Due to the different chemical makeup of HFC and HLP fluids, sealing materials proven and traditionally used with HLP fluids, though effective in HFC applications, do not necessarily provide effective performance or length of life in HFC media. In tests, Trelleborg Sealing Solutions has identified sealing materials that offer extended life in HFC applications.
HFC fluids, or water glycols, are the most commonly used fire-resistant hydraulic fluids and with their higher ignition temperature they are increasingly being used instead of HLP media or even being made mandatory in hydraulic oil & gas applications with a high fire risk. A research program by Trelleborg Sealing Solutions has resulted in identification of alternative sealing materials that give better performance and extended life in HFC fluids.
Eric Bucci, Oil & Gas Segment Manager Americas, Trelleborg Sealing Solutions, says: “Oil & gas hydraulic applications often involve demanding dynamic movements, for instance in the case of offshore motion compensation cylinders, and due to long strokes, sealing systems can be subjected to significant wear. Compared to oil-based HLP media the water base of HFC fluids typically increases seal wear. As oil & gas applications increasingly use HFC fluids and length of life needs to be extended to avoid costly downtime, it is imperative that we provide operators with information on the optimum sealing material for HFC fluids.”
Trelleborg undertook a series of tests on a number of sealing materials to investigate their effect on sealing systems in HFC fluids with regard to friction, wear resistance and leakage. The materials tested included the traditional choice in hydraulic applications, polytetrafluoroethylene (PTFE) based materials with various fillers, alongside the alternatives of proprietary polyethylene Zurcon® Z80 and thermoplastic polyurethane Zurcon® Z13.
The two materials that demonstrated the least weight loss, and therefore wear, were Zurcon® Z80 and Zurcon® Z13. With these materials there was also no apparent leakage. In addition, visual inspection showed the best results were achieved with Zurcon® Z13.
While Zurcon® Z80 showed slight extrusion after one million load cycles, no abnormality is seen in Zurcon® Z13 with the same seal geometry. The filled PTFE based materials were significantly worn after 200,000 cycles.
Dr. Mandy Wilke, Technology Specialist Fluid Power Europe, Trelleborg Sealing Solutions, who was responsible for conducting the tests, says: “During the tests, strong influences were observed in the behavior of the seals in relation to friction and wear. Due to the significant fluctuation of the mixing ratios (water/glycol) in HFC fluids and in operation, reliable behavior of sealing systems can only be predicted to a limited extent.
“To ensure seal life and performance in hydraulic applications, it is important to know the type of hydraulic fluids in service and using test results and experience, match the correct sealing material to the hydraulic fluid. Despite the successful use of PTFE based materials with HLP fluids, alternative sealing materials, such as Zurcon® Z80 and in particular Zurcon® Z13 could offer better wear resistance and extended life in HFC fluids.”
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