Patent Publication Number: US-2010107503-A1

Title: Astragal with expandable boot

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to an astragal for closing a space between two double doors, and more particularly relates to an astragal having an expandable boot for selectively blocking a relief area below the astragal. 
     BACKGROUND 
     Double doors are common in homes and buildings. Typically, a set of double doors includes an inactive door and an active door. The two doors are positioned adjacent to each other within a common door frame. Although both doors are capable of opening, the active door is generally used for routine ingress and egress, while the inactive door is generally kept closed and is only opened in special cases, such as when a wider opening is desired. 
     The inactive door is usually associated with an astragal, which is a jamb-like structure extending along a free edge of the inactive door, opposite from a hinged edge. Embodiments of astragals are disclosed in U.S. Pat. No. 5,350,207 to Sanders and U.S. Publication No. 2005/0116424 by Sanders, each of which is incorporated by reference. The astragal may facilitate locking the inactive door in a closed position. For example, the astragal may house upper and lower locking bolts that are operatively connected to a lever or other actuator. When the lever is engaged, the bolts may extend into corresponding wells in the door frame to lock the inactive door against the door frame. The lever may also retract the bolts from the wells to unlock the inactive door. 
     The astragal also may facilitate locking the active door against the inactive door. For example, the astragal may have a flange that forms a stop for capturing the active door as it closes. The astragal may also have an opening surrounded by a strike plate, and the active door may have a door knob with a bolt. When the active door is closed, the bolt of the active door may enter the opening in the astragal to hold the active door closed against the astragal. 
     The astragal may also form a seal between the two doors when the active door is closed, to reduce the passage of air, light, water, debris, and critters into the home or building. For example, the astragal may provide a mounting surface for a sealing member such as weather stripping. 
     The astragal may be coupled to the inactive door and may move with the inactive door as the inactive door opens and closes. To permit such movement, the astragal may not extend all the way to the floor. Instead, the astragal may be slightly spaced apart from a lower sill of the door frame, forming a small relief area. The relief area may permit the astragal to move with the inactive door without contacting the lower sill of the door frame or the floor. 
     One common problem is that the relief area provides a point of access into the home or building for air, light, water, debris and critters. To limit such access, the lower end of the astragal may be fitted with a boot or other closure piece. Typically, the boot is a sealing structure formed from a flexible material such as rubber. The boot may limit ingress through the relief area without limiting movement of the door, such as by partially but not completely filling the relief area. An embodiment of a boot is illustrated in U.S. Design Pat. No. D544,337 to Pepper et al., which issued on Jun. 12, 2007. 
     Although the boot may partially fill the relief area, the boot presents problems of its own. For example, the height of the relief area may vary widely, depending on variations and inaccuracies in the double door installation. For example, the inactive door may be hung too low, or adjacent portions of the lower sill or floor may be sloped. If the inactive door is hung too low or if the floor slopes upward away from the door frame, the boot may scrape against the floor as the inactive door is opened. On the other hand, if the inactive door is hung too far from the floor, the boot may not sufficiently fill the relief area, and ingress may be permitted. The boot may also sag, crumble, deteriorate, or otherwise fail with the passage of time, which may result from abrasion against the lower sill of the door frame. 
     One proposed alternative is a movable boot of the type described in U.S. Pat. No. 5,857,291 to Headrick, which is incorporated by reference. Such a movable boot may be moved into and out of the relief area, to fill or vacate the relief area as appropriate. One issue with the movable boot is that its size is fixed, meaning that the movable boot may only be suited for filling a relief area of a corresponding size. In other words, the movable boot may not be appropriately sized to fill relief areas of non-standard heights, which may be common due to variations or inaccuracies in installation. Another issue with the movable boot is that it may be difficult to operate. Specifically, the moveable boot may be lowered and locked by sliding a hand slide and twisting a recessed knob, which may be cumbersome for some, such as a lady with longer fingernails or a person with arthritis. The moveable boot also may not be adequately held against the sill to form a seal. 
