Using the Undo and Redo Functions
When you add a single pipe or a single node in the Drawing pane, you can undo the add pipe or node action to remove the pipe or node from the Drawing pane. If you change your mind about an undo action, you can redo the pipe or node in the Drawing pane.
To undo an add pipe or node action in the Drawing pane, click the Undo button, 
, on the tool bar or select Edit | Undo.
To redo an undo action in the Drawing pane, click the Redo button, 
, on the tool bar or select Edit | Redo.
NOTE: If you added new components, such as fittings or flow demands, to a pipe or node, and you then click the Undo button or select Edit | Undo, and then click the Redo button or select Edit | Redo, then the pipe or node will be re-added to the Drawing pane without the components. When you use the undo action for a pipe or node with components, any components that were not drawn as part of the default pipe are permanently removed from the pipe.