In remote locations requiring a portable power supply, the decision is usually between pneumatic and hydraulic pumps.
In remote locations requiring a portable power supply, the decision is usually between pneumatic and hydraulic pumps.
Weda electric submersible pumps are designed to perform dewatering tasks efficiently.
Weda electric submersible pumps are designed to perform dewatering tasks efficiently.
Submersible pumps use the proximity and pressure of the surrounding water to aid fluid movement through the hose, so less energy is needed.
Submersible pumps use the proximity and pressure of the surrounding water to aid fluid movement through the hose, so less energy is needed.

Choosing the right pump for the right job requires some basic knowledge and understanding of the task and situation in hand. This article describes the main factors to be considered when selecting a submersible dewatering pump.

If the suction lift required for dewatering using a surface pump is more than about 7 m, a submersible pump would normally be used instead. Designed to be totally submerged, it uses the proximity and pressure of the surrounding water to aid fluid movement through the hose, so less energy is needed.

As well as clean or dirty water, submersible pumps will handle liquids with high suspended solid loads. They can work continuously at great depths, in harsh environments and even under ice. 

Most are centrifugal pumps, in which the rotation of an impeller creates low pressure at the inlet and draws in the liquid. Pneumatic submersible pumps offer a choice between centrifugal and diaphragm mechanisms. With the pneumatic submersible pumps, the air-driven action of pistons on flexible diaphragms sucks liquid in and then pushes it through the pump.

There are three main categories of submersible dewatering pumps:

• Electric – powered by mains electricity (smaller-capacity pumps may alternatively be supplied by a portable generator)
• Pneumatic – powered by a portable air compressor
• Hydraulic – powered by a portable generator

Here are five key considerations which will help to choose the right submersible dewatering pump for your application:

Why electric?
If mains electricity is available, an ­electric pump will be the best choice in most cases. This is the simplest, most energy-efficient and most economical approach. Electric submersible pumps provide high power in light and compact packages. They are easy to transport, handle, install and operate, with low maintenance requirements and simple servicing procedures further reducing the cost and effort involved.

When dealing with large volumes of liquid, requiring rapid flow rates, electric pumps are really the only option. Their additional advantages include a small footprint, which is perfect for reaching into restricted spaces. Emission-free operation means they are ideal for work in mines and tunnels, while their quiet running is welcome in residential areas.

The main limitation is their reliance on a mains electricity supply, although small models can be run economically from a portable generator. However, as supply networks expand and strengthen to meet increasing demand for clean power, the number of sites without mains electricity is decreasing.

It is worth noting that a fluctuating mains supply can cause problems in some remote areas. Look for a pump whose motor and starter are equipped with inbuilt electrical protection against varying voltage, phase failure and human error.

Why pneumatic?
A pneumatic submersible pump is the obvious choice where an air compressor is already present on site to power drilling equipment. Another important application is in potentially flammable situations, where sparks must be avoided, as the pump itself has no electrical components.

Provided that the pump is well separated from its engine-powered compressor, there is no problem with exhaust emissions and leakage of fuel or oil. This pump category also has the advantage of independence from mains electricity, so it can be used in remote locations.

For general dewatering, choose a centrifugal pneumatic pump. For abrasive, acidic, corrosive or flammable liquids, or higher solid concentrations, select the diaphragm type.

Why hydraulic?
While pneumatic pumps have advantages in specific circumstances, it would not be cost-effective to invest in an air compressor solely to provide pumping on remote sites. Where mains electricity is unavailable, a portable generator and hydraulic pump are the sensible option.

Models with spark-proof hydraulic motors can be chosen if flammable liquids are an issue. If necessary, the hydraulic power pack can be set up at some distance from the pump to minimise atmospheric pollution and avoid fuel or oil leaks in the working area.
Larger hydraulic submersible pumps can be especially useful for dealing with the biggest suspended particles. 

What’s in the water?
The nature of the liquid being pumped has a major bearing on selection of pump types and models. Although they are all described as submersible dewatering pumps, they can be broadly subdivided into the following groups:

• Dewatering or drainage pumps – for clean or dirty water, possibly containing small solids such as sand and clay
• Sludge pumps – for viscous mixtures of liquids and solids, including soft wet mud and by-products of industrial or refining processes
• Slurry pumps – for semi-liquid mixtures, typically loaded with fine particles of materials like manure, cement or coal 

In addition to the liquid’s general composition, as summarised above, the concentration and size of its suspended particles needs to be considered. The largest solids are best handled by slurry pumps. 

Account should also be taken of the liquid’s pH, temperature and chemical content.
The more difficult the liquid, the greater is the need for protection through features such as hardened, clog-free impellers and wear-resistant rubber diffusers. In addition, seek a high-quality, durable construction which is resistant to corrosion and rough treatment. 

Performance needs?
In terms of capacity, the pump’s performance must match the amount of liquid required to be moved and the speed with which that movement is needed. An overly specified model will be unnecessarily expensive, while an under-capacity pump will struggle to do the job and will wear out quickly. It must have enough capacity to cope with fluctuations in water level, versatility may also be needed to deal with the demands of different sites.

The manufacturer’s published pump curve, showing head height against flow rate, is one of the first things to check. Make sure it covers the duty point required.

The prospective pump supplier should be given the following details of the application:
• Flow requirement
• Head requirement
• Sump measurements – including depth   
  and size of opening
• Distance to discharge point
• Discharge hose diameter, length,  
  ­material and connection type
• Duration of pumping operation

Having shortlisted the pumps meeting those criteria, compare information on their electricity or fuel consumption, build quality and maintenance. All of these will affect the ongoing costs.

Conclusion
As long as the pumping site has access to mains electricity, the needs are most likely to be met by an electric submersible pump. The main advantages of this category include simplicity, energy efficiency, low maintenance costs and portability.

In remote locations requiring a portable power supply, the decision is usually between pneumatic and hydraulic pumps. If there is already an air compressor on site, a pneumatic pump makes good sense. It is also a safe, spark-free option in the presence of flammable liquids. Aside from those situations, a hydraulic pump and portable generator will work best. 

There are many more factors to consider when choosing a pump. First there is the nature of the liquid to be pumped, which is often much more than just water. Then there are the physical demands it has to meet, such as the required head and flow. 

Using the five sections above as a checklist, the supplier can be given a detailed description of the pump’s intended application. From that, a specialist can advise on which models are best suited to the job. Do not forget to factor in the energy economy, durability and servicing expense for each pump offered.