In Revit, the split command cuts a pipe or duct in two, leaving a fitting between each piece.
If you need to really separate the two endings, you need to break twice and delete what remains between.
There is a button "split with gap", but this button does nothing on pipes or ducts.
See video for example: https://knowledge.autodesk.com/community/screencast/0a216a02-ccb7-40e9-9581-9396182b1ea4
In AutoCAD MEP, splitting a pipe or duct leaves a real gap between each ending which size we can choose.
See example: https://knowledge.autodesk.com/community/screencast/7727df0d-81fb-4aa3-a416-86932626be8f
AutoCAD MEP does it clearly more fluently. Could it be possible that Revit does it as good?