The insert you're seeing is probably a rubber umbrella valve stem seal. Normally you'd only have single springs and maybe a flat-wound damper spring which fits very closely to the inner diameter of the round single spring. Maybe you have dampers, maybe not. The damper is an interference fit with the single round wire outer spring and is meant to cancel harmonics in the spring. Actual "dual valve springs" will be 2 round wire springs and you'd be able to see both of them. Some dual springs also include the flat wound damper spring, some don't. I'm not for sure, but I don't think you can run dual springs with umbrellas, not enough room.
http://store.yahoo.com/cranecams/dualvalsprin5.html