Flexible impeller pumps offer significant advantages when it comes to handling viscous fluids compared to traditional centrifugal pumps. Martin Ruse, a pioneer in flexible impeller technology at Jabsco, explains the basic principles of how these pumps operate and highlights their benefits in terms of installation, maintenance, and overall performance.
Positive displacement pumps, such as flexible vane pumps, are increasingly used as an alternative to centrifugal pumps in various industrial applications. Invented by Jabsco Corporation (now part of ITT Industries Group for Momentum and Flow Control) around 60 years ago, the flexible impeller pump excels in managing thick, viscous materials that can be challenging for centrifugal pumps. This makes them ideal for applications where fluid consistency varies widely.
The operation of a flexible impeller pump is based on the movement of an eccentric cam that causes the impeller to rotate. As the impeller turns, the volume of the cavities within the pump decreases, creating a partial vacuum at the inlet. This vacuum draws the fluid into the pump, and as the cavity volume reduces further during the discharge phase, the fluid is pushed out through the outlet. This mechanism ensures consistent flow, even with high-viscosity fluids.
One of the key benefits of flexible impeller pumps is that their flow rate is directly proportional to the pump speed. Two main factors influence this: internal friction within the pump and friction between the fluid and the pump’s walls. High viscosity increases internal friction, which can drastically reduce the efficiency of centrifugal pumps. While reducing speed might help, it often leads to poor performance since centrifugal pumps rely heavily on rotational speed. Flexible impeller pumps, however, adjust automatically to changes in speed, viscosity, and pressure, making them more versatile in real-world conditions.
When transporting viscous fluids, getting the fluid into the pump is a critical challenge. Friction losses in the inlet piping can create a pressure drop that prevents proper suction. To minimize this, the inlet pipe should be larger and as short and straight as possible. If the fluid is too thick, a supply tank with an overflow hopper placed 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 are often limited to being installed below the liquid level, flexible impeller pumps can be mounted in more convenient locations—above ground or even underground. This not only improves safety but also avoids potential damage from traffic or other external factors. Additionally, they can connect easily to containers like barrels or cans without requiring a bottom outlet, simplifying the setup.
These pumps are also user-friendly, especially for operators who may lack experience. They require minimal start-up procedures—just a simple switch-on action—making them ideal for environments where quick and reliable operation is essential.
Maintenance is another area where flexible impeller pumps shine. Their design allows for easy access and emptying during service, eliminating the risk of spills or leaks. Unlike submersible pumps, which are often difficult to reach and maintain, flexible impeller pumps can be quickly serviced without complex procedures. The rubber impeller adapts to wear and tear, maintaining good sealing and self-priming capabilities over time, unlike rigid components found in other pump types.
Real-world applications demonstrate the effectiveness of these pumps. For example, in food processing, they are used to handle highly viscous materials like butter, jam, and cream fillings. These materials often require specific pumping speeds—70–100 RPM for cake fillings, for instance. Some materials, like jams, may need pressure plates in the hopper to assist feeding, while others rely on their own weight.
In cases where the material is extremely thick, starting at a low speed (20 RPM) and gradually increasing to the optimal setting helps prevent emulsification. Pump speed is always adjusted based on the material’s properties, with examples including 500 RPM for syrup and 1000 RPM for double milk cream.
Jabsco’s 28 Series Hygienic Flexible Impeller Pumps are designed for clean environments, made with 316 stainless steel and EPDM rubber impellers that meet U.S. sanitary standards. They are not only easy to clean but also suitable for handling abrasive or particulate-laden fluids without damage, making them ideal for industries like food, pharmaceuticals, and chemical processing.
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