Flexible impeller pumps offer significant advantages when it comes to handling viscous fluids, especially when compared to traditional centrifugal pumps. Martin Ruse, a pioneer in flexible impeller technology at Jabsco, explains the core principles of how these pumps operate and highlights their benefits in terms of installation, maintenance, and overall performance.
Positive displacement pumps, like flexible vane pumps, have become a popular alternative to centrifugal pumps in various industrial settings. Invented by Jabsco Corporation (now part of ITT Industries Group for Momentum and Flow Control) around 60 years ago, the flexible impeller pump excels at moving thick, viscous materials that can be challenging for centrifugal models. This makes them ideal for applications where fluid consistency varies significantly.
The operation of a flexible impeller pump is based on the movement of an eccentric cam, which causes the impeller to compress and expand the pumping chamber. As the impeller rotates, the cavity volume decreases, creating a vacuum that draws fluid into the pump through the inlet. When the volume increases again, the fluid is pushed out through the outlet. This mechanism ensures consistent flow without relying heavily on speed, making it more adaptable to different viscosities.
One of the key benefits of using a flexible impeller pump is that its flow rate is directly proportional to the pump speed. However, there are two main factors to consider: internal friction within the pump and friction between the fluid and the pump walls. Viscous fluids can increase internal friction, leading to reduced efficiency in centrifugal pumps. While lowering the speed might help reduce this, it also affects performance since centrifugal pumps depend largely on impeller speed. Flexible impeller pumps, on the other hand, adjust automatically to changes in speed, viscosity, and pressure, offering better control and reliability.
When transporting viscous fluids, getting the material into the pump is a critical challenge. Friction losses in the inlet piping can create a pressure drop that prevents the fluid from entering the pump. To minimize this, the inlet pipe should be as large as possible and kept short with minimal bends. For very thick fluids, a supply tank with an overflow hopper positioned above the pump can provide the necessary positive pressure to ensure smooth operation.
Installation flexibility is another major advantage of flexible impeller pumps. Unlike centrifugal pumps, which often require being placed below the liquid level, flexible impeller pumps can be installed in more convenient locations, even above ground. This reduces the risk of damage from traffic or accidental contact. Additionally, they can connect directly to containers that lack standard bottom outlets, such as drums or lined tanks, using simple hose connections at the top.
These pumps are also user-friendly, especially for operators who may not be highly trained. Their start-up process is straightforward—just turn them on, without the need for complex priming procedures.
In terms of maintenance, flexible impeller pumps are designed for easy access and cleaning. They can be emptied during service, eliminating the risk of spills. In contrast, submersible pumps are often difficult to maintain due to their immersion in liquids, which can make repairs time-consuming and costly. The design of flexible impeller pumps allows for quick replacement of worn parts, such as the impeller, ensuring continued efficiency over time.
Self-priming performance is crucial for flexible impeller pumps, and factors like air leaks or internal wear can affect this. However, the rubber impeller adapts to wear, maintaining a tight seal and preventing loss of vacuum. This helps the pump retain its self-priming ability and volumetric efficiency over long periods.
Real-world applications show the versatility of these pumps. For example, in food processing, they efficiently handle high-viscosity materials like butter, jams, and cream fillings. These materials often require specific feeding methods, such as pressure plates for thick substances, while others rely on gravity. The pump’s adaptability allows it to work effectively across a wide range of viscosities and operating conditions.
Jabsco’s hygienic flexible impeller pumps, such as the 28 Series, are made from stainless steel and use EPDM rubber, meeting strict sanitary standards. They are ideal for batch processing and can be easily cleaned in place (CIP), ensuring compliance with hygiene requirements.
Overall, flexible impeller pumps are a reliable, efficient, and versatile choice for handling viscous and abrasive fluids in various industries, from food and beverage to chemical processing. Their ease of use, maintenance, and adaptability make them a preferred solution for many applications.
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