A machine for converting a web of preformed pouches into inflated dunnage units, the pouches defined by transverse seals extending from a remote edge to within a predetermined distance from an inflation edge, the machine comprising: a guide pin (56, 856) for insertion between the transverse seals and the inflation edge to define a path of travel of the web; a tensioning device for frictional engagement with the web, wherein the tensioning device holds the web taught during downstream travel, wherein the tensioning device comprises: an inflation arrangement (160, 960) for inflation of the preformed pouches; a sealing arrangement (162, 962) positioned to provide a longitudinal seal that intersects the transverse seals to close the preformed pouches and form a dunnage unit, the sealing arrangement (162, 962) having at least two sealing belts (70, 870), each belt powered by a drive roller and positioned to engage a surface of the web and pull the web through sealing elements (64, 864) positioned on either side of the web; and a clamping arrangement (110, 910) positioned to pinch the two layers of the web during travel through the sealing elements (64, 864), the clamping arrangement (110, 910) having at least two pinching belts, each belt powered by a drive roller and positioned to engage a surface of the web and pull the web and pinch the web through the sealing elements (64, 864) wherein the two sealing belts (70, 870) are disposed between the two pinching belts and the inflation edge; wherein the at least two sealing belts (70, 870) and the at least two pinching belts are driven in sync; characterized in that the tensioning device further comprises: a shelf member with a horizontal portion below a centerline of the guide pin (56, 856) and a downstream and upwardly angled portion; and a pivotable arm mounted to the machine, with one end of the arm attached to a spring and a roller rotatably attached to the other end of the arm; wherein the roller engages the web and the web frictionally engages the shelf member. a guide pin (56, 856) for insertion between the transverse seals and the inflation edge to define a path of travel of the web; a tensioning device for frictional engagement with the web, wherein the tensioning device holds the web taught during downstream travel, wherein the tensioning device comprises: an inflation arrangement (160, 960) for inflation of the preformed pouches; a sealing arrangement (162, 962) positioned to provide a longitudinal seal that intersects the transverse seals to close the preformed pouches and form a dunnage unit, the sealing arrangement (162, 962) having at least two sealing belts (70, 870), each belt powered by a drive roller and positioned to engage a surface of the web and pull the web through sealing elements (64, 864) positioned on either side of the web; and a clamping arrangement (110, 910) positioned to pinch the two layers of the web during travel through the sealing elements (64, 864), the clamping arrangement (110, 910) having at least two pinching belts, each belt powered by a drive roller and positioned to engage a surface of the web and pull the web and pinch the web through the sealing elements (64, 864) wherein the two sealing belts (70, 870) are disposed between the two pinching belts and the inflation edge; an inflation arrangement (160, 960) for inflation of the preformed pouches; a sealing arrangement (162, 962) positioned to provide a longitudinal seal that intersects the transverse seals to close the preformed pouches and form a dunnage unit, the sealing arrangement (162, 962) having at least two sealing belts (70, 870), each belt powered by a drive roller and positioned to engage a surface of the web and pull the web through sealing elements (64, 864) positioned on either side of the web; and a clamping arrangement (110, 910) positioned to pinch the two layers of the web during travel through the sealing elements (64, 864), the clamping arrangement (110, 910) having at least two pinching belts, each belt powered by a drive roller and positioned to engage a surface of the web and pull the web and pinch the web through the sealing elements (64, 864) wherein the two sealing belts (70, 870) are disposed between the two pinching belts and the inflation edge; wherein the at least two sealing belts (70, 870) and the at least two pinching belts are driven in sync; characterized in that the tensioning device further comprises: a shelf member with a horizontal portion below a centerline of the guide pin (56, 856) and a downstream and upwardly angled portion; and a pivotable arm mounted to the machine, with one end of the arm attached to a spring and a roller rotatably attached to the other end of the arm; a shelf member with a horizontal portion below a centerline of the guide pin (56, 856) and a downstream and upwardly angled portion; and a pivotable arm mounted to the machine, with one end of the arm attached to a spring and a roller rotatably attached to the other end of the arm; wherein the roller engages the web and the web frictionally engages the shelf member.