7231 Piped medical gas systems (0) Piped systems to distribute medical quality oxygen, nitrous oxide, nitrogen, carbon dioxide and gas mixtures to all user points 7232 Piped medical compressed air systems (0) Piped systems to distribute medical quality compressed air at designated pressures to all user points 7233 Piped medical vacuum systems (0) Piped systems to make available suction at user points 7234 Medical vacuum aspiration systems (0) Piped systems to make available suction at user points by aspiration