Finding the Right Submersible Pump

Contributed by: Bill Hein at Nagle Pumps

The appeal of a submersible pump comes in part from the ability to simply drop the pump into either a tank or sump without worrying about the structural integrity.

However, despite the ease of installation, the submersible pump is the one of the most misused pumps on the market, largely due to its cost effectiveness in comparison to a vertical unit. In fact, many of the submersible pumps used in industrial applications are often not much more than a “cellar drainer” type pump available at a hardware store. The challenge is finding a submersible pump that matches the needs of the desired operation.

Recognizing the unique features of a submersible pump

There are a few key differences between submersible and vertical pumps that every user should be aware of:

1. Submersible pumps use the motor shaft and rely on the motor bearings to handle the application’s loads—such as radial load from the pump impeller, specific gravity of the pumpage and the temperature of the liquid. These are loads that a standard vertical pump shaft is designed to handle and are often overlooked when using a submersible motor.

2. Once placed into the liquid, the submersible pump motor requires a seal to keep the internal components free from contamination. The seal is crucial to the operation of the motor and is generally the No. 1 cause of submersible pump failure. However, vertical pumps don’t need such a seal.

3. A good slurry type vertical pump should have a way to allow for pump shutoff or deadhead conditions. This feature should also be available in a submersible design. However, most submersible motors are mounted directly to the pump unit. This not only prevents bypass, which is crucial when running this unit at a deadhead condition, but it also subjects the motor seal to the full fury of the pumpage.

The submersible pump does have a few advantages overall vertical unit. The first is the ability to start the pump at any level of liquid without being limited to the depth of the pumping level. Submersible pumps are usually much lighter and more portable than vertical pumps. They are also more flexible and can handle several applications within the facility.

Submersible pump challenges and solutions

For most pump companies, the challenge is incorporating the features associated with their vertical slurry pump design into the submersible pump.

The successful integration produces not only a more effective pump, but also one that lasts longer. Here are a few key features to look for in a submersible pump:

•  A submersible motor that offers shaft and bearing capabilities that match the loads of the pump.
• A strong motor seal with seal faces of adequate hardness to combat the potential wear.
• Clearance between the motor and the pump that allows the pump to bypass some flow, allowing the unit to run at deadhead conditions.

Finally, to complete a successful installation, take care selecting the construction materials, solids passage, sizing and horsepower. The pump speed should be matched to each application. The impellers should be large enough in diameter to select a speed that is appropriate for the liquid pumped.

Address these factors and you’ve turned a pumping challenge into a dependable solution.

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Permission to reproduce this article was given by its origional author Bill Hein, General Manager at Nagle Pumps. To learn more about their products visit NaglePumps.com.

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