Decisions, decisions!

18 June 2018

Specifying a pump for handling food products is never straightforward as there are so many variables that need to be considered. Food Processing spoke to a variety of pump suppliers to try and get clarity on some of the most typical food industry requirements.

Continue reading this article

Register now for free and access every article and to register for the print edition.

Specifying pumps for use in food processing applications will depend on a myriad of issues specific to the environment and the products being handled. The British Pump Manufacturers Association (BPMA) has added a pump search tool to its web site (www.bpma.org.uk) with the aim of making the task a little bit easier and to help users identify the most suitable options for them, based on a variety of criteria including pump types and applications.

Food Processing spoke to a selection of BPMA members to get their thoughts on some of the things that need to be considered when making pumping choices in food production applications.

Q: Hygiene is a big consideration in food handling applications. Can you offer some advice on what to look out for when specifying a new pump?

Alfa Laval: FDA approved materials are a minimum expectation of any food contact components. When referring to hygiene we often are actually referring to cleanability and European Hygienic Engineering & Design Group (EHEDG) certified products are tested for cleanability as well as for hygienic design. However, even this does not give an absolute guarantee that a specific pump will be 100% residue free after cleaning because there will always be so many individual process variables such as particle content, fluid viscosity and the CIP regime applied to that piece of equipment.

KSB: The first step is to divide the production plant into primary areas (with high hygiene requirements) and periphery (no/low hygiene requirements). For high hygiene areas pumps should to be selected exactly for the duty point and need to provide cavitation-free operation. Look for EHEDG-certified pumps and specify materials that conform with the valid specifications of the plant or operator and with legal regulations such as FDA, Regulations (EC) Nos. 1935/2004 and 2023/2006. To ensure that complete drainage is possible installation conditions also need to be taken into account and sealing elements must be selected for the fluids being handled, the temperature of the fluid and any necessary cleaning processes. All wetted components must be of high surface quality (electropolished), made of high-grade stainless steel, and should be traceable.

MDM Pumps: Look out for a pump with a hygienic design and manufactured from 316L stainless steel (1.4404). The best are manufactured from solid bar, as cast products can have porosity. All the pump internal surfaces should be smooth with a minimum 3mm radii and with a surface finish of 0.8µmRa.

Triark Pumps: Most hygienic pumps are available in pre-process and post-process designs. Pre-process pumps are used when the food product will subsequently be sterilised by cooking. Post-process pumps are used for products that will not undergo any further sterilisation processes. These pumps should be stainless steel, polished to a mirror finish in accordance with EHEDG advice.

Q: Why and when might someone consider swapping out an old pump that appears to still be working?

Alfa Laval: In the case of centrifugal technology, energy efficiency can be a driver to consider updating any pump (young or old) in an existing system. In our experience any older pump is unlikely to be optimised for its current task, as these change over time so it is probable that a pump may not be performing at/or close to its best efficiency point. This is not necessarily a result of the age (mechanical deterioration) of the pump itself; it can also apply to relatively new pumps. There are often significant energy savings to be found in both young and old pumps by reviewing current performance and duty of the pump and modifying or replacing it with a more efficient solution. Pump modifications can be relatively simple and inexpensive to implement and a complete replacement can very often be justified by potential energy savings with a return-on-investment (ROI) of between two and three years.

KBS: It is time to consider changing your pump when you find a newer solution that will help improve your process and provide greater energy efficiencies. Another scenario might be when the an old pump is still fully operational but can no longer be cleaned without leaving any residues due to eroded or damaged surface parts. New pumps often also offer time savings too – they will be faster to clean and will result in fewer unplanned downtimes.

MDM Pumps: You might want to swap out an old pump for a number of reasons – to benefit from better hygiene features, to obtain traceability of the materials in contact with the product, to improve reliability, to increase mechanical seal life, to increase efficiency, to accommodate a change in duty, or because spare parts for the pump become difficult to obtain.

Triark Pumps: Pumps lose efficiency as they wear and there does come a point when spare parts become unavailable. In this case, pump distributors can really come into their own as many will carry essential spares for older pumps. Some older pumps will also benefit from the use of more energy efficient motors.

Q: Do you believe there is a best 'all-round' food handling pump type?

Alfa Laval: When handling viscous foods the pump technology of choice should be positive displacement. There are many technologies within this pump category, all of which will have advantages and disadvantages depending on the product being pumped and the process in which it is placed. If I had to pick one positive displacement technology it would be a rotary lobe pump as this is the most versatile and widely used solution.

