Here are a couple of movies submitted for your perusal: They describe piping systems with parallel pipes, the first with two parallel pipes, the second with 8 parallel pipes.
Here's the situation:We're given a certain geometry (some number of pipes, their lengths, material--for establishing surface roughness--and the length and material of the one pipe that they flow into. We're also given the total pressure drop through the entire parallel-series system. O.K. What we want to find is how much water flows through each pipe. WELL, the solution is one where we first guess how much pressure is lost across the parallel section, figure out what flow would cause this pressure loss, then estimate how much water flows in the single pipe that the parallel pipes flow into by the same method. Then we check the sum of all the parallel flows versus the single pipe flow (they should be equal). We adjust our original guesses of pressure loss based on any inequality, and try again. Eventually, everything smooths out and we consider that we've figured out the real flows in all the pipes.
What the movies show:The two movies listed below show lines of different colors, each one representing the flow in one of the pipes in the system. They begin from a basically cruddy first guess to being very correct (and so very little change) in the later adjustments. Several are bunched together (the parallel ones), and there's one much higher than the rest (the one they all flow into). 2-Pipe Movie
shows how the flow calculations are adjusted in a system where there are two pipes feeding into a single one. And just to show off the flexibility of my very clever program, 8-Pipe Movie
shows how the flow calcs go for an 8-into-1 setup. Yeehaw! Enjoy 'em!