     From the above, it is apparent that a need exists for a boot that can selectively close a relief area between an astragal and a lower surface, including relief areas of varying sizes. 
     SUMMARY 
     Described below is a system that may selectively block an area at an end of an astragal. The system may include an expandable boot and an actuator. The expandable boot may be positioned at the end of the astragal, and the expandable boot may be movable between a compacted shape and an expanded shape. The actuator may be operable to move the expandable boot between the compacted shape and the expanded shape. 
     Also described below is an astragal that may include an astragal jamb member, an expandable boot and an actuating member. The expandable boot may be coupled to an end of the astragal jamb member, and the expandable boot may be movable between a compacted shape and an expanded shape. The actuating member may extend from an end of the astragal, and the actuating member may be movable between a retracted position and an extended position. The actuating member may expand the expandable boot as the actuating member moves from the retracted position to the extended position. 
     Other systems, devices, methods, features, and advantages of the disclosed astragal with expandable boot will be apparent or will become apparent to one with skill in the art upon examination of the following figures and detailed description. All such additional systems, devices, methods, features, and advantages are intended to be included within the description and are intended to be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, and components in the figures are not necessarily to scale. 
         FIG. 1  is a perspective view of an embodiment of an astragal, illustrating the astragal positioned between double doors. 
         FIG. 2  is a top cross-sectional view of the embodiment of the astragal shown in  FIG. 1 , taken along line  2 - 2 , illustrating the astragal positioned between double doors in a closed position. 
         FIG. 3  is a partial side cross-sectional view of the embodiment of the astragal shown in  FIG. 1 , illustrating an expandable boot of the astragal in the compacted shape. 
         FIG. 4  is a another partial side cross-sectional view of the embodiment of the astragal shown in  FIG. 1 , illustrating the expandable boot as it assumes the expanded shape. 
         FIG. 5  is another partial side cross-sectional view of the embodiment of the expandable boot shown in  FIG. 1 , illustrating the expandable boot after achieving the expanded shape. 
         FIG. 6  is a top cross-sectional view of the embodiment of the astragal shown in  FIG. 1 , taken along line  6 - 6 , illustrating a profile of an embodiment of the expandable boot. 
         FIG. 7  is a partial side cross-sectional view of another embodiment of an astragal, illustrating an expandable boot of the astragal in a compacted shape. 
         FIG. 8  is a partial side cross-sectional view of the embodiment of an astragal shown in  FIG. 7 , illustrating the expandable boot of the astragal in an expanded shape. 
     
    
    
     DETAILED DESCRIPTION 
     Described below are embodiments of an astragal with an expandable boot. The astragal may be associated with an inactive door of a double door set. The expandable boot may be positioned on a lower end of the astragal adjacent to a sill of the door frame. The expandable boot may be selectively expanded and compacted. More specifically, the expandable boot may be expanded to substantially fill a relief area between the astragal and the lower sill of the door frame, to impede the passage of air, light, water, debris, and critters through the relief area. The expandable boot also may be at least partially removed from the relief area, so that the inactive door may be opened. The expandable boot may variably expand to fill relief areas of varying heights, which may be desirable in view of inaccuracies and variations associated with the double door installation. 
     In embodiments, the expandable boot may be operatively associated with a locking mechanism, which is otherwise employed to selectively lock the inactive door against the sill. In such embodiments, locking the inactive door may simultaneously expand the expandable boot to fill the relief area, while unlocking the inactive door may simultaneously compact the expandable boot to at least partially void the relief area. Thus, the relief area may be substantially filled by the expandable boot when the inactive door is locked, so that air, light, water, and other matter are blocked from passing through the relief area. However, the relief area may be at least partially unblocked by the expandable boot when the inactive door is unlocked, so that the inactive door may be opened without scraping the expandable boot against the lower sill of the door frame or the floor. 
