A pressure vessel assembly comprising: a vessel (22, 24, 26) including a wall defining a chamber (40, 42, 44); a nozzle assembly (94; 96) including a tube (104; 128), characterised in that the pressure vessel assembly further comprises: a circumferentially continuous lip (100; 118, 124) projecting into the chamber (40, 42, 44) from the wall, the lip (106; 118, 124) defining a through-bore (102; 120, 126) in fluid communication with the chamber (40, 42, 44), wherein the tube (104; 128) projects at least in-part into the through-bore (102; 120, 126); and an o-ring (115; 137) disposed between and in sealing contact with the tube (104; 128) and the lip (100; 118, 124), wherein: the nozzle assembly (94; 96) includes a flange (106; 130) projecting radially outward from the tube (104; 128) and in contact with the wall; the tube (104; 128) includes a first portion (108; 132, 134) projecting axially into the chamber (40, 42, 44) from the flange (106; 130) and into the through-bore (102; 120, 126) and an opposite second portion projecting axially out of the chamber (40, 42, 44) from the flange (106; 130); the first portion (108; 132, 134) includes an outer surface having a contour (114; 135) constructed and arranged to engage the lip (100; 118, 124); the contour (114; 135) is circumferentially continuous; the contour (114; 135) is a barb (114; 135) constructed and arranged to produce a sealing friction between the lip (100; 118, 124) and the outer surface when the internal pressure of the vessel assembly is positive; and the vessel (22, 24, 26) includes a layer enveloping the wall, the flange (106; 130) is disposed between the wall and the layer, and the second portion projects through the layer. a vessel (22, 24, 26) including a wall defining a chamber (40, 42, 44); a nozzle assembly (94; 96) including a tube (104; 128), a circumferentially continuous lip (100; 118, 124) projecting into the chamber (40, 42, 44) from the wall, the lip (106; 118, 124) defining a through-bore (102; 120, 126) in fluid communication with the chamber (40, 42, 44), wherein the tube (104; 128) projects at least in-part into the through-bore (102; 120, 126); and an o-ring (115; 137) disposed between and in sealing contact with the tube (104; 128) and the lip (100; 118, 124), wherein: the nozzle assembly (94; 96) includes a flange (106; 130) projecting radially outward from the tube (104; 128) and in contact with the wall; the tube (104; 128) includes a first portion (108; 132, 134) projecting axially into the chamber (40, 42, 44) from the flange (106; 130) and into the through-bore (102; 120, 126) and an opposite second portion projecting axially out of the chamber (40, 42, 44) from the flange (106; 130); the first portion (108; 132, 134) includes an outer surface having a contour (114; 135) constructed and arranged to engage the lip (100; 118, 124); the contour (114; 135) is circumferentially continuous; the contour (114; 135) is a barb (114; 135) constructed and arranged to produce a sealing friction between the lip (100; 118, 124) and the outer surface when the internal pressure of the vessel assembly is positive; and the vessel (22, 24, 26) includes a layer enveloping the wall, the flange (106; 130) is disposed between the wall and the layer, and the second portion projects through the layer. the nozzle assembly (94; 96) includes a flange (106; 130) projecting radially outward from the tube (104; 128) and in contact with the wall; the tube (104; 128) includes a first portion (108; 132, 134) projecting axially into the chamber (40, 42, 44) from the flange (106; 130) and into the through-bore (102; 120, 126) and an opposite second portion projecting axially out of the chamber (40, 42, 44) from the flange (106; 130); the first portion (108; 132, 134) includes an outer surface having a contour (114; 135) constructed and arranged to engage the lip (100; 118, 124); the contour (114; 135) is circumferentially continuous; the contour (114; 135) is a barb (114; 135) constructed and arranged to produce a sealing friction between the lip (100; 118, 124) and the outer surface when the internal pressure of the vessel assembly is positive; and the vessel (22, 24, 26) includes a layer enveloping the wall, the flange (106; 130) is disposed between the wall and the layer, and the second portion projects through the layer.