A chute system having a pneumatically actuated access door where the door is journally mounted to an access port in the wall and communicates with the chute to direct objects inserted into the access port to the chute. When an operator actuates a switch, the door may be opened by a pneumatic forcer connected between the access port frame and the door so as to form a lever arm about the door journal. The pneumatic forcer is mounted to the door with a slidable journal such that the door may be opened manually. The duration of the open state of the door is determined by a timing mechanism which removes the pneumatic pressure after a time has elapsed, enabling a spring to urge the door into the closed position.

This application claims the benefit of U.S. provisional application No.:60/536,798, filed on Jan. 15, 2004, which is incorporated herein by reference. 


   BACKGROUND OF THE INVENTION 
   This invention relates to the art of chute systems, and more particularly to chutes for the collection and disposal of refuse of various kinds, as well as the collection and distribution of materials. Further, this invention relates to a mechanism for opening a chute door. 
   Chute systems are found in numerous applications, such as for the collection of trash in high rise buildings, the collection of laundry in hotels and hospitals and for the collection of medical or other waste. They may also be found in materials handling applications in industrial facilities. For safety or sanitary reasons, chute systems may be fitted with a door closing the opening into the chute during times that material is not being introduced into the chute. This prevents the discharge of particulate matter, odors or other contaminants into the surrounding environment. Also, in the case of a fire or explosion in the chute system, the door provides a barrier which mitigates the effect of the event. 
   Existing door systems are normally manually operated where the operator opens the door, inserts the material for which the chute is designed, and closes the door. Doors may be fitted with an opening handle and a latch mechanism, such as may be found on a conventional room door, to ensure that the door remains closed when not in use, and may also be fitted with a closing mechanism to urge the door closed. The closing mechanism may be in the form of a spring, with coil spring, leaf spring air spring and pneumatic spring mechanisms being known in the art. 
   Manually operated doors normally require that the operator use one hand to open the door, and to hold the door open during the period where the material is being introduced into the chute system through the door. If the load is heavy or the operator is handicapped, this may be both awkward and dangerous. In addition, a manually operated door may be opened even if dangerous conditions exist in the chute system, such as a fire, smoke or noxious fumes. 
   Electrically operated chute doors are known, and they mitigate some of the problems mentioned above, but themselves have disadvantages. Complex mechanical linkage mechanisms are required to effect the door opening and closing, and the electric motor is susceptible to overheating and burn out in the event the door becomes jammed in any position, open, partially open or closed. One means of preventing the continued operation of the motor is to place the motor on a timer, but the motor will operate against the resistance of the jammed door for the entire period that the timer permits. Other means of preventing the continuing operation of the motor include microswitches to sense the open and closed position of the door. It is well known that microswitches present a maintenance and adjustment problem. Another problem associated known electrically actuated doors is that the mechanical linkage mechanism may not permit the door to be opened manually. Attempting to open the door manually may place undesirable stresses on the mechanical linkages and result in a requirement for frequent maintenance. 
   BRIEF SUMMARY OF THE INVENTION 
   Features of the present invention may mitigate the difficulties previously described, as well as improve the operation and safety of chute systems. These objectives are achieved while minimizing the complexity of the mechanical components needed to effect the automatic opening and closing of the chute door. 
   In accordance with the present invention, a chute system, which is a generally vertically oriented enclosed space, having a vertical extent generally at least equal to the highest story of a building or facility to be serviced, is fitted with a door assembly at each story to be serviced by the system. The chute itself is normally enclosed in a fireproof material for safety reasons. The door assemblies are constructed of material ordinarily intended to retard fire or explosion in accordance with local or industry building codes, or to meet the requirements of the designer. The opening of the door is initiated by an operator actuating a switch located in proximity to the door, or by a sensor that determines the presence of an operator. The door may be disposed such that it is journalled to a frame which is mounted so as to fill an opening in the wall of the chute system, the door closing an opening in the frame when the door is in a closed position. In one aspect, the door may be mounted such that, when it opens, an end of the door distal to a journalled base end rotates outwardly (that is, towards the operator) with respect to the chute such that the door makes an angle of approximately 45 degrees with respect to the horizontal when fully opened, although other orientations and opening limits may be employed. The extent and direction of the door opening and depends on the specific design requirements. Preferably the angle is less than 90 degrees with respect to the horizontal, so as to provide an inclined surface to direct the material into the chute. 
