The transfer node underneath will pull the obsidian out as soon as the lava transforms. One stone barrel should have a water source block on top of it to turn the lava into obsidian. Use transfer pipes connected to the transfer nodes to a barrel that collects the products. Each stone barrel should have a transfer node underneath it to pull out what it produces.
Attach three stone barrels to the transfer pipe, each a space apart from each other and the last crucible. The six transfer pipes should be in a line with the liquid transfer nodes. Connect six transfer pipes to the end of the liquid transfer nodes on the side of the crucibles. Running down the length of the of the crucibles put a liquid transfer node on each crucible. It will begin filling rapidly with cobblestone as will the crucibles, and they should immediately begin melting the cobblestone in the crucibles into lava. Put a barrel on top of the transfer pipe at the far end away from the cobblestone. On top of the crucibles, run transfer pipes that connect to the transfer node on top of the cobblestone block.