Help w/ jammed bridge in cistern

[Tetrafish]

Return to the Machine room (or whatever it's called, you know what I mean :-p ) where you placed the pipes on the wall. Look and see if there is a shadow of a gear on the floor. If it is rotating then you've completed the Machine Room 'puzzle'.

If that's not it then I don't know what else to suggest. But you can have the pipes on the wall but not in their correct places (even though they stay on the wall).