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Overcoming pumping challenges

01 October 2017

Lesley Eaton explains how progressive cavity pumps are able to overcome many traditional food processing pumping headaches. 

Despite pumps being key to most food processing operations, there are still many challenges associated with pumping foodstuffs – not least the ability to handle solids as well as liquids, and maintenance of product integrity. Developments in progressive cavity (PC) pump technology means that they can overcome some of the food industry’s biggest pumping headaches.

Maintaining product integrity: The design of the PC pump moves the product through the pump in a series of cavities, which prevents slip from the discharge back through the pump. Slip creates shear, so compared to other pump designs, which have clearances between the lobes, screws or gears, PC pumps have a very low shear action. This preserves the quality of shear-sensitive products; even whipped products and those containing entrained air. Because there is no squashing action either, very soft solids can be handled with little or no damage. 

Lifting products: High suction lifts of up to 9m can be achieved, making PC pumps suited to lifting products from IBC, barrels or mixing tanks. The ability to pump against almost a full vacuum enables the efficient use of degassing equipment and enhances the quality of the final product. Furthermore, surface-mounted PC pumps can lift from wastewater sumps, removing the need for submersible equipment.

Batch and continuous dosing: The cavities have a given chamber volume which makes the PC pump suitable for batch dosing applications where specific amounts of product must be dosed extremely accurately; for example, batch dosing tomato sauce directly onto pizza dough or ingredients into mixing vessels. Because the flow has very low pulsation, dosing into products or pipelines delivers the right amount in a smooth, continuous action, meaning that the accurate addition of ingredients or chemicals into a liquid flow is possible without complicated controls or lengthy calibration methods.

Handling solid particles: The PC pump is able to handle solid particles without compromising either the product or pump efficiency. For example, sauces containing mustard seeds or spice particles can be pumped without the danger of sticking ball valves; which is often a problem with other types of positive displacement pump. In addition, the development of auger mechanisms in some PC pumps allows them to handle and mix solids – liquid can be added to solids in the feed auger, or solids can be added to a paste, with the action of the auger mixing the two before feeding them into the pump. 

Variable flow rates: PC pumps are available with flow rates from 100ml/hr to 500m³/hr, and the ability to handle temperatures ranging from -20 to 220°C. As the flow volume is constant for each cycle of operation, and is proportional to the rotational speed, calibration is simple and is unaffected by the viscosity of the product, unlike some pumps which stop when viscosity is high. This linear accuracy means that only one variable – pump speed – needs to be changed to vary the flow volume. 

Viscosity: Although PC pumps have good suction characteristics and can handle viscous and sticky products, there are some instances where they need a helping hand – specifically when the product doesn't free flow – hence the development of auger mechanisms to constantly feed viscous media into the pumping elements. The auger is fabricated as part of the integral coupling rod between the drive and rotor, using the rotation produced by the drive to push forward viscous and even solid products. As a result, media with dry solids content up to 45% and viscosity in excess of 1,000,000cps can be successfully transferred.  

Hygiene: Ingredient dosing, product transfer, accurate metering of product directly into production processes, and filling of finished products can be achieved using PC pumps with cleaning-in-place (CIP) as standard, which comply with the strict hygiene standards demanded by today’s food processors. What’s more, PC pumps can be constructed – and the product feed mechanism adapted – in line with the application requirements. A fully stainless steel pump with CIP capability, for example, can be used for hygienic applications, while one used to dose corrosive or abrasive chemicals can be manufactured from chemically resistant materials.  

Operating pressures: Pumps have to overcome pressure when transferring products. These can be generated by several factors, for example pipework and valve configuration, and also the length of pipework. The need to overcome operating pressures of downstream equipment such as heat exchangers also puts demands on the pump. PC pumps are able to generate pressures up to 48 bar as standard, due to the interference fit between the rotor and stator and the absence of slip between the pumping elements.

Installation and operation: PC pumps have both forward and backward pumping action in the same pump, so one PC pump can often do the job of two alternative designs. System costs are also reduced as check valves and pulsation dampeners are not needed, and neither are calibration pots. They can be installed horizontally or vertically, taking up very little floor space. 

Waste disposal: By-products and solid and liquid waste from food and beverage production can be removed in hygienic, enclosed systems using PC pumps. They are capable of transporting products over long distances to waste reception areas and can also enhance the value of waste by segregation for biogas production or to comply with waste regulations. 

Lesley Eaton is business development and marketing manager at Seepex. 


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