Abstract: An emergency exit is provided through a revolving door, having leaves angularly spaced from each other and rotatable in an enclosure in an operating condition, by automatically aligning all of these leaves parallel to a line of exit traffic through the enclosure. The revolving door leaves may be so aligned by first biasing the leaves toward each other, but maintaining the leaves angularly spaced by releasable retention against the bias exerted by such biasing, and by thereafter releasing such retention in response to an emergency condition and aligning the leaves automatically by force of the bias.

Abstract: Door control apparatus is provided for opening and closing the passenger doors of a transit vehicle and the cooperating doors of a station, which apparatus includes conductors respectively coupled with a station power supply and the station door motors and extending along the station platform where passengers load and unload relative to the vehicle, such that a shunt connection member carried by the vehicle and coupled with the vehicle door motor is operative to energize the vehicle door motor and the station door motor for operating the passenger doors and the station doors when the vehicle is positioned at the station platform to load and unload passengers in relation to the vehicle.

Abstract: A control system for an illumination lamp installed in a building equipped with a door operation control apparatus. The system comprises a door opening and closing instructor, a control circuit responsive to an instruction signal from the instructor to produce a door control signal and a lamp control signal, a door driver responsive to the door control signal to drive the opening and closing of a door, an illumination lamp for illumination of the interior of the building, a detector for detecting the movement of a human body and producing an electric signal representative of the movement, and a circuit which is responsive to the lamp control signal and the electric signal to turn on the illumination lamp and keeps the illumination lamp turned on for a predetermined time extending from the termination of the lamp control signal and the electric signal.

Abstract: An electropneumatic door control for vehicles is disclosed which consists of a pneumatic portion and an electronic portion. The electronic portion processes successive commands actuated by the vehicle operator to channel the signals to the pneumatic portion of the apparatus to activate alternate door openings and closings. Any blockage of the door movement is detected and signals processed to reverse the door closing or to halt the opening until the fault is corrected. The electronic portion also assures that the vehicle doors can only be opened after the vehicle has come to a stop, that when the vehicle doors are open the station or parking brake is held engaged, and that an audible warning signal sounds for a predetermined interval before the closing of the door.

Abstract: An anti-security control for unlocking the normally locked door which separates the corridor side and the stairwell side of buildings, such as hotels. The anti-security control is preferably adapted for use with and draws power from any conventional-type of smoke and fire detection and alarm system. When the detection and alarm system senses the existence of a dangerous level of smoke or fire, current is shunted to a solenoid which operates to unbolt the normally locked separation door. A depressible button may be operatively affixed on the corridor side of the door to provide access from corridor to the stairwell regardless of whether a smoke or fire condition is sensed by the detection system.

Abstract: An automatic door operator for a swing door supported by a door supporting frame to swing about a vertical axis. The automatic door operator includes a mechanism for opening and closing the swing door, a drive for driving the door opening and closing mechanism to open the swing door, the drive including a prime mover for driving the door opening and closing mechanism, a door closer including a resilient device for storing part of mechanical energy provided by the drive in opening the swing door and for exerting driving force on the door opening and closing means by using the stored mechanical energy to close the door, a unit for electrically controlling the drive to swing the swing door, and a sensor for sensing a body accessing the door and thereby providing an electric signal to open the door to the controlling unit.

Abstract: A control circuit for unlatching a door, particularly a pet door, includes a transmitter coil (L1), a pulse driver (11) for pulse energizing the coil, and a discriminator (12, 13) for detecting a.c. components in the coil current caused by currents induced in an outside tuned circuit brought adjacent the coil, e.g. around the neck of a pet seeking entry, and for comparing the frequency of the a.c. components with a standard. A latch drive circuit (14) responds to the discriminator for operating the door latch if the frequency comparison is satisfactory.

Abstract: This invention is a method and an apparatus by which a barrier is automatically placed before partially opened doors, which barrier is automatically removed when the door is fully opened and safe for travel. The invention includes means to detect when the door is fully opened and thereupon to activate barrier removal means, together with barrier placement means automatically activated at any time when the door is not fully opened.

Abstract: A home security and garage door operator system includes a gas sensor for detecting the level of toxic gas in the garage. When the gas level exceeds a predetermined threshold the garage door is automatically opened. Lock out circuitry is provided for preventing the door from being accidentally closed as long as the gas sensor detects an excessive level of toxic gas in the garage. A two button transmitter is used to sequentially close the garage door and set a security alarm subsystem. Warning devices are activated if the security alarm is attempted to be set without the garage door and windows in the home being closed. Once the security alarm has been set, the lock out circuitry also disables the garage door motor control circuitry until the security alarm is first deactivated. The transmitter generates a digital pulse train according to a preselected code, with the operation of the dual buttons changing the state of a particular control bit in the pulse train.