KSB: There is no best ‘all-round’ solution! Every pump type will have its pros and cons which is why every application requires a pump that is tailored to match the task in hand. ?MDM Pumps: The centrifugal pump is an excellent all-round pump where liquids are similar to water (ie with viscosities less than 300cP).

Triark Pumps: The ‘perfect’ pump simply does not exist, but in our experience air-operated double diaphragm (AODD) pumps are the preferred choice when pumping food. They offer a gentle handling solution with minimal shear which makes them a good choice for products containing fruit or vegetable particulates.

Q. What type of pump would you suggest to handle viscous food products, and why?

Alfa Laval: Rotary lobe pumps offer a good combination of price, cleanability and gentle handling of shear sensitive products.

KSB: A positive displacement pump would require much less power than a centrifugal pump. Also, a centrifugal pump may be unable to handle the fluid, depending on its degree of viscosity.

Triark Pumps: Viscous product is often pumped using an air driven pump, but not an AODD pump, which can only be used up to viscosities of 10,000 centipoise. Viscosities over this and up to 1,000,000 centipoise, can be pumped using high ration piston pumps mounted on rams.

Q. What type of pump would you suggest for shear-sensitive food products, and why?

Alfa Laval: There are a variety of factors in a rotary pump that could cause product shear. Generally, we would suggest the use of a high volumetric pump, at low RPM with optimised internal geometry.

KSB: A rotary lobe pump, or sinusodial pump, would offer a good solution because the fluid spends a comparatively short time in the pump, the contact surface is small, the fluid is only squashed minutely in the inlet and outlet of the pump, and the pumps are operated at low speed.

?Triark Pumps: When it comes to shear-sensitive products, an AODD would be our suggested solution as they can pump very slowly without the need for specialist cooling on the motors and in the case of chocolate, can be easily heat jacketed to prevent the product cooling on its journey through the pump.

Q. What type of pump would you suggest for food products containing solids, and why?

Alfa Laval: Firstly, we would need to know whether the solids are hard or soft as this would be a significant determining factor on which pump technology and configuration would be specified. Other factors to take into consideration would be the amount and size of the solids and the viscosity of the carrying fluid. A universal rule of thumb would be to use a pump which is volumetrically efficient (in case of low viscosity carrying fluid), running at relatively low RPM, and which has as large a pump chamber as possible to allow solids to pass freely, with minimum interaction with the pumping elements as possible. In short, low speed, large pumps with optimised rotor design.

KSB: The choice would depend on the base fluid being pumped. When pumping a liquid which contains solids a centrifugal pump is usually a good choice if the solids are smaller than the free passage of the pump. To keep pump wear caused by solids to a minimum, anti-swirl baffles could be used.?If the base fluid has a high viscosity then a positive displacement pump, such as a rotary lobe pump or a screw pump, would be a better solution. Because solids can have an abrasive effect on the pump parts, avoid pumps lined with plastic or elastomer (such as progressive cavity pumps). Our advice when handling any solids would be to match the pump and shaft seal exactly to the fluid being handled and the solids it contains, to ensure the longest possible service life.

MDM Pumps: Centrifugal pumps can be used for pumping liquids containing solids. The maximum size of deformable particles that can be handled is typically equal to the impeller vane width, and the maximum size of non-deformable particles is half this.

Triark Pumps: Specifying an AODD pump with ‘flap’ instead of ‘ball’ valves would allow solids almost as large as the port size to safely pass through the pump. For example, a 25mm ported flap valve pump will allow solids through up to 24mm. We have used AODD to pump hard-boiled eggs in brine and the eggs have passed through the pump unscathed.

Conclusion
We leave the last word to Steve Schofield, director at the BPMA, who said: “Whatever your food processing requirements, there will always be a range of pumping solutions available, but the final selection must be related to the specific parameters of the product being pumped. The BPMA membership accounts for approximately 85% of the UK market for liquid pumping equipment, and is made up of a range of companies of all sizes and offering a myriad of pump types. All BPMA member companies are bound by a stringent ‘Code of Conduct’, so anyone looking to purchase and install pumps and related equipment within the food and drinks sector, can ‘buy with confidence’ from a BPMA member company. The online pump selection tool mentioned earlier in this article can offer an ideal starting point for any pump selection process.”

Food Processing would like to thank the following spokespeople who kindly contributed their thoughts to create this article:
Russell Jones, global portfolio manager – pumps at Alfa Laval.
Steve Howell, national sales manager – projects & installed base at KSB.
David Peterson, managing director at MDM Pumps.
David Rozee, managing director at Triark Pumps.