       FIG. 1  is a perspective view of an embodiment of an astragal  100 , illustrating the astragal  100  positioned between a set of double doors  200 . As shown, the double doors  200  generally include an inactive door  200 A and an active door  200 B. The doors  200  are positioned adjacent to each other within a common door frame  202 . More specifically, each door  200  may include an upper edge  204  that abuts the door frame  202  about an upper jamb head  206 , a lower edge  208  positioned adjacent to the door frame  202  near a lower sill  210 , an outside or hinged edge  212  that is mounted to the door frame  202  along a vertical jamb  214 , and an inner or free edge  216  located opposite from the outside or hinged edge  212 . 
     Extending along the free edge  216 A of the inactive door  200 A is the astragal  100 . The astragal  100  may include an astragal jamb  217 , which may be, for example, an extruded member formed from aluminum, vinyl, fiberglass, plastic or wood, among others or combinations thereof. The astragal jamb  217  may be coupled to the free edge  216 A of the inactive door  200 A and may move with the inactive door  200 A. To accommodate such movement, a relief area  218  may be formed below the astragal  100 , which permits the astragal  100  to move with the inactive door  200 A without dragging against the lower sill  210  of the door frame  202  or the floor. The relief area  218  may have a height that varies depending on the double door installation. For example, the relief area  218  may have a height in the range of about  0 . 25  inches to about  0 . 75  inches, although other dimensions are possible. As shown, the relief area  218  may be occupied by an expandable boot  114  associated with the astragal  100 . The expandable boot  114  may at least partially block, fill, close, or otherwise occupy the relief area  218  to prevent or impede access through the relief area  218 . The expandable boot  114  may be operated via an actuator, which may be a locking mechanism  106  that is otherwise adapted to lock the inactive door  200 A against the lower sill  210 . 
       FIG. 2  is a top cross-sectional view of the embodiment of the astragal  100  shown in  FIG. 1 , taken along line  2 - 2 . As shown in  FIG. 2 , the astragal  100  may form a seal between the two doors  200  when both of the doors  200  are closed. More specifically, the astragal  100  may include a rearward or inner portion  102  that becomes captured between the two doors  200  when the doors  200  are closed, and a forward or outer portion  104  that remains exposed outside of the doors  200  when the doors  200  are closed. Thus, the astragal  100  may limit passage through the doors by filling a space between the doors  200  with the rearward or inner portion  102  and by extending over the free edges  216  and a portion of the door surfaces with the forward or outer portion  104 . Due to this shape, the astragal  100  may be referred to as a T-astragal. In most cases, the outer portion  104  of the astragal  100  directly abuts the inactive door  200 A, while the outer portion  104  astragal  100  indirectly abuts the active door  200 B via a weather stripping or other flexible seal  120 , as shown. 
     With reference to  FIG. 3 , the astragal  100  may include a locking mechanism  106  suited for locking the inactive door  200 A in a closed position. For example, the astragal  100  may house an actuating member, such as a locking bolt  108 , that is operatively connected to an actuator  110 . The actuator  110  may be, for example, a lever, a slider, a button, or a switch, among others or combinations of these and others. The actuator  110  may be engaged to move the locking bolt  108  between an extended position and a retracted position. In the extended position, the locking bolt  108  may extend into a receiving well  220  in the lower sill  210  to hold the inactive door  200 A closed. In the retracted position, the locking bolt  108  may be retracted into the astragal  100  so that the inactive door  200 A may be opened. 
     In the illustrated embodiment, the locking bolt  108  is positioned on a lower end of the astragal  100 , and the receiving well  220  is formed in the lower sill  210 . In other embodiments, locking bolts  108  may be positioned on lower and upper ends of the astragal  100 , and corresponding receiving wells  220  may be formed in both the lower sill  210  and the upper jamb head  206 . In such embodiments, the locking bolts  108  may employ a shared actuator or independent actuators. In still other embodiments, the locking bolt  108  may be positioned on the upper end of the astragal  100  but not on the lower end of the astragal  100 , in which case the actuator  110  may extend or retract the locking bolt  108  from a receiving well  220  in the upper jamb head  206  alone. 
