2 routes.
Upper route, from the parking area up from the mini-roundabout head away from the village along the right hand track passing some open pits, at the top of the hill, look for a ruined stone building on the right and a large gap in the fence and an obvious path which almost immediately heads down into a pit and into the mine. This is the air receiver chamber.
Lower route, From the parking area, head along the lower track, at the gate go straight on through the gate and follow the path to a small bridge over a stream. Follow this stream upstream (some bits are over wellie depth so it's best to stick to the bank) until you come to the adit.