Emerald pipes are round robin.
Meaning: If you have 2 different items, it will pull the first item, then wait for the second before pulling out the first item again.
This allows you to create an exact ratio: If you want 5 of item A for every item B, you put item A in the list 5 times, then item B once. However, it does mean that if you just want to sort out two different items and not maintain a specific ratio that you need two different pipes.