Abstract:
A door system used in a doorway, which may be circular, of a pressurizable compartment of a high temperature structure, having a screw for compressing the door and a thrust collar providing clearance between the thrust collar and a bearing member during decompression of the door such that in the event the pressurizable compartment is pressurized, the pressure is relieved through the doorway while the door remains in contact with the doorway. The screw includes a shoulder, and the thrust collar is carried on the screw between the shoulder and the bearing member. The collar is configured to bear against the bearing member and the shoulder upon compression of the door. A debris guard covers and protects the screw during advancement and retraction of the screw, and a door frame is provided having weld slots for facilitating welding of the door frame to the high temperature structure.

Description:
[0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 10/909,240, filed Jul. 30, 2004, and U.S. Provisional application Ser. No. 60/491,370, filed Jul. 31, 2003, the entirety of the disclosures of which are incorporated herein by reference thereto. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to a door system, and in particular, to a door system suitable for use for high temperature applications such as boilers, flues, bag houses, precipitators, scrubbers, and the like.  
         [0003]     To gain access to compartments inside of boilers or other high temperature-type structures for inspection, repair, maintenance, such structures usually includes one or more access openings with doors. One such door is disclosed in U.S. Pat. No. 5,158,043, issued to Jon Emsbo, entitled “High Temperature Application. Door Installation.” This door is configured for a gas-tight sealing engagement with an access opening in a high temperature environment, and includes an outer door panel, and an inner door assembly with an inner door plate having one or more transversely extending yokes mounted thereon.  
         [0004]     Each yoke is pivotally attached at one end from one side of the door frame by hinges, and cooperates with a latch pin locking arrangement at the opposite end, which is used to maintain the door in a closed position. A handle is provided which, upon being turned, forces the inner door plate and yoke apart, and this reaction between the yoke and its associated mounting hinges and latch pin causes the inner door plate, which includes a peripherally-mounted sealing gasket, to be pressed firmly into engagement with the door frame, thereby sealing the door opening.  
         [0005]     U.S. Pat. Nos. 4,574,973 and 4,685,586, both issued to Lewis, et al., also disclose doors for high temperature applications.  
       SUMMARY OF THE INVENTION  
       [0006]     Generally, the present invention includes a door system having an improved yoke assembly and also a door frame design which facilitates attachment of the door system, and in particular the welding of the door frame, to a structure.  
         [0007]     The yoke assembly of the present invention includes a turning screw having two threaded portions. The first threaded portion is threadingly engaged with a nut block and contacts the front side of the inner door plate to cause the door, which is normally in a concave configuration, to flatten upon advancement of the turning screw, such that the inner door seals tightly around its periphery of the door frame. The second threaded portion receives a nut for fastening a handle to the turning screw.  
         [0008]     In sealing the door, the four corners of the door first contact the door frame. As the turning screw advances, however, the peripheral edges of the door also seal against the door frame due to the flattening of the concave, or dome shaped, configuration of the inner door against the door frame. This flattening feature is also due to an X-shaped bracing arrangement which is attached, preferably by welding, to the backside of the inner door panel. This bracing arrangement serves to more equally distribute the force supplied by the turning screw about the periphery of the door plate.  
         [0009]     The turning screw of the present invention also includes two projections, or, shoulders. The first shoulder acts as a bearing surface against which a thrust collar bears. The thrust collar is carried between the first shoulder and the backside of a plate of the yoke assembly, and allows for turning of the turning screw, even when the inner door is under pressure due to the pressure in the compartment, or such as when the door has been fully shut and the normally domed-shape of the inner door flattened. When the door is in this configuration, the dome shape of the door exerts an outward force on the turning screw, and simultaneously, if the door is sealing a pressurized environment within the structure, the pressurized environment would exert an outward force on the inner door. The second shoulder is located at the intersection of the second threaded portion of the screw.  
