A tying assembly, arranged along a line for the processing of substantially elongated products wrapped in a sheath, comprising: - at least one dispenser of twine, adapted for tying at least one protruding flap of the sheath, and - a slider for sending the product wrapped in the sheath to a processing station connected to said dispenser, said processing station comprising: - at least one compartment for accommodating the product, - a pneumatic circuit adapted for entraining the twine and consequently bending it around said compartment, in order to form and tighten a knot around the protruding flap of the sheath, and - a pair of mutually facing plates (5, 6), which are joined and crossed by a duct, which constitutes said compartment and is arranged along said processing line, characterized in that - said plates (5, 6) have mutually facing faces (5a, 6a) provided with a plurality of grooves that are sequentially connected so as to form a channel, - said pneumatic circuit comprising a pneumatic unit for entraining the twine along said channel formed inside said plates (5, 6) and outside said duct, - adapted partitions comprising elastically movable laminar elements, being arranged along said grooves of at least one of said faces (5a, 6a) of the plates, at the intersection points between facing portions of said channel, in order to shut off the grooves of the two plates at the intersection points, when the two plates are in contact with each other and the twine is bending into the channel in a first configuration for an arrangement to a subsequent knotting of the twine; said adapted partitions being suitable for allowing the exit of the twine from the channel by means of elastic bending of the partitions, when the plates (5, 6) are remove away each other and the twine is tightening in a second knotting configuration, in order to obtain the tightening of the knot around the sheath. - at least one dispenser of twine, adapted for tying at least one protruding flap of the sheath, and - a slider for sending the product wrapped in the sheath to a processing station connected to said dispenser, said processing station comprising: - at least one compartment for accommodating the product, - a pneumatic circuit adapted for entraining the twine and consequently bending it around said compartment, in order to form and tighten a knot around the protruding flap of the sheath, and - a pair of mutually facing plates (5, 6), which are joined and crossed by a duct, which constitutes said compartment and is arranged along said processing line, characterized in that - said plates (5, 6) have mutually facing faces (5a, 6a) provided with a plurality of grooves that are sequentially connected so as to form a channel, - said pneumatic circuit comprising a pneumatic unit for entraining the twine along said channel formed inside said plates (5, 6) and outside said duct, - adapted partitions comprising elastically movable laminar elements, being arranged along said grooves of at least one of said faces (5a, 6a) of the plates, at the intersection points between facing portions of said channel, in order to shut off the grooves of the two plates at the intersection points, when the two plates are in contact with each other and the twine is bending into the channel in a first configuration for an arrangement to a subsequent knotting of the twine; said adapted partitions being suitable for allowing the exit of the twine from the channel by means of elastic bending of the partitions, when the plates (5, 6) are remove away each other and the twine is tightening in a second knotting configuration, in order to obtain the tightening of the knot around the sheath. - at least one compartment for accommodating the product, - a pneumatic circuit adapted for entraining the twine and consequently bending it around said compartment, in order to form and tighten a knot around the protruding flap of the sheath, and - a pair of mutually facing plates (5, 6), which are joined and crossed by a duct, which constitutes said compartment and is arranged along said processing line, - said plates (5, 6) have mutually facing faces (5a, 6a) provided with a plurality of grooves that are sequentially connected so as to form a channel, - said pneumatic circuit comprising a pneumatic unit for entraining the twine along said channel formed inside said plates (5, 6) and outside said duct, - adapted partitions comprising elastically movable laminar elements, being arranged along said grooves of at least one of said faces (5a, 6a) of the plates, at the intersection points between facing portions of said channel, in order to shut off the grooves of the two plates at the intersection points, when the two plates are in contact with each other and the twine is bending into the channel in a first configuration for an arrangement to a subsequent knotting of the twine; said adapted partitions being suitable for allowing the exit of the twine from the channel by means of elastic bending of the partitions, when the plates (5, 6) are remove away each other and the twine is tightening in a second knotting configuration, in order to obtain the tightening of the knot around the sheath.