   A pneumatic supply, which may be installed in a common area, provides pressurized air to one or to a plurality of door opening mechanisms. When the opening of a door is initiated as described above, pressurized air is introduced into a main pneumatic cylinder or pneumatic forcer disposed between the door and the door frame of the door assembly. The main pneumatic cylinder rod actuates in response to the air pressure and urges the door open. The door is rotatably moved from a closed position to the fully opened position. A spring is also connected between the frame and the door, and it is actuated by the opening and rotation of the door, resulting in the development of a restoring force about the journal, said force initially being less than the opening force exerted by the main pneumatic cylinder. The door continues to rotate until a mechanical limit is reached, or the rotational forces about the journal exerted by the main pneumatic cylinder and the spring balance each other. 
   The door is held in its open position as long as the pneumatic pressure is applied to the main pneumatic cylinder. The time duration of this pressure is controlled by a pneumatic timer valve. The duration may be fixed or adjustable in accordance with the details of the design. At the end of the opening time period, the pneumatic pressure is relieved in the main pneumatic cylinder and the pneumatic spring urges the door closed. Mechanical or pneumatic springs may be used. 
   In accordance with another aspect of the present invention, the door is also capable of being opened manually. The main pneumatic cylinder is attached to the door and to the frame such that a force applied to the outside of the door by an operator grasping a provided handle is operable to rotate the door as if it had been urged by the main pneumatic cylinder. The door may be opened to any rotational extent between the closed position and the fully open position. A restoring force is provided by the spring so that the door will close when the operator releases the handle. In this manner, the door may be opened manually if the operator desires, and the door may be opened even in case of a fault in the pneumatic system. 
   In accordance with still another aspect of the present invention, the door may have a latch mechanism to secure the door in a closed position. This may be similar to a conventional door latch where a bolt in the door is urged by a spring so as to engage an opposing hole in the frame, or some similar arrangement. In order for the pneumatic opening mechanism to operate to open the door, this bolt must be released at the beginning of the opening operation. An actuator may be arranged in the hole in the frame engaged by the bolt so as to urge the bolt towards the door such that it no longer engages the hole in frame. The actuator may operate by electrical or pneumatic means, and may have a spring return such that it retracts when the activating means is discontinued, permitting the latch to re-engage the hole in the frame as the door reaches a closed position. Alternatively, the actuator may be urged into a retracted position by the spring force applied to the latch bolt when it is positioned opposing the hole in the door frame. 
   In any aspect of this invention, the pneumatic operation of the door may be prevented if there is an unsafe condition in the chute as determined by one or more temperature sensors or one or more smoke or contaminant sensors. In particular, a sensor may be installed in a collection area at the base of the chute to determine if a sensing threshold has been exceeded and to actuate a shut off valve to interrupt the pneumatic supply to the door actuation mechanism. Preferably, the pneumatic pressure being supplied to the door assemblies may also vented to the ambient environment when the solenoid is actuated so that a door cannot be pneumatically opened with any residual air pressure in the system. This feature prevents the door from opening or remaining open for a preset time due to residual pressure in the pneumatic supply when there is a safety hazard determined by the appropriate sensor. In addition, a locking mechanism may be provided for each door, which operates to prevent opening of the door where an unsafe condition has been determined to exist by a sensor. A locking mechanism may also act to prevent the opening of the door when another door in the chute system is open. 
   The pneumatic supply may be located inside or outside of the chute, and the pneumatic pressure supplied to a plurality of doors by a flexible hose, which may be enclosed in a conduit for mechanical protection. 
