New thermoplastic fitting won’t crack under pressure

One-piece fitting molded from PAEK polymerA Swiss manufacturer of valves and fittings for analytical, biomedical and biocompatible precision instruments is the first company in the world to offer a one-piece fitting molded from PAEK polymer supplied by Victrex (Thornton Cleveleys, UK). The fitting, suitable for liquid chromatography instruments, is capable of withstanding pressures up to 1,000 bar (14,500 psi).

The pressures required in liquid chromatography have been rising steadily for more than five years, given that the particles of the separation materials (usually modified silica gels) now frequently have a grain size of two micrometres or less, said Vici AG International (Schenkon, Switzerland) in a press release. Consequently, substances within mixtures can be separated more quickly.

To satisfy customer demand for flexibility and ease of handling, Vici has introduced the one-piece fitting, which is capable of withstanding up to 500 bar (7,250 psi) pressure when tightened by hand. The limit for conventional PEEK fittings is 350 bar (5,000 psi). When tightened with an appropriate tool, the carbon-fiber-reinforced Victrex HT fittings can withstand significantly higher pressures up to 1,000 bar (14,500 psi), according to Dr Andre Hütz, Product Manager at VICI. These pressures, which occur between the pump and column in ultra-high performance liquid chromatography (UHPLC) systems, typically require stainless-steel connecting capillaries fastened with appropriate fittings to achieve a pressure-tight connection between system components.

Compared with unreinforced PEEK, the Victrex HT polymer prevents the fitting from breaking apart when it is being tightened, since the carbon fibers are aligned in parallel during the injection molding process. The extra strength extends the service life of the fitting and allows several cycles of tightening and loosening. In the past, this has only been possible in the high-pressure range using conventional two-piece nut-and-ferrule fittings or complicated one-piece fittings, which generally are only suitable for a specific connection and usually just for single use.

“Assisted by Victrex and its material and processing expertise, we have developed and commercialized a new product in this segment to offer users greater flexibility, reusability and, above all, easier handling compared with steel screw fittings,” explained Hütz in a press release. “Being manufactured by injection molding, it is favorable in cost terms, too.”

Tests conducted by the company reportedly show that, when tightened by hand, the new Victrex HT fittings can be used at 500 bar and above. When tightened with a tool, they can also be reused at least three times after their first use at a test pressure of 950 bar.

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