Dewatering: Selecting the Best Pump for Your Application
While dewatering is a common process in the construction industry, it is an operation that requires careful planning. The right pumping equipment can reduce dewatering time, ensure pump longevity, and minimize construction costs.
Dewatering is a must on many construction sites. Many excavated areas can get filled with excess water due to various reasons including rain, melting ice, or a high water table at the site location. Removing this water is essential for keeping the work area safe and maintaining the structural integrity of the excavation.
Industrial pumps are typically used to carry out dewatering operations; however, all pumps are not created equal. (Read also: Cost-Saving Trenchless Dewatering in Construction Projects) Each pump has functions and features that lend themselves to different applications. Therefore, for best results, it is essential to select the most appropriate pump for the specific job.
In this article, we will take a look at some of the crucial factors you should consider when choosing a dewatering pump for your open cut or trenchless construction site.
Factors to Consider When Selecting a Pump for Your Construction Site
Multiple factors dictate what kind of pump you should use for a particular scenario. Even a specific job site may need different pumps as situations may change over the course of a single project. Some of these factors are discussed below:
Pump size determines the equipment’s maximum processible load. Industrial models start from 1-2 kW and can go up to 10 kW. Continuously running the pump at its maximum capacity might cause mechanical problems and disturb pumping operations.
Therefore, if pumping is expected to continue for an extended period, multiple pumps distributed throughout the site should be considered. This technique, known as parallel pumping, ensures that the equipment remains operational for longer periods.
The flow rate determines the total time the pump will take to finish the job. Selecting a pump with the appropriate flow rate ensures that the site is dewatered in the desired time. This parameter is dependent on the size of the site and the quantity of water to be removed.
In cases where water needs to be removed quickly from larger areas, engineers may use pumps capable of discharging more liquid volume per minute.
Another factor that is often overlooked is the pH resistance of the pumping system. Some site water may have an extreme value on the corrosion index. If the water has acidic properties, it can corrode the pipeline or the internal components of the pump, whereas highly alkaline water can lead to scale buildup. This is a common problem in the mining industry, where groundwater may contain specific minerals and chemical compounds.
If the water is acidic, it is best to use pumps constructed from corrosion-resistant materials, like stainless steel. (Read also: QUIZ: Corrosion and Protection of Underground Pipelines.)
For some projects, it may not be practical to have dedicated pumps for every waterlogged area on the construction site. In this case, it is essential to ensure that the selected pump can be moved around easily.
Construction budget and manhours also play a role in equipment selection. For example, it may be more cost-effective to get an expensive, but portable model rather than a cheaper one that needs more time and resources to relocate.
Solid Processing Capability
Construction dewatering is rarely a simple, clean job. Groundwater, in particular, usually contains various types of sediment, gravel, and other abrasive solids that can deteriorate a regular pump with low tolerance.
Furthermore, excavated soil and cement on the construction site can also mix with the water to create a slurry that is beyond the capacity of some pumping systems. In terms of solid removal capabilities, industrial pumps can be separated into three classes:
- Drainage pumps – These pumps are used for removing water with minimal suspended solids
- Sludge pumps – As their name suggests, sludge pumps are best suited for non-abrasive sediments and sludge removal
- Slurry pumps – These pumps are used for removing water with heavy suspended solids, such as sand, gravel, or concrete (Read also: Slurry Pump Capacity & Flow Rates Explained: Sizing Slurry Pump Capacity to Match Project Conditions.)
Common Types of Dewatering Pumps
Industrial pumps are divided into several categories according to their applications and capabilities. Below, we will discuss three major pump categories that are commonly used in the trenchless construction industry.
Centrifugal pumps are one of the most popular pump types due to their versatility. They are best suited for low-pressure applications requiring high flow rate transfers of liquids of low viscosities. These pumps rely on one or more impellers that spin the water to direct its flow towards the discharge end.
Depending on the pressure requirements, a single-stage centrifugal pump (one impeller) or a multi-stage one (more than one impeller) may be needed.
Centrifugal pumps cannot process air and, therefore, require priming. Priming is the process of manually adding water in the pump’s inlet to allow proper operation. These pumps only need to be primed at startup, after which the pump will continue to operate normally. There are, however, some self-priming centrifugal pump models, which can function immediately without manual priming. It is important to note that most portable pumps are self-priming.
Trash pumps are a special kind of heavy-duty centrifugal pump that can process various types of abrasive solids and viscous fluids, like sludge and mud. They typically have a portable design and are frequently used in the construction industry.
Displacement pumps use fluid displacement as their primary pumping mechanism. In these types of pumps, liquid is drawn into a fixed-volume compartment at the inlet, where a reciprocating or rotary motion pushes a controlled amount of liquid through the outlet.
These pumps are renowned for their ability to handle high-viscosity fluids. They also are best suited for high-pressure applications since their output flow is not affected by inlet pressure. Although centrifugal pumps are more commonly used, positive displacement pumps are ideal for situations where fluid properties and high pressures may cause centrifugal pumps to fail.
Displacement pumps are also self-priming, allowing them to handle fluids with certain amounts of entrained air.
As their name suggests, submersible pumps operate while completely immersed in water. The pumping unit has a slim, cylindrical design, making it ideal for removing water from deep or narrow spaces, like sumps. While they do not possess the capacity of displacement pumps, they are still capable of handling gritty fluids.
Since these pumps are submerged in the water, they do not require priming. However, submersible pumps present the risk of electrocution, thus requiring additional safety precautions. (Read also: Trenchless Operations Safety Do's and Don'ts.)
While dewatering is a common process in the construction industry, it is an operation that requires careful planning. The right pumping equipment can reduce dewatering time, ensure pump longevity, and minimize costs. Engineers and construction managers, therefore, need to assess site conditions to ensure that the appropriate pump is selected for a given project.
Written by Krystal Nanan | Civil Engineer
Krystal is a civil engineer and project manager with an MSc in Construction Engineering and Management. Her experience includes the project management of major infrastructure projects, construction supervision, and the design of various infrastructure elements including roadway, pavement, traffic safety elements and drainage.