as earlier noted in open communication with dispersal duct 7 to provide for opening and closing movement of upright support structure 2 the same is rail supported by pairs of upper and lower gear racks indicated at 26 and 27 upper racks 26 are secured in place on beams 29 affixed at their ends to support structure 1 and to a pair of braces at 28 lower racks 27 are secured to floor 3 to assure uniform movement of upright structure 2 rail engaging upper and lower pinions at 30 and 31 are in toothed engagement with their respective racks a drive motor at 33 fig3 on support structure 2 is in driving engagement with upper and lower pinions 30 and 31 by a right angle reduction drive 34 output shaft 35 sprockets 36 37 and roller chains 38 39 which in turn drive sprockets 40 and 41 affixed to pinion carrying shafts 42 43 pillow block bearings at 44 and 45 carry the shafts motor 33 is reversible to power support structure 2 toward and away from support structure 1 a motor control is indicated at 46 on stationary support 1 limit switches as at 49 limit motor operation a switch 47 on structure 1 at an operator 39 s station is in circuit with a solenoid valve 48 in a steam line sl to permit operator control of steam flow into the airflow of duct 9 and ultimately to the draperies.