KRAL - Triple screw pump (G Series)
The KRAL G Series three-screw pump is a compact unit for the lubrication systems of rotating machinery: compressors, gearboxes and turbines. Manufacturer — KRAL, Austria. The series is built on a modular principle: a single frame size covers different connection, sealing and mounting options without any change to the hydraulics.
How a three-screw pump works
The working element consists of a drive screw and two idler screws. They form closed chambers that travel from inlet to outlet at constant volume. Hence the even, virtually pulsation-free delivery, low noise level and absence of any churning of the liquid inside the pump.
Internal hydraulic balancing relieves axial forces, so the bearings operate under gentle conditions. The screws are made of nitrided steel: the surface hardness maintains the working clearance over long service, and the unit's life is determined mainly by oil cleanliness.
More about the operating principle — in the article Features of screw pumps.
KRAL G Series technical specifications
| Parameter | Value |
|---|---|
| Capacity | 5–660 l/min (6 frame sizes) |
| Max. differential pressure | 25 bar |
| Operating viscosity | 10–500 mm²/s |
| Cold start | up to 1200 mm²/s |
| Fluid temperature | −10…+120 °C (mechanical seal) · up to +300 °C (magnetic coupling) |
| Inlet pressure | up to 6 bar (mechanical seal) · up to 16 bar (magnetic coupling) |
| Housing material | high-strength cast iron EN-GJS-400 or steel |
| Screws | nitrided steel |
Versions and options
The casing, suction cover and flange covers rotate in 90° steps, so the inlet can be made axial or radial right at installation.
- Seals: mechanical seal to DIN 24960, cartridge seal to API 682, lip seal or magnetic coupling in hermetic design
- Installation: flanged pump, tank mounting, design to API 676
- Certificates: ABS, BV, DNV, LRS; ATEX version on request
The magnetic coupling removes the limits on temperature and inlet pressure — it is chosen for hot oil and closed circuits where no leakage is permissible. Separate version: KRAL — three-screw pump with magnetic coupling.
Where the G Series three-screw pump is used
- compressor lubrication units
- gearbox lubrication systems
- lubrication circuits of steam and gas turbines
- circulation circuits with mineral and synthetic oils of 10–500 mm²/s viscosity
For other media, higher flow rates and higher pressures the manufacturer's range includes separate series, and a three-screw pump for a specific duty is selected from among them — see all KRAL pumps.
Selection and service from Steiner Ukraine
A pump is selected not by catalogue number but by viscosity at operating temperature, the required differential pressure, NPSH margin and cold start conditions. We calculate the duty point for your existing scheme, agree the seal type and materials, and supply the unit complete with motor and baseplate. Then come commissioning, spare parts and service throughout the whole service life. Steiner Ukraine has been on the industrial equipment market since 2006.
