Is it a woodworking vice? There's one Rededa which is a 7in (possibly a 9in version also?) wide wood vice which has it's own mechanism, needing no spring, just gravity.
You can tell if it's this one because it has a vertical slot rather than a round hole on the front jaw. To quick release, just lift the handle/tommy bar boss and move the jaw to desired position, drop the handle and give it a final turn.
This mechanism works fine, but doesn't open as wide as some.
