Abstract:
A flexible fabric tube is provided for heating, ventilation and air conditioning use having batten pockets longitudinally spaced and extending circumferentially around the tube and having flexible support members therein to maintain the tube in an open position.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to flexible air ducts, and more specifically, to a method for maintaining the lumen of a flexible air duct in open position. 
       BACKGROUND OF THE INVENTION 
       [0002]    Duct work used in connection with heating, ventilating and air conditioning systems is often formed of rigid metal, such as steel or aluminum. Flexible metallic ducts may be utilized in home buildings where they generally rest upon an attic ceiling. However, in warehouses, manufacturing plants, agricultural buildings, and many other structures, the ducts are suspended from the roof or ceiling and are thus exposed. For functional and economic reasons, it may be desirable to utilize flexible fabric ducts in these buildings. These fabric ducts typically have a flexible fabric wall that inflates to a generally cylindrical shape by pressure of the air being conveyed through the duct. Fabric ducts are relatively inexpensive and seem to inhibit the formation of condensation. In addition, the porosity of fabric and the ease of locating additional ventilation openings along the length of fabric duct work, allows fabric duct work to broadly and evenly disperse air throughout the room or building being conditioned or ventilated. 
         [0003]    In many cases, once the air supply fan for a room or building is turned off, the resulting loss of air pressure in the duct deflates the fabric tube causing it to sag. The sagging creates an unattractive appearance and when the duct is reinflated, the duct can create a visual movement and audible popping sounds as it becomes taunt. 
         [0004]    A number of efforts have been made to eliminate or reduce the sagging and popping noises and to achieve this goal, some inflatable ducts include a structure that helps hold a deflated duct in a generally expanded shape. Examples of ducts supported in such a manner are disclosed in U.S. Pat. No. 6,280,320 and U.S. Pat. No. 3,357,088. A significant drawback of these systems is the amount of supporting hardware necessary to keep the duct expanded. U.S. Publication 2008/0113610 discloses another attempt to maintain the shape of a fabric air duct when not being filled with pressure from an air supply fan, in the nature of hangers that attach to each side of the fabric duct and possibly also in the center top. While an improvement over prior systems, this latest published invention also requires substantial hardware and many attachments of the fabric duct to the suspension system. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    Therefore, it is an objective of the invention to provide an inexpensive, lightweight and simple method to maintain the lumen of fabric ductwork in an open position. This may be accomplished by adding a batten pocket around the circumference of the fabric tube and utilizing a support member, such as a length of polypropylene tubing, within the batten pocket to maintain the shape of the lumen even in the absence of air pressure from a ventilation blower. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a sectional view of a fabric duct tube suspended by a single connector at a top central portion of the tube, depicting the tube in its inflated and circular shape. 
           [0007]      FIG. 2  is an illustration of the fabric tube of  FIG. 1  in a deflated state when no air pressure is applied. 
           [0008]      FIG. 3  is an illustration of a prior art support hanger that attempts to maintain an open lumen in a fabric duct tube by utilizing multiple exterior fastening positions. 
           [0009]      FIG. 4  is an illustration of a fabric duct tube with only two external supports. 
           [0010]      FIG. 5  is a perspective view of a fabric duct tube having a batten pocket according to the present invention. 
           [0011]      FIG. 6  is an enlarged view of the opening of a batten pocket and a plastic tube support member according to the present invention. 
           [0012]      FIG. 7  is a side sectional view of a fabric duct according to the invention. 
           [0013]      FIG. 8  is an enlarged sectional view of a batten pocket on a fabric duct tube according to the present invention. 
           [0014]      FIG. 9  is a sectional view of a fabric duct according to the invention. 
           [0015]      FIG. 10  is a top plan view of an alternative batten pocket design with a fold down corner. 
           [0016]      FIG. 11  illustrates a commercial embodiment of a fabric tube according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring to  FIG. 1 , prior art fabric tube  12  is illustrated with a top central portion  32  and a top hanger mechanism consisting of fabric strap  14 , connector  22 , and overhead suspension line  34 . The tube  12  is shown in its fully inflated state as when an air blower is causing ventilating air to pass through lumen  15  of the tube  12 . 
