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Gentle action pumps for food processing

28 January 2013

Many fluid handling problems arise because the pumps are neither designed nor suitable for applications and/or conditions for which they have been selected. It is the application that will always determine the type of pump to be used.

Once the nature of the pumped media is established, other parameters including, delivery volume and pressure, temperature, flow characteristics, vapour pressure, solids content, corrosiveness, toxicity and hygiene need to be considered. For food and drink processing, the materials should be selected according to the properties of the pumped media and compliance with EHEDG, FDA and 3A regulations is a basic requirement.

Pumping media containing substantial solids is a problem that arises at various stages of the food processing cycle.  Either the solids need to be pumped without bruising, or transferred without damaging the pump itself. The pump technologies that have high profiles within food processing include rotary lobe, rotary piston, reciprocating positive displacement, progressing cavityand air-operated double diaphragm (AODD) designs. However, where a gentle pumping action and ability to handle media containing solids is the priority then rotary piston, rotary lobe and AODD pumps should be given every consideration.

Rotary piston pumps
A good example of this pump type is Waukesha Cherry-Burrell’s Universal IIpump which employs an operating principle known as the external circumferential piston (ECP). In this design the arc-shaped rotary pistons, or rotor wings, travel in annular-shaped cylinders machined in the pump body. The resulting long sealing path reduces slippage and produces a smooth product flow without destructive pulses or pressure peaks, and without the need for valves or complex parts. However, unlike progressing cavity and rotary lobe pumps, the WCB Universal pump is not adversely affected by varying or viscous products even with large particles that may settle in the pump. Because the rotors produce a scooping action, they do not squeeze and compact the medium being pumped. 

Manufactured from stainless steel and suitable for CIP cleaning, the pump’s close clearances allow the pumping of water against back pressures, whilst its simple design enables operators to completely strip it down for inspection in situ without the need to remove connecting pipework. Where high viscosity fluids and solids are involved, the large fluid cavities of the rotors, together with the large easy-entry anti-cavitation ports enable efficient pumping.
 
Rotary lobe pumps
The rotary lobe pump employs timing gears which eliminate contact between the rotors andenables them to handle non-lubricating fluids.  Providing low shear and gentle handling of the liquid, thereby minimising product degradation, rotary lobe pumps are also easy to clean in place (CIP) or strip clean between operations for batching applications.Ahygienic lobe pump offers manufacturers many possibilitiesparticularly where transferring, filling and emptying both high and low viscosity liquids can benefit from a pump providing excellent volumetric efficiency.

Waukesha has designed its MDL rotary lobe pump (Fig. 1) for processing duties where a low shear force is required and liquids containing solids in suspension are encountered. This pump can be integrated into existing production lines as it has a modular design and compact size. A feature of this particular pump is the ‘TRI LOBE’ rotor, which is easy to mount and can be accurately positioned without there being any risk of mechanical error. The inclusion of standard mechanical seals, contribute to the pump’s ease of maintenance which can be performed in-place without the need to dismantle piping. 

Air-operated double diaphragm pump
The number of applications for air operated double diaphragm (AODD) positive displacement pumps is simply enormous (Fig.2). This is because they can transfer anything and everything. In addition, they are portable, straightforward to use, easy to maintain and are suitable for operation in the most difficult conditions as well as clean room environments. The absence of close fitting parts allows solids to pass through the pump without harm, whilst abrasive and viscous products can be pumped without any damage to the fluid characteristics.

Air-operated double diaphragm pumps (AODD) use compressed air to act upon the diaphragm and draw the liquid media into the pumping chamber and then eject it, so there are no rotary parts involved. This pump is ideally suited to applications in the food processing industries where a gentle action is required. The deep liquid chamber design results in superior handling of delicate particulates and solids that tend to settle because there is a large gap between the clamped area of the diaphragm and the liquid chamber wall. Unlike other pumps, the product particles do not get wedged in this area, thus eliminating a factor that can cause product contamination.

Summary
The consequences of wrong pump specification can go beyond frequent downtime, maintenance costs and high demand for spares. There can also be penalties resulting from unnecessarily expensive and complex plant installations, occasioned by a need for control, monitoring and safety devices, which, in turn attract additional maintenance costs. There is a risk of producing substandard product, but worst of all may be the prospect of health and safety risks.

Author: Tony Peters, Managing Director AxFlow

For product information, contact:
Tony Peters
AxFlow Limited
Orion Park
Northfield Avenue
London
W13 9SJ
Tel: 020 8579 2111
Email: info@axflow.co.uk
www.axFlow.co.uk



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