Twin ferrule compression fittings: incorrect tightening – part 2

Published:  11 December, 2015

This is part of a series of articles based on guidance provided in the British Fluid Power Association’s newly introduced training course titled ‘Small Bore Tubing Integrity Course – using twin ferrule compression fittings’. This month, we present the second of a short series looking at the problem of incorrect tightening.

Pre-swage (assembly)

For sizes up to and including 1” or 25mm some manufacturers recommend the optional pre-swage (or pre-assembly) of the front and back ferrule. Such installations where this would be beneficial include; where large diameter and/or heavy wall tubing is used (tube thickness typically more than 0.065” or 2mm). Pre-swaging helps to ensure correct installation when using smaller sizes in hard-to-reach applications where space constraints makes it difficult to either count the number of turns of the tube nut or use the gap gauge to verify correct installation.

Pre-swaging also helps to prevent gravity moving the tubing and ferrules away from the position required for the correct assembly. For these reasons some companies who use twin ferrule compression fittings pre-swage every end irrespective of size and type of material being used.

Once pre-swaged, the initial installation is treated differently depending upon the manufacturer. If in doubt always consult the manufacturer/supplier.

For sizes 1¼” or 28mm and larger most manufacturers stipulate that a hydraulic pre-swage, or pre-assembly tool is used to correctly assemble the front and back ferrule on the tubing prior to installation in to the fitting body. Each manufacturer of hydraulic pre-swage tool will supply their own set of instructions to enable its correct use. Where a hydraulic pre-swage tool is used the initial installation after pre-swage is treated differently depending upon the manufacturer. If in doubt always consult the manufacturer/supplier.

To aid the assembly process when assembling larger sizes, typically 1” or 25mm and above, most manufacturers recommend that lubrication the tube nut thread and back ferrule is required.

More information

The above information has been edited from course booklet for the British Fluid Power Association’s new training course titled ‘Small Bore Tubing Integrity Course – using twin ferrule compression fittings’. For more information about the new course and how you or your staff can enrol, please contact the Association at: info@bfpatrainingacademy.co.uk. For general enquiries, please contact: enquiries@bfpa.co.uk, or Tel: 01608 647900.

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