The Filter from Redpower has two major functionalities.
If placed near any block with an inventory, it acts as an advanced Transposer with the benefit of choosing what types of items and what quantity will be pulled out of the connected inventory. The default number of items pulled out of the connected inventory per pulse is a stack of same items (does not have to be a full stack though!). Like the Transposer, it will only pull the items out of the inventory when it receives a redstone pulse.
If placed between two Pneumatic Tubes, it acts as a filter. That is, only items that are listed in the Filter's inventory can pass through. If the inventory is empty, filter will allow any and every item to go through. In this mode, it doesn't require a redstone signal to operate, but when a constant redstone signal is applied, it will prevent all items going through to the connected Tube network.
The Filter can also tag items passing through it with a color chosen by the player. It's done by clicking on a gray box in the filter's GUI.
To continue pulling items out of connected inventories, it needs a redstone pulse, by using a connected Timer on high frequency for fast extraction.
The filtering function will only work as intended if Pneumatic Tubes are connected to the input and output ends exclusively. Any other side of the filter will input any item in to the filter's internal storage.
Unused items returned to the Filter (for example from a Regulator) are "stored" in the first Pneumatic Tube connected to the output face.
- If you only want the Filter to pull out a stack of a certain items per pulse, you must put a stack of that item in the filter, not just one single item.
- The Filter and Transposer look very similar, but the filter has a bar at the bottom of the side, closer to the output circle.