   The door may be fitted with flanges, mounted near the two vertical edges, and extending towards the chute so as to guide the material into the chute. The height of the flanges may vary from a high value at the base of the door where the door is journalled to the frame, to a low value at distal end of the door. The lower ends of the rods extending from the main pneumatic cylinder and the pneumatic spring that are more distal from the cylinders of each may be journally attached to flanges near the base of the door. The flanges are preferably mounted orthogonally to the door and facing the chute, and may be positioned near the side edges of the door. The rods are journally attached to the door flanges at the flange end closest to the door journal, positioned such that a suitable lever arm exists between each attachment point at the flange end closest to the door journal and the door journal. The ends of the cylinders more distal from the rods are each journally attached to the frame, to a flange extending from the frame, or to a fairing joining the frame to the chute. 
   Alternatively, a strut may be disposed near the base end of the door, extending orthogonal to the door surface, in the direction of the interior of the chute. The distal end of the rod extending from the main pneumatic cylinder may be connected to the strut so as to create a lever arm with respect to the door journal. The spring may also be connected in this manner. Further, the strut may be connected directly to the journal, or an extension thereof. 
   The rod of the main pneumatic cylinder may be restrained by a sliding bracket, which may be journalled to the door flange or the strut such that the door may be opened manually as an alternative means of operation, or in the event of failure of the pneumatic supply. 
   The main pneumatic cylinder and the spring may be positioned such that they are disposed between the door flanges and the door frame, or between a strut and the door frame, such that the width of the door is not increased over that of a manually operated door, while providing the same width of opening. Alternatively the main pneumatic cylinder and the spring may be attached to a strut extending orthogonal to an extension of the door journal, such that the strut is not positioned within the door opening in the frame. 
   In addition, the actuating switch for initiating the opening of the door may be located on the door frame or at some other convenient location. The pneumatic control mechanism may also be located on the door frame or at some other convenient location. 
   These and other advantages of the present invention will become apparent to those skilled in the art on reading the following detailed description and viewing the drawings, in conjunction with the claims. 


   
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a elevation cross-section view of a chute system in accordance with an aspect of the present invention having a plurality of pneumatically actuated access doors; 
       FIG. 2  is a front view of a pneumatically actuated access door in accordance with an aspect of the present invention showing an operation switch and a handle for manual operation; 
       FIG. 3  is a rear view of the pneumatically operated door illustrating the placement of the main pneumatic cylinder and the air spring in an embodiment of the present invention; 
       FIG. 4  is a side view of the pneumatically operated access door a showing aspects of the door in a closed and an open position; 
       FIG. 4A  is a detail taken along line A—A of  FIG. 4 , illustrating the operation of the latch bolt in accordance with an embodiment of the present invention; 
       FIG. 4B  is a detail illustrating the relationship of the journalled slide bracket to the rod of the main pneumatic cylinder when the door is in a closed position, and when the door has been manually or pneumatically opened; 
       FIG. 5  is a block layout diagram illustrating the control system for the pneumatically actuated door; 
       FIG. 5A  is a detail of the pneumatic supply for the situation illustrating a connection of the interlock latch to the pneumatic supply 
       FIG. 6  is a detail of the pneumatic supply for the situation where the door may be locked closed when another door has been opened. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention may be better appreciated with reference to the drawings and description, which are understood as representing aspects of the invention, but not intending to limit the scope thereof, which is set forth in the claims. Corresponding elements in drawings are identified by the same numeral or symbol. 
     FIG. 1  illustrates a chute system including the pneumatically actuated doors. The chute system  1  comprises a vertical enclosure  2  designed to meet mechanical, environmental and safety requirements associated with the structure in which the chute system  1  is to be installed. Inside the vertical enclosure  2  is a chute  3  extending from the lower end of the vertical enclosure  2  to the top end of the vertical enclosure  2 , with the base end  4  of the chute  3  being closed by a flap  5  held in place by a spring (not shown) or a counterweight (not shown) such that the material introduced to the chute  3  can open the flap by the weight of the material and be deposited in an area  7 , which is typically a trash room or service area, for subsequent removal. The upper end of the vertical structure  2  may extend through the roof and be fitted with a ventilation cap  8  such that odors may be exhausted to the outside air, and to provide access to the chute system for maintenance. 
