digraph G {
rankdir=LR;
node [shape=box, style=filled, fillcolor=lightgrey];
Inlet [label="Air Inlet", shape=circle];
C1 [label="Chamber 1\n(Water Filter)", fillcolor=lightblue];
C2 [label="Chamber 2\n(Water + Humidifier)", fillcolor=lightblue];
C3 [label="Chamber 3\n(Petrol + Humidifier)", fillcolor=orange ];
C4 [label="Chamber 4\n(Water Seal / Arrestor)", fillcolor=lightblue];
Stove [label="Gas Stove / Burner", shape=doubleoctagon, fillcolor=red ];
Inlet -> C1 [label="Bottom Feed" ];
C1 -> C2 [label="Top to Bottom" ];
C2 -> C3 [label="Top to Bottom" ];
C3 -> C4 [label="Top to Bottom" ];
C4 -> Stove [label="Final Gas Output"];
{rank=same; C2 C3}
}