Abstract: A safe remote-control door opening-and-closing device for an automotive vehicle by which the door can not be opened or the door now being opened is closed, even if the driver operates the door open switch, in the case where there exists an obstruction within a predetermined warning region near the vehicle door or around the vehicle. The safe remote-control door device according to the present invention comprises an obstruction sensor for detecting the presence of an obstruction, if any, and a switching unit for disconnecting the door open switch from the door driving device or for connecting the door open switch to the reverse revolution terminal of the driving device in order to close the door now being opened, in addition to a conventional remote-control door opening-and-closing device.

Abstract: A light barrier is restricted to detecting blockage in a limited, constant region before the closing edges of a lift cabin-twin door. Two light emitters or transmitters are displaceably arranged in the door sill and are operatively associated with entrainment elements fastened to the lift cabin doors. The light emitters are synchronously displaced with light receivers mounted at the upper edges of the cabin doors. To increase reliability of operation, the lower edges of the lift cabin doors are provided with cleaning devices which clean the light exit locations of infrared luminescent or light-emitting diodes forming the light emitters during every opening and closing operation. Thus, the cleaning device of one door is arranged to clean the infrared luminescent diode of the light emitter of the other door and vice versa.

Abstract: A movable thermal barrier for a two-story building having a glass wall facing in a southerly direction and comprising a thermally insulated horizontal stationary rail panel adjacent to the glass wall. A thermally insulated horizontal movable inner panel is positioned between the rail panel and the glass wall, and is movable from horizontal alignment with the rail panel to above the rail panel. A similar outer panel is positioned between the inner panel and the glass wall and is movable from horizontal alignment with the rail panel to below the rail panel. Panel mounting means supported from the building are adapted to movably support the inner and outer panels so that one may be moved above and the other below the rail panel to provide a translucent thermal barrier between the upper and lower portions of the glass wall and the inside of the building. The inner and outer panels are of similar weights so they balance each other.

Abstract: A home security and garage door operator system includes a gas sensor for detecting the level of toxic gas in the garage. When the gas level exceeds a predetermined threshold the garage door is automatically opened. Lock out circuitry is provided for preventing the door from being accidentally closed as long as the gas sensor detects an excessive level of toxic gas in the garage. A two button transmitter is used to sequentially close the garage door and set a security alarm subsystem. Warning devices are activated if the security alarm is attempted to be set without the garage door and windows in the home being closed. Once the security alarm has been set, the lock out circuitry also disables the garage door motor control circuitry until the security alarm is first deactivated. The transmitter generates a digital pulse train according to a preselected code, with the operation of the dual buttons changing the state of a particular control bit in the pulse train.

Abstract: An apparatus responsive to electric power failure for opening curtains or doors normally covering ventilation openings in a confinement house of the type used for raising poultry and livestock is disclosed. An electromagnet (59) is provided which is energized by the electric power supply (41) to the house (10) and is de-energized upon failure of the electric power supply (41). A pivoted metal strip (61) is normally in contact with the magnet (59) and is interconnected by means of a cord (66) with the winch (25) which is used to raise and lower the curtains (16). When the electric power (41) fails and the electromagnet (59) is de-energized, the cord (66) releases, and allows the curtains (16) to fall under their own weight. A capacitor (78) prevents de-energization of the magnet (59) when momentary power failures occur.

Abstract: Apparatus for an electrically moved sliding window, used illustratively in automotive applications, having first, a built-in safety device, for providing a signal whenever the window has been raised or lowered to a preselected height and second, a proximity detector is described. The device and detector comprise a plurality of conductors, bonded to the surface of the window. These conductors are, in turn, connected to an integrated circuit element which is also mounted to the surface of the window. This circuit element controls a power stage which, in turn, supplies power to the drive motor which raises and lowers the window. The circuit element and the conductors are placed directly on the window in a stationary position with respect to one another.

Abstract: Pressure equalization between the upper and lower compartments of an aircraft is provided through normally covered openings along the edges of the floor of the upper compartment. The covers each are comprised of a double-flap arrangement in which one flap is constructed as two hinged panels with locking features in order to hold the other flap in a clinging position. The space between the flaps participates in the air-conditioning circulation. In the case of a pressure drop in the lower compartment, the pressure differential tends to fold the winged panels, thereby releasing the locks so that air pressure can be equalized through uncovering of the openings.