   Each floor requiring access to the chute system is provided with a pneumatically actuated access door  6 , whose operation will be described later. The motive power to operate the pneumatically actuated access doors  6  may be provided by an air compressor  8  and an air distribution system  9 . The air distribution system has a shut-off valve  10  for maintenance purposes and a solenoid shut-off valve  11 , whose operation is controlled by a sensors  12 , which may be temperature, smoke or other environmental sensors such that, if a preset threshold is exceeded, the air supply is not provided to the pneumatically actuated access doors  6 . The air from the compressor  8  is supplied to each of the pneumatically actuated access doors  6  by a flexible tube. The tube may be made of ¼″ HD polyethelene tubing or similar material and the tube may be contained in a flexible conduit  13  to protect the tube against damage from the material being introduced to the chute  3 . In the event that the solenoid shut off valve  11  is actuated, the flexible tube may be vented to the ambient environment such that residual air pressure is removed from the pneumatically actuated access doors  6 . 
   As will be described later, the air supply is routed to each floor in sequence by a method that permits the independent actuation of any of a plurality of pneumatically actuated access doors  6 . More than one door may be independently actuated to open during a particular time period or, alternatively, the pneumatic control system may permit only one door to be open at a time. Depending on the number of floors in the installation, it may also be desirable to deliver the air in a larger tube to a higher starting floor, thus segmenting the system into zones, and ensuring adequate air pressure throughout. A separate compressor  8  may be used for each zone, or multiple compressors used for redundancy. 
   The chute  3  may be square, rectangular, circular or any other regular cross section, depending on the design requirements. The pneumatically operated door assembly  6  penetrates the vertical structure  2  through an opening  14  provided in the vertical structure  2 , and also in any conventional structural walls enclosing the chute system. Additionally it penetrates the chute  3  such that a fairing  44  may join the frame  21  (see  FIG. 4 ) of the pneumatically actuated access door assembly  6  and the chute  3  so as to prevent material from entering the space between the vertical structure  2  and the chute  3 . 
   The chute  3  may be constructed of prefabricated components having an appropriate cross section, and being stacked one on top of another, with attachment members to keep the sections in alignment. Preferably a support  17  is provided for the chute by connection to the vertical structure  2 . 
     FIG. 2  is a front view of a pneumatically actuated access door assembly  6  in a closed position. The door  20  is fitted to a frame  2  which is sized to fit the hole  14  provided in the vertical structure  2 , corresponding to the opening in the chute  3 . The frame  21  may be manufactured of welded steel elements such as angle brackets, bent sheet stock and the like. Materials other than steel which meet the safety and design requirements may be used. At the upper end of the frame  21  a cover plate  22  provides access to the pneumatic door control unit  51 , and may support the door opening command switch button  23 . Pressing the command switch button  23  initiates the door opening process, which will be described later.  FIG. 3  is a partial back view of the pneumatically actuated access door assembly  6 . The main pneumatic cylinder  31  or pneumatic forcer is disposed such that the upper end is journalled to the rear of the frame  21  or to a flange  44  extending rearward from the frame  21 , adjacent to the door  20 , and the lower end, being an extensible rod  25  extending from the main pneumatic cylinder  31 , passes through a journalled slide bracket  30  attached to a door flange  26  which may be orthogonal to the door  20  and which projects towards the chute  3 . A door closing device, which may be an air spring  32 , or a metal spring or the like may be journalled to the rear of the frame  21  or to the frame flange  44  at a side opposite that of the main pneumatic cylinder  31 , at its upper end and journally connected to a door flange  26 . Alternatively, both the door closing device and the main pneumatic cylinder may be located at the same side of the door. 
     FIG. 4  shows a partial side view of the pneumatically actuated access door assembly  6 , illustrating the door  20  in both an open and closed aspect. When the door is in a closed position, the rod  25  of the main pneumatic cylinder  31  is in an extended position, and the rod  34  of the air spring  32  is in an extended position, when measured with respect to the positions of each respectively, when the door is in an open position. Operation of the journalled slide  30  will be described subsequently. 
     FIG. 5  is a layout of an embodiment of the pneumatic door control unit  51 . This may be located behind the access panel  23  at each pneumatically controlled access door assembly  6 . Alternatively, the pneumatic door control unit may be located at some other convenient place and only the pneumatic pressure needed to actuate the door supplied to the door assembly  6 . The air supply from the compressor  8  may be routed in turn to each of the pneumatic door control units  51  by the conduit enclosed flexible hose  13 . The pneumatic door control unit  51  consists of a timer  52 , an compressed air routing switch  53 , a bolt actuation mechanism  54 , if required, the operator command switch  55  and air distribution and regulation components, which will now be described in conjunction with the operation of the pneumatic door control unit  51 . 
