Split john guest fitting

[Slev]

Went out to check on how my brew was progressing in the keg, only to find that my gas cylinder (5kg) was empty.
On inspection, i found that the john guest fitting at the disconnect has a noticeable split (photo attached).
Really annoyed. (tis only my second keg with the cylinder). Generally, i turn off the valve on the regular, but forgot to on Friday.
I had noticed a similar issue with another fitting, shortly after setting the system up, but caught it early, and assumed that i had overtightened, so was cautious about all other fittings.
Is this common?

(cylinder, regulator et al is set up with the keg in an undercounter fridge. Temp around 5c. The connections received  no abuse)

[DEMPSEY]

They break very easy. Use only a good hand tighten or a gentle spanner turn.

[Slev]

Was only a light tighten. Took 3 weeks for it to fail.

[dcalnan]

It looks like you're using ptfe tape on the threaded fitting, that's what caused it to crack, it got over tightened. Flared fittings work by sealing the against the recessed inner surface of of the John guest fitting, that's why the disconnect has that little bit of plastic at the end of the male flare fitting. I like to use Barb fittings or gas so I can avoid any threads where gas could escape.

[Slev]

Had a look at the other jg connections installed. Another one was split (it had no hose connection). All three that split, split at the same location- on the shaft, not on the join seam, but slightly to the side. Looks like a manufacturing flaw. There is an indent mark, slightly curved, about 10mm, at the failure point, which was visible before the failure.
Got them all with my taps, from a chap on ebay. I've no reason to think that these are simply a bad units from a batch. I got 6 at the time and 2 of them don't show this flaw.
Just, highlighting this, as it may save some hassles for others

[johnrm]

Do your Disconnects look like this?


As DC says, use of PTFE is the most likely issue.
The gastight seal happens at the tip of the disconnect.
The thread on the disconnect is mechanical, its purpose is to hold the disconnect and fitting together, compressing/securing the gas seal.

[Slev]

I did have ptfe on 2, of the failed connections third didn't. One was overthightened, one was only finger tight, and the third, i cant say (but very lightly tightened at most).  But the others with the defect shown, are unsed.
But yes, lesson learned wrt tape.