: a head of up to 15 m and a flow rate of 30–1400 l/s. The specification and brochure provide 6–1500 l/s and up to 20 m. The operating point for a specific project is confirmed by the manufacturer during selection.
For duties exceeding 1500 l/s, the Hidrostal Group offers submersible axial flow pumps from its sister company, Bedford Pumps, with capacities up to 10,000 l/s (36,000 m³/h).
How does a vertical turbine pump differ from a column pump?
A vertical turbine pump is a mixed-flow centrifugal pump. The manufacturer does not describe it as a screw-centrifugal pump: this is a different hydraulic design, intended for a different range.
It is used when the water level is below the operating limits of a volute centrifugal pump — for example, from a borehole or a deep reservoir. The vertical layout takes up little floor space.
Priming issues do not arise: the impellers are submerged in the liquid. The first impeller can be lowered further by increasing the sump depth, thereby providing the required NPSH margin.
The multi-stage design yields a higher efficiency at conditions with a high head and lower flow rate. The modular construction allows the pump to be adapted to a specific application. Numerical ranges of flow rate and head for this execution are not provided by the manufacturer on the product page — they are determined during selection.
Where is the Hidrostal axial pump used?
The manufacturer lists seven typical tasks for an axial column pump:
- storm and flood water pumping stations
- irrigation and drainage systems;
- gentle return activated sludge pumping;
- pumping of oily water with reduced emulsification;
- coastal protection and flood protection;
- water level regulation;
- fish-protecting drainage of storm and flood water
The manufacturer positions vertical turbine pumps for most water supply and drainage applications, in particular where water is drawn from a borehole or reservoir.
How is a pump installed in a pipe chamber?
The pump is lowered into a vertical pipe chamber, where it rests on a horizontal support surface. Sealing to the sump is provided by an elastomeric ring supplied with the pump, which is pressed down by the unit's own weight.
The same mass secures the pump to the counter-flange of the pipe chamber. Additionally, the pump features a mechanical anti-rotation device.
The manufacturer cites the small footprint, simple construction, tube-sheet sealing and low installation cost as the advantages of this solution.
What materials and control measures are available?
The flow path is made of cast iron, ductile iron, Hidrohard alloy, stainless or duplex steel. The motor housing is made of cast iron, stainless or duplex steel. The wear cone is replaceable, and optionally adjustable.
Available controls:
- built-in motor winding temperature breakers
- conductive sensor and float switch for seal leakage detection;
- bearing temperature sensors
- screened cables for electromagnetic compatibility (option).
Frequently Asked Questions
What is the maximum flow rate of the Hidrostal axial pump?
1500 l/s (5400 m³/h) for an axial column pump. For higher flow rates, the Hidrostal group offers Bedford Pumps submersible axial pumps — up to 10,000 l/s.
What head does an axial pump deliver?
Up to 20 m according to the manufacturer's specification. It is a low-pressure machine: it is chosen for large volumes, not for delivery head.
What is the efficiency?
Over 82%, according to the manufacturer’s brochure, for an axial column pump.
Can return activated sludge be pumped?
Right. Delicate pumping of return activated sludge is specified by the manufacturer among typical duties. The single-channel screw-centrifugal hydraulics causes little damage to sludge flocs.
Is the pump suitable for fish protection stations?
Fish-friendly drainage of stormwater and floodwaters is listed by the manufacturer among the applications. The reason for this is the large free passage of the wheel.
What diameter of tube chamber is required?
From 400 to 1500 mm (16–60 inches) depending on the model size.
Does the engine get overloaded when changing modes?
The manufacturer specifies a flat power consumption curve across the entire operating range, so motor overload does not occur.
What is needed for the selection?
Design flow rate, geodetic delivery head, medium characteristics (stormwater, drainage, activated sludge, oily water), diameter of the existing pipe chamber or the possibility of its installation, material requirements, power supply method (direct or via frequency converter).
