Picasa,
I'll try to explain this as best I can, please reply with questions if you need clarity.The floating tubesheet is captured between the backing ring and the floating head flange. The outside diameter of the backing ring and the floating head flange is normally greater than the inside diameter of the main shell.The only way that the bundle can be removed from the exchanger is to pull the floating tubesheet (on the bundle skid bars) through the main shell.If you do not remove the floating head assembly, then you cannot remove the bundle from the shall.The split key normally fits into a groove in the floating tubesheet.The outside diameter of the split key is larger than the inside diameter of the backing ring.To remove the bundle : loosen off the floating head assembly studs;seperate the floating head flange (attached to the dished cover) from the backing ring.Push the backing ring towards the main shell, away from the split key.Since the key is in two halves, remove the key.With the key removed, the backing ring can be slid over the floating tubesheet.In this manner, the floating head assembly can be removed from the floating tubesheet.Look closely at the drawing you have, or see TEMA Fig.RCB 5.141.Assembly in the opposite manner.
Hope this helps.
John