   The air supply  13   a  enters the pneumatic door control unit  51  through an entry box, and is fed to a “Y” connector  56 , connected such that one of the legs of the “Y” connector is connected to another conduit enclosed flexible hose  13   b  that exits the pneumatic door control unit  51  and continues to another pneumatically controlled access door assembly  6 . The remaining leg of the “Y” provides the compressed air supply to the pneumatic door control unit  51 . The air supply is routed to a “T” connector  58 . An output of the “T” connector  58  is routed to an input port  59  of the operator command switch  55 , which may be a push-button switch, lever switch or similar air control device or it may be a device that senses the presence of a person, such as an infra-red detector. Ordinarily this switch will be of a momentary-operation type and permit the air to flow from the input port  59  to the output port  60  when it is actuated by depressing the operator command button  23 . The output  60  of the operator command  55  switch is routed to the input of a two port alternate action transfer valve  53 . The input to the two-port alternate action transfer valve is the other output of the “T” connector  58 , and the output port  62  of the two-port alternate action transfer valve is fed to the input port  65  of the pneumatic timer valve  52  through a “T” connector  63  and a splitter  64 . 
   The pneumatic timer valve  52  may have a manual adjustment means, such as a knob  71 , which is arranged such that it controls the time duration of the cycle. 
   When the operator command button  23  is depressed, compressed air present at the input port  59  of the operator command switch  55  is permitted to reach the output port  60  while the operator command button  23  continues to be depressed and is then routed to a first control port  66  of the two-port alternate action transfer valve  53 , causing the valve to switch such that the compressed air routed to input port  61  thereof is allowed to reach the output port  62 . Once this switch action occurs, the transfer valve remains in this state, even if the operator command button  23  is released, until there is a pneumatic input to the second control port  67 . The compressed air output  62  from the transfer switch is routed through a “T” connector  63  to actuate the main pneumatic cylinder  31 , to apply air pressure to the pneumatic timer valve  52 , and to also supply air pressure to the latch release mechanism  54 , if required. A flow control regulator  68  is inserted in the output of the “T” connector between “T” connector  69  and the input to the main pneumatic cylinder  31 . The flow control regulator  68  functions to regulate the rate at which air can be supplied to the main pneumatic cylinder  31 . The flow control regulator  68  provides for an adjustment to regulate the rate at which the door  20  opens when the air pressure is applied, and may also be used to compensate for pressure drops in the feed lines, which may depend on the distance between the compressor  8  and a specific door  6 . 
   An output of the “T” connector  64  is routed to the pneumatic timer valve  52 . When air pressure is applied, the timer valve  52  begins the timing cycle in accordance with a preset value. When the time has expired, the compressed air is routed from the input port  65  of the timer valve  52  to the output port  70  of the timer valve  52 . The compressed air output from the timer valve  52  is routed to the input of the second control port  67  of the two-position transfer valve  53 , causing the switch to return to its original position, thus removing the air pressure from the main pneumatic cylinder  31 , the timer  52  and the latch release  54  (if installed). 
   With the operation of the pneumatic control unit having been described, the physical operation of the door is now described. As shown in  FIG. 4 , the door  20  is journalled  43  at its base end to the frame  21 , and both the main pneumatic cylinder  31  and the air spring  32  (not shown in this view) are connected between an upper side of the door frame  21  or door flange  44  and an end of the door flange  26  proximal to the journal  43 . The locations of the journal attachment points on the door flange  26  are spaced such that a lever arm is created between each attachment point and the journal  43 . When the operator command button  55  is actuated, the pneumatic control unit acts to apply compressed air to the main pneumatic cylinder  31 . This urges the push rod  25  to retract into the cylinder  31 . The stop  27  ( FIG. 4B ) comes into contact with the lower end  29  of the journalled slide bracket  30  and applies and a rotational force about the journal  43  that attaches the door  20  to the frame  21  urging the door  20  to rotate about the journal  43  so as to open. As the door  20  begins to rotate open, the rod  34  of the air spring  32  is urged into the air spring  32  and the restoring force increases as the rod  34  is urged further into the air spring  32 . This results in rotational force applied through a lever arm on the journal  43  resisting the opening force provided by the main pneumatic cylinder  31 . 
