Normally when you right click on a translocator you get a GUI where you can specify a filter so that only certain items go through the translocator. If you right click with a diamond nugget on a translocator you will see a light blue ring in the middle of it appear. This allows you to set amounts of items to maintain in the inventory the translocator is attached to. For example, you have two chests connected by a pair of translocators. The left chest is full of cobble, the right one empty. You put a diamond nugget on the right chest's translocator and set in the GUI to regulate 64 cobble. When you click with an empty hand the translocators so that items start to flow from left to right, the left chest will stop giving cobble to the right one when the right chest has 64 cobble in it. As soon as you take that cobble out of the right chest, the left chest will start giving it cobble again.
Imagine the same set up I just described expect you put the diamond nugget on the left chest. Set the left translocator to regulate 64 cobble. Then it will keep giving the right chest cobble until it has <= 64 cobble in its inventory.