Abstract: A system for protection against getting caught in automatically operable doors or windows, particularly of vehicles. Specific intervals of time within which the closing or opening door should reach a given position are preset. When the door does not reach one of these positions within the time allowed, the reversing motion is initiated or the cycle of motions is stopped. For this purpose, an electric signal generator coupled to the door motion delivers electric position signals when predetermined positions of the door are reached. An electric storage element is set by the position signals and after a predetermined time interval automatically reset, with the logic value of its output signal changing.

Abstract: A device for adjusting the position of a drive element for automatically opening and closing a sliding door which is automatically opened upon stepping on of a mat switch by a customer who intends to enter a store and is automatically closed upon releasing of the mat switch by the customer who entered the store. The drive element of the automatically opening and closing sliding door is adjusted by merely once manually opening and closing sliding door. The drive elements such as limit switches are slidably mounted, not on the sliding door but on an endless wire such as an endless belt. Thus, adjusting the drive element so that the sliding door may stop just upon completely opening or closing of the door when mounting such an automatic sliding door can be rapidly and readily accomplished.

Abstract: A garage door operation control apparatus includes a door operating system for opening and closing the main door of a garage, a main detection circuit for detecting the open or closed condition of the main door, an auxiliary detection circuit for detecting an open condition of a window or an auxiliary door of the garage, a fire in the garage or generation of a special gas therein, an alarm and a signal processing circuit. Electrical signals from the detection circuit are logically analyzed thereby to control the door operating system and the alarm.

Abstract: A home security and garage door operator system includes a gas sensor for detecting the level of toxic gas in the garage. When the gas level exceeds a predetermined threshold the garage door is automatically opened. Lock out circuitry is provided for preventing the door from being accidentally closed as long as the gas sensor detects an excessive level of toxic gas in the garage. A two button transmitter is used to sequentially close the garage door and set a security alarm subsystem. Warning devices are activated if the security alarm is attempted to be set without the garage door and windows in the home being closed. Once the security alarm has been set, the lock out circuitry also disables the garage door motor control circuitry until the security alarm is first deactivated. The transmitter generates a digital pulse train according to a preselected code, with the operation of the dual buttons changing the state of a particular control bit in the pulse train.

Abstract: Between floors or landings the elevator car door may be opened allowing passengers to open the hall door. To prevent this from occurring, a stop apparatus is attached to the car door and hall door. This apparatus allows the car door to only be opened to a certain minimum acceptable distance when the car is above a predetermined distance above the landing.

Abstract: This invention is a method and an apparatus by which a barrier is automatically placed before partially opened doors, which barrier is automatically removed when the door is fully opened and safe for travel. The invention includes means to detect when the door is fully opened and thereupon to activate barrier removal means, together with barrier placement means automatically activated at any time when the door is not fully opened.

Abstract: A solar shutter system including a pair of insulating panels pivotally mounted adjacent a glazed opening. Insulated and uninsulated counterbalance pressure tanks are mounted at opposite ends of one of the panels. The counterbalance tanks are interconnected by tubing and contain a partially vaporized fluid, such as Freon. The uninsulated tank, exposed to the sunlight, heats up during the day forcing liquid Freon from the uninsulated tank into the insulated tank to pivot the panels away from the opening. A solar collection tank beneath the glazed opening absorbs the radiant energy passing through the opening. During normal daylight hours the temperature within the uninsulated tank is greater than the temperatures in the insulated tank so that the panels remain open.

Abstract: A pressure sensing mat utilizes a thin sheet of semiconductor material that has an electrical conductivity generally invariable as to pressure applied to the mat material. The sheet of semiconductor material is sandwiched between sheets of copper, steel or aluminum foil which are in mechanical contact with the semiconductor sheet to define a pair of electrodes. The electrodes are connected to various circuits including a pressure (voltage) threshold detector, a learning circuit for establishing a learned threshold, a circuit for matching time-pressure patterns and a circuit for detecting pressures between a predetermined maximum and minimum level. A matrix of pressure sensing mats is utilized with various circuits to detect sequential pressure patterns.