         [0010]     The turning screw also includes two flats which are received within a slot of the turning handle, and the slot prevents the turning handle from movement relative to the turning screw. The edges of the two flats are threaded, and a steel jam nut is threadingly carried thereon.  
         [0011]     A nut block is preferably bolted to the yoke assembly with two or more bolts, rather than being welded. This allows for easy maintenance and disassembly of the nut block, if necessary. The upper surface of the nut block includes a slot through which the stem of a T-shaped dust cover slides, as the turning screw is advanced towards and away from the inner door plate.  
         [0012]     The thrust washer provides for accurate spacing of the door and of the turning screw. This spacing allows, once the door has been closed, for a slight amount of play in the turning handle when it is desired to back out the turning screw in order to open the door. Through use of this play, or “window of opportunity,” the turning screw can be moved slightly and stopped. If the chamber to which the door is attached is under pressure, pressure from inside the compartment will immediately begin to be released from inside of the compartment, and such pressurized gas or fluid will immediately escape about the periphery of the door, while the four corners of the door still remain in contact with the door frame. This is a safety consideration in that should an attempt be made to open the door fully when the compartment sealed by the door is under pressure, by slightly turning the handle, it will be readily apparent that the door should not be opened, and the handle can then be turned in the direction to advance the turning screw inwardly, to again reseal the inner door. The resealing of the inner door is accomplished by flattening out the concave or dome-shaped configuration of the inner door.  
         [0013]     Further, in certain situations, there may be fly ash or other material physically pressing against the door, even if the compartment is not in a pressurized state. If the door is then attempted to be opened, the turning handle can be rotated slightly through the “window of opportunity,” and it will likely become apparent that fly ash or other materials are pressing against the door, prior to the door being fully opened. Again, the turning handle could be turned in the opposite direction to advance the turning screw inwardly to reseal the door, prior to the door being fully opened.  
         [0014]     In conjunction with the foregoing features of the door system of the present invention, a release pin is provided which prevents the door from inadvertently becoming opened. Once the door is sealed, it is very difficult to remove the pin, since it is under pressure due to its flattened concave state. However, as the turning handle is rotated in a direction to retract the turning screw, there will come a point where pressure is relieved in the yoke assembly as the door returns to its normally-concave configuration. At this point, the release pin can be removed. However, as noted above, when using the window of opportunity, the turning handle can be rotated a slight distance, which slightly opens the door, while still maintaining the four corners of the door in physical contact with the door frame. At this point, the release pin is still under lateral pressure, and is not removable. However, as noted above, also at this point, it can be readily determined whether the compartment is under pressure, or if material, such as fly ash is pressing against the door. In such an event, the door should again be resealed and the release pin maintained in place.  
         [0015]     Accordingly, the present invention includes a method of rotating the turning handle slightly to cause the door seal against the door frame to be broken, while still retaining the door generally in place and subject to reclosure. By breaking the seal, the operator is alerted if the chamber or compartment being sealed by the door is pressurized, or if there is undue pressure being applied against the door by fly ash material.  
         [0016]     In one preferred embodiment, there is a clearance of approximately twenty-four to twenty-five thousandths between the inner door and the thrust collar. The thrust collar is not threaded, and should not wander or creep. The thrust collar serves to accurately set and maintain the clearance, thereby allowing for the window of opportunity.  
         [0017]     The door system of the present invention includes components of a modular construction, and in particular, the nut block and handle, which allows for such components to be reassembled and parts replaced as necessary. In certain other doors in the prior art, for example, certain components may be welded, and such did not allow for easy maintenance and disassembly. Also in such doors, a dust cover was provided which was fixedly attached to the yoke and did not travel with the turning screw as the turning screw moved. This meant that the dust cover only protected part of the turning screw, as when the turning screw was fully advanced in a door sealing configuration. It is desirable to cover the turning screw with the dust cover in order to prevent fly ash and other corrosive materials and debris from settling on the threads of the turning screw. When such debris is deposited and accumulates on the threads of the turning screw, this can cause the threads of the turning screw to gall within the nut block, thereby potentially causing premature failure of the turning screw.  
