Device for sealing bags or packages in a heat-sealable plastic material provided with parts for regulating the welding pressure

A sealing device for one of sealing bags and packages in a heat-sealable plastic material, each of said packages containing a portion of product, said packages being sealed in a packaging machine, wherein a tubular strip is longitudinally fed and gradually filled with said portion of product, said sealing device comprising:

• at least two welding elements transverse to said strip and opposite one another;
• a respective support element carrying each of said at least two welding elements;
• means for driving the support elements of said at least two welding elements along a respective circular path to move said support elements close to one another and a longitudinal section moving with the web so that said at least two welding elements compress opposite edges of said tubular strip against each other, thereby welding said edges, and to separate said support elements for allowing passage of said tubular strip between said at least two welding elements, said sealing device, by welding the opposite edges of said tubular strip, defining a plurality of packages;
• said driving means comprising at least a first and a second cylinder for a pressurized fluid provided between each of said at least two welding elements and their respective support elements, said first and second cylinders for the pressurized fluid having a respective piston and a respective compression chamber, each respective compression chamber containing the respective piston, said piston being integral respectively to one of said at least two welding elements corresponding thereto and being integral respectively to one of the support elements corresponding thereto, each of said compression chambers containing a pressurized fluid having a fluid pressure that is maintained substantially at a constant level for allowing said at least two welding elements to be pressed against each other along said longitudinal section when the circular paths of the at least two welding elements cross.