Abstract: A system is disclosed for controlling a motor which drives an operating mechanism for moving a door, such as an overhead garage door, in either direction between a closed position and an open position in response to actuation of a start switch. The control system includes an encoder including a rotatable disc driven by the motor and control circuitry including an encoder pulse verification circuit associated with the encoder for detecting the direction of door movement as well as increments of travel by the door when the door is moved by the motor under control of a motor command circuit in response to actuation of the start switch. The start switch and a start circuit cooperate with the motor command circuit for energizing the motor to move the door in one direction, for de-energizing the motor to stop the door at any position, and for re-energizing the motor to reverse the door in response to repeated actuation of the start switch.

Abstract: A home security and garage door operator system includes a gas sensor for detecting the level of toxic gas in the garage. When the gas level exceeds a predetermined threshold the garage door is automatically opened. Lock out circuitry is provided for preventing the door from being accidentally closed as long as the gas sensor detects an excessive level of toxic gas in the garage. A two button transmitter is used to sequentially close the garage door and set a security alarm subsystem. Warning devices are activated if the security alarm is attempted to be set without the garage door and windows in the home being closed. Once the security alarm has been set, the lock out circuitry also disables the garage door motor control circuitry until the security alarm is first deactivated. The transmitter generates a digital pulse train according to a preselected code, with the operation of the dual buttons changing the state of a particular control bit in the pulse train.

Abstract: An apparatus to provide improved safety for use in a motor vehicle equipped with a transmission having a "park" setting, a door to allow the operator to enter and leave the vehicle, and a gear shift handle having a park position and being moveable by the operator to select the transmission setting desired. The present improvement involves a connecting spring rod, gear shift assembly and automatic transmission which is capable of causing the transmission and gear shift assembly to move to park upon opening of the door. This apparatus provides that both the transmission and gear shift assembly will be in park when the operator leaves the vehicle via the door.

Abstract: The device comprises for each window an electric driving motor and a selector which is adapted to ensure the selective supply of current to the motor, in one direction or the other, through a control circuit acting on a supply source. The supply source is of the type capable of delivering at least two distinct energy levels. The control circuit comprises means for applying to an input of the supply source an energy level control signal which produces, as a function of the position of the selector, the application of a torque to the motor when raising the window which is higher than the torque applied when descending the window.

Abstract: A proximity detector processes voltages induced across the sections of at least one antenna.The antenna sections are each connected to means (30, 31 and 36 to 39) for rectifying the positive and negative alternations of the alternating signal providing two first and second signals relating, one, to the "peak" value of the voltage induced across the section whose voltage is the highest and, the other, to the mean value of the voltage across the various sections, the first signal supplying an adder controlled by a gate and the second signals are supplied to another input of the adder led by a limiter said means being, in turn, connected to means (21, 22) for analyzing these two signals.The detector may be used with elevator doors.

Abstract: A fluid pressure motor having a normally used internal electrical heating element which vaporizes internal fluid to actuate the motor. The motor further includes means in heat transfer proximity to the outside of the motor which can be caused to convert its stored energy to sufficient heat to actuate the motor.

Abstract: An emergency air vent structure actuated by smoke, gas or oxygen deficiency sensors to permit the influx of fresh air to an enclosure. The emergency air vent structure is characterized by a spring-actuated panel which is released by means of a rocker arm and latch actuated by a solenoid which solenoid is operated by any one of a number of detectors such as smoke, gas or oxygen deficiency. Upon opening of the panel, an alarm is sounded giving an audible warning of the unsafe conditions within the building.

Abstract: A traffic responsive control system for controlling one-way traffic through a door in which the door opening means is disabled when power is initially applied to the control system while permitting the door opening means to respond to a door opening signal on the traffic side of the door immediately after termination of a safety signal on the safety side of the door.

Abstract: Ventilating device for rooms having air passage apertures and closure means movable by an electric drive between an open position and a closed position, a noxious gas sensor and electrical control means responsive to the gas sensor for operating the electric drive so that the closure means is moved to the open position when the gas sensor senses noxious gas concentration in the room above a predetermined level.

Abstract: A thermally sensitive actuator for opening and closing a louvre window of the type in which the louvre blades are mounted fast with bell-cranks having their free ends pivotally connected to an operating member which has a pivotal link coupled thereto. The thermally sensitive actuator comprises a housing for mounting on the frame of the window and containing a channel of uniform cross-section having a block slideably mounted therein, and a piston and cylinder assembly, the cylinder of which contains a thermally expansible flowable material and is mounted on the housing with the piston in engagement with the slideable block so that expansion of the flowable material causes displacement of the block. The side walls of the housing contain elongate slots through which projects a pivot pin which is movable in an oblique slot in said block and has connecting means on its projecting end for attachment to the pivotal link of the louvre window.

