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Discussion in 'FAQs' started by justind, Dec 9, 2002.
What does it mean when you see "Sprung" in the description for switch mechanisms?
I think it means that the points are held against the rails by a spring wire somewhere in the mechanism. Whatever moves the points (solenoid, motor, fingers) has to overcome the pressure of the spring to get them off the rail they're on. Peco is that way, don't know about others.
If you're talking about models, I'll use ground throws as an example. Caboose industries make little plastic mechanisms for changing your switch by hand. They come in 2 variations--the cheaper ones just move sideways a certain distance and you have to match that with your turnout. The more expensive ones have a spring in the throwbar and it moves farther than the switch points and the spring takes up the difference.
There are also mechanisms with "over-centre" springs that hold the points in position. The spring holds the mechanism at one end or the other and has to be stretched then released when it is changed.
If you're talking about prototype, there's a thread on page 2 of technical Q&A called turnout position where prototype spring switches are discussed.
I think in a sprung switch the turnout points are held in one position (say the straight route) by a soft spring. So the train running from the point end into the turnout always goes straight. However when a train comes from the other side on either route it can pass the turnout without derailing. On the diverging route the wheels just open the switch, then the points return to the straight position again.
This can be used e.g. on a balloon track which is alway passed the same way - here straight into the balloon and back from the diverging route.
Take care about electrical polarity when you aren't running DCC, however!