3.2.15 Food processing pumps
Food processing pumps
Food processing pumps are selected based on the food fluid characteristics and most important actors are viscosity, the pumped product sensitivity to shear and size of solids in the product. The viscosity factor will decide whether to use a centrifugal pump or a positive displacement pump. Viscosity is a key factor in many different foods and we don’t want the pump to change the product viscosity, and also, a high viscous product will not be suitable to pump with a centrifugal pump, a positive displacement pump will be a more suitable and efficient choice.
Some food products, or fluids, are susceptible to shear while others are not. Pumping cream can turn cream into butter. If butter is the intended final product, that might be good but if the product is supposed to be cream, then maybe not so much. The selection might be between a PD pump or a centrifugal but in the case of pumping cream it’s probably more a question of selecting a pump with an impeller and with a impeller speed that doesn’t damage the fluid properties.
Another consideration is food containing solid particles, including anything from ground spices, nuts, pieces of meat to whole fruits and everything in between. For example, pumping strawberry jam, do you want small pieces of strawberry, chunks or the whole strawberry in the final product? Other considerations like the fluids chemical composition (acids) and temperature needs to be taken into consideration when selecting pump materials.
Within dairying food processing industry, primarily special centrifugal pumps are used, their shape being distinctive and determined by the hygienic and sterile requirements. The materials used are usually acid resistant or stainless steels with gaskets, O-rings etc. of approved food processing quality. Both exterior and interior surfaces must be smooth to approved hygienic standards, it should also be possible to disassemble the pump quickly for cleaning and washing. There are also pumps available for cleaning without disassembling, Cleaning In Place (CIP) and pumps that can be Sterilized In Place (SIP) if specified. It must be possible to carry out this process quickly and effectively and requires that all components and clearances are designed for this purpose, especially with respect to temperature. To simplify external cleaning, the electric motor is often encased in a polished stainless steel casing.
For reasons of hygiene many foodstuffs pumps may not have fluid lubricated shaft bearings. Food processing centrifugal pumps are normally available up to approximately 30 kW. Centrifugal pumps cannot be used for viscous and sensitive products such as yoghurt, cheese, liver paté etc. In such cases lobe rotor pumps are generally used.
Figure 3.215a Food processing centrifugal pump.
Hygiene standards and requirements
It is often referred to some common standards regarding food pumps. For example, the US Food and Drug Administration (FDA), 3A Certificate and EHEDG (European Hygienic Engineering & Design Group) are common standards.
EHEDG
Special needs for CIP or SIP capacity, gentle food product management and easy maintenance must be carefully considered for pumps used in food processing. These requirements, their implementation principles and associated design are described in detail in EHEDG based on the EC Machinery Directive, the document establishes additional requirements for such equipment in order to fulfill good mechanical and hydraulic properties as well as thermal efficiency by following modern design methods and guaranteeing cheap manufacturing.
3-A Hygiene Standard
3-A SSI is an independent, non-profit, organization focused on machine equipment for hygienic applications in the food, beverage and pharmaceutical industries. The specification contains material requirements regarding type of material, material composition, construction, surface finish, etc.
Example:
3A1 Industry / Hygiene Standard, Finishness Ra ≤3,2 µm
3A2 Sterile standard, Surface finish Ra ≤0.8 µm
3A3 Sterile standard, Surface finish Ra ≤0,4 µm
Material: Electropolished stainless steel, Cr-Ni-Mo, AISI316L (DIN 1.4404 / 1.4435)