Centrifugal slurry pumps for severe-duty applications
Developed specifically for pumping abrasive slurries, such as SAG mill discharge, KREBS® millMAX™ centrifugal slurry pumps were the first to feature our proprietary wear ring technology. Tackling the two major challenges of slurry pump operation – mechanical grinding of solids and inefficient flow recirculation – millMAX pumps are now available in high-head and high-pressure applications. In this blog, Roman Van Ommen, Head of Pumps, Valve and Cyclones for Europe, Central Asia, NW Africa explains some of the main factors to consider.
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Setting the slurry pump standard
Slurry pumps must operate reliably in some of the most challenging pump applications. These pumps must not only operate reliably in severe – and often remote – conditions; they must also handle slurries that expose the pumps to high levels of wear. This gives rise to two connected problems:
- Mechanical grinding of solids between the suction liner and impeller
- Flow recirculation back to the suction side impeller eye
These issues shorten pump operating life and increase power consumption – and they progressively worsen in a vicious cycle. Mechanical grinding exacerbates wear, which opens the gap between impeller and suction liner. This increases recirculation and causes the flow and head to drop, which requires the speed of the pump to be increased to maintain performance levels. But this only further increases wear.
Our proprietary wear ring assembly is designed to combat these two challenges. It allows the suction-side gap to be closed when the pump is in operation, restoring performance without needing to speed up the pump.
KREBS millMAX pumps
The first pumps to feature the wear ring assembly were KREBS millMAX centrifugal slurry pumps. The original millMAX range covers a wide range of sizes from 80 x 50mm up to 700 x 650mm. High-head and high-pressure versions are also now available, while the compact millMAX-e slurry pump range offers sizes down to 50 x 40mm and up to 400 x 350mm.
The key advantages of the millMAX pump design are lower power consumption (up to 25% less) and longer wear life. They thus naturally last longer, meaning less plant downtime and lower operating and maintenance costs. The bottom line is a pump that delivers lower cost-per-ton pumped and enhanced cyclone separation.
Features of standard millMAX pumps
- A casing designed to reduce turbulence and minimize wear
- A high-efficiency impeller with high expelling vanes designed to clear large solids and prevent crushing of material inside the pump, as well as to reduce casing slurry pressure at the impeller eye
- A suction liner that matches the full diameter and profile of the impeller for close operating clearance
- A heavy-duty cast iron pedestal with external bearing assembly adjustment mechanism
- Multiple flange options, drilled to suit various pipe requirements
- Reverse-taper roller bearings that increase the effective load span for improved life. The design also ensures grease is discharged to the outside, preventing the ingress of slurry and eliminating the risk of over-greasing
Clearance between both the impeller and backliner and impeller and suction liner is optimised to support pump performance. Between the impeller and backliner, narrow clearance reduces pressure at the gland and assists the centrifugal dry gland seal. Clearance is wider between the impeller and suction liner, which also helps to prevent crushing of solids in the pump, increasing wear life and reducing power consumption.
High-pressure applications: millMAX HP slurry pumps
The millMAX high-pressure (HP) pump line has the same internal design as standard-pressure millMAX pumps but features a tie-bolt design that enables these pumps to handle operating pressures of more than 500 psi. The tie-bolt design also allows ultrasonic casing thickness measurements, which provide operators the ability to predict and schedule maintenance before failure occurs; something that is simply not possible with split-casing designs.
Importantly, due to its smaller cross-sectional area, wear ring adjustment has proven to be as straightforward under high pressures as in standard-pressure applications. Suction-side sealing is thus easily maintained, with the associated benefits of higher pumping efficiency and constant operating speeds at a given discharge heads. This contrasts with traditional designs that rely on full face adjustments – which are nearly impossible, if not unsafe, in high-pressure applications – to maintain suction-side sealing.
High-head applications: millMAX HH slurry pumps
For pumps dealing with high total dynamic heads, radial thrust on the impeller is a particular challenge. Caused by differential pressures within the pump casing when the pump is operating outside of its best efficiency point (BEP), this thrust can cause shaft deflection and premature failure of the bearings and gland seals.
The millMAX high-head (HH) pump solves this challenge with a concentric casing that creates uniform clearance around the impeller and thus delivers even velocity and pressure around the casing, regardless of where the pump is in relation to its BEP. The casing also has a higher-pressure rating to enable the pump to handle high-speed and multi-stage applications.
One example of such operating conditions would be a filter press feed, where pump duties range from low head and high flow to high head and low flow. The millMAX HH would also be well suited to any environment where high heads are needed in one or two-stage pumping systems.
A more compact solution: millMAX-e pumps
Pumping designs often come with space constraints that are not best served by the average heavy-duty, split-case slurry pumps. The answer is the KREBS millMAX-e pump. Like all pumps in the millMAX family, these pumps include the proprietary wear ring assembly – with all the benefits this brings. But they have been optimised to deliver a more compact, lower-CAPEX slurry pump solution.
- An unlined wet end design helps to reduce the total pump weight – and thus the capital and replacement parts costs – as well as allowing easy maintenance
- A hydraulically advanced impeller and overall efficient design allows the motor to be downsized to further minimise costs
- The power frame utilises the same bearing and shaft components as the standard millMAX frames, ensuring the millMAX-e can handle high-speed and -power applications
- Heavy-duty thick outer casings are available in a range of erosion- and corrosion-resistant alloys
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