Hi Mark
Our 450GPD was orginally supplied through Peter Fogwill.
The membranes were all connected in parallel - the feed from the carbon filter was split 3 ways, each supply the inlet of each membrane housings. The wastes were all joined together then through a restrictor/flush valve.
The pure oulets from each housing were again joined together to the IBC tank.
I have also seen 2 other variants over the years.
The first has been linked in series. The first membrane was connected from the carbon filter, the waste from that became the inlet for the second membrane housing and the second membrane's waste became the inlet for the third. The third's waste went to a restrictor. All pures were joined together. (I personally couldn't see the point of this setup other than that is reduced the no of 't' pieces in the assembly.)
http://www.ro-man.com/instructions/RO-MAN%20Reverse%20Osmosis%20manual%20for%20200%20and%20300%20GPD%20systems.pdfThe second variation I have seen is the pipe from the carbon filter is split into 2 and they each feed the first 2 membranes. The waste pipes from these 2 membranes are joined together and become the inlet of the third membrane. The third membrane's waste then goes to the restrictor. All the pures are joined up.