The At Pac was made with a couple different versions of the inflator hose/fitting assembly. The plastic version was subject to cracking and this was one of the main reasons many were eventually retired. The metal version of the inflator hose fitting was much more durable but subject to corrosion over time. (I have noted that the old proprietary At Pac inflator quick disconnect is for all practical purposes dimensionally identical to the current standard fitting used by most companies with the exception that the At Pac QD used a 1/8" NPT thread rather than a more normal 1/4" NPT thread.)
The other common reason for At Pac retirement was the tendency for the seams to let go rather catastrophically on the bladder when they got old.
The At Pac looks a lot like a BP/Wing and while the general design is back in style and the At Pac was great in it's day, don't be lulled into thinking it did not have it faults.
One serious design fault with the At Pac was the incorporation of the over pressure relief valve for the bladder into the inflator hose assembly. It was a little too small and could create the potential to rupture the bladder in a rapid ascent. If you are going to get badly bent on an uncontrolled ascent, it is even worse if your badly bent unconcious self then sinks back to the bottom due to a ruptured wing.
Another serious design fault was that the shot needed to be large enough not to fall out the cracks in the gate at the bottom of the pack but was then consequently large enough to pack, form a bridge and consequently not dump reliably when you needed it to. It also required marbles to be loaded in the top to take up extra space and prevent the shot from shifting, so adjusting weight was a real PITA as all the shot had to come out, then the marbles, then remove shot, add marbles, re-install and then repeat if neccesary. It was I think the oprignal integrated weight system but was a little ahead of it's time and needed just a bit more engineering.
In short, it has probelms with the basic design and you would be far better served with a modern BP/Wing. It's faults were apparent by the end of 70's and early 80's and I switched to a Scubapro back inflate BC as it incorporated a large OPV on the bladder, used a normal power inflator and hose and was generally more durable.
Weight integration of a sort could be accomplished with the SP wing by filling the backpack with shot. It could hold about 11 pounds but was not readily removeable. The SP wing went out of production in the early 80's however as wings were considered "bad" by that time and I was stuck diving with jacket style BC's for the next decade and a half.
The original Seatec wing is still made:
http://www.lloydbaileysscuba.com/Seatec.html
It could be used with any of the integrated weight pockets form OMS, Dive Rite, etc that mount on the harness in the corner formed by the waist and shoulder straps. (which is also a far better and safer approach to weight integration with an At Pac) But it is a little spendy and for the money you could go with a regular BP and wing from OMS, Dive Rite or a variety of other companies.