         [0018]     The door system of the present invention includes a movable dust cover, including a T-shaped flat plate, preferably made of stainless steel. The plate includes a stem, which passes between two bolts used to fix the nut block to the yoke assembly. The nut block defines a recess, or, track in which the stem slides as the turning screw advances inwardly and retracts outwardly. Thus, the full length of the turning screw is generally covered by the stem of the dust cover as the turning screw moves inwardly and outwardly.  
         [0019]     The door system of the present invention also includes a door frame having slots defined in the face of the periphery thereof. These slots allow for the door frame to be welded to the structure from the front side of the door frame, thereby allowing for easy access. With certain doors in the prior art, the door frame required to be welded about the inner periphery, and also the outer periphery (in order to prevent the outer periphery from drawing in upon the inner being welded). In certain situations, it may be particularly difficult to weld the outer periphery since such outer periphery could be difficult to reach, particularly, if such door frame was against an outcropping or other projection of the structure, since clearance around the outer periphery would be minimized.  
         [0020]     Thus, with the slots defined in the face of the door frame, the inner periphery of the door frame can be readily welded, as well as the face or outer portions of the door frame.  
         [0021]     The present invention further includes a door generally round in shape having a turning screw with at least one lubrication passage and a generally circular gasket, which, in one preferred embodiment, has a generally D-shaped or a semi-circular-shaped cross-section. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The foregoing, as well as other objects of the present invention, will be further apparent from the following detailed description of the preferred embodiment of the invention, when taken together with the accompanying specification and the drawings, in which:  
         [0023]      FIG. 1  is a perspective view of a door system constructed in accordance with the present invention, with an. outer door in place;  
         [0024]      FIG. 2  is a perspective view of the door system illustrated in  FIG. 1 , with the outer door removed, and the inner door exposed;  
         [0025]      FIG. 3  is a perspective view a door system constructed in accordance with the present invention with the inner door open;  
         [0026]      FIG. 4  is an enlarged partial perspective view taken from the  FIG. 4  inset of  FIG. 3 ;  
         [0027]      FIG. 5  is a front elevational view, with parts cut away, of a door system constructed in accordance with the present invention;  
         [0028]      FIG. 6A  is a sectional view taken along line  6 - 6  of  FIG. 5 , illustrating an inner door of a door system constructed in accordance with the present invention, showing the inner door sealed;  
         [0029]      FIG. 6B  is a sectional view taken along lines  6 - 6  of  FIG. 5 , illustrating an inner door of a door system constructed in accordance with the present invention with the inner door in an intermediate configuration between being opened and sealed;  
         [0030]      FIG. 7A  is a sectional view taken along lines  7 - 7  of  FIG. 5 , illustrating an inner door of a door system constructed in accordance with the present invention in a sealed configuration;  
         [0031]      FIG. 7B  is a sectional view taken along lines  7 - 7  of  FIG. 5 , illustrating an inner door of a door system constructed in accordance with the present invention in a intermediate position between being sealed and open;  
         [0032]      FIG. 7C  is a sectional view taken along lines  7 - 7  of  FIG. 5 , illustrating an inner door of a door system constructed in accordance with the present invention in an open position;  
         [0033]      FIG. 8  is an exploded view of a yoke assembly of an inner door of a door system constructed in accordance with the present invention;  
         [0034]      FIG. 9  is a perspective view of an alternate embodiment door system constructed in accordance with the present invention, wherein the door is generally round in shape;  
         [0035]      FIG. 10  is a perspective view the alternate embodiment door system shown in  FIG. 9 , with the door being open;  
         [0036]      FIG. 11  is a front elevational view, with parts cut away, of the alternate embodiment door system shown in  FIG. 9 ; and  
         [0037]      FIG. 12  is a sectional view illustrating the alternate embodiment door system shown in  FIG. 9  in an intermediate configuration between being opened and sealed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0038]     The accompanying drawings and the description which follows set forth this invention in its preferred embodiment. However, it is contemplated that persons generally familiar with door systems will be able to apply the novel characteristics of the structures illustrated and described herein in other contexts by modification of certain details. Accordingly, the drawings and description are not to be taken as restrictive on the scope of this invention, but are to be understood as broad and general teachings.  
