Try this. An easy one I think.
Graigwen - The last time I was at Jackdaw Quarry Cave, it was draughting inwards too. I sprayed canned smoke in the final dig/crawl to the shaft, back out towards the entrance and it reversed quickly, blew through the crawl but went up the shaft, into the boulders above towards the surface, not down the shaft, even though there was water falling.