32 PROCESSING TECHNOLOGY
Best practice in water pumps for injection systems
Mogens Roy Olesen describes the essential challenges in terms of both design, performance and purity for water pumps used in injection systems.
Mogens Roy Olesen décrit les défis essentiels en termes de conception, de performance et de pureté pour les pompes à eau utilisées dans les systèmes d’injection.
Mogens Roy Olesen beschreibt die wichtigsten Herausforderungen bezüglich Design, Leistung und Reinheit von Wasserpumpen für Injektionssysteme.
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Above Single and multistage sanitary pumps made of stainless steel 316L, easily cleanable, easily serviced and with the highest surface finish.
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hoosing the correct pumps for water for injection (WFI) systems can optimise the
operational reliability and increase product safety. Te pumps must maintain the required pressure and flow and are also an important factor in ensuring the sterile condition of the water for injection.
Used in final formulation in the pharmaceutical industry, it is absolutely essential that water for injection (WFI) maintains its sterile condition. Tis is why the WFI system – and in particular the
pump – must be carefully designed to deal with the demanding physical properties of pure water. Equally important, the pumps must be able to cope efficiently with the required flow and pressure and ensure that the sterility of the water is not jeopardised. Te European, the Japanese and the US pharmacopoeia may differ slightly from one another but the pump challenges encountered in WFI productions are essentially the same. And so are the benefits of going for the optimum pump solution.
With the conductivity typically below 1.5microS/cm and the pH value between 5-7 the physical properties of WFI place great demand on the pump material. Te water finds itself in a state of unstability and in trying to regain its natural status the media becomes highly aggressive to the material it is in contact with – even to high grade stainless steel, which is the preferred material of construction for all wetted pump components in WFI systems. For this reason the
recommended type of stainless steel is AISI 316L with a ferrite content less than 1 per cent. As for the surface finish the roughness must be less than 0.5ųm in order to reduce the risk of microbial growth.
Shaft seal
Te shaft seal is one of the most critical components in terms of the pump’s operational reliability in WFI systems. As a barrier between the pumped liquid and the surrounding environment, the shaft seal plays an important part in eliminating any risk of contamination of the sterile water – and in preventing leakage. In choosing the optimum shaft seal solution in WFI pumps the following critical aspects must be taken into account:
Exposure to an ‘aggressive’ liquid (WFI). Exposure to high temperature water (typically 80°C).
Te optimum choice in material for shaft seals exposed to WFI is silicium carbide. Silicium carbide is
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