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Hygienic pumps and their application

02 December 2022

There are many pump technologies available for use in processes where hygiene is an issue. Pablo Martinez-Moore offers some insights into which pump type may be best suited for which application. 

Selecting the most appropriate pump technology for a process not only depends on the fluid characteristics, but also the requirements of your process – factors such as whether it is for a continuous process, levels of cleanliness, duty point required, ease of maintenance or temperature handling all weigh in as to the final choice made.

Although making a choice may seem daunting, what it does mean however, is quite often there is more than one way to accommodate your process and deliver your outcome. Pumps are often designed to work most effectively within a specific set of defined criteria that varies between applications. They are almost prescriptive in nature, and so unless the application is tightly defined, it is not always possible to recommend one pump type over another for a process. 

So, what pump types are available and what are their typical applications? 

Air Operated Diaphragm pump (AOD):  A surface mounted pump which is widely used. Driven by compressed air it can run dry without damage and can handle liquids ranging from thin oils to viscous pastes. It is typically used for the bulk transfer or dosing of fluids and as it is good at building pressure and is often used in filter presses to filter solids from liquids. 

Barrel pump: This pump design is immersed within a container such as tote, drum or IBC to decant or dispense liquids into process. It is a good option for dispensing a range of fluids from thin liquids such as oils, solvents, and chemicals to viscous fluids including honey, sauces and pastes at low to medium flow rates, and low pressure.

Centrifugal pump:  This is one of the most common pumps used with low viscosity liquids similar to water which are either pure or contain solids in suspension. It is normally utilised for the bulk transfer of liquids, or cooling and circulation of fluids.

Flexible impeller:  This versatile pump is good for sensitive products such as milk, yogurt or cream where, if not handled correctly, their characteristics can be altered. The pump shares characteristics of a centrifugal pump and that of a positive displacement pump making it suited for low and medium volume transfer of clean, and solid laden fluids at low pressures. Typical applications include wine, dairy, syrup, Jam and honey decanting and transfer.

Gear pump: This pump design is usually only specified for use with clean fluids due to the tight tolerances within rotating parts and can be limited by high temperature liquids which are thin. It is good at producing high pressures and flows and can handle high viscosity liquids with lubricating properties without issue.

Lobe pump: This pump is offers versatility with liquids containing solids but also those which are clean at low to medium flows and pressures. It can be fitted with hoppers to feed units with non-flowing liquids containing solids which can be fed from conveyors.

Piston pump:  Similar in working principle to a gear pump it contains tight tolerances making it suited for clean liquids at high pressures and low to medium flows. Due to the number of parts it can be difficult to maintain and is usually found in barrel emptying applications. 

Peristaltic pump: Containing just one wearing part – a hose – this pump is easy to maintain and is good for thin or viscous liquids at low to medium pressure. Offering a non-slip design, it can transfer high temperature oils without loss of flow due to recirculation, and also viscous pastes such as tomato puree transfer. 

Progressing cavity pump: This pump is able to handle almost any solution, having the ability to accommodate liquids thicker than cement (up to 1M cst). The technology is used to handle everything from thin lubricating liquids which include oils to viscous and abrasive fluids. 

The inlet is customisable with a hopper which can be designed to mash, pulp, shred or portion large objects which would otherwise be difficult to pump, or transfer in an application handling objects. 

Screw pump: This pump produces gentle, low pulsations, handling liquids up to 1M cps such as viscous creams and pastes in bakeries. It has high suction capabilities, produces medium to high flows, at high pressure, but operates with clean liquids only. 

Figure 1.
Figure 1.

Sinosuidal pump: This pump has an impeller shaped like a Sine wave meaning it is able to transfer whole pieces of fruit without damage. It is good for low to medium pressure applications where a gentle working motion is required as it does not produce pulsations.

Vane pump: Predominately used with lubricating fluids, such as oils, molasses, and alcohols it offers an economical method of transferring bulk amounts of fluid at low to medium pressures. 

With so many different pump types available it can often be more advantageous to discuss the ways in which a pump may be best suited for an application:

Constant pressure pumps: In this scenario pumps which are of positive displacement design will deliver a constant flow across a variety of pressures, and viscosities without a reduction in flow rate which can occur when viscosity changes with temperature, there is an ingredient change due to shortages, seasonality with changing recipes or changing consumer tastes.

Solids and abrasive handling: Depending on the outcome desired solid handling requires careful consideration. Solid ingredients can be transferred gently as complete or undamaged items, with partial damage as a compromise or in some cases aggressive agitation effectively assists the next stage of a process – all considerations which can drastically affect the best choice of pump. 

Some units may be ok with soft fruit, but if stones or large amounts of seeds are encountered it can severely reduce some pumps life. 

Low viscosity fluid transfer: Low viscosity fluids require careful consideration as if not handled appropriately it can mean slippages occurs where fluid recirculates back to inlet, efficiency is lost or a process is not effective as it should be. 

High viscosity / Shear sensitive pumps: Viscous and shear sensitive fluids require a different approach when pumping due to the nature of the liquids. High Viscosity fluids require a positive displacement pump to ensure transfer is made without fluid flowing back to the inlet, and shear sensitive liquids need handling gently to avoid them being transformed either in consistency or viscosity. Examples of sensitive fluids include Milk, Egg Whites, Cream, and Chocolate where if agitated too much the viscosity of the fluid can be altered.

Making a choice

When looking to specify a unit for your process, what matters most is that all relevant factors are considered. This may sound obvious but often solely the required performance can be considered. As to which pump is best suited to a process, importance should be given to the total lifetime cost, the ability to clean or automate cleaning, ease of maintenance and versatility to accommodate all your requirements without compromise.

To quickly establish which pump can be used with each process North Ridge Pumps has developed a comparison table of pump types to show the main differences between differing designs (See Figure 1).

With a seemingly overwhelming choice of pumps for hygienic applications, how can you begin to whittle down and select the most appropriate design of pump best suited for your process? 

The first step is to have a conversation with a provider not tied to a specific pump technology, who understands your application, its requirements and what is most important. A supplier who has experience in similar applications, who can not only advise on the pump for your current requirements, but also provide insights into what may be important to have for the future and whether that could be accommodated in some way as an option. 

Pablo Martinez-Moore is commercial and marketing director at North Ridge Pumps. 

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