         [0039]     Further, the entirety of U.S. Pat. Nos. 5,158,043, 4,574,973, and 4,685,586 are incorporated herein by reference thereto.  
         [0040]     Referring now to the drawings in detail, wherein like reference characters represent like elements or features throughout the various views, the door system of the present invention is indicated generally in the figures by reference character  10 .  
         [0041]     Turning to  FIG. 1 , door system  10  is shown installed in a typical application within the wall, generally W, of a structure, generally S. Door system  10  includes an outer door, generally OD, within an exterior door frame, generally  14 . Outer door OD is held in place by rotatable retainers, generally  18 , which are pivotally connected to exterior door frame  14 . Handles  20  are attached to outer door OD to facilitate removal of outer door OD upon pivoting of retainers  18  to a position whereby outer door OD can be removed.  
         [0042]      FIG. 2  illustrates the inner door assembly, generally ID, of door system  10 , outer door OD having been removed. Note retainers  18  have been pivoted to a position which allows for removal of outer door OD from exterior door frame  14 , or installation of outer door OD within door frame  14 .  
         [0043]     Inner door assembly ID includes a compressible inner door  22  to which a bridge, cross-member structure, or, as referred to herein, a “yoke,” generally Y, is connected. Although the drawings of the present invention illustrate only one yoke Y being used in connection with inner door assembly OD, it is to be understood that multiple yokes could be used on inner door assembly ID, depending on the size and configuration of an inner door  22  used in a particular application, or as otherwise desired.  
         [0044]     Yoke Y includes a hinge, generally H, which pivotally attaches yoke Y to inner door frame, generally  24 . The other end of yoke Y includes a latch pin locking arrangement, generally  28 , ( FIG. 5 ) which includes an upper receiver  30  and a lower receiver  32  with an opening for receiving a latch pin  34 . A receiver  36  is fixed to inner door frame  24 , and is also configured for receipt of pin  34 , such that upon receivers  30 ,  32  being generally in line with receiver  36 , pin  34  may be inserted therein to securely lock inner door  22  in place within inner door frame  24 .  
         [0045]      FIG. 2  further illustrates a rotatable handle, generally  38 , attached for rotation with respect to yoke Y, as discussed in more detail later, handle  38  is fixed to a turning screw, generally  40 , having a jam nut  42  fixed thereto.  
         [0046]     A sag rod assembly, generally  44 , is connected between yoke Y and an upper hinge arrangement, generally  48 , which allows the upper end  50  of a sag rod  44  to pivot with respect to inner door frame  24 , as inner door  22  is moved between the open and closed positions.  
         [0047]      FIG. 3  illustrates the backside  54  of inner door  22 . A gasket  58  is provided about the periphery of inner door  22 . Gasket  58  is preferably constructed of material able to withstand high or extremely high temperatures, such as would be experienced in boilers, flues, scrubbers, precipitators, bag houses, and the like. Also provided on the inner surface  60  of inner door  22  is bracing, generally  62 , preferably in the form of an X, and preferably constructed of steel and being attached, such as by welding, to inner surface  60 . The X-shaped bracing helps to more evenly distribute forces applied to inner door  22 , particularly with respect to turning screw  40 .  FIG. 3  also illustrates a cable  64  attached to pin  34  in order to retain pin  34  on inner door  22  during use and during those times when pin  34  is removed from receivers  30 ,  32 , and  36 . The other end of yoke Y, which is attached to hinge H, includes hinge H having a hinge pin, generally  68 , which passes through upper and lower receivers  70 ,  72 , and also through a suitable receiver  74  within end  78  of yoke Y.  