Abstract: A safety apparatus is associated with otherwise conventional revolving doors which are rotatable about a vertical axis. A pair of closure components are positioned adjacent to the respective sides of a revolving door and are displaceable in the horizontal direction. The closure components include profiled surfaces which delimit access space of the revolving door. In case of emergency situations, e.g. caused by a fire, the closure components are moved away from one another under the power of two respective jacks, leaving access space around the sides of the door wide enough for the passage of persons.

Abstract: A power plant utilizing solar energy as the heat source has a radiant energy heat receiver having a controllable entry aperture for the incoming radiant energy, the aperture being defined by at least three movable shutters, each shutter having a temperature sensing device and operating means which are operable in dependence of the sensed temperature to maintain each shutter in a position corresponding to a predetermined temperature at the entry aperture.

Abstract: An emergency ventilation system especially adapted for use with an electrically-powered fan driven ventilation system in an enclosed livestock confinement structure includes solenoid actuated, hydraulically driven ventilation door control apparatus which is responsive to the presence or absence of the delivery of commercial electrical power service to the main ventilation system for automatically opening or closing one or more spring biased access doors in lower regions of the structure in order to assure ventilation of the structure at all times, even in the event of electrical power failures. A hydraulic cylinder assembly for shifting the position of each of the doors is operated by a hydraulic control system provided with a normally closed, solenoid operated valve which is electrically connected with the commercial power lines delivering power to the main ventilation system.

Abstract: The present invention relates to a safety interlock system that is associated with the door of a vehicle such as the door of a school bus, and which assures that the door of the vehicle is not inadvertently open and that certain safe conditions exist before the door can be opened. The safety interlock system comprises an electrically actuated locking mechanism, that includes a manual override, for locking the door handle of the vehicle. Forming a part of the safety interlock system along with the locking mechanism is an array of switch control means, all of which must be simultaneously actuated in order to unlock and release the door handle in order that the door be opened. First, the array of switch control means includes two independent switches that must be actuated by two separate individuals, preferably the driver of the vehicle and another individual such as the passenger or a monitor.

Abstract: A sensing system for use in a garage or other similar enclosure having an automatic door operator for automatically opening a garage door responsive to a lack of sufficient oxygen therein including a gas detector located within the enclosure responsive to actuate a detection relay which in turn will close a normally open detection switch, the closing of the detection switch will normally cause operation of the door operator to allow oxygen to enter into the enclosure through the door opening, the detection switch being located in a door opening control circuit which includes therein a first limit switch which is open whenever the door is open in order to prevent actuation of the door operator when the door is already open, the door opening control circuit also including a delay clock and delay switch which will be normally closed to allow operation of the door operator, this system also including a time delay circuit with a second limit switch therein which is adapted to be normally open and to close only whe

Abstract: An illumination and ventilation system for buildings and other enclosures utilizing at least one closure unit mounted in one or more sides of the building or other enclosure. The closure unit has a frame within which are a plurality of pivotally mounted, independently, movable, downwardly extending, blades. The blades are mounted within the frame with the pivot axii of the blades parallel and lying in a sloping plane when the closure unit is installed in the side of a building, or other enclosure. In a rectangular plan building or enclosure, four or more closure units should be employed; one or two for the windward side or sides, and three or two for the nonwindward and leeward sides. With this system, the windward and leeward and nonwindward closure units, will operate independently of each other and will be individually responsive to the net resultant wind pressures on each side of the building.

Abstract: A relay system maintains an emergency door opening device circuit open so that a door of a structure remains closed as long as an electrically energized ventilation system of the structure is supplied with electrical energy from a commercial power source. When the power fails, the relay system closes the emergency door opening device circuit, which includes its own power source, to operate a door opening device which opens a door to the structure to provide emergency ventilation for the structure.

Abstract: A device for opening a door on an airplane to expose a refueling receptacle having latches for connection to a fueling nozzle deployed from a tanker airplane so that the airplane may be refueled in flight. The device has a hydraulic actuator for opening and closing the door, first valve means for controlling the first actuator, a second valve means for controlling another hydraulic actuator that locks and releases the latches, a spring for opening the door when there is a failure in the supply of pressure fluid for the first actuator, and a means to prevent closing of the door before the latches are released from the nozzle.

