A ventilator for use with alternative hose systems , wherein the ventilator comprises: at least one respiratory gas source ; at least one device outlet and one device inlet ; at least one respiratory gas path , 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 by switching at least one switching apparatus , 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 and one device inlet ; at least one respiratory gas path , 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 by switching at least one switching apparatus , 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. <EOS>