   The door rotates about the journalled axis  43  so as to swing from the vertical towards the horizontal, but its motion is stopped at a point which may be determined by one of several design methods. The main pneumatic cylinder rod  25  may reach the full extent of its permitted motion into the cylinder  31 , a mechanical stop may be constructed such that an extension of the door  20  abuts the frame  21  after a specific angular rotation, or the restoring torque developed by the air spring  32  becomes equal to the opening torque provided by the main pneumatic cylinder  31 , when measured about the journal  43 . 
   Once the door has rotated to its open position  20   a , and motion has been stopped, by any of the previously described mechanisms, the operator may introduce the desired material into the chute. The door remains open, since the pneumatic pressure continues to be applied to the main pneumatic cylinder  31 . After the expiry of the preset time interval, the timer  52  permits the application of air pressure to the second control port  67  of the two-port transfer switch  53  such that the compressed air is no longer supplied to the main pneumatic cylinder  31 . At this time the opening force is reduced as the air pressure is vented outside the compressed air system through a breather  72  fitted to the two-port control valve  53 , the rod  34  extends and the air spring  32  urges the door  20  to return to a closed position. The door  20  rotates to the closed position, and the latch reengages. 
   The operation of the main pneumatic cylinder  31 , the air spring  32  and the journalled slide bracket  30  are now further described in the context of an opening and closing sequence of the door  20  by pneumatic means. When the door is in a closed position, the rod  25  of the main pneumatic cylinder  35  is in an extended position and the rod  34  of the air spring  32  is in an extended position. The air spring  32  may continue to exert a small force urging the door  20  closed against the frame  21 . This may help ensure proper closure of the door over a period of use when the friction in the journal  43  may increase, or due to misalignment of mechanical components. When the door open command button  23  is pushed and air pressure is applied to the main pneumatic cylinder  31 , the air pressure urges the rod  25  to retract into the main pneumatic cylinder  31 . The stop  27  comes into contact with the bottom end  29  of the slide bracket  30 , resisting the retraction of the rod  25 , and urging the door  20  to rotate about the journal  43 . As the door  20  begins to rotate to an open position  20   a , the rod  34  of the air spring  32  is urged into the air spring  32  causing the air spring  32  to increase the resistance to further entry of the rod  34 . This increased force may be used to limit the motion of the door  20  to a maximum rotation, or a mechanical stop may be used. When the door has reached its maximum rotation it is restrained from closing by the continued force exerted by the main pneumatic cylinder  31  until such time as the pneumatic control unit  51  removes the air pressure from the main pneumatic cylinder  31  and permits the pressure to vent to the external environment through the breather  70 . As the removal of air pressure results in a greater rotational force being applied by the air spring  32  than is being applied by the main pneumatic cylinder  31 , the door  20  is urged to rotate into a closed position. As the door  20  rotates into a closed position, the rod  25  extends from the main pneumatic cylinder  31 , being urged to do so by the force exerted by the bottom of the slide bracket  29  on the stop  27 . Since the air flow out of the main pneumatic cylinder  31  may be restricted, some opposing force to closure may be encountered, with the main pneumatic cylinder  31  acting as a damper during this portion of the cycle. During the closure of the door, the rod  34  extends from the air spring  32  in response to the urging by the force built up in the air spring  32  during the opening part of the cycle. 
   If the door begins to close before the operator has completed introducing the intended material, the operator command switch  23  may again be actuated, the air pressure reapplied and the timer reset as if a new door opening cycle had been commenced. Since the air pressure will be limited to that of the air supply to the pneumatic control unit, reapplication of the air pressure prior to door closure does not cause any damage or malfunction. 
