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Be positive about your pump choices

21 January 2019

Malcolm Walker looks at the different types of positive displacement pumps that are now making their mark in the food processing industry. 

One element that is common to all fluids handling tasks across all process industries is the requirement for positive displacement pumps that are able to move delicate or sensitive media without causing damage to, or physically altering, the structure of the media. In the food and beverage industry, in particular, there is a need for such pumps because many applications require a gentle pumping action.
Within food processing the pump technologies most often employed are rotary piston, rotary lobe, twin-screw, air-operated double diaphragm pumps. There is no shortage of pump types to choose from, so matching the right pump to an application is an important consideration. 
Hygiene requirements
Although there is still no legal obligation on food manufacturers to use hygienically certified fluid handling equipment the increasing costs and potential harm to a brand’s reputation resulting from hygienically defective products has resulted in pressure being put on food manufacturers to utilise the correct hygienic process equipment.  

There are two basic groups of approval, those that apply to material compatibility and those to the actual design of the pump. Taking those concerning material compatibility, there are several globally recognised approval bodies the oldest being the US Food and Drug Administration (FDA) and the new kid on block – EC 1935/2004 – has by and large superseded FDA. 
The pumps that can accommodate many applications in food processing are rotary lobe and external circumference piston (ECP) pumps because their large rotor cavities can handle solids and particles that may be present in the fluid being pumped. There is very little difference between a rotary lobe and an ECP pump as they both essentially use the same operating principle. 

A recent addition to the Waukesha Universal pump range is the Universal TS pump which exploits the benefits of twin screws to pump various media containing large particulates, lowering damage to the pump and reducing maintenance. It also features high suction capability and a range of operating speeds which means that only one pump is required to transfer product and undertake CIP, reducing the number of pumps, valves and control instrumentation required and so contributes to reduced costs and simpler, more compact systems.

The twin screws’ rotating geometry creates a pulse-free flow which makes the pump suitable for applications such as feeding homogenisers. 

Pumps in action
One international producer of ice cream mix started to experience problems with premature failure of rotors and shaft parts in pumps in its ice cream mixing system. The pumps used in this system were being replaced every six months so it was also looking to reduce its cost of ownership. The problem was solved by installing a new mixing system fitted with ECP pumps from Waukesha. The rotors of the company’s Universal range of ECP pumps were able to stand up to the plant’s demanding performance requirements and eliminate pump downtime. Also its simple ‘O’ring shaft seals offers a good alternative to the more costly and sensitive mechanical seals that had been supplied with the original pumps.

In another dairy plant producing white mass for Greek yoghurt, the producer was experiencing multiple issues with its lobe pumps, in particular excessive shearing when pumping the mix and high maintenance costs resulting from pump break-downs. Over several years the producer evaluated a variety of other pumping solutions to determine which would impart the least amount of damage to the white mass, which would provide the best cleanability and which offered the lowest cost of ownership.

At the end of the trials the Waukesha Universal 2 pumps, with single mechanical seals were selected. These pumps have proved to be durable in this application and have helped maintain product the integrity.

Malcolm Walker is product manager at AxFlow.

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