         [0018]      FIG. 2  depicts the fabric tube  12  of  FIG. 1  when the ventilating fan is de-energized and the tube collapses due to the absence of air pressure. Phantom circle  11  illustrates the position occupied when the ventilating fan is energized and air pressure fills the lumen of tube  12 . 
         [0019]      FIG. 3  depicts the structure of prior art U.S. Publication 2008/0113610 in which a fabric tube  12  has a support  14  at the top center  32  and also has a support strap  25  on the left side and second support strap  27  on the right side which are attached to hanger  20  at left side  26  and right side  28 . A central portion  30  of hanger  20  may be received directly on suspension line  34  and the side straps  25 ,  27  and center strap  14 , may be longitudinally offset from hanger  20 . 
         [0020]      FIG. 4  illustrates the deflated configuration of tube  12  when a tube is supported only by left and right suspension straps  25 ,  27 , typically from left and right suspension lines, while phantom circle  11  illustrates the inflated circumference of the tube. 
         [0021]    Turning then to the present invention,  FIG. 5  shows a perspective view of fabric tube  12  having air vents  7  for ventilation, support strap  14  extending upward to a suspension line (not shown) from a top central portion  32  of the tube and batten pocket  55 . As shown in detail in  FIG. 6 , batten pocket  55  may be formed by attaching a fabric strap  50  around the circumference of a fabric tube  12  creating a pocket space  52  into which support member, such as plastic tube  51  may be inserted. In the illustrated embodiments, edges  53  of batten pocket  55  are finished in a straight line and spaced apart from each other by about 1-2 inches. 
         [0022]      FIG. 7  illustrates a longitudinal sectional view of fabric tube  12  with ventilation openings  7  and batten pocket  55 . A detailed view of batten pocket  55  is shown in  FIG. 8  with the opening  52  within batten pocket  55  filled by plastic tube  51 . A side sectional view of tube  12  in  FIG. 9  highlights the opening  60  at the top central portion of tube  12 . In the embodiment of the opening section shown in  FIG. 10 , one side of the batten pocket  55  is finished with a straight end  53  while the other side  58  is finished with a folding corner to facilitate entry of the support member such as plastic tube  51  within the pocket. The top central portion and folding corner may be fitted with hook and loop fastening material to secure the plastic tube  51  in the pocket space  52 . 
         [0023]      FIG. 11  illustrates a commercial embodiment of fabric tube  12  with ventilation tube opening  7  and batten pockets  55 . The support straps  14  extend upward from the top center portion of the tube to suspension line  34 . Suspension line  34  is in turn supported by guide rail  70 . 
         [0024]    The batten pocket  55  is advantageously performed by simply sewing or otherwise fastening a strip of cloth  50  around the outside of the diameter of the fabric duct work to form a pouch  52  that is preferably accessible from the top center portion  32  of the fabric duct  12 . The insertion of an appropriate length of plastic tubing, ideally of a length to completely encircle the outer circumference of the fabric duct work and provide an overlap sufficient to permit each end to entirely cross the opening section in the top center and be concealed within the batten pocket on the opposite side, provides sufficient rigidity to maintain the lumen  15  in a generally circular shape. Thus, plastic tubing having a length of about 6 inches or more in excess of the circumference of the outer diameter of the inflated duct work is desirable. The presently preferred support element for the batten pocket is polypropylene tubing having a diameter between about 1/4 th  inch and 1/2 inch (preferably 3/8 th  inches), thereby providing sufficient flexibility to insert into the pouch and form a circular configuration while having sufficient rigidity to hold the fabric duct open in a substantially circular state when no ventilating air pressure is present. The fabric or material utilized to form the batten pocket is typically the same fabric as the duct work, however, it may be made of different material or color in order to provide visual contrast. The support member need not be tubing but may also be a solid rod or shape having the desired flexibility, stiffness and resilience. 
         [0025]    The result of the invention is provide fabric duct work with improved aesthetics, easier installation, and smoother start ups through the absence of inflation movement and audible pop. This allows for smoother and quieter inflation upon equipment startup and avoids the necessity of unusual hanger structures and multiple attachment points around the circumference of the tubing.