Tips for choosing a pump system for food and beverage applications

Other applications include dosing or metering processes used to apply coatings, like placing chocolate onto a pretzel.

Depending on the size of the facility, there could be hundreds of pumps at a food or beverage processing plant. Pump types could range from centrifugal pumps to positive displacement (PD) pumps, including rotary lobe (RL) and progressing cavity (PC).

The pumps used for these processes are subject to a variety of nationally and internationally manufacturing and hygiene standards and guidelines. The most significant – and the baseline for all pumps in the food market – is the US Food and Drug Administration’s requirement calling for use of “approved” materials.

Use of FDA-approved materials like 300-grade stainless steel is required for the pump housing. Elastomer materials used in pump seals must also be submitted and approved. FDA-approved food-grade lubricants are required for pump lubrication.

Beyond the basic FDA requirements, there are additional national and state requirements. For example, many companies in the US follow standards set by 3-A Sanitary Standards, Inc. (3-A SSI), an independent, not-for-profit corporation dedicated to advancing hygienic equipment design for the food, beverage, and pharmaceutical industries.  

Those exporting internationally follow guidelines issued by the European Hygienic Engineering & Design Group (EHEDG), which supports European legislation requiring that handling, preparation, processing, and packaging of food is done hygienically using hygienic machinery and in hygienic premises.

Both 3-A SSI and EHEDG provide a third party evaluation of a company’s equipment by running it and testing it to make sure it can be cleaned properly. 

Pump types – advantages & disadvantage

The types of pumps typically used in food and beverage applications include centrifugal pumps and positive displacement (PD) pumps, including progressing cavity (CP) pumps, and rotary lobe (RL) pumps.

Centrifugal pumps are the most commonly used kinetic-energy pump. Centrifugal force pushes the liquid outward from the eye of the impeller where it enters the casing. Differential head can be increased by turning the impeller faster, using a larger impeller, or by increasing the number of impellers. The impeller and the fluid being pumped are isolated from the outside by packing or mechanical seals.

A progressive cavity pump transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is turned. This leads to the volumetric flow rate being proportional to the rotation rate (bi-directionally) and to low levels of shearing being applied to the pumped fluid.

A rotary lobe pump has two counter-rotating pumping elements (rotors), each with two or more lobes. The drive shaft counter-rotates the driven shaft using oil- or grease-lubricated timing gears located outside of the pumping chamber. With rotary lobe pumps, fluid flows around the interior of the casing.

The main advantage of a PC pump is it does not produce shear, which could change the product consistency. Shear is defined as a strain in the structure of a substance produced by pressure, when its layers are laterally shifted in relation to each other. The PC pump operates quite gently, so it does not impart shear and does not change product consistency. RL pumps are also a good choice for similar applications. Both are gentle, impart little shear, and can handle shear sensitive products. In addition, they can pass solids through the pump.

Yogurt is one product that benefits from this gentle transfer. A high speed centrifugal pump, on the other hand, would change the consistency of the yogurt. In addition, if the yogurt includes fruit, the PC and RL pumps can move the fruit with the yogurt through the pump without causing any damage to the fruit.

Recently, a yogurt company based in Connecticut selected this type of pump for use in a product line that incorporates granola and a variety of other candy toppings.

The main advantage of an RL pump is its footprint is smaller than a PC pump, so it takes up less real estate on the processing line. It also offers good clean-in-place and steam-in-place (CIP/SIP) characteristics. The food industry has been leaning toward RL pumps in recent years, but there are limits to its use, mainly based on the discharge pressures under which it can operate. A PC pump can handle much higher head pressure than those of a RL pump.

Therefore, one would employ a PC for higher discharge pressures, for example if you are running a long distance with a very viscous product. The pump type needed depends on how the plant is laid out. If there is a storage tank outside the plant, say 500-600 feet away from where the product must be delivered, the pump needs to create a higher pressure due to line loss than if it was 20 feet away. Also, a PC pump can handle higher viscosities than an RL pump. Finally, with a progressing cavity pump, designs are available for pumping material very high in chunky solids quite long distances.

One application that comes to mind involves pumping apple chunks to a press for juice extraction. With one pump, and no other apparatus, the operator can unload the apple chunks into the hopper or pump and the pump would push the material through successfully. The example is a Pennsylvania-based growers’ cooperative made up of fruit growers along the Appalachian Mountains and throughout the Midwest who recently installed NETZSCH’s BO series pump for an expansion to its juicing line. The open-hopper model PC pump feeds apples to a press used for juice extraction.

Another example is a bakery in the Midwest that – among other baked treats - specializes in fruit desserts, including all American favorites such as cherry, apple and blueberry pie. For a cake line, however, they needed a pump to move 20 gpm of blueberry cake batter thru a 2.5 inch diameter pipe without damaging the blueberries, which are about ½ inch (12 mm) in diameter. The process required the batter to be pumped 20 feet and up 8 feet into an open tank. Their original rotary lobe pump was crushing the berries. After switching to a progressing cavity pump, they were able to deliver the cake batter into the tank with no damage to the berries.

Cleanability, serviceability, and durability are the most important features to look for when purchasing a pump for this industry. A good starting point is to make sure the pump has been certified by 3-A SSI. With regard to cleanability, find out if the pump can be cleaned in place (CIP) and/or steamed in place (SIP). All pumps are CIP-able; but RL pumps are also SIP-able. This gives RL pumps an advantage over PC pumps; with the PC, one has to disassemble piping to steam-clean it.

A factor affecting durability is the speed at which the pump runs. For example, centrifugal pumps run at 1800 or 3600 revolutions per minute (rpm), whereas many PC pumps run at 300-400 rpm. The PC, running at the slower speed, will not wear as quickly.

Centrifugal pumps are designed for moving water or other thin fluids. When working with more viscous products, one would lean toward one of the PD pumps. For metering applications, PD pumps are also a better option.

Another factor to consider is a centrifugal pump cannot handle any changes in viscosity or discharge head that may occur. Once designed for an application, the centrifugal pump can best be used for those conditions only. If these conditions change, so does the performance. By contrast, a PD pump is a lot more forgiving with changes of viscosity and changes in discharge head.

The net positive suction head (NPSH) requirements are typically much lower on an RL and PC pump compared to those of a centrifugal pump. A pump requires a positive head to be able to draw; there is a minimum positive head required on any pump. If there is not enough positive pressure feeding the pump, the material to be pumped will not get through. Centrifugal pumps may need 32 feet of positive head, compared to a PC pump, which may only need 5 feet of positive head. This difference can be critical, depending on pump placement in relationship to the head. Also, both the PC and RL pumps feature self-priming suction lift, but this is not the case with centrifugal pumps.

Pump accessory features, including variable speed drives, load cells, and monitoring systems, must be examined, too. Most pump systems include a variable speed control system that allows users to change pump speed, which will vary the flow rate. Some pumps are mounted on a frame or bed plate, with load cells under the tank to regulate flow going into the system based on weight. Also to be considered are flow monitoring systems, made up of flow meters, pressure transducers, pressure switches, and temperature controls.'

Pete Ciorrocco, regional sales manager, NETZSCH Pumps North America.