         [0048]      FIG. 3  shows, and  FIG. 4  also shows in more detailed, inner door frame  24  having slots, generally  80 , provided about the periphery of inner door frame  24 . Inner door frame  24  is generally attached to frame members, generally F, of structure S by welding. In attaching such inner door frame to structure S, the interior periphery of inner door frame F is welded to the structure S as shown in  FIG. 4 , and the slots  80 , having weld surfaces  81 , provided in generally planar portions of frame  24  are also welded via welds  83  to structure S in order to maintain dimensional stability of inner door frame  24 , and in particular, to prevent warping or bending of inner door frame  24  upon welding of the inner periphery thereof to structure S. Note inner door frame  24  includes vertical flange portions  82 , and horizontal edge flange portions  84 .  
         [0049]      FIG. 5  illustrates inner door assembly ID in a position within inner door frame  24  characterized in that pin  34  is received in upper and lower receivers  30 ,  32 , and fixed receiver  36 . As shown in  FIG. 6A , which is a sectional view taken along lines  6 - 6  in  FIG. 5 , inner door  22  is shown in a closed, sealing position, with gasket  58  tightly sealing, in a gas-tight relationship, inner door  22  against inner door frame  24 . As also shown in  FIG. 6A , yoke assembly Y includes turning screw  40  being forwardly advanced in order to sufficiently compress and flatten inner door  22  from its normally concave, or dome-shaped configuration, as shown in  FIGS. 6B, 7B , and  7 C.  
         [0050]     Yoke assembly Y includes upper and lower cross-members  88 ,  90  and a receiver, or nut plate,  92  fixedly attached therebetween by two bolts  94 ,  96 . Nut plate  92  includes a threaded bore  98  for threading engagement with threaded portion  100  of turning screw  40 .  
         [0051]     As shown in  FIG. 8 , turning screw  40  has a threaded end portion  101 , with flats  102  for receipt in a cooperating slot  104  in handle  38 . The cooperation of flats  102  of turning screw  40  with slot  104  of handle  38  prevents relative rotation of handle  38  with respect to turning screw  40 . Jam nut  42  is used to fixedly attach handle  38  to turning screw  40 .  
         [0052]      FIG. 6A  illustrates a generally circular plate, or bearing member,  108  which is attached to arms  109  extending outwardly from inner door panel  22  ( FIG. 8 ) using bolts  111 .  
         [0053]     Turning screw  40  includes a first shoulder  110  ( FIG. 8 ), which engages the backside of handle  38 , and also a second shoulder  112  which provides a bearing surface against which a thrust collar  114  bears during operation of door system  10 . Thrust collar  114  is carried between shoulder  112  of turning screw  40  and the backside of plate  108 , and acts as a thrust bearing during inward advancement of turning screw  40  during sealing of inner door  22 , and also bears against the backside of plate  108  during reverse rotation of turning screw  40  when inner door  22  is to be opened. However, there is a slight amount of clearance, or, gap  116 , preferably on the order of twenty-four to twenty-five thousandths of an inch (0.024″-0.025″) to provide, as discussed above, the “window of opportunity,” when inner door  22  is to be opened. It is to be understood, however, that the present invention contemplates windows of opportunity involving clearances other than that specifically set forth herein. This clearance allows for a certain amount of rotation of handle  38  to relieve pressure applied by turning screw  40  to inner door  22 , by an amount such that, as shown in  FIG. 6B , inner door  22  begins to decompress and move slightly towards its normally concave profile, while, at the same time, maintaining the four corners of inner door panel  22  in contact with inner door frame  24 . However, continued rotation of handle H in a direction for withdrawing turning screw  40  eventually causes the four corners of inner door  22  to no longer contact inner door frame  24 , as shown in  FIG. 7C .  
         [0054]      FIG. 7A  shows inner door  22  in a closed, sealing position with respect to inner door frame  24 . In this configuration, pin  34  is received within upper and lower receivers  30 ,  32 , and fixed receiver  36 . Pin  34  is securely held in this configuration, and is not subject to being removed.  