     The actuator  110  may receive an actuating force from a user and may transfer the actuating force to the locking bolt  108 , causing the locking bolt  108  to translate between the extended and retracted positions. In embodiments, the actuator  110  may amplify the actuating force applied by the user. For example, the actuator  110  may include a spring  112 . When the actuator  110  is engaged to unlock the inactive door  200 A, the actuating force may cause the locking bolt  108  to retract while simultaneously loading the spring  112 . When the actuator  110  is engaged to lock the inactive door  200 A, the actuating force may release the spring  112 , which may drive the locking bolt  108  into the receiving well  220  to lock the inactive door  200 A against the lower sill  210 . Due to the release of the spring  112 , the driving force applied to the locking bolt  108  may exceed the actuating force applied to the actuator  110  by the user. In such cases, locking the inactive door  200 A may be relatively less difficult than unlocking the inactive door  200 A, as locking the inactive door  200 A may employ the assisting force of the spring  112 . 
     As shown, the astragal  100  may include an expandable boot  114  positioned adjacent to the relief area  218 . The expandable boot  114  may be coupled to a lower end of the astragal  100 , as shown. For example, an upper edge of the expandable boot  114  may be affixed to a lower edge of the astragal  100 , although other configurations are possible. The expandable boot  114  may be adapted to expand or contract, so that the expandable boot  114  may selectively fill or vacate the relief area  218  as desired. More specifically, the expandable boot  114  may be movable between a compacted shape in which the expandable boot  114  at least partially voids the relief area  218 , as shown in  FIG. 3 , and an expanded shape in which the expandable boot  114  at least partially fills the relief area  218 , as shown in  FIG. 4 . For example, the expandable boot  114  may substantially fill, close, or block the relief area  218  when in the expanded shape. 
     The expandable boot  114  may have any configuration that enables filling relief areas  218  of varying sizes. In other words, the expandable boot  114  may not have a fixed or finite height when in the expanded shape. Instead, the expandable boot  114  may have a variable height. When the expandable boot  114  is in the expanded shape, the boot  114  may assume a height that substantially matches the height of the relief area  218 , so that the boot  114  substantially fills the relief area  218 . For example, the expandable boot  114  may have walls that are accordion shaped, in which case a body of the expandable boot  114  may be a substantially hollow bellows. In such cases, the expandable boot  114  may be formed from a flexible material, such as rubber or other elastomeric material. In other cases, the expandable boot  114  may have other shapes or configurations that permit varying the height of the boot  114  to substantially fill the relief area  218 . For example, the expandable boot  114  may be formed from a series of interconnected telescoping members as described below with reference to  FIGS. 7 and 8 , among other configurations. 
     In embodiments, the expandable boot  114  may be operatively connected to the locking mechanism  106  that locks the inactive door  200 A against the lower sill  210 A. In such embodiments, locking the locking mechanism  106  may simultaneously expand the expandable boot  114  until the relief area  218  is substantially filled. Similarly, unlocking the locking mechanism  106  may simultaneously compress the expandable boot  114  until a void is formed in the relief area  218 . To accomplish such a configuration, the expandable boot  114  may house a flexible transfer structure  116 . The flexible transfer structure  116  may be adapted to transfer movement of the locking bolt  108  to the expandable boot  114 . More specifically, the flexible transfer structure  116  may be adapted to transfer movement of the locking bolt  108  to the expandable boot  114  until the relief area  218  is filled, and to absorb movement of the locking bolt  108  thereafter. Thus, the flexible transfer structure  116  may facilitate expanding the expandable boot  114  until the relief area  218  is filled. 