   The means of attachment of the lower end of the main pneumatic cylinder rod  25  to the door flange  25  by the journalled slide bracket  30  is such that the door may be opened manually from outside the chute by pulling on a handle  24  attached to the door  20 , after rotating the handle, or otherwise disengaging the latch bolt  74 . The journalled slide bracket assembly  30 , being slidably attached to the rod  25  and journalled to the door flange  26 , may slide with respect to the rod  25  such that the rod  25  may remain in its extended position with respect to the main pneumatic cylinder  31  when the door is being opened manually. To do this the slide bracket assembly  30  slides along the push rod in the direction opposite to the stop  27 , and thus does not exert any force on the journal  43 . The opening of the door  20  in the manual mode is resisted by the entry of the rod  34  into the air spring  32 . The door may be manually opened until either a mechanical stop prevents further rotation, or the operator has exerted a force equal to that of the restoring force of the air spring  32 , as determined about the door journal  43 , or the air spring has reached its maximum travel in the compressed direction. When the door is manually operated and reaches an open position, and the operator releases the handle  24 , the restoring force of the air spring  32  urges the door closed. 
     FIG. 4B  illustrates the relationship of the journalled slide bracket  30  to the rod  25  in several aspects of the door position. When the door  20  is in a closed position, the rod  25  extends through the journalled slide bracket such that one end enters the main pneumatic cylinder  31 , and the end more distal from the cylinder is terminated in a stop  27 . The stop  27  may be threaded and inserted into an end of the rod  25  such that the distance between the stop  27  and a lower surface  29  of the journalled slide bracket  30  may be adjusted for the situation when the door is in a closed position. Alternatively, the end of the rod may be threaded and one or more nuts threaded onto the rod to achieve a similar adjustment. The stop  27  may also be applied to the end of the rod  30  by swaging, welding or other technique that may not permit adjustment. 
   The journalled slide bracket  30  may be journally attached to the door flange  26  by a pin or bolt  28  so that the rod and the door flange  26  may rotate angularly with respect to each other when the door  20  is opened by rotation about the journal  43 . 
   When air pressure is applied to the main pneumatic cylinder  31 , the rod  25  is urged into the main pneumatic cylinder  31  and, if the stop  27  is not already in contact with the bottom surface  29  of the journalled slide bracket  30 , the movement of the rod  25  into the main pneumatic cylinder  31  causes such contact. As the rod  25  is urged further into the main pneumatic cylinder  31  by the air pressure, the force exerted by the stop  27  on the lower surface  29  of the journalled slide hinge  30  acts through the lever arm of the door hinge  26  about the door journal  43  providing the rotational force urging the door  20  into an open position. When the door  20  has reached an open position, the relationship of the rod, the stop and the journalled slide are shown in  FIG. 4B  as elements  25   a ,  27   a , and  30   a , respectively. 
   When the door  20  is opened manually, the rod  25  is not urged into the main pneumatic cylinder  31  and remains in an extended position, so that the stop  27  remains in approximately its original position, but has rotated angularly as shown in element  27   b . The force to open the door  20  is provided by a person operating the handle  24 , resulting in a rotational moment about the door journal  43 . As the door rotates into an open position, the journalled mounting bracket  30  slides freely along the rod  25 , permitting the rotation of the door  20  about the door journal  43 . In this situation, the stop  27  is not in contact with the bottom  29  of the journalled slide bracket  30 . When the operator releases the handle, the air spring  32  urges the door  20  into a closed position and the relative positions of the components returns to the aspect shown in  FIG. 4B  in solid lines. 
   Another aspect of the present invention is a lockout, shown in  FIG. 5A , which prevents the door from being opened manually in the same circumstances where the door is prevented from being opened pneumatically. A pneumatically operated latch bolt  84  is fitted to the frame  21  such that it engages a hole  85  in the door  20 . The latch bolt  84  is normally retracted by the air pressure in the system applied to pneumatic cylinder  81 . When the air pressure is vented to the environment, exemplary of a situation where door is to be prevented from opening, for example, due to an environmental problem, the latch bolt  84  engages the hole  85  in the door  20 . The latch bolt has a beveled surface  87  whose orientation is such that the door may close completely if it is in an open position at the time that the locking event occurs. The door then cannot be opened again until the air pressure is restored. 
