Operational tips to reduce your total cost of ownership in slurry pumping

Q: Is MD a new pump?

DA: Yes and no. The first Metso MDs were launched in 2015 in smaller and medium sizes. Since then, the company has periodically added additional sizes, including up to size 900 which was launched in 2022. We now have over 260 global installations, making it one of the latest and most modern mill pump developments in the market compared to other manufacturers. Its recent development allowed Metso to learn from our customers what would be the most optimal pump for their operation and what kind of maintenance features it has. See the below customer success stories that justify our proven design.

Q: How does Metso's full process flowsheet offering enable it to provide pumping solutions that fit not only the required material flow properties but also the processes that occur upstream and downstream of these pumps?

DA: We do boast a broad portfolio, which gives us the ability to analyze the entire project with a one-stop-shop approach. In this regard, we can size the pumps not only for the cyclones (and if the cyclones are Metso, we can source them as well), and we can make sure they are at the optimum level from the cyclone float selection to the pump selection to the ancillary equipment selection, all the way down the stream.

The advantage of using a single supplier is that it eliminates safety factors. When you go through different suppliers, each one applies a safety factor of their recommendation. Those safety factors add up, and you might end up with a situation where your cyclones are too big for your mill pump or your mill pump is too big for your cyclones. This kind of mismatch can easily be avoided by using Metso as your partner for the whole process.

Q: Why adjust the mill pump?

TO: Simple answer: It’s about wear and uniformity of wear. When referring to adjusting a slurry pump, you’re closing the gap between the rotating part (the impeller) and the stationary part on the suction side (the inlet liner). The gap is set at the optimum level by the manufacturer to achieve the highest efficiency and the least amount of recirculation within the pump. When fluid enters the eye of an impeller, it is pushed out by the vanes into the casing, and that’s where it pressurizes. So, the pressure is very low at the inlet of the impeller, and very high at the exit of the vanes into the casing.

We all know that everything flows from high to low pressure, so you have this connecting path in front of the impeller from the high pressure of casing to the low pressure of the inlet pipe. That path becomes the pathway of least resistance for slurry to recirculate. That eats away at the front face of the inlet liner and the impeller, thus causing extensive wear. Usually, the casing is not generally the weak link (if it is then there are other issues), but generally you run into situations where the impeller or the inlet liner is wearing out really fast. Closing this gap and maintaining it in the optimal range over the pump’s operational life is critical to longer uptime.

Q: Can mechanical seals be used?

DA: Mechanical seals need a clean environment, which is challenging in class 4 mill pumps. While some sites have tried double mechanical seals and class 4 applications with limited success, traditional stuffing box arrangements or throat bush arrangements are still the proven norm. The throat bush feature in Metso’s  EnviroSet™ channels a certain direction of flow, flushing out particles and keeping the area clean.

In my opinion, mechanical seals are not as prevalent nowadays in class 4 mill duty applications. Cost is another big factor to consider, with double seals being expensive and bigger pumps requiring custom sizes.

Q: Does Metso do retrofitting jobs for other brand pumps by replacing with a Metso impeller and liner?

TO: No, Metso does not do component-level replacements due to proprietary ownership and designs.

Q: Typically, how long does it take to change out a mill pump?

TO: Depending on the size and the expertise in the field, timing could vary. As a general rule, we normally estimate 8 hours for complete change out.

Q: How much safety factor on motor power is generally recommended?

DA: In the application, we recommend a minimum 20% safety factor on the maximum duty.

Q: Can we use expeller seals in mill duty pumps?

DA: Yes, when it comes to a medium sized pump (up to 400 size inlet). However, while there have been successful cases in South America for medium sizes, practicality and trade-offs on efficiency may come into play for larger pumps.

Q: How do you see MD technology advancing over the next 10 years?

DA: In the future, I hope to see digital and sensor technology integrating more with pumps. Having the ability to predict failure points using collected data and applicability of the data to the pump's performance could be established. It would also be great for pumps to optimize without user input, such as adjusting internal clearances, which could be automated. Who knows – one day, a pump could just sit there and operate with least amount of human attention and maintenance – just turn it on, and it lets you know when it’s time for component changeout.

I see it going towards that direction, but for now, the focus is on increasing efficiencies, wear life, and matching maintenance cycles to mill times to ensure the pump is not the bottleneck in the process.

Q: Why do we need process data? Can we estimate or does it need to be accurate?

DA: Process data is basically like a fingerprint. That’s where you’ve been, where the system has been, and where the concentrator has been working over a period of time. The longer the data, and the more accurate the data, the better average we can get. If we can consistently see the bandwidth which the pump is fluctuating during operation, this allows us to select the best pump for the duty based on its efficiency, inlet velocities and proximity to the Best Efficiency Point (BEP). Ultimately, this will result in increased uptime.

Uniform wear is very important. As an operator, you’ll have lesser headaches, and you won’t have to change your parts too often. With implementing process data monitoring, your pump could be so optimum that flows within it are so streamlined that they wear in a uniformed fashion, and you’ll no longer have localized high depth wear and eventual pre-mature failure.

Q: What would you consider best practice to ensure Metso MD Series pumps maintain performance over the full life cycle of the product?

TO: This comes down to maintenance and upkeep. I strongly suggest adjusting your pump periodically as often as permissible, as it’s been proven that when you keep your internal clearance to the recommended level – between the impeller and the inlet liner – you maintain a reduced wear-rate, thus increasing your equipment life. Especially if you’re experiencing wear on the front side or the inlet side of the pump.

Metso also provides Life Cycle Services for pumps, for more simplicity, predictability, availability and overall maximum pump life. Rather than looking at each part individually, you should consider a complete solution for the entire process. This is where Metso comes in. We are here to support you with pre-packaged and custom programs.