A ventilator for use with alternative hose systems (33, 33a, 33b, 33c), wherein the ventilator comprises: at least one respiratory gas source; at least one device outlet (30, 30a) and one device inlet (31, 31a); at least one respiratory gas path (27, 29, 29a, 29b), which comprises a first respiratory gas path and a bypass, wherein the first respiratory gas path extends between the device inlet and the device outlet; and a gas control device for presetting the ventilator for the use of the alternative hose systems (33, 33a, 33b, 33c) by switching at least one switching apparatus (13, 13a, 46, 47), wherein the gas control device is designed to open the respiratory gas path for a respiratory gas flow for the use of one of the hose systems, which is a leakage system; wherein the first respiratory gas path comprises a respiratory gas drive and the gas control device with the bypass, the switching apparatus, and a check valve, wherein the respiratory gas drive is designed to guide an inspiratory respiratory gas flow from the device inlet through the check valve to the device outlet, wherein the check valve is arranged and designed to prevent a respiratory gas flow in the direction of the device inlet, wherein the bypass is arranged and designed to enable a respiratory gas flow to bypass the check valve, and wherein the switching apparatus is arranged and designed to at least temporarily enable or interrupt a respiratory gas flow through the bypass to bypass the check valve; characterized in that the switching apparatus is designed as a first valve and a further switching apparatus is designed as a second valve, wherein the second valve is designed to at least temporarily switch a return breathing pressure of an expiration of a patient to the first valve as a control pressure. at least one respiratory gas source; at least one device outlet (30, 30a) and one device inlet (31, 31a); at least one respiratory gas path (27, 29, 29a, 29b), which comprises a first respiratory gas path and a bypass, wherein the first respiratory gas path extends between the device inlet and the device outlet; and a gas control device for presetting the ventilator for the use of the alternative hose systems (33, 33a, 33b, 33c) by switching at least one switching apparatus (13, 13a, 46, 47), wherein the gas control device is designed to open the respiratory gas path for a respiratory gas flow for the use of one of the hose systems, which is a leakage system; wherein the first respiratory gas path comprises a respiratory gas drive and the gas control device with the bypass, the switching apparatus, and a check valve, wherein the respiratory gas drive is designed to guide an inspiratory respiratory gas flow from the device inlet through the check valve to the device outlet, wherein the check valve is arranged and designed to prevent a respiratory gas flow in the direction of the device inlet, wherein the bypass is arranged and designed to enable a respiratory gas flow to bypass the check valve, and wherein the switching apparatus is arranged and designed to at least temporarily enable or interrupt a respiratory gas flow through the bypass to bypass the check valve; characterized in that the switching apparatus is designed as a first valve and a further switching apparatus is designed as a second valve, wherein the second valve is designed to at least temporarily switch a return breathing pressure of an expiration of a patient to the first valve as a control pressure.