     The flexible transfer member  116  may be an internal spring  118 , as shown in  FIGS. 3-5 . The internal spring  118  may be generally semi-cylindrically shaped and may be formed from a flexible material, such as a thin sheet of metal. As shown in the illustrated embodiment, the internal spring  118  may have feet  120  that project outward from its peripheral edges. The feet  120  may be positioned in receiving folds  122  formed adjacent to a lower walls of the expandable boot  114 . In some cases, the feet  120  may be movably positioned within the receiving folds  122 , so that the feet  120  may travel laterally as the internal spring  118  flexes, while in other cases the feet  120  may be directly or indirectly coupled to the receiving folds  122  or other portions of the expandable boot  114 . In other embodiments, the feet  120  may be omitted, in which case peripheral edges of the internal spring  118  may be rest against or be coupled to walls of the expandable boot  114 . In still other embodiments, the flexible transfer structure  116  may any shape or configuration, or may be omitted completely. 
     So that the internal spring  118  is operatively associated with the locking mechanism  106 , the locking bolt  108  may extend through a hole  124  formed through the internal spring  118 . Above the hole  124 , the locking bolt  108  may have a projecting rim  126 . The projecting rim  126  may have diameter that exceeds the diameter of the hole  124 , so that the projecting rim  126  may engage and disengage the internal spring  118  as the locking bolt  108  travels through the hole  124 . 
     The operation of the expandable boot is described below with reference to  FIGS. 3-5 , which illustrate the relationship between the expandable boot  114  and the locking bolt  108  as the inactive door  200 A is locked, meaning as the locking bolt  108  moves from the retracted position to the extended position. When the inactive door  200 A is unlocked as shown in  FIG. 3 , the expandable boot  114  is in the compressed shape, the locking bolt  108  is in the retracted position, and the internal spring  118  is at rest. The projecting rim  126  of the locking bolt  108  may be positioned above the internal spring  118 , slightly spaced apart from the hole  124 , and the feet  120  of the internal spring  118  may be positioned within the receiving folds  122  slightly spaced apart from their walls. When the inactive door  200 A is locked as shown in  FIG. 5 , the expandable boot  114  is in the expanded shape, the locking bolt  108  is in the extended position, and the internal spring  118  is loaded. The projecting rim  126  of the locking bolt  108  may press against the internal spring  118  about the hole  124 , and the feet  120  of the internal spring  118  may contact the expandable boot  114  to hold the boot  114  down. 
     To move the expandable boot  114  from the compressed shape to the expanded shape, the inactive door  200 A may be locked. More specifically, the actuator  110  of the locking mechanism  106  may be engaged. Engaging the actuator  110  may impart a driving force on the locking bolt  108  that causes the locking bolt  108  to translate downward. With downward translation, the projecting rim  126  of the locking bolt  108  may contact the internal spring  118 . The locking bolt  108  may transfer a portion of the driving force to the internal spring  118  through the projecting rim  126 . In turn, the internal spring  118  may transfer a portion of the driving force to the expandable boot  114 , causing the walls of the expandable boot  114  to extend downward. For example, the feet  120  of the internal spring  118  may engage the receive folds  122  to cause the walls of the expandable boot  114  to extend from the accordion shape. The expandable boot  114  may continue such expansion until the lower wall of the expandable boot  114  contacts the lower sill  210 , as shown in  FIG. 4 . Thus, the expandable boot  114  may be expanded to a variable height, and the relief area  218  may be substantially filled. 
     With continued downward translation of the locking bolt  108 , the internal spring  118  may flex to absorb the force imparted by the projecting rim  126 , as shown in  FIG. 5 . The feet  120  of the internal spring  118  also may translate outward to contact the receiving folds  122 . The locking bolt  108  may become firmly seated in the receiving well  220 , so that the inactive door  200 A is locked. The internal spring  118  may become captured between the projecting rim  126  and the lower sill  210  to hold the expandable boot  114  down, such that the relief area  218  is filled and a tight seal is formed. 
