Iron Fireman stoked pipe replacement

I used a picture I found elsewhere on this site. My stoked was missing the pipe on the left. It's an odd size, but I did manage to find something to work to replace it, but I'm now noticing the small diameter pipe branching off from the front of the middle auger feed pipe, over to the pipe on the left which is the blower pipe. So it essentially appears to be diverting a little air to the front of the auger feed. I can make this mod, but I was wondering if someone could tell me the purpose? Thanks

It keeps smoke and fumes from backing up the pipe and into the hopper.

Much appreciated. Thanks!