24 analytical & laboratory EquipmEnt
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company’s decision to switch to peristaltic pumps in special silicon tube ranges developed to meet growing
the production of its Dipslide bacterial contamination demand for very accurate dispensing.
test kits has proved to be “a self-funding investment – a One such example is Pumpsil-D. This is post-cured
finance director’s dream”. Paine is managing director of after extrusion to remove residual linear and cyclic
Casp Products, which introduced peristaltic pumps from siloxanes that can leach out of other platinum-cured
Watson-Marlow Bredel to dispense viscous nutrient silicone tubing.
media at 50ºC on to the Dipslides in a process requiring The post-curing process allows
more than 5000 individual 3.5ml high-precision doses per cross-linking between the silicone molecules, resulting
shift, at a rate of under a second each. in tighter bonds that maximise the tube’s resistance to
“Since the pumps were installed, the resulting flexing stress. This improves the tube’s restitution, its
improved dosing accuracy has increased production ability to revert to its original shape after compression
yield by 5–8 per cent,” Paine says of the dispensing during the pumping action – a vitally important feature in
pumps selected following successful trials on a 500 series maintaining dispensing accuracy.
unit with twin 313 pumpheads. In many ways this one Product manager Martin Johnston says: “Pumpsil-D is
application highlights many of the individual attributes the result of over two years’ research and development,
of the company’s wide range of dispensing solutions, all including a six-month testing period of trialling the
based on its proven peristaltic pump technology. product both internally and at customer sites. Over
Take hygienic processing, for example. Casp Products’ 80 per cent of those involved in the trial are now using it
manufacturing takes place in a cleanroom environment as a selected product.”
and it’s vital that the nutrient media is not contaminated Another important aspect of the Pumpsil-D
in any way. tubing, particularly to highly regulated industries
In a peristaltic pump, the fluid being pumped only like pharmaceuticals, is that each piece of tubing is
comes into contact with the inside of the tube. As the permanently laser-etched, end-to-end, with part number,
roller mechanism is external to the tube, there are no lot number and use-by date. This “LaserTraceability”
shaft seals to worry about that could leak – in either feature meets all the necessary requirements for validated
direction – causing contamination of the product or processes – requirements, such as cGMP, that often also
the surrounding environment. And, because the tube is demand full traceability of the material being handled by
always occluded by at least one roller, there is no need the pump.
for additional check-valves in the line, which can wear These demands are also met by the company’s
and need cleaning or replacing. dispensing pumps, which connect to a PC for display,
In some applications, particularly those involving storage and printing of batch records, complete with all
different batches of material being dispensed sequentially dispensing parameters such as dates, times and operator
through the same pump, residues of product have been ID. With or without a PC, the pumps all feature their own
known to cause contamination, but peristaltic pumps in-built software to control the dispensing action.
such as the new 520Di model are entirely crevice-free and At Aurora Scientific, manufacturer of water quality
it’s a very easy job to change the tube between batches. testing systems, the handling of chemicals such as acids
This last point was in fact one of the major selling is coupled with the need for accurate dosing. Having
points behind the Hutchison/MRC cancer research centre selected to use a 520Di dispensing pump, the company
at Cambridge University becoming one of the first users of is able to operate the pump using process signals fed
another new pump – the Sci-Q 323 model. Again chosen back from the production equipment, signalling when the
after an extensive trial, this pump excelled in its ease pump is to begin dosing.
of tube replacement. “An important requirement,” says “It was immediately apparent that peristaltic
Karen Hébert, Hutchison’s media unit supervisor, “was technology suited our production applications,” explains
the ability to swap tubes quickly and simply. Because Brian Hepburn, proprietor at Aurora Scientific. “Moreover
we often deal with media that needs to be kept within the pump also had no problem meeting the high dosing
specific temperature ranges under aseptic conditions, we accuracy and repeatability requirements we had”.
sometimes need to change tubes in seconds – to start Ramp settings are particularly useful when the
dispensing before the media cools.” pumps are being used in filling operations. Basically,
The 323 at Hutchison/MRC is used on tasks involving programmable ramping allows filling to start and stop
dispensing volumes of between a few millilitres up to without splashing or foaming – the flow being gradually
20 litres – a range of operations catered for by the wide ‘ramped’ up to a constant speed, and then decelerated
range of tube diameters available, and the choice of five towards the end of filling.
drives and five pumpheads in the 323 range. Similarly, end-of-dose dripping is prevented by the
The importance of the tube in peristaltic pumping is, programmable drip control, which momentarily reverses
of course, paramount. the roller direction at the end of each dose. u
Watson-Marlow Bredel’s new £1.4m tubing extrusion
plant at its hq in Cornwall, England, features a class Ashley Shepherd is UK sales manager at Watson-Marlow
J10 000 cleanroom which is used in the manufacture of Bredel. www.watson-marlow.co.uk
www.scientistlive.com
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