About 20-25 lbs should be OK
There's about 2# of air in that pony tank (around 0.8 or 0.9 KG)
If you're lifting something heavy off the bottom, maybe a lift bag would be safer....
Anyway, I've got a little 20-pound wing (or maybe it's about 22#?) on a SS back plate, bought from Halcyon about 20-years. It's a nice little set-up. I've used it for much larger Aluminum "80" though.
I checked it by floating it in the pool recently.
weight with marker buoy + fingerspool attached = 13.44#
weighs 4.65# negative when submerged in a saltwater swimming pool (basically fresh water)
approx 18# reserve lift
Just curious: Why the preference for a shoulder pull dump valve?
My old Zeagle BC for recreational dives had that feature and I liked it and used it all the time, so I get it! Possible to dump air without raising your hand over your head.
It would be very easy, I think, to retrofit that onto almost any wing. Pretty sure there are only two thread types for the air cell attachments to inflator hose elbows and OPV's. Coarse thread and fine thread. Just need to get the correct elbow and then run a cable down through the corrugated hose and pin it off to the LPI.
