Slurry Pump Selection & Reliability in Tailings Service

Understanding failure modes and keeping pumps running in high-solids applications.

Nicholas Guenther | Hevvy Pumps

Anyone who has spent any time around a tailings pond already knows the textbook numbers can only get them part of the way there. Specific gravity, particle size distribution, pH—all of it is necessary information, but the knowledge alone is not sufficient for proper reliability. What actually determines whether a pump station runs for three years or three months usually comes down to a handful of decisions made before the pump ever gets bolted down, and a handful of habits practiced (or skipped) after it is running.

This article presents a rundown of the questions worth asking first, the failure modes that recur across different sites and industries and what has actually worked in the field to improve uptime in high-solids service.

| IMAGE 1: Double-suction lineshaft design built as a direct drop-in replacement (Images courtesy of Hevvy Pumps)

Submersible vs. Lineshaft: It Is Rarely the Configuration’s Fault

This question comes up constantly, usually after someone has had a bad experience with one or the other. Both configurations have a legitimate, and often overlapping, place in tailings service.

Lineshaft pumps—which are vertical-style units with the motor mounted above the baseplate, a shaft extending through a column/support structure to the wet end and a shaft support (bearing/bushing) near the wet end—do offer a key advantage: The motor remains dry and accessible. Maintenance personnel can monitor bearings, check alignment and detect early warning signs without requiring a crane. However, unlike cantilever pumps, which have no submerged bearings or seals with shorter setting lengths, lineshaft pumps can be maintenance-heavy, particularly when multiple shaft designs or long setting lengths open up a variety of resonance and tolerancing-related failures.

Submersible pumps eliminate multiple shafts and line bearings, as the sealed motor is positioned at the bottom with the pump end. This design removes many vibration, alignment and tolerance issues and accommodates fluctuating pond levels without the need to adjust column length. However, a motor or seal failure requires removing the entire unit, typically with a crane or hoist, and this eliminates above-deck inspection access.

Where submersibles sometimes get a bad reputation is a specific, well-understood failure mode: units left idle and submerged for extended periods—common in standby or emergency containment service where operators are unsure what to do with the pump during shutdown periods—where solids settle and compact around the impeller and casing.

On reactivation, that compacted, sometimes partially hardened material causes real mechanical stress via partial impeller blockage, seal damage and bearing seizure. This exact sequence played out in an emergency containment pond application at high elevation handling fine, high-density tailings classified as a Class 3 (silica-type abrasive). The pumps were not failing because they were submersible; they were failing due to poor operating practices and because nothing was addressing what happens to fine solids during long idle periods underwater.

The fix was not a different pump type. It was a mechanical hoist to periodically lift the units clear of the slurry when not running, a jet ring system tied into the process water line to resuspend settled solids ahead of every startup and retrained startup protocols for site personnel to properly dredge the settled solids. After the retrofit, the installation went from roughly 74% pump availability to 97%, with mean time between failures exceeding 18 months and no further seal failures. That is an argument for engineering the whole system, including startup behavior, partial dredging operations and how the slurry actually behaves when the pump is not moving.

Where this really comes together is when agitation is designed into the pump itself rather than bolted on afterward as a retrofit. An integrated agitator at the intake of the pump keeps solids in suspension continuously, so the pump is not relying on a separate jet system to undo settling before every start. It is a good example of why “submersible vs. lineshaft” is often the wrong first question. The more useful one for tailings transfer ponds/sumps could be how the solids behave at that specific site and system setup, including during downtime, and whether the pump is equipped to handle it. Here are some factors to consider when selecting a slurry pump for an application:

Pond/sump geometry and depth: Submersibles generally handle fluctuating levels well since they can be hoisted up and down dynamically during operation while providing dredging action of any settled solids.
Standby vs. continuous duty: If a unit sits idle and submerged for long stretches, handling the settling solids (agitation, dredging, sealing) matters more than pump type.
Access for maintenance: Crane/hoist availability
Redundancy strategy: Sites with a proper redundancy A/B operation with a spare ready can tolerate more downtime, therefore being more aggressive on pumping the solids, than single-pump critical applications.
System design: Recirculation, agitation, sump wall slope, hoisting, inlet location, pump location, debris and trash potential
Application details: Total dynamic head (TDH), flow, slurry rheology, system curve, liquid levels, upset conditions and temperature

Solids concentration is not always steady, and debris is not always accounted for. For example, one installation handles spillage from a pelletizing conveyor. Cast iron pellets and wash water are collected into a sump, with concentration varying depending on how much material was shoveled or washed in on a given shift, plus occasional rags and debris.

The pump spec that worked there was not just about the pellets themselves; it was about a high-chrome wet end sized for a swinging concentration range, paired with a suction design tolerant of intermittent debris. A spec built only around the “typical” concentration would have been underbuilt.

| IMAGE 2: Submersible slurry pump

| IMAGE 3: High chrome submersible slurry pump with cooling jacket at a mining beneficiation plant

| IMAGE 4: Submersible pump on a hoist system at a Peruvian mine

Reducing Downtime in High-Solids Systems

Selection provides a pump matched to the job. Keeping it running is a separate discipline, and it is usually where the bigger gains are sitting unclaimed.

Condition monitoring beats calendar-based maintenance. Wear rate in high-solids service is rarely linear enough for a fixed replacement schedule to be efficient. Vibration monitoring and, where practical, wear-sensing pickups embedded in liners give an actual trend line instead of a guess. Logging discharge pressure and flow against motor amperage at regular intervals will flag wear-driven efficiency loss well before a failure.

Maintaining standby capacity is more cost-effective than experiencing unplanned outages. Single-pump critical paths in tailings/emergency systems are too common. Implementing an A/B + 1 configuration, even with a basic automatic changeover, turns a pump failure into a routine maintenance task rather than a production stoppage.

What happens during idle periods matters as much as what happens while running. As the emergency containment example above shows, a pump sitting idle underwater is not a neutral state—settling, compaction and startup torque spikes are a real and predictable failure path. Building resuspension and lift-out into standard operating procedure, not just using them as an emergency fix, prevents the problem rather than reacting to it.

Suction conditions cause more failures than people expect. Cavitation and air entrainment from poor sump design, inadequate submergence, settling solids or vortexing at the intake accelerate wear and can cause mechanical failure well before a pump’s expected service life. A pump that looks undersized on paper is sometimes actually failing because of sump/pond geometry, system design and operation practices, not just pump selection.

Spare parts strategy should match actual wear data. Sites that track their own wear rates and stock liners, impellers and seals based on that data—rather than a generic recommended spares list—consistently see shorter unplanned downtime, because the part that fails first is the one sitting on the shelf.

The Custom Approach

Problematic applications are solved by treating each one as its own engineering problem—field slurry data, duty cycle, data trending, idle behavior and a little bit of care—rather than defaulting to a standard spec sheet. The pumps that run longest in tailings service are the ones where selection, materials and maintenance practices were all matched to the actual slurry and operating pattern, not the typical specification copied and pasted throughout the industry.

Nicholas Guenther is managing director of engineering, P.Eng., at Hevvy Pumps. He has spent 20-plus years in slurry pump engineering, working on installations across diverse industries worldwide, from tailings to oil and gas. Colleagues refer to him as the Yoda of slurry pump technology and best practices. For more information, visit hevvypumps.com.

In This Issue

Cover Series Wastewater