   A further aspect of the present invention is a lockout which prevents the door from being opened whenever another door is open, shown in  FIG. 6 . It also acts in a similar manner with respect to all of the doors in the event that the main pneumatic supply is vented as described above. The same latch mechanism for preventing the opening the door described in the previous paragraph may be used, with additional components, which will be described. A pneumatic limit switch  62  senses whether the door is open or closed. When the button  23  of the operator command switch  55  of a door assembly  6  is pressed and the door  20  opens as previously described, the pneumatic limit switch  62  causes the air supply line  63   b  to the higher floors to be vented to ambient. The air line  63   b  is connected to the air line  63   a  of the next higher floor. The air line  63   a  is only connected to the main air supply  13   a  at the lowest door in the arrangement (that door being shown in  FIG. 6 ). At the top of the series of doors having the lockout, the air supply line  63  is connected to an air supply line  73 , which runs from the top door to the bottom door, having an input to an “AND” valve at each door. Air pressure is applied to the pneumatic switch  55  only when air pressure is present in both the air supply line  63  and the air supply line  73 . Thus, if any door is open, another door cannot be opened. 
   The operation of the control mechanism will now be described with particular reference to  FIG. 6 , but many alternative arrangements of realizing this aspect of the invention will be apparent to persons skilled in the art. In the state where no door is open, air pressure is present in air supply lines  63  and  73 , and any door may be opened. In this state, each “AND” valve  64 , having air pressure applied at both input ports, is in an “on” state and operates such that air pressure is present at an input side of operator command switch  55 . When an operator presses a command push button  23 , the door mechanism operates in a normal manner as previously described. As the door  20  begins to swing open, this is sensed by the pneumatic limit switch  62 , which vents the air supply line  63   b  to ambient. Since this supply line is connected to the air supply line  63   a  of the next higher door, the air supply line  63   a  for the next higher door assembly  6  will not have air pressure, the “AND” valve  64  at the next higher door assembly  6  will be in an “off” state, and no air pressure will be supplied to the input of the operator command switch  55 . Thus the next higher door  20  cannot be opened. This situation pertains to all higher doors. Although it will be appreciated that the process of opening the door initiated in this manner will result in the “AND” switch  64  for the door being opened changing to the “off” state, as the air supply lines  63  and  73  are vented to ambient by this action, the pneumatic timer  52  has already been actuated, and the air pressure will be applied to the cylinder  31  for the duration of the door opening cycle. This discussion has described the situation where a lower door has been opened. 
   Now the situation where a higher door is opened is described. Since the air supply line  63  is connected to the air supply line  73  at the top of the sequence of doors, the opening of any door below the connection point of the two air supply lines will result in the venting of the air pressure in air supply line  73 . In this situation, each “AND” valve will be in the “off” state, and no air pressure will be supplied to any of the operator command switches  55 , and no other door can be opened. 
   When the door that is presently open returns to a closed position, the associated limit switch  62  terminates the venting of air to ambient and resulting in repressurizing the air supply lines  63  and  73  at all of the doors. Another door may now be opened. 
   In the situation as described, the lockout cylinder  81  is only supplied with air pressure when the door with which it is associated is activated to be opened. The air pressure applied to the cylinder  81  retracts the bolt  84  from the hole  85  in he door  20 , permitting it to be opened. When no air pressure is applied to the cylinder  81 , a spring  83  urges the bolt  84  into the hole  85 , preventing the door  20  from opening. 
   In a further aspect, the latch release cylinder  54  and the associated spring loaded bolt  74  may be omitted, and only a pulling handle  24  affixed to the door, as the lockout mechanism may serve the purpose of securing the door closed. 
   In a further aspect, an indicator  65  which senses air pressure may be connected to the operator command switch side  55  of the “AND” valve  64  such that the indicator  65  provides an operator with an indication that the door  20  may be opened. Indicators of various types may be used, including those which are directly pneumatically actuated as well as electromechanical and electronic types. 
   The invention has been described with respect to a number of exemplary embodiments. It will be apparent to persons skilled in the art that many modifications and alterations to these embodiments are practical. The invention is therefore limited only by that which is claimed.