- Turn around from the third valve and go back to the intersection of beams behind you and look to the West.
- Above you is a shooting target switch.
- If you do not want to climb anymore, you can simply shoot the switch from here.
- Otherwise, you will want to jump (and mantle) into the window and onto the balcony beyond it.
- Turn to the right and climb up onto the beam coming out of the wall.
- Continue to the right and climb through the opening above the beam.
- Across from you is is the Target Valve you need to shoot to activate.
- Shoot it to add the last ingredient of fuel.