Question Lift bag with internal OPV confusing me

[crowndiver]

I found this lift bag at a garage sale. It has an internal OPV, which is clearly intentional because there's a cord that runs down the inside to the opening at the bottom. I was messing around with it in the pool and while it holds air, the OPV doesn't seem to do anything. How does this thing work?

I've searched all around and while I did see someone mention one in another SB thread, I don't see any explanations as to how they work.

Please see pics--the fourth pic is a view up the opening to where you can see the OPV inside. It's hard to tell but it is just an ordinary looking OPV.

 

[tursiops]

Mine like that is designed to be a snag-free way to release some air from the bag while using it to move something underwater. You put air in, and adjust for neutral. If you go up a bit, you need to release a bit more. It sounds like your OPV might be stuck and not opening when you pull the cord.

 

[rongoodman]

Which is why modern lift bags have the OPV at the top, not on the bottom like SMBs.

 

[grf88]

There may not have been enough pressure in the bag to allow it to work if you were just trying it at the surface. Add a weight and take it down a few feet and then try it.

 

[crowndiver]

Thanks all, it did work with more weight and a firmer pull