The reducers in the duct ventilation and air-conditioning systems serve the purpose of increasing or decreasing the pressure in the air supply system. They are available in two
versions: A - nipple version (e.g. F09-RPCL-125-100) to be joined on both sides with the ventilation spiro pipes; B - sleeve-nipple version (e.g. F09-RPCFL-125-100) in which the smaller diameter enters into the round pipe, and the larger
diameter overlaps another fitting – most frequently the T-pipe.