Balanced Flow State
Network analysis is based on two major principles:
Mass flow into a joint in the network must be equal to mass flow out of the joint. Assuming that the fluid density does not change, the total flow rate entering the node must equal the total flow rate leaving the node.
Figure 125 Flow balance at a join point
The pressure drop in the pipes around a loop must be equal to zero. In a recirculation loop the pressure loss in each pipe must be the total of the fluid head energy being provided by the driving force (normally a pump). In a loop where the flows are in opposite directions, the total pressure loss in each pipe with a clockwise flow must equal the total pressure loss in each pipe with an anticlockwise flow.
Figure 126 Pressure balance around a loop