         [0055]     In  FIG. 7B , inner door  22  has been slightly opened, perhaps through use of the window of opportunity, and the upper and lower edges of inner door  22  are still in contact with inner door frame  24 . In this configuration, pin  34  is still held in place within receivers  30 ,  32 , and  36 .  
         [0056]     In  FIG. 7C , however, inner door panel  22  has been pulled away from inner door frame  24  in a sufficient manner, through withdrawal of turning screw  40 , such that pin  34  can be removed from receivers  30 ,  32 , and  36 .  
         [0057]      FIG. 7C  also illustrates a generally vertically extending plate  118  to which a boss  120  is attached. Attached to boss  120  is a preload spring  122  which acts between yoke Y and inner door  22  for exerting a biasing force between inner door  22  and yoke Y. This thereby places a frictional load on pin  34 , preventing inadvertent the removal of pin  34 , which assists in preventing opening of inner door  22 . Also, this helps prevent damage to gasket  58  due to inadvertent interference between gasket  58  and inner door frame  24 .  
         [0058]     Turning to  FIG. 8 , it is noted that handle  38  includes offset portions  126 ,  129 , which provide relief for a user&#39;s hands by allowing the user&#39;s hands to be spaced further away from upper and lower cross-members  88 ,  90 , thereby improving the usability and potential comfort of handle  38 .  
         [0059]      FIG. 8  also illustrates a debris, or, dust, guard  130  constructed in accordance with the present invention. Dust guard  130  is of a generally T-shaped profile and serves to cover the threaded portion  101  of turning screw  40  during generally the full range of motion of turning screw  40 , as turning screw  40  advances to seal or retracts to unseal inner door  22 . Dust guard  130  includes a stem portion  132  and a transverse portion  134  connected thereto. Stem portion  132  is slidingly received within a recess  138  defined in the upper surface of nut block  92 . Stem portion  132  slides within recess  138 , and in a passage between bolts  94  and  96  as turning screw  40  is moved inwardly and outwardly, and shields threaded portion  101  from fly ash and other debris. By preventing accumulation of such debris on threaded portion  101 , the service life of turning screw  40  is improved in that galling and binding of turning screw  40  within the threads of nut block  92  is reduced.  
         [0060]     Turning to  FIGS. 9 through 12 , an alternate embodiment of the present invention is shown. In this embodiment, inner door assembly ID 1  includes an inner door  222  round in shape and operable to selectively close a round opening  255  in inner door frame  224 . Operation of inner door  222  is much the same as the operation of inner door  22  discussed above with inner door  222  having a yoke Y 1 , a hinge H 1 , and a sag rod  254 , the upper end  250  of which being attached adjacent an upper hinge arrangement  248 . A handle  238  is connected for rotation of a turning screw  240  and operates in substantially the same manner as handle  38  discussed above.  
         [0061]     Handle  238  is fixed to turning screw  240 , having a jam nut  242  fixed thereto. Inner door  222  is of a generally domed shape, particularly when inner door  222  is in the open position. Inner door  222 , however, becomes somewhat flattened upon being compressed through the turning of handle  238  upon sealing of door  222 . It should be noted that inner door  222 , due to its domed shape, does not require the bracing  62  discussed above with respect to inner door  22 , such bracing  62  being in one preferred embodiment in the form of an X.  
         [0062]      FIG. 10  illustrates inner door  222  separated from inner door frame  224 . Inner door  222  includes a circular, or ring-shaped, gasket, generally  258 , which is compressible, as is gasket  58  discussed above. However, gasket  258  includes a generally hemispherical cross section which flattens out somewhat upon compression and closure of inner door  222  against inner door frame  224 . In one preferred embodiment, the cross section of gasket  258  is generally hollow, defining a void, generally  259  ( FIG. 11 ), and is generally semi-circular, and in particular, generally D-shaped. Alternately, void  259  could include or be filled with gasket material, as shown in  FIG. 12 .  
