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30


November/December 2009


Valve Innovation Optimises Chromatography Process; Removing Dead Legs, Minimising Hold-Up Volumes & Increasing Yields


Brett Davies, DMA Europa Ltd, 2nd Floor, Snuff Mill Warehouse, Park Lane, Bewdley, Worcs. DY12 2EL. Tel: 01299 405454 • E-mail: bd@dmaeurope.com


Helen Christopher, Burkert Fluid Control Systems, Brimscombe Port Business Park, Brimscombe, Stroud, GL5 2QQ. Tel: 01453 731353 • E-mail: helen.christopher@burkert.com


There are a number of important considerations in the optimised design of a chromatography process; the selection of valves being not least amongst them. The importance of correct valve selection is evidenced by the benefits it provides. As well as delivering equipment and installation savings, optimised valve selection can eliminate all dead legs, meaning that sterility is easier to ensure and maintain. It can also mean faster flow shifts and reduced risk of cross contamination. In addition, the compact design of the latest single diaphragm valves, combined with manifold blocks, ensures minimal hold-up volumes, increasing product yields, with less media waste.


Typical challenges for valve solutions in chromatography: Valve selection is usually a crucial discussion point amongst design engineers, with traditional solutions generally based around diaphragm valve technologies. These solutions make use of very closely welded cluster arrangements, with the shortest possible tangents and optimised positioning according to draining/cleaning requirements. However, even with optimised design, the requirement for minimised hold-up volumes in complete chromatography systems can often be compromised by complex valve clusters. This is because, the more valves needed, the more welds, pipe lengths, T- pieces that are required, and, ultimately, the more hold- up volume generated.


In addition, valve clusters can also militate against fast and accurate flow shift, which is essential for process efficiency. In downstream applications such as chromatography, the ability to shift quickly means higher yield capture, and more efficient batch control. If the accuracy of the flow shift is higher and reliable, then the


relationship between concentrated product and the separation step can be controlled more closely. This will subsequently reduce product loss and have a positive impact on the return on investment of the installation.


A further major challenge with the clustering approach is that, in larger systems the complex arrangement of valves, as well as their physical individual size, can result in large and heavy clusters that have to be supported, and be easily accessible for maintenance. In addition, the larger the valves required, the more overall space is required, and when considering the need for fully drainable and cleanable systems, this is not ideal.


Such challenges which are closely associated with valve solutions in chromatography have led to technology and manufacturing advances, which have resulted in a new design based upon unique Robolux valves and custom manufactured stainless steel valve blocks. With this design, hold- up volume is eliminated by reducing - by half, or more - the number of valves, diaphragms, pipe fittings and welds required in a system.


The patented Robolux valves can be used on fixed or mobile separation units, and are designed for operation on general- purpose or multi- purpose systems in LP to MP (Low Pressure / Medium Pressure) chromatography applications. The valves are downstream items located immediately after the separation process, where they are used as efficient diverters for the separated media on the column outlets/system outlets. They are also used on agent distribution lines when adding agents to the columns/system.


Based on


diaphragm valve technology, this generation of valves combines’ independent dual process switching functions or “2 seats” in a single body with a single diaphragm and single actuator.


The actuator has independent pistons – one for each seat, offering a compactly- designed


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