CONTROL VALVE FOR STEAM BOX

PCT No. PCT/US86/00269 Sec. 371 Date Mar. 14, 1986 Sec. 102(e) Date Mar. 14, 1986 PCT Filed Feb. 4, 1986.A control valve (22) is disclosed for controlled both the flow of steam (S) from a steam header (18) and air (A) into a steam box (12) of a web drying machine. The control valve (22) includes a valve body (26) defining a longitudinal passageway (28). The passageway (28) has a first and a second end (30,32) with the first end (30) of the passageway (28) being connected to, and in fluid communication with, the steam header (18). The second end (32) is connected to and in fluid communication with an air header (19). A first and a second valve seat (34,36) are disposed adjacent to the first and the second ends (30,32) of the passageway (28) for controlling respectively the flow of steam (S) and air (A) into the steam box (12). An elongate valve stem (38) having a first and a second valve closure (44,46) is movable axially within and along the passageway (28), the first and second closures (44,46) being disposed adjacent to a first and second end (40,42) of the valve stem (38). A stepping motor (48) is drivingly connected to the valve stem (38) for selectively moving the valve stem (38) axially relative to the passageway (28) such that when the valve stem (38) is moved, the change in flow of stem (S) into the steam box (12) is inversely proportional to the change in flow of air (A) through the second valve seat (36).