1) Generally a pipe through which air might pass. In coal-mining it had to do with ventilation.
Eg. in 1651, ‘air was forced by bellows through trunks or wooden pipes’. Such pipes are mentioned several times in the records of Beeston Pit near Leeds: in 1754, for example, there were payments for fetching air pipes from Horton [near Bradford] and, in 1755, for nails to mend the Air Pipes.