Dewatering is an aspect of almost all construction projects. Examples include lowering the water table prior to excavation, removing standing water or planning for rainfall. Overlooking or underestimating dewatering increases your costs and causes delays in construction.
Selecting the right construction dewatering pump can have huge implications on project success. Many construction project managers underestimate the importance of selecting the right pump. Premature pump wear or unexpected failure can significantly increase project expenses and delay project schedules.
The best pump choice for construction dewatering is a submersible pump. Some project managers use self-priming dewatering pumps because they are more portable. However, a long suction hose going into your self-priming dewatering pump causes frequent loss of prime and stalled pumps. Also, self-priming dewatering pumps tend to only dewater solids in the pit rather than remove them.
Below, we’ll explore the main considerations for selecting the right submersible pump.
Where Are You Pumping the Water?
The first thing you need to understand is where the water is coming from and where you want it go. Is it rain water or ground water? Are you pumping it into the sewer, a holding pond or drainage ditch? If it’s a sewer, be sure it can handle the extra influx of water.
Once you know where it’s going, understand the path to get the water there. You’ll need to know the static head (vertical distance the dewatering pump needs to push the liquid) and how far it needs to travel. Knowing how far the water will travel helps you calculate friction head losses in your piping system. Friction loss is commonly overlooked, but can have a major impact on the dewatering pump size you need. For example, rubber hoses or fire hoses create higher friction losses than PVC piping. This means you need more energy to move the water. Being too far off in your calculations can cause the dewatering pump to dead head and not provide any flow. Also, a lower than expected flow rate may not be enough to keep up with the inflow.
Once you have the right flow rate (gallons per minute – GPM) and head calculations, you can research pumps and their performance curves. The curves show you the level of performance the pumps will deliver. Your pump supplier can show you how to read the curves and help you determine if the pump will operate within the optimal levels. A pump operating too far from optimal flow and head rates can vibrate and cavitate which damages the seals and bearings.
What Size Generator Do You Need?
Most constructions sites don’t have power so construction managers bring in generators. The motor horsepower of the selected dewatering pump will determine the generator size you need. Underestimating the generator size results in the pump not coming up to speed which will burn out capacitors in the motor (single phase only). If you don’t know, it’s important that you ask your supplier how much power you need as they may not always tell you. Most construction managers don’t realize they’re running an undersized generator until it ruins the pump motor.
What Is In your Water?
Just as important as the factors above is knowing what makes up your liquid. You’re dealing with outside elements, so the water likely includes some types of solids. The type and size of the solids have a major impact on the dewatering pump you need. With sand or other abrasives in the soil, you’ll likely need a durable light slurry pump. A pump with an agitator to keep particles from settling at the bottom of the pit where clogs can result is even better.
On other sites, you may deal with larger solids like leaves, branches, and even bottles and cans in the pit. In these cases, you’ll need a solids handling pump to pass these types of solids through the pump. Heavier solids require shredder pumps.
Since 1983, BJM Pumps and our highly-qualified distributors have partnered with our customers to provide reliable, long-lasting submersible pumps for construction applications. We can help you select the right pump for the specific issues you are having. Customers receive unparalleled service from specification through installation and continued support throughout the life of the pump. Contact us at 860-399-5937 for more information.