The Network Valve Pipe is a pipe added by Project Red since v4.7.0pre11. It can be used in the middle of a pipeline or in a junction and allows the player to lock manually the movement paths in order to prevent/allow transport in certain direction (see Usage).
An example of a pipe system is shown in the picture. The Network Valve Pipes (here in the junctions) can be adjusted with a Screwdriver or an Electric Screwdriver. Simply right-click with the screwdriver on the outgoing pipe parts of the Network Valve Pipe. The gray arrow shows the locked direction (only input / only output). If no arrow is displayed, then input and output is allowed.
For example in the picture, items from the chests on the bottom can only be transported to the middle and then to the right to the Routed Request pipe, and not in the upper part of the pipe system. Items from the upper part can only be transported to the middle, and not in the lower part of the pipe system.