In many user's eyes this is the biggest new feature that was added with the release of Civil 3D 2013. Although in the past we were able mimic pressure pipe design using the existing catalog, Civil 3D is now equiped with the necessary tools to design these networks.
Pressure networks share much of the same "feel" as gravity networks we all know and love. Similarities such as parts contained in a catalog, and populating a parts list. Layout is also very similar, meaning you will be prompted with similar options to associate the network with: surface, alignment. When actually laying out the network you will notice that will be constrained based on the available angles in the parts list. The "compass" as it is called will guide you with your available layout options.
Although this is just a brief introduction, I am sure many of you out there are excited to see this coming with the release of 2013. For more information and videos, please visit Civil 3D 2013 New Features.