Proof of systems performance, all valves work as advertised. The only parts that do not function are the four check valves, but they don't effect operation or capability. (In fact I’m not really sure why Boeing put them there, there are valves on both side of each one to control flow.)

Photo shows left external tank feeding #7&8 engines, with main tank pumps off.
Source--L. EXTERNAL
Force-- switch 17 (pumps on)
And a Place to go-- follow the lines across the bottom, up next to the AFT BODY, thru 14 and 10, across the top, thru 12 and into the #4 pylon manifold.

The engine guages in the upper left show the motors run fine like that!

The astute copilot will recognize that there are 3 other paths you can take also.

--Dan

---