A packaging apparatus for forming a plurality of sealed packages filled with a pourable product comprising: - a conveying device adapted to advance a web of packaging material along an advancement path; - a tube forming and sealing device being adapted to form and longitudinally seal a tube extending along a longitudinal axis from the, in use, advancing web of packaging material; wherein the conveying device is also adapted to advance the tube along a tube advancement path; - a delimiting element moveably arranged, in use, within the tube and designed to divide the tube in a first space being in fluidic connection with an inner environment and a second space being arranged downstream of the first space along the tube advancement path; - a filling device having a filling pipe arranged, in use, within the tube and being adapted to direct, in use, a pourable product through the filling pipe into the second space; - a sterile gas supply device having a gas supply pipe being arranged, in use, within the tube and being configured to direct through the gas supply pipe a main flow of sterile gas into the second space in such a manner that the gas pressure within the second space is higher than the gas pressure within the isolation chamber; wherein the delimiting element is arranged such that the delimiting element is adapted to move into a first direction and a second direction being opposite to the first direction and the first direction and the second direction being substantially parallel to the longitudinal axis of the tube and between at least a first end position and a second end position, the first end position being upstream of the second end position along tube advancement path; wherein the gas supply pipe or the filling pipe comprises a main abutment portion; wherein the delimiting element comprises a main engagement portion configured to abut against the main abutment portion with the delimiting element being in the first end position; characterized in that it further comprises an isolation chamber separating said inner environment containing a sterile gas from an outer environment, wherein the tube forming and sealing device is at least partially arranged within the isolation chamber, and in that the main abutment portion and/or the main engagement portion are designed such that at least one opening and/or at least one channel is present between the main abutment portion and the main engagement portion with the delimiting element being in the first end position; wherein the at least one opening and/or the at least one channel are configured such to establish a fluid connection between the inner environment and the gas supply pipe through at least one opening and/or the at least one channel, so as to allow, in use, an auxiliary flow of gas to flow between the main abutment portion and main engagement portion with the delimiting element being in the first end position. - a conveying device adapted to advance a web of packaging material along an advancement path; - a tube forming and sealing device being adapted to form and longitudinally seal a tube extending along a longitudinal axis from the, in use, advancing web of packaging material; wherein the conveying device is also adapted to advance the tube along a tube advancement path; - a delimiting element moveably arranged, in use, within the tube and designed to divide the tube in a first space being in fluidic connection with an inner environment and a second space being arranged downstream of the first space along the tube advancement path; - a filling device having a filling pipe arranged, in use, within the tube and being adapted to direct, in use, a pourable product through the filling pipe into the second space; - a sterile gas supply device having a gas supply pipe being arranged, in use, within the tube and being configured to direct through the gas supply pipe a main flow of sterile gas into the second space in such a manner that the gas pressure within the second space is higher than the gas pressure within the isolation chamber; wherein the gas supply pipe or the filling pipe comprises a main abutment portion; wherein the delimiting element comprises a main engagement portion configured to abut against the main abutment portion with the delimiting element being in the first end position; characterized in that it further comprises an isolation chamber separating said inner environment containing a sterile gas from an outer environment, wherein the tube forming and sealing device is at least partially arranged within the isolation chamber, and in that the main abutment portion and/or the main engagement portion are designed such that at least one opening and/or at least one channel is present between the main abutment portion and the main engagement portion with the delimiting element being in the first end position; wherein the at least one opening and/or the at least one channel are configured such to establish a fluid connection between the inner environment and the gas supply pipe through at least one opening and/or the at least one channel, so as to allow, in use, an auxiliary flow of gas to flow between the main abutment portion and main engagement portion with the delimiting element being in the first end position.