Control valve for a steam box

A valve for controlling both the flow of steam from a steam header and air from an air header into a steam box of a web drying machine, said valve comprising in combination:

• a valve body means disposed adjacent to the steam header for controlling the flow of steam and air relative to the steam box;
• longitudinal passageway means defined by said valve body means, said passageway means having a first and a second end, said first and second ends of said passageway means being connected to, and in fluid communication with respectively, the steam header and the air header for permitting the passage therethrough of steam and air;
• a first and second valve seat disposed adjacent to said first and second ends of said passageway means for controlling respectively the flow of steam and air into the steam box;
• an elongate valve stem movable axially within and along said passageway means, said valve stem having a first and a second end;
• a first valve closure disposed adjacent to said first end of said valve stem for cooperating with said first valve seat for selectively controlling the flow of steam from the steam header into the steam box;
• a second valve closure disposed adjacent to said second end of said valve stem for cooperating with said second valve seat for selectively controlling the flow of air into the steam box;
• and
• a stepping motor drivingly connected to said valve stem for selectively moving said valve stem axially relative to said passageway means such that when said valve stem is moved, the change in flow of steam into the steam box is inversely proportional to the change in the flow of air through said second valve seat so that when said first valve closure is progressively opened relative to said first valve seat, flow of steam into the steam box is increased and said second valve closure is progressively closed relative to said second valve seat to correspondingly reduce the flow of air into the steam box, and when said first valve closure is progressively closed relative to said first valve seat, flow of steam into the steam box is reduced and flow of air into the steam box is correspondingly increased.

A valve for controlling both the flow of steam from a steam header and air into a steam box of a web drying machine, said valve comprising in combination:

• a valve body secured between the steam box and the steam header such that distortion between the steam box and the steam header due to thermal stresses is allowed for, said valve body defining a longitudinal passageway;
• said passageway having a first and second end, said first and second ends of said passageway being connected to, and in fluid communication with respectively, the steam header and an air header;
• a first and second valve seat disposed adjacent to said first and second ends of said passageway for controlling respectively, the flow of steam and air into the steam box;
• an elongate valve stem movable axially within and along said passageway, said valve stem having a first and a second end;
• a first valve closure disposed adjacent to said first end of said valve stem for cooperating with said first valve seat for selectively controlling the flow of steam from the steam header into the steam box;
• a second valve closure disposed adjacent to said second end of said valve stem for cooperating with said second valve seat for selectively controlling the flow of air into the steam box;
• and
• a stepping motor drivingly connected to said valve stem for selectively moving said valve stem axially relative to said passageway such that when said valve stem is moved, the change in flow of steam into the steam box is inversely proportional to the change in flow of air through said second valve seat, so that when said first valve closure is progressively opened relative to said first valve seat, flow of steam into the steam box is increased and said second valve closure is progressively closed relative to said second valve seat, to correspondingly reduce the flow of air into the steam box, and when said first valve closure is progressively closed relative to said first valve seat, flow of steam into the steam box is reduced and flow of air into the steam box is correspondingly increased.