When it comes to backfilling mines with paste, transporting the paste material from the surface plant down into the stopes is critical. The reliability of this transport network, known as the underground distribution system (UDS), directly impacts mining schedules, binder consumption, and ultimately, operating costs.
A key part of this system is the paste pump. For many operations, the location of the paste plant and orebody geometry means gravity flow isn’t enough; a pump is needed to provide the necessary driving head to push high-density paste through the UDS.
The Challenge: Transients in Paste Backfill Pipelines
Positive displacement (PD) pumps are commonly selected, but their performance — especially how they handle transient conditions — has a major effect on both the design and long-term reliability of the UDS.
Because PD pumps operate with reciprocating pistons, the discharge flow rate naturally fluctuates. Each piston stroke introduces a small but rapid change in velocity, which generates transient pressures (or “water hammer”) in the pipeline.
These surges matter because they:
- Increase cyclic loads on pipelines and supports
- Accelerate fatigue and risk of coupling failures
- Influence paste quality by forcing operators to dilute mixes or increase binder
- Raise capital costs if higher pressure rated pipes and stronger anchors are required
Most PD pumps are equipped with pulsation dampeners designed to smooth these fluctuations. However, not all dampening systems perform equally well. Poor dampening can leave a UDS exposed to significant transient pressures.
Modelling Transient Effects
To quantify these effects, Paterson & Cooke engineers used transient flow modelling software to simulate a typical backfill pipeline system:
- Pipeline length: ~2.75 km
- Pipe size: DN200 (8 inch)
- Pump duty point: 100 m³/h at 7,500 kPa
- Paste properties: 76% solids, 280 Pa yield stress, 2.8% binder
This provided a basis to compare different PD pump types:
- Hydraulic piston pumps (the most common choice for paste backfill)
- Two-cylinder, single acting design
- Pre-charging reduces pressure differences during piston switchover
- Flow curves vary depending on vendor and dampening system
- Piston diaphragm pumps
- Use diaphragms to separate hydraulic oil from paste
- Flow is generated by multiple pistons working out-of-phase
External dampeners (air vessels or accumulators) are often included.
Positive displacement pumps. (a) Hydraulic piston pump (complete with poppet valves) (Vlot & Keijers 2018); (b) Piston diaphragm pump (Abel Pump Technology)
What the Analysis Showed
The simulations highlighted several important findings:
- Pump selection strongly influences transients
Although each pump was rated for the same flow and pressure, the resulting transient pressures varied significantly. One hydraulic piston pump option required an additional 180 m of extra head in the pipe pressure rating to withstand surges — driving up pipeline costs. - Diaphragm pumps produce lower forces
Even without a functioning dampener, a piston diaphragm pump generated lower transient forces compared to some hydraulic piston pumps, because velocity changes occurred over a longer duration. - Cyclic loading is a hidden risk
Many backfill systems are designed to handle occasional transients (e.g., from pump trips or valve closures), but not constant cyclic loading from poor dampening. Over time, this can cause fatigue failures in couplings and anchors (as seen in real-world failures). - High-quality measurement is essential
To correctly evaluate pump performance, pressure must be measured with high-speed transducers (1 kHz or faster). Low-resolution data acquisition smooths out surges, leading to incorrect conclusions about dampening effectiveness.
Why Paste Pumps Matter for Design and Operations
For engineers designing or operating backfill systems, the choice of a paste pump has far-reaching consequences:
- Safety: Preventing pipeline failures caused by transient surges protects personnel underground
- Cost: Poor dampening increases binder consumption and requires more robust (expensive) pipelines
- Quality: Diluting paste to manage pressures reduces stope fill strength, impacting geotechnical performance
- Reliability: Avoiding cyclic fatigue ensures longer pipeline life and fewer unplanned shutdowns
Takeaway
Pump performance is not just about meeting flow and pressure specifications. How a pump manages transient pressures can fundamentally change the design requirements, operating costs, and long-term safety of a paste backfill system.
By carefully considering pump type, dampening system, and measured transient data, engineers can design UDS pipelines that are safer, more cost-effective, and capable of delivering paste at the quality required by the mine.
Paterson & Cooke is a leader in the design, execution, and ongoing management and support of mine backfill systems. Find out more about how we can support your backfill challenges.
MSc Engineering (Chem) cum laude, Bachelor of Engineering (Chem)
Leslie joined our team in 2008 and leads Paterson & Cooke’s Global Backfill Group. He specialises in the design and implementation of paste backfill plants and underground reticulation systems, with extensive project experience in Africa and the Americas.