November 26, 2024

Avoid the Vortex: Protect Your Pump

There are multiple ways to dewater a construction site, such as creating a wellpoint or using an eductor. But one of the most cost effective and simple is an end-suction pump, connected to a sump. The sump, a pit or a hollow that exists naturally on site or that’s been excavated, collects the water. That water is then pumped out, using a dewatering pump, at a specified discharge point. This technique is used both for construction dewatering applications or stream diversions.

But simple isn’t always easy. If you don’t create a proper sump when setting up, the pipe attached to the dewatering pump won’t be deep enough and you’ll create a vortex: a mass of whirling water. That’s bad for the job, because it interrupts flow and slows down the project, but it’s even worse for your pump.

Why? Because vortex=cavitation=air in your pump, and that can damage your dewatering pump.

 How does a vortex occur and what are the signs?

A vortex can manifest when the surface of the water is drawn down too close to the inlet pipe. This can cause air to enter the system. Air entrainment pulls more air into the water as it swirls around the inlet pipe. The resulting suction creates a visible whirlpool on the surface of the water.

This spinning whirlpool causes the water to rotate around a center point and a low-pressure zone forms. This zone, or cavitation, forms pump damaging bubbles where water used to be.

Other signs of a vortex that can damage your dewatering pump include:

• Changes to the rate water is moving, as determined by monitoring the flowmeter
• Atypical fluctuations in the pump’s pressure gauge values
• Increased or abnormal noise

What’s the potential damage to a dewatering pump?

The low-pressure cavitation forms bubbles, as stated above.

As a pump pulls water into its impeller, the rotating iron or steel disc that’s key for a dewatering pump to function, it lowers the water pressure and, at a certain point, the water vaporizes. This creates small pockets of water vapor that form and quickly collapse as the pressure increases. The bursting of vapor pockets, over time, damage the impeller. When there are additional bubbles traveling through the system it can cause further erosion and pitting of the impeller and other components of the dewatering pump.

A pump with a damaged impeller is going to slow down, and may add expense to, the project.

Avoid the vortex by building a good sump

The best way to avoid a vortex is to create a proper sump when setting up. If you can excavate in the area you can make a sump that will hold the water at a depth that works best for your dewatering equipment.

If it’s not possible to excavate, for instance if there’s a stream and environmental impact is an issue,  look for a low spot in the water to place the pump.  In this case, the sump can often be improved by hand removal of rock and stone to create and improve depth.

When it’s not possible to build the perfect sump

If you know that you are at risk of a vortex, because of sump size or other concerns, check the dewatering pump for specific features. Vortex impellers, which direct fluid away from their center, and anti-vortex plates, which create a barrier between the surface of the water and the impeller, will help.

It’s also an option to increase the inlet diameter, which reduces the inlet velocity. Slowing the inlet velocity allows the water level to be drawn down lower before a vortex occurs.

No matter how you do it, whether it’s creating the perfect sump or investing in a new dewatering pump that has anti-vortex features, protect your pump and your project by avoiding the vortex.

Dewatering pumps for rent or purchase in the Mid-Atlantic
FieldForce provides equipment and engineering services for the municipal, construction, manufacturing, and industrial sectors. Our inventory includes Atlas Copco pumps, compressors, and generators for rent or purchase, and temporary piping, filtration equipment, light plants, and heaters available to rent. We maintain our fleet at yards in the greater Pittsburgh area and in central Pennsylvania for convenient availability.