Failure of back-plate single tank adapter (Bolts)

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johndiver999, my hog SS BP has slots and what you suggested is one I'm thinking on trying

The Hog Wing has tank two bars on it that act like a sta, yet not enough as my tank moves around with out the STA.
 
I like the STA and gave gotten into the habit of check it before every dive. After a while it seems to have stopped coming loose or as often but I still check it frequently.

I don't think that the bolts would come loose in a single dive but over time and should be able to be caught before separating.
 
Hope this helps someone else.

Spent the wknd in Florida's east coast and had a great time, until.

Last of five dive wknd and this happened as I was getting back into the boat on the ladder.

Single Tank Adapter separated from back-plate and tank also had 4.00 lbs extra weight in pockets. I run a long hose setup and had clipped off the primary to my d-Ring and use my snorkel to swim/wait for the boat.

As I climbed up the ladder, the tank separated from the back plate and fell back into the water, which pulled me back into the water. Entire system was separating and the tank was going down/floating away and dragging me via the short hose (bungee'd to my neck).

Got the short hose off my neck (lost snorkel and mask in process) and grabbed the attached long hose primary back in my mouth. I got back to the boat (After dropping weights) and with the help of others got all the pieces back on the boat including the tank.

Back-plate, harness still attached to me, single tank adapter and tank cam bands attached to the tank and my wing floating around in the water like a life vest.

Come to find out both single tank adapter bolts were gone and no signs of stress on the back-plate.

Ok, I see and have experienced a point(s) of failure with a single tank adapter.
1) Two stainless steel bolts with wing nuts (how they failed is beyond me this was dive 30 on this setup)
2) All the load was on the two bolts. Failure was the tank separated from the back-plate.

I'm going to research a way to route the cam-bands through the back-plate and use the adapter (instead of through the single tank adapter) and have the adapter also attach to the back-plate.
This will put all the weight of the tank on the back-plate + cam-bands and not on two bolts.


Thoughts/suggestions

Are you regularly checking that the wing nuts, etc., are tight?
 
+1 on Marie13's suggestion: check and tighten each time. I also run the bands through the backplate and so do not need a STA.
 
Glad you're OK and got all your stuff back..............but....... stop doing whatever you were doing, or not doing.

Re using the built-in "stay" : soak the cam-bands before tightening. They get looser when wet especially when new. Also, the bands should take effort to close, so that once they get past the fulcrum, they snap themselves closed.
 
Unless I have misread your post, it is not clear that you have documented 'failure' of the bolts. If I have misread your post, my apologies. You say that the 'bolts were gone'. Are you saying that the threaded bolts were completely missing from the STA? That would be extraordinary - for the bolts to be completely missing, both bolts would have to shear right beneath the bolt head, so that the STA would cleanly separate, the bolt heads would drop out from under the cam band threaded through the slots in the STA, AND the bolts, with wing nuts attached, would then have to drop out of the backplate. Not impossible. But, improbable. And, the fact that, per your description, the wing was still attached to the STA, suggests that the bolts were still in place on the STA.

In my experience, it would be equally probable that the wings nuts simply came unscrewed.
1) Two stainless steel bolts with wing nuts (how they failed is beyond me this was dive 30 on this setup)
I am going to presume something here - that you had kept your rig assembled the whole time, rather than breaking it down after each dive trip.

IF that was the case, there is no surprise. The wing nuts get loose over time. Yes, there is - or there certainly SHOULD BE - a lock washer (hopefully present, in your case) between the wing nut and the flat washer. Nonetheless, as a ROUTINE part of your gear set-up, you should check the wing nuts for tightness.

IF you routinely disassembled your rig between dive trips, then the culprit is most likely a failure to appropriately tighten the wing nuts when you assembled your rig.
apivonka:
2) All the load was on the two bolts. Failure was the tank separated from the back-plate.
Actually, as I understand your post, the failure was that the STA separated from the BP, and the cylinder was attached (by cam band) to the STA.
aviponka:
This will put all the weight of the tank on the back-plate + cam-bands and not on two bolts.
Yes, that is true. But, the issue is most likely NOT the weight on the bolts. It is whether the wing nuts were sufficiently tight.
apivonka:
Thoughts/suggestions
Certainly, if you wish to thread your cam bands through the plate, and avoid use of a STA, that is fine. If you wish to use a STA, then you need to regularly check the tightness of the wing nuts.

I routinely use a STA. I have had wings nuts come loose several times - when I failed to check their tightness before a dive. In each case, that was user error on my part, not equipment failure. In each case, I sensed there was a problem simply because the cylinder seemed to 'swing' from side to side during the dive. On one occasion, I even executed that OW skill that some divers suggest is completely unnecessary - I removed the scuba unit underwater (at 110 feet), tightened the wing nuts, re-donned the scuba unit, and continued the (otherwise uneventful) dive.
 
M.M.O. stabilisers keep the tank close and permit NO movement and NEVER loosen
with a spring washer and wingnut
tightened with a tool

full.jpg


and would never loosen more with a nyloc nut

full.jpg



Tank stabilisers are made from a longitudinal slice of rubber hose and a length of bungee
flim flam at the best, and stabilisers not utilising the plate slots, are defeating the purpose



So tighten your wingnuts with a tool

Doubles is different
 
M.M.O. stabilisers keep the tank close and permit NO movement and NEVER loosen
with a spring washer and wingnut
tightened with a tool

View attachment 543976

and would never loosen more with a nyloc nut

View attachment 543977


Tank stabilisers are made from a longitudinal slice of rubber hose and a length of bungee
flim flam at the best, and stabilisers not utilising the plate slots, are defeating the purpose



So tighten your wingnuts with a tool

Doubles is different
Where did you get that? Something I'd like to try.
 
In my opinion the direct cause of this incident was both wingnuts unscrewing and dropping of the bolts. Most likely they were not screwed tightly on the mandatory spring washer. Vibration of a motorboat can do real magic to loose bolts. Good all ended OK and the only harm was the embarrassment. As others said, check your nuts before diving.
It was mentioned in this thread to ditch STA or put cambands through the wing and the plate (if possible). For me this is not a solution. Exactly the same problem might affect doubles where the STA/cambands trick is not an option. Not to say that dropping doubles are more harm than a single tank. IMHO the only acceptable solution is checking the wingnuts before each dive. Same as checking each second stage reg, gauge, beer can, etc.
 
https://www.shearwater.com/products/perdix-ai/

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