Its because of the 4-way pipes. the octagon of the pipe is pointy-side-down. By the time I realized it was a bad choice, it was already too late.
I could possibly edit and reexport every pipe if enough people complain. or just modify the valve to not actually fully shut off the view through the pipe.
I'll put up a poll and if it gets enough votes i'll redo it. but that will mean i can't work on the XCOM weaponset update, previewed in this post from the 3d modeling topic.
xcom weaponset remodeling