Choosing the right chocolate pumping solution

Tuesday, 31 March 2009

Throughout the various stages of cocoa bean and chocolate production, there is a need for pumps that are capable of handling the aggressive ature of the product and also addressing the issue of shear sensitivity. Alongside these demands, producers require pumps that provide leak-free performance It is important that manufacturers of chocolate and chocolate products recognise that pump selection has to be based on the physical state of the product at each stage of the production cycle in order to achieve a high quality product. It is for this reason that fluid handling systems suppliers AxFlow recommends three positive displacement pump types for use in chocolate production, these being the Blackmer sliding vane, the Blackmer Mouvex C Series and the Waukesha Cherry-Burrell Universal rotary pump.  A positive displacement pump causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe. When running at a constant speed, this pump type positively displaces a liquid volume at almost a fixed rate, irrespective of the resistance the flow of the liquid encounters. The job of transferring cocoa mass and chocolate can be a tough assignment, which is a why a special pump is required and the Blackmer sliding vane pump more than fits the bill. Designed to handle difficult liquids, this pump has been adapted to meet the specific requirements of cocoa and chocolate processing and can be found in many plants around the world. Available in sizes able to handle flow rates up to 75m3/hr and pressures up to 6 Bar, it offers high performance characteristics coupled with easy and economical maintenance. The Blackmer vane pump contains a number of vanes that are free to slide into and out of slots in the pump rotor. When the drive mechanism starts the rotor, centrifugal force, push rods and/or pressurised fluid causes the vanes to move outward in their slots and bear against the inner bore of the pump casing forming pumping chambers. As the rotor revolves, fluid flows into the areas between the vanes when they pass the suction port. This fluid is transported around the pump casing until it reaches the discharge port. At this stage, the fluid is squeezed out of the discharge port. Constant performance An influential factor in specifying pumps for chocolate processing is the requirement for constant performance, including priming and draining, over extended periods. The Blackmer pump provides automatic adjustment of key performance characteristics, with flowrates being maintained without the need for any increase in pump rotation speeds. Resistance to the abrasive properties of cocoa liquor and chocolate mass is provided by the cast iron pump body with ISO PN 16 flanges, which can further be enhanced by chrome plating. The treated steel vanes, which are the main wearing parts, can be easily replaced in a matter of minutes for maintenance purposes without the pump pipework being removed. Effective sealing can be performed either by Teflon coated packings or by mechanical seals, whilst the possibility of the pumped media solidifying is prevented by the provision of externally positioned heating jackets. Pumping high-viscosity media The Waukesha Cherry-Burrell Universal series rotary piston pump has a well-established place within many sectors of food processing particularly where the pumped medium has a high viscosity or contains solids or particles. Using an operating principle known as the external circumferential piston (ECP), the arc-shaped rotary pistons, or rotor wings, travel in annular-shaped cylinders machined in the pump body. Because the rotors of the Universal Series ECP pump produce a scooping action, they do not squeeze and compact the medium being pumped. The ECP’s 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. “The Waukesha Universal ECP can handle both thick and thin mixes without causing any damage to the pumped product,” says AxFlow’s Ian Payne. “It combines a gentle, pulse-free pumping action with the high suction capacity necessary to allow the thick mix to be drawn into the pump without any separation of the ingredients. The low shear action of the pump guarantees that all ingredients arrive at the depositing line in pristine condition every time. The WCB pump is also used successfully for icing sugars and fondants.” Where the aggressive nature of cocoa liquor and the issue of shear sensitivity have to be addressed, AxFlow has a history of supplying manufacturers with the Mouvex C Series pump. The EHEDG compliant Mouvex pump is based on the operation of an oscillating eccentric piston that produces the pumping performance of a rotary positive displacement pump. However, its action is far more sensitive making it ideally suited to applications where shear and potential leakage are major issues. The Mouvex C Series pump differs from other types of positive displacement pumps in that it does not agitate the pumped liquid. Rather, the liquid is pumped by the eccentric movement of the oscillating piston within the pump chamber, this being a very gentle action. The unique design of the pump does not require either mechanical seals or magnets whilst providing leak-free performance. The eccentric movement pump consists of a cylinder and a pumping element mounted on an eccentric shaft. As the eccentric shaft rotates, the pumping element creates chambers with the cylinder. This has the effect of increasing the size of the intake port and drawing fluid into the pumping chamber. The fluid is transported to the discharge port where the size of the pumping chamber decreases moving the fluid out into the discharge pipework. Suitable for throughputs up to 36m3/hr and pressures of up to 9 Bar, the Mouvex C Series pump provides manufacturers with a constant product flow that is independent of both pressure and viscosity. This, together with the presence of automatic piston/cylinder wear adjustment, ensures full flow efficiency and high levels of product stability at all times. In addition, the design ensures that very high levels of accuracy can be attained for volume metering and dosing. Self-priming and capable of dry-running, this type of pump will clear both the intake and discharge lines of any residual liquid. Lubrication of all moving parts is provided by the pumped medium. Cleaning can be easily performed in place, without the need for disassembly. “Many fluid handling problems arise because the pumps are neither designed nor suitable for applications and/or conditions for which they have been selected,” said Payne. “These three very different pump types all have a clearly designated role to play in cocoa bean and chocolate production and it is the application that will always determine the type of pump to be used.” www.axflow.com

 

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