     In embodiments in which the locking mechanism  106  includes a spring  112  as described above, the spring  112  may facilitate sealing the expandable boot  114  against the lower sill  210 . For example, the spring  112  may force the projecting rim  126  against the internal spring  118  of the expandable boot  114 , as shown in  FIG. 5 . Thus, the internal spring  118  may be partially loaded, such that the internal spring  118  holds the expandable boot  114  against the lower sill  210 . However, other configurations are possible in other embodiments. 
     With reference back to  FIG. 3 , the expandable boot  114  may be maintained in the compacted shape when the inactive door  200 A is unlocked. Further, the expandable boot  114  may be moved from the expanded shape to the compacted shape as the inactive door  200 A is unlocked, meaning as the locking bolt  108  moves from the extended position to the retracted position. For such reasons, an end of the locking bolt  108  may be fitted with a movable tip  128 , which may assist with compacting the expandable boot  114  and maintaining the boot  114  in the compacted shape. 
     More specifically, the movable tip  128  may be movable between an outwardly projecting position, in which the tip  128  projects laterally outward from a central axis of the locking bolt  108  as shown in  FIG. 3 , and an upwardly projecting position, in which the tip  128  projects longitudinally upward along the central axis of the locking bolt  108 , as shown in  FIG. 5 . In embodiments, the tip  128  may be normally maintained in the outwardly projecting position, such as via a small spring near the tip  128 . 
     When the locking bolt  108  is in the retracted position as shown in  FIG. 5 , the tip  128  may be in the outwardly projecting position. Thus, the tip  128  may engage the expandable boot  114  to maintain the expandable boot  114  in the compacted position. For example, the tip  128  may contact a lower surface of the internal spring  118 . As the locking bolt  108  translates downward into the extended position, the tip  128  may contact the lower sill  210 , causing the tip  128  to rotate upward into the upwardly projecting position. Thus, when the locking bolt  108  is in the extended position as shown in  FIG. 5 , the tip  128  may fit within the receiving well  220 . As the locking bolt  108  translates upward into the retracted position, the tip  128  may become removed from the receiving well  220  and may return to the outwardly projecting position under the force of the spring, or alternatively, under the force of gravity. With continued upward movement of the locking bolt  108 , the tip  128  may catch against expandable boot  114  to pull the expandable boot  114  into the compacted shape. For example, the tip  128  may contact and pull the internal spring  118  upward, which may raise the walls of the expandable boot  114 , such as through the interaction of the feet  120  with the receiving folds  122 . Thus, retracting the locking bolt  108  from the receiving well  220  may simultaneously compact the expandable boot  114  into the compacted shape so that a void is formed in the relief area  218 . Thereafter, the expandable boot  114  may be maintained in the compacted shape until the actuator  110  is again engaged to translate the locking bolt  108  downward. 
     As described above, the expandable boot  114  may be operatively coupled to the locking mechanism  106  of the inactive door  200 A. In other embodiments, the expandable boot  114  may have its own actuator. The actuator may be separate from the locking mechanism  106 , in which case the locking mechanism  106  may or may not be provided. Further, the expandable boot  114  may be positioned on an upper end of the astragal  100  in other embodiments. In such cases, the expandable boot  114  may close a relief area above the astragal  100  adjacent to the upper jamb head  206  of the door frame  202 . In still other embodiments, the astragal  100  may have expandable boots on both upper and lower ends of the astragal, in which case both expandable boots may be associated with the same or different actuators, which actuators may or may not be the same as the actuators that operate the locking bolt or bolts. 
