Maybe a bug, or they just suppose to work so far from what I used to in other pipe mods that I can't get them to work for me, senario:

How are item pipes suppose to work, tried to move items from 3 sources to one goal block.

Block character map:
S: source (item creator/source)
G: goal block (chest)
E: item extractor (with lever)
P: Item Pipe
H: hopper

== Try 1 ==
First i used 3 extractors and 2 pipe:

SSS
EEEPG

but items got stuck between extractors.

== Try 2 ==
guessed that extractors don't let items pass,
so switched to 3 pipes:

SSS
EEE
PPPG

also used the hammer to remove the connection between the extractors.

The problem just moved, now items gets stuck in the pipes instead.

== Try 3 ==

Removed the connections between the pipes, and made a chain of hoppers:

SSS
EEE
PPP
HHHG

works, but takes up 3 rows, so moved the hoppers ontop of the pipes.

== Applying to building ==

connecting that up on all 4 sides of the source building and i got:

____HHHHHHH
____EEE___H
____SSS___H
___BBBBB__H
HESB___BSEH
HESB___BSEH
HESB___BSEH
H__BBBBB__H
H___SSS___H
H___EEE___H
HHHHHHHHHHG

so an 11x11 hopper-line around the 5x5 building.
If i rebuild the building one level up, i could have just built a 7x7 hopper line under the source-blocks..

(modpack project ember, melting gold blocks into gold plates)

Read the codex entry for how the pipes work, and hold a tinker's lens to understand the flow better

The pipes will always prefer to move items straight

If theres a split and it can't go straight, it will split items to both sides

if an item goes somewhere where it can't continue, it clogs

Use item transfers to control directional flow, if there is a transfer it will always take priority over other pipe paths

And note that they always need to arrive at an output storage or it will be backed up since the items move continuously through pipes rather than when they can go to a storage

For your example, you would not want to use extractors like that next to eachother. The items will split since they can't go straight and will attempt going back toward the other item sources and clog

Video example I just made for flow control
https://www.youtube.com/watch?v=SzR4zwTUSjs

Thanks for trying to explain it, even if there was no audio in the video.

So if an item "turns" in the wrong direction, it can't turn back.
And a circle including the extractors don't work,

but a circle of pipes kind of solves it:

But when the pipes between 2 joins get colliding deliveries, (of the same item), they still clog.

So in every pipe-join it goes both left and right, making items going both CW & CCW, but then it clogs due to the items going both directions.

Think I'll just give up and stick with hoppers.

If you want to merge pipes you'll have to use item transfers, they act as a one-way pipe. You can also combine both outputs into one chest and pipe out of that to merge them but it's bulkier.

combining 12 sources with [item transfer]s or combine them into 4 bins and re-excract them, both seams a lot bulkier then my earlier solution with the hoppers.

If there was a one-way pipe block that accepted input from all other sides, it may be useful, but hoppers already do that well.

Compared to other item pipes like: pipez, mekanism, Modern Dynamics, they all feel easier to use then hoppers, but the ember pipes may work well for pipes with one source, but feels very messy for multiple sources.

Gave up and added pipez to my world: