When assembling compression-style tube fittings, you should always precisely follow the
manufacturer’s instructions to ensure correct compression. For Swagelok-brand instrument tube
fittings 1 inch in size and smaller, the general procedure is to tighten the nut 1-1/4 turns past fingertight.
Insufficient turning of the nut will fail to properly compress the ferrule around the tube, and
excessive turning will over-compress the ferrule, resulting in leakage. Unlike pipe fittings, tube fittings may be disconnected and reconnected with ease. No special procedures are required to “re-make” a disassembled instrument fitting connection: merely tighten the nut “snug” to maintain adequate force holding the ferrule to the fitting body, but not so tight that the ferrule compresses further around the tube than it did during initial assembly.
A very graphic illustration of the strength of a typical instrument tube fitting is shown in the
following photograph, where a short section of 3/8 inch stainless steel instrument tube was exposed
to high liquid pressure until it ruptured. Neither compression fitting on either side of the tube leaked
during the test, despite the liquid pressure reaching a peak of 23,000 PSI before rupturing the tube.
manufacturer’s instructions to ensure correct compression. For Swagelok-brand instrument tube
fittings 1 inch in size and smaller, the general procedure is to tighten the nut 1-1/4 turns past fingertight.
Insufficient turning of the nut will fail to properly compress the ferrule around the tube, and
excessive turning will over-compress the ferrule, resulting in leakage. Unlike pipe fittings, tube fittings may be disconnected and reconnected with ease. No special procedures are required to “re-make” a disassembled instrument fitting connection: merely tighten the nut “snug” to maintain adequate force holding the ferrule to the fitting body, but not so tight that the ferrule compresses further around the tube than it did during initial assembly.
A very graphic illustration of the strength of a typical instrument tube fitting is shown in the
following photograph, where a short section of 3/8 inch stainless steel instrument tube was exposed
to high liquid pressure until it ruptured. Neither compression fitting on either side of the tube leaked
during the test, despite the liquid pressure reaching a peak of 23,000 PSI before rupturing the tube.
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