     As mentioned above with reference to  FIG. 2 , the active door  200 B may indirectly abut the outer portion  104  of the astragal  100  via the weather stripping  120 . So that the weather stripping  120  does not drag against the floor as the inactive door  200 A is opened, the weather stripping  120  may not extend into the relief area  218 . Instead, the weather stripping  120  may stop at about the lower end of the astragal  100 . In such cases, the expandable boot  114  may have a profile or outer shape that is selected to include the portion of the relief area  218  located below the weather stripping  120 , as shown in  FIG. 6 . More specifically, the expandable boot  114  may be shaped to substantially fill the relief area  218  located below the rearward or inner portion  102  of the astragal  100  between the doors  100 , and also located below the forward or outer portion  104  of the astragal  200  in the vicinity of the weather stripping  120 . Such a profile may be selected to ensure the expandable boot  114  forms a tight and complete seal, although other profiles are possible in other embodiments. 
     The description above pertains to just one example embodiment of an astragal with an expandable boot, although other configurations are possible in other embodiments. For example,  FIGS. 7 and 8  are partial side cross-sectional views of another embodiment of an astragal  700  with an expandable boot  714 , with the expandable boot  714  shown in a compacted shape in  FIG. 7  and an expanded shape in  FIG. 8 . 
     As shown, the expandable boot  714  may include telescoping walls  730 . As shown the telescoping walls  730  may include fixed walls  732  and movable walls  734 . The fixed walls  732  may be fixed in a vertical direction, and the movable walls  734  may be movable in the vertical direction. More specifically, the movable walls  734  may be associated with the locking rod bolt  708  or other actuating member via a flexible transfer structure  716 . The flexible transfer structure  716  may transfer movement of the locking bolt  708  to the movable walls  734 , to move the expandable boot  714  from the compacted shape to the expanded shape. In the illustrated embodiment, the fixed walls  732  are on the outside of the expandable boot  714  and the movable walls  734  are on the inside, although the configuration may be reversed or altered in other embodiments. 
     When the expandable boot  714  is in the compacted shape, the expandable boot  714  may be relatively “compacted” in the vertical direction. The movable walls  734  may be in a vertical upward position with reference to the fixed walls  732 , such that the vertical height of the expandable boot  714  as a whole may be at a minimum. As shown in the illustrated embodiment, the movable walls  734  may actually may be extended, hanging freely under the force of gravity, and yet the vertical height may be at a minimum due the relatively elevated position of the movable walls  734  within the expandable boot  714 . 
     As the expandable boot  714  moves from the compacted position to the expanded position, the vertical height of the expandable boot  714  may increase. More specifically, as the locking bolt  708  translates downward, the movable walls  734  may translate downward with reference to the fixed walls  732 . At some point, the movable walls  734  may contact the lower sill  210 A, such that the expandable boot  714  assumes the expanded shape. Thus, the vertical height of the expandable boot  714  in the expanded shape may be relatively greater than the vertical height of the expandable boot  714  in the compacted shape. With continued downward translation, the movable walls  734  may compress slightly against the lower sill  210 A, forming a tight seal. 
     The flexible transfer structure  716  may have a range of configurations. For example, the flexible transfer structure  716  may include washers  736  attached to the locking bolt  708 , and flexible shims  738  extending from the washers  736  to the movable walls  734 . In use, flexible transfer structure  716  may transfer movement of the locking bolt  708  to the movable walls  734 . More specifically, the washers  736  may translate with the locking bolt  708 , and such translation may be transferred to the movable walls  734  through the flexible shims  738 . Once the movable walls  734  contact the lower sill  210 A, the flexible shims  738  may absorb at least a portion of the further displacement of the locking bolt  708 , forming a tight seal against the lower sill  210 A. The movable walls  734  may also partially flex with reference to the lower sill  210 A, although other configurations are possible 
     While particular embodiments of an astragal with an expandable boot have been disclosed in detail in the foregoing description and figures for purposes of example, those skilled in the art will understand that variations and modifications may be made without departing from the scope of the disclosure. All such variations and modifications are intended to be included within the scope of the present disclosure, as protected by the following claims.