         [0063]     Gasket  258  is preferably formed such that its contact surface  258 A ( FIG. 12 ) presents a relatively smooth, unwrinkled and pucker-free face for mating with inner door frame  224  during use. Gasket  258  is attached to the inner surface  260  of inner door, preferably, about the outer periphery thereof. In one preferred embodiment, gasket  258  is constructed of Viton® material, although other suitable materials could also be used.  
         [0064]     Inner door  222  includes a hinge pin  234  connected via cable  264  to yoke Y 1  in similar manner as to cable  64  and pin  36  discussed above. Similarly, yoke Y 1  includes an upper receiver  230  and a lower receiver  232 . Inner door frame  224  includes upper receiver  270 , and lower receiver  272 , for engaging with an end  274  of yoke Y 1 . A hinge pin  268  is received within a receiver  274  of yoke Y 1 .  
         [0065]     Inner door frame  224  includes a plurality of slots  280  having weld surfaces for allowing inner door frame  224  to be welded in a manner as discussed above with respect to inner door frame  24 . Pin  234  is received within a receiver  236  mounted on an inner door frame  224  in similar manner as pin  34  is received in receiver  36 , as discussed above.  
         [0066]      FIG. 11  shows inner door  222  in a closed position with pin  234  being received within receiver  236 . A yoke Y 1  attached to inner door  222  includes upper and lower cross members  288 ,  290 , respectively.  
         [0067]      FIG. 12  illustrates inner door  222  in an intermediate configuration between being opened and sealed, and is similar in that respect to  FIG. 7B  discussed above concerning inner door  22 . In  FIG. 12 , inner door  222  has been slightly opened, perhaps through use of the window of opportunity, and the upper and lower edges of inner door  222  are still in contact with inner door frame  224 . In such a configuration, pin  234  may still be held in place within receivers  230 ,  232 , and  236 .  
         [0068]      FIG. 12  also illustrates an alternate embodiment turning screw  240 . Turning screw  240  operates in a similar manner as does turning screw  40  discussed above. However, turning screw  240  includes a longitudinally extending passage  307  for carrying a lubricating fluid, such as oil, grease, silicon, etc. A lubrication supply, such as a fitting  305 , which could be a zerk fitting, or some other suitable fitting is provided for receipt of a lubricant. Lubricant supplied via fitting  305  passes into passage  307  and ultimately out radially disposed passages  303  having outlets or ports, generally  303 A and  303 B, for lubricating the interface between the threads defined in nut plate  292  and the threads defined on turning screw  240 . In one preferred embodiment, three ports  303 A and three ports  303 B are provided generally equidistantly spaced from one another, i.e., in approximately 120 degree intervals. By providing lubrication in this manner, the likelihood of turning screw  240  seizing within nut plate  292  is reduced, as such threads are provided lubrication to facilitate turning of screw  240 .  
         [0069]     It is to be understood that although inner doors  22  and  222  are shown in rectangular and round configurations, respectively, the inner door of the present invention is not limited to either such shapes, and could be other shapes, such as oval, oblong, triangular, polygonal, octagonal, or other shapes as required or otherwise desired for a particular application.  
         [0070]     Inner door  222  may find particular use in connection with the sealing of a cylindrical pressure vessel (not shown), such as a fiberglass industrial scrubber unit. Use of inner door  22 , by virtue of its round shape, allows for a circular doorway  255  to be used, and circular doorway  255 , by virtue of its circular shape and corresponding lack of corners, facilitates reduction of stress risers in the doorway.  
         [0071]     From the foregoing, it can be seen that the door system of the present invention provides numerous improvements and advancements over door systems found in the prior art.  
         [0072]     While preferred embodiments of the invention have been described using specific terms, such description is for present illustrative purposes only, and it is to be understood that changes and variations to such embodiments, including but not limited to the substitution of equivalent features or parts, and the reversal of various features thereof, may be practiced by those of ordinary skill in the art without departing from the spirit or scope of the following claims.