KRAL - Triple screw pump (C Series)
The KRAL C-series high-pressure pump is a self-priming triple-screw pump designed for pressures up to 100 bar. Manufacturer: KRAL, Austria. The series is divided into three sub-series: CK for simple applications with easy installation, CL for stable operation at high pressure, and CG with the widest viscosity range — up to 1,000,000 mm²/s.
What are the differences between the CK, CL and CG sub-series?
CK — a basic high-pressure version for various media, designed for easy installation. A pressure rating of 100 bar is available for the smallest size; for sizes ranging from 15–26 to 370–450, the pressure rating is 70 bar, whilst for the largest sizes (550–880), it is 40 bar.
CL — Designed for consistently high pressure: 100 bar across the entire range, except for the two largest sizes, where the limit is 80 bar. A full range of seals is available, including a magnetic coupling.
CG — the most flexible solution. The same pressure of 100 bar, but with a flow rate of up to 3,550 l/min and a viscosity of up to 1,000,000 mm²/s. This is the solution for very viscous fluids, which other triple-screw series cannot handle.
On the principle of operation of a screw pair — how a screw pair works.
Technical specifications by sub-series
| Parameter | CK | CL | CG |
|---|---|---|---|
| Qth flow rate (1450 min⁻¹, 0 bar) | 5–880 l/min | 5–880 l/min | 15–3,550 l/min |
| Max. discharge pressure | 100 bar (5–10) · 70 bar · 40 bar (550–880) | 100 bar · 80 bar (the two highest) | 100 bar |
| Maximum viscosity | 10,000 mm²/s | 10,000 mm²/s | 1,000,000 mm²/s |
| Temperature, cuff seal | 90 / 150 °C | 150 °C | 150 °C |
| Temperature, standard end face | — | 150 °C | — |
| Temperature, end-face of solid materials | — | 180 °C | 180 °C |
| Temperature, magnetic clutch | — | 300 °C | 300 °C |
| Max. inlet pressure, gauge pressure | 10 bar | 10 bar | 10 bar |
| Max. inlet pressure, end face | — | 30 bar | 30 bar |
| Max. inlet pressure, magnetic coupling | — | 16 bar | 100 bar |
The minimum viscosity for CK is 1.1 mm²/s; for the largest size, it is 1.4 mm²/s according to the series data sheet; the manufacturer’s brochure specifies 1.5 cSt. When calculating at the limits of the range, it is advisable to use the higher value.
Common to the series:
| Parameter | Value |
|---|---|
| Type | three-phase, self-priming |
| Housing material | spheroidal graphite cast iron, steel or aluminium |
| Screws | nitrided steel |
| Temperature range | −20…180 °C · up to 300 °C with a magnetic coupling |
What are the benefits of choosing a seal from the C series?
The C series is available in four variants: lip seal, standard face seal, face seal made from hard materials, magnetic clutch and gland packing.
This choice affects not only the temperature but also the permissible pressure at the suction flange — and this is often a decisive factor when operating against a head. A mechanical seal provides 10 bar at the inlet, a face seal 30 bar, and a magnetic coupling in the CG model 100 bar. For circuits with high supply pressure, this is the determining factor in the choice.
Certificates and explosion protection
Classification societies: ABS, BV, CCS, DNV, GL, LRS, MRS, NK, RINA, KR.
Explosion protection: ATEX II 2 GD b/c, Group II, Category 2.
The manufacturer’s brochure also refers to API 676, 614, 682 and 685, and EN 13445 — the specific set is confirmed upon request.
A full list of models in the series can be found on the manufacturer’s website KRAL.
Where are C-series pumps used?
The manufacturer lists the uses specifically as follows:
- injection pumps
- feed pumps
- fuel supply pumps for burners
- hydraulic lift system pumps
- transformer oil purification pumps
- hydraulic pumps
And, in general, any application where a reliable high-pressure pump for lubricants is required.
If the pressure does not exceed 25 bar and the application involves the lubrication system of a rotating machine, the more economical solution is KRAL G Series. For medium pressure at low flow rates — KRAL L Series.
Selection and service from Steiner Ukraine
The C series is selected based on the pressure on both sides: the required discharge pressure and the pressure already present at the inlet. The former determines the sub-series and size, whilst the latter determines the seal type, as it is this that limits the back pressure on the suction side. Next come the viscosity at operating temperature and the casing material. We calculate the operating conditions for the given system and ensure service and spare parts. Steiner Ukraine has been operating in the industrial equipment market since 2006.
