Twin ferrule compression fittings: incorrect tightening – part 3

Published:  04 February, 2016

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 third of a short series looking at the problem of incorrect tightening.

Reassembly

Always ensure that the system is depressurised, isolated and locked out prior to disassembly. The following method is recommended by most manufacturers when the disassembly and reassembly of Small Bore Twin Ferrule Compression Fittings is required.

1) Using a felt tip pen mark the tubing at the back of the tube nut. Also, mark a line along the tube nut and fitting body as per below.

2) Insert the tubing with the pre-swaged ferrules and tube nut on to the fitting until the front ferrule contacts the fitting. For larger sizes it may be necessary to lightly lubricate the thread of the fitting body and the rear face of the back ferrule (which contacts the shoulder of the tube nut). This step is shown below.

3) Whilst restraining the fitting body assemble the tube nut on to the fitting body, initially by hand and then by using the correct size spanner. As the line on the tubing becomes fully visible and the line of the tube nut aligns with the line on the fitting body there will be a significant increase to the resistance felt with the spanner.

At this point the tube nut needs to be tightened slightly more (several manufacturers state that even after several remakes the tube nut should only have moved less than half a hexagon flat). This step is shown below.

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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