KRAL - Three screw pump (W Series)
The KRAL W-series coolant pump is designed for fluids that damage conventional pumps: water-miscible lubricating and cooling fluids, cutting emulsions and lubricants, and contaminated media containing abrasive particles. Manufacturer: KRAL, Austria. The challenge here lies not in viscosity, but in the combination of low viscosity with high pressure and solid particles — this is precisely what the W series screw pump pair is designed for.
For which liquids is the W series designed?
The manufacturer describes the scope of application as ‘complex fluids’: low-viscosity fluids that need to be delivered under high pressure and which contain abrasive particles. A typical example is the coolant circuit on a machine tool: the fluid is diluted with water, its viscosity is close to one, and swarf dust is present in the flow.
A standard three-screw pump quickly loses its clearance in such an environment. In the W series, the screws are made of nitrided steel and fitted almost tightly, whilst the housing is available with a polymer coating — this ensures a long service life even where viscosity is insufficient to maintain a hydraulic film.
On the principle of operation of a screw pair — how a screw pair works.
Technical specifications of the KRAL W Series
| Size | Qth flow rate (1450 min⁻¹, 0 bar) |
|---|---|
| 15-26 | 15–26 l/min |
| 32-54 | 32–54 l/min |
| 55-85 | 55–85 l/min |
| 105-118 | 105–118 litres per minute |
Parameters common to a number of items:
| Parameter | Value |
|---|---|
| Type | three-screw pump |
| Pressure at the discharge flange | up to 120 bar |
| Pressure at the suction flange | up to 6 bar |
| Minimum viscosity | 1.0 mm²/s |
| Maximum viscosity | 10,000 mm²/s |
| Housing material | high-strength EN-GJS-400 cast iron, with a polymer coating, or other materials to order |
| Screws | nitrided steel |
The manufacturer’s specifications cover a wider range of sizes — from W 15 to W 275. Sizes outside these four ranges are available to order on a case-by-case basis.
The seal determines the operating temperature
In the W series, the temperature depends not on the housing but on the type of seal. This is the key factor in choosing a model.
| Gaskets | Max. fluid temperature |
|---|---|
| Cuff-type, NBR | 90 °C |
| Cuff-type, FKM | 150 °C |
| Standard end-face | 150 °C |
| End-face made from hard materials | 180 °C |
| Magnetic clutch | 300 °C |
For the mechanical seal, the manufacturer’s instructions specify 80 °C instead of 90 °C. This difference should be taken into account when performing calculations at the limits of the range.
The polymer-coated casing has its own temperature limit — up to 60 °C, according to the manufacturer’s instructions.
Where are W-series pumps used?
- coolant supply in the circuits of metal-cutting machine tools
- cutting emulsions and high-pressure lubricants
- systems with tool-fed delivery, where pressure is required at low viscosity
- contaminated liquids containing abrasive residues and metal swarf
- contours where the fluid has no inherent lubricating properties
If the environment is clean and requires lubrication, the manufacturer’s range includes more cost-effective solutions — KRAL K Series for general-purpose tasks and KRAL G Series for lubrication systems in rotating machinery.
Certificates
The manufacturer’s documentation for the series refers to Directives 2006/42/EC, 2014/68/EU, 2014/30/EU, 2014/35/EU and 2014/34/EU (ATEX). The manufacturer’s list of documents includes separate ATEX annexes for the series. The specific set is confirmed upon order.
A full list of models in the W series is available on the manufacturer’s website KRAL.
Selection and service from Steiner Ukraine
The W-series pump is selected based on the purity of the fluid and the type of seal: first, the composition of the medium, the presence of abrasives and the operating temperature are determined, and the type of seal – sleeve, mechanical or magnetic coupling – is then selected accordingly. Next come the model and size based on flow rate, pressure and casing material. We calculate the operating conditions for the existing circuit and ensure service and spare parts. Steiner Ukraine has been operating in the industrial equipment market since 2006.
