w trash pump parts

How to choose a mine dewatering pump

Multiflo®, Warman® and GEHO® dewatering pumps are used across a wide variety of industries and environments.

We explore the key factors that will determine which dewatering pump is right for your needs.

Weir Minerals’ dewatering specialists are there to help you every step of the way as you determine which pump is right for your application.

In this article, we explore the major factors which will influence that decision, starting with the most important questions: What are you pumping and where does it need to go?

Where does it need to go? Understanding your net positive suction head

The available net positive suction head (NPSHa) is the static pressure you have available in a system to force the water into the pump, and will largely determine which model within a style of pump is right for your application.

NPSH can be affected by a number of variables, such as the static differentiation between a pump’s suction and the water level, the length of the suction pipeline and the pump’s elevation above sea level. Other factors including temperature and specific gravity play a role.

Every pump has a minimum NPSH requirement to ensure continuous flow, which depends on its operating duty point – so the net positive suction head available (NPSHa) needs to be compared to the net positive suction head required (NPSHr) to select a dewatering pump.

NPSH a must always be more than NPSH r, typically with a 1-1.5m safety margin to prevent suction cavitation.

Our dewatering specialists can work with you to calculate these values and help determine which pump would be best suited for the application.

What are you pumping? Working with different slurries

The demands on a pump transporting clear liquid are substantially different to those moving slurry or tailings, from both an energy and wear perspective.

Multiflo® models such as the PB and PJ pumps can handle clear, corrosive liquids efficiently. For slurries with high solids content or corrosive properties, GEHO® positive displacement pumps provide reliable, highly efficient long-distance transport. They also last longer than most pumps between maintenance, and combine high availability with a low total cost of ownership.

For higher solids applications requiring a high head, Warman® DWU horizontal dewatering pumps offer robust wear life, and have a number of sealing options to reduce the dilution of the slurry and lower the required flow of gland water. When dealing with clear water, low-flow gland seals are an efficient, low maintenance option for sealing. When dealing with mixed slurry, the Warman® Hi-Seal™ expeller’s large diameter offers excellent performance, while mechanical seals can cope with high pressure environments.

When selecting a replacement pump for an existing project, it’s vital to obtain up-to-date data on the chemical composition of the liquid to be dewatered. Factors like acidity can change significantly over time as the operation moves into different sections of the ore body, and some seemingly minor pH changes can lead to dramatically reduced wear life and potentially an unplanned shutdown.

Are you working underground?

Underground dewatering presents a number of potentially expensive challenges not present on the surface, including the need to lift liquids to significant heights, deal with higher-solids content and contend with strict space limitations.

One of the key decisions facing any underground application is whether to employ a series of pumps to bring liquid up out of the mine (a multi-stage approach), or just lifting via single pump, such as a GEHO® positive displacement pump.

While the upfront cost of acquiring several smaller pumps for a multi-stage approach is usually less than a larger pump which can perform the entire lift, there are a number of factors which can make single lift a more attractive proposition in certain circumstances.

Among these is the need for additional space to host each stage of the operation. In some underground mines, the cost of excavating extra room will overshadow the cost savings of the smaller pumps.

A single long-distance pump requires less maintenance than a series of units and is often more energy efficient, which can translate into a lower total cost of ownership.

When you need a self-priming pump

For many pump operators, manually priming pumps is the most frustrating part of their job. Manually primed pumps require regular, time-consuming adjustment, and the process is prone to failure and can lead to inefficient operation if air isn’t correctly removed from the pump.

While some static dewatering applications can make do with a manually primed pump, more dynamic applications benefit from an automatic vacuum priming system that prevents the pumps from losing prime.

Multiflo® self-priming CF and RF pump models use a “ball float” priming system, which quickly and efficiently lifts water up into the priming tank and ensures it remains primed at all times. It requires no adjustment and operates without a compressor, removing the inefficiencies and hazards of air prime.

When to use submersible pumps

For situations where a feeding sump would be too expensive or physically impractical, Weir Minerals offers submersible dewatering pumps that cater to a variety of sump and pond sizes, throughputs and conditions.

Due to their portability, quick setup time and high availability, submersible pumps are frequently used for a number of temporary applications, either for smaller temporary sumps or as stop-gap solutions until a permanent sump-fed solution can be established.

For submersible applications with high solids content, the all-chrome wet end of Warman® SHW pumps provides long wear life in demanding applications, while the Warman® SJG offers efficient dewatering for clear liquids.

In applications where the pump is at risk of pumping itself out (where the motor must run unsubmerged), a cooling jacket ensures smooth operation by pumping water up into the motor of the pump, preventing it from overheating. This is particularly important where the flow rate can vary without someone to actively adjust the pump rate.

It’s also important to consider the minimum spacing between dewatering pumps, to prevent them from counteracting one another and operating inefficiently. Weir Minerals engineers can provide guidance on the best way to ensure pumps don’t interfere with each other’s operations.

Should you use diesel or electric driven dewatering pumps?

For most applications, electric pumps are preferred over diesel, especially in fixed positions, as they’re simpler to operate and cost effective, as long as the site has reliable power.

Diesel is used mainly in mobile dewatering pumps, such as those operating at the bottom of a mine pit, which require frequent relocation alongside the mine’s sumps as the mine develops.

In these scenarios, a manually primed centrifugal pump would require a very time-consuming exercise each time it was moved. This makes a self-priming pump highly valuable, as time and personnel are already at a premium.

For sites with high electricity costs or limited capacity, our engineering specialists can help you find the most power efficient pumping options that will help drive down total cost of ownership.

No two dewatering projects are the same. Whether you need a small, submersible pump as stop-gap solution for a high-solids slurry or a comprehensive pumping solution to handle a high quantity of clear water, our dewatering specialists have the experience to guide you to the right dewatering pump.