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Saturday, August 30, 2014

Flexible Impeller Pumps: Set for Greater Things in Food Applications

While the past 10 or so years might have been a period of consolidation for the flexible impeller pump market, in the coming years, the sector will see some great changes in materials of construction and pressure and flow capabilities. That is the expectation of Keith Evans, product manager at pump supplier Xylem’s Applied Water Systems business unit.

While “it can take four to five years to design, manufacture, and test a new impeller for a new pump,” Evans notes, and “the process is very time consuming,” flexible impeller pumps will experience technological advancements and further application adoption.

Xylem says it is behind the production of more than 60 percent of the world’s flexible impeller pumps. The minimal meshing action and low-speed capability of its Jabsco brand of flexible impeller pumps reportedly allow both viscous fluids and solid particles to pass through without damage. In food processing applications, cream fillings which become easily emulsified, jams, and pie fillings which contain fruit pieces are all said to be handled with ease.

Flexible rubber impeller gives pumps their self-priming capabilities. Credit: Xylem

Flexible rubber impeller gives pumps their self-priming capabilities. Credit: Nikkiso

“Variable frequency drives (VFDs) are another great option for flexible impeller pumps,” Evans notes. “The VFD allows the user to adjust the pump speed, customizing the flow rate for different applications. This avoids damage to the product transferred while, additionally, the variable speed nature extends the life of the pump components.”

In the food industry, this can be particularly beneficial. Says Evans: “Due to the variable line-speed to flow ability of the flexible impeller pump and the addition of a VFD, you can custom set the speed of the pump to match the viscosity of the product transferred. A thicker product should be transferred at a slower speed. This is what allows thick product transfer with no damage. This is ideal for batters, egg whites, chocolate, syrups, tofu, and a huge variety of other food products.”

A recent product development at Xylem is the VFD-equipped VeraFlex FIP Cart System that offers up to 60 gpm (gallons per minute) output while incorporating gentle pumping action to carefully handle thin, viscous, and particle-laden fluids. The VFD adjusts the speed of an electric motor to provide continuous control of the specific demands of the application work being performed. VFDs are said to be an excellent choice for food processing applications, as they allow operators to fine-tune processes while reducing costs for energy and equipment maintenance.

For food applications, Xylem offers three NSF-certified compound materials of construction for its pumping equipment. “The compound we use depends on what type of product will be pumped and the viscosity of the product to transfer,” Evans says. “For example, pineapple juice is heavily acidic and abrasive on pump components, so the pump material will need to be of a strong quality.”

Another benefit of flexible impeller pumps is that they are self-priming, which helps in terms of the flexibility of plant layout. Self-priming allows the material to travel from below ground to ground level, easing delivery and distribution.

“They are referred to as positive displacement pumps and can pretty much pump air,” notes Evans. “For example, if you have a tank positioned below ground, a positive displacement pump can pull the product up to ground level and deliver the product to the desired end location. Non-self-priming pumps don’t have the capability of pulling up a product as efficiently as self-priming pumps do.”

Xylem's flexible impeller cart system handles thin, viscous, particle-laden fluids.

Xylem’s flexible impeller cart system handles thin, viscous, particle-laden fluids.

There are several good pump options for food transfer, according to Xylem. “For example, roller pumps work well as there is no direct contact, since it uses a tube in plastic (chemically compatible product),” notes Evans. “There are also [progressive cavity pumps], but those can impart metal and rubber particles into food and fail. Flexible impellers offer the largest range of versatility when it comes to moving food products that have varying consistencies and composition.”

Another supplier of flexible impeller pumps, this time from the other side of the Pacific, explains the operational principle of these pumps. “The pump actually operates more like a vane pump,” says Akira Takahashi, general manager of overseas business development at pump maker Nikkiso Eiko, based in Tokyo.

Vane pumps operate using the principle of volume change. “When the impeller rotates, the rubber blades flex, thereby varying the volume between individual blades,” explains Takahashi. “This generates the suction effect, and the pump can thus run from dry. It also gives a lot of flexibility as to where you can place the pump.” Suction lifts of 1 to 6 m (approx. 3 to 20 ft) are attainable.

Nikkiso Eiko has developed a rubber-based inclined blade impeller design that reportedly requires less than half the torque for rotation compared with conventional rubber impellers, features a 50 percent longer service life, and produces half the noise level. For reference, standard rubber impeller life is around 3,000 to 4,000 hours at ambient temperature and 1,450 rpm; the inclined impeller can rotate at up to 2,500 rpm.

The impeller is fabricated from either chloroprene rubber (CR) or nitrile butadiene rubber (NBR), but CR enables greater suction lift. According to Takahashi, typical applications where the pump finds usage are chemical plants, scum recovery, dewatering, breweries, wineries, and milk collection. The pump comes in port sizes of 10 to 65 mm.



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