Abstract: A new and improved smoke and heat vent including a frame assembly pivotally attached to a curb member adapted for placement on the roof of a building or the like. The frame assembly supports a dome-shaped cover and is movable between a closed, dome supporting position and an open, released position in which the dome-shaped cover is allowed to fall or slide downwardly by itself to clear an opening for the escape of heat and smoke under emergency conditions. The initial fall of the dome-shaped cover is retarded to remove any extra load such as snow on the cover and the cover is caught by several bands attached to the curb member so that it will not fall to a floor below.

Abstract: A sonar device for controlling movement of an object such as a transport drawer for delivery of material or things under security conditions to a customer. Examples of such transport drawers are bank drive-up window deal drawers or similar deal-type drawers for secure delivery and sale of pharmaceuticals fast foods, library books and packages of valuable things. The sonar device detects when a predetermined fixed distance has been established or occurs between a moving object such as a banking equipment deal drawer, and an object or body such as a vehicle being served by or using the drawer; and signals that the fixed distance exists, which signal may trigger stopping of a motor drive for the drawer to avoid collision of the drawer with the vehicle.

Abstract: An automatic opening smoke vent door is provided which serves as a normal, self-closing exit door, and which is capable of being connected to a fire alarm circuit so that the door opens automatically in the event of a fire to allow smoke to be vented. The invention provides a member, preferably an L-shaped sub-frame, hinged to the normal door frame, and with an opening device acting between the door frame and the hinged member to urge this member from a closed position to an open position disposed at about 90.degree. to the door frame. The hinged member is normally held in the closed position by a solenoid operated latch, which is released to allow the member to open in the event of a fire. The door is itself hinged to the hinged member, and a normal door closer is connected between the hinged member and the door to allow the door to operate in the usual way when the hinged member is in the closed position.

Abstract: A door or hatch operating mechanism is blocked by a bolt when the aircraft moves in that dynamic pressure is sensed by a spring biased displaceable large piston moving a small piston which acts on a hydraulic link acting, in turn, on another spring biased piston which holds the bolt in locking position or releases it.

Abstract: A releasable door hold-open device or assembly is mounted on the header over a door panel. The assembly has a track channel with a top web and depending flanges. A door panel connector arm has a traveller movable in the track channel. A solenoid operates a detent in the track channel near the hinge end of the traveller path. A conductor channel is fastened to the top web and communicates with the track channel through an opening. A connector block releasably adjoins the track channel and the conductor channel at the hinge end thereof. A smoke detector underlies the connector channel at the other end of the track channel. Conductors from outside extend through the connector block, through connecting plugs in the block and track channel and to the solenoid and through the conductor channel to the smoke detector.

Abstract: A normally pressure-free, failsafe, emergency door closer for use in hospitals, nursing homes or other locations where handicapped persons are housed, comprising an actuating mechanism triggered by a sensing device such as a smoke detector, a spring-loaded arm with a bumper on one end to engage the door and the other end of the arm rotatably attached to the wall adjacent to and above the door and free to rotate in a horizontal plane. The spring-loaded arm is retained in an open position by a vertical pin engaging the horizontal closer arm. The pin is mechanically linked to the armature of an electromagnet opposed by a coil spring. On signal from the sensing device the electromagnet releases the armature and the coil spring urges the pin upwards releasing the closer arm, the end of which engages the door and closes it.

Abstract: A vent structure for equalizing the pressure on opposite sides of a structure including a plenum formed at least in part by movable vent panel and a hinged panel supporting wall having overcenter biasing means, the plenum being pneumatically connected to the side of the structure which will be the high pressure side so that the condition requiring venting applies a differential pressure across the hinged wall which tends to force it overcenter against the overcenter biasing means thereby removing the normal support from the vent panel which moves to open a vent passageway. Spring-loaded flapper doors may be included in the plenum forming structure to enable relief of pressure in the opposite direction.

Abstract: An automatic date-stamping system for vehicles entering a parking area for a relatively long period of time, i.e., for more than one day rather than several hours, so that the accumulated charges of the parking costs at the time of leaving, are easily and reliably determinable. The date is stamped automatically on the side-wall of a tire of the vehicle in invisible ink, so as not to mar the appearance of the vehicle, before the blocking and/or signalling means are operated to permit entry of the vehicle into the parking area. Exposure of the date-imprint to ultra-violet light or other rays to which the printing ink is responsive, renders it visible for reading at the time of leaving the parking area, or before that time, if such is necessary.