US3344555A

US3344555A - Hydraulic drive means for a swinging door or the like

Info

Publication number: US3344555A
Application number: US497388A
Authority: US
Inventors: Hugle Gebhard
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-10-18
Filing date: 1965-10-18
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03

Description

Oct. 3, 1967 G. HUGLE 3,344,555

HYDRAULIC DRIVE MEANS FOR A SWINGING DOOR OR THE LIKE Filed Oct. 18, 1965 f/ME REVERE/1V6 fi Inventor:

Goikard -fli/ &

United States Patent 3,344,555 HYDRAULIC DRIVE MEANS FOR A SWINGING DOOR OR THE LIKE Gebhard Hiigle, Aach-Linz, near Pfullendorf, Germany Filed Oct. 18, 1965, Ser. No. 497,388 a 12 Claims. (Cl. 49-340) The present invention relates to hydraulic drive means for turning a door or the like in which movement of an hydraulic piston is transmitted by means of a linkage arrangement to the door for turning the latter about a turning axis.

It is an object of the present invention to provide hydraulic drive means for turning a door or the like about a turning axis between two end positions in which the drive means are constructed and arranged to fixedly hold the door in either of the tWo end positions thereof so that separate locking means or holding means for holding the door in either of the two end positions thereof become unnecessary.

It is an additional object of the present invention to provide for hydraulic drive means of the aforementioned kind which are extremely compact in construction so as to require relatively little space.

It is a further object of the present invention to provide for drive means of the aforementioned kind which are composed of relatively few and simple parts so that the whole arrangement can be constructed at very reasonable cost and will stand up perfectly under extended use.

With these objects in view, the arrangement of the present invention mainly comprises support means, a door mounted on the support means turnably between two end positions about a turning axis, a cylinder member, a piston member movable in the cylinder member between opposite ends thereof and including a piston rod projecting with one end thereof beyond the cylinder member, in which one of the two members is pivotally mounted at one end thereof to the support means. The arrangement includes further means for feeding a fluid under pressure into one end of the cylinder member and for discharging the fluid from the opposite end thereof and vice versa for reciprocating the piston member in the cylinder member, lever means mounted on the support means pivotable about a pivot axis and pivotally connected at a portion thereof to that end of the other of the two members which is farthest from the end at which said one member is pivotally mounted on the support means to be moved between two end positions during movement of the piston member between the ends of the cylinder member, elongated substantially straight guide means pivotally connected at one end thereof to the support means for pivoting movement about a tilting axis, said guide means having a length at least equal to the distance between the pivot axis and a free end of said lever means and being operatively connected to the door for turning the latter about the turning axis during tilting movement of the guide means, and engaging means projecting from said free end of the lever means and engaging the guide means for tilting the latter about the tilting axis during pivotal movement of the lever means. The lever means and guide means are arranged with respect to each other and to the door in such a manner so that, in either end position of the lever, the door will be in a corresponding end position and so that the portion of the lever means between the pivot axis and said free end thereof includes in either end position of said lever means an angle of substantially 90 with the guide means, whereby the door will be fixedly held in either end position and can be moved only by feeding pressure fluid into one end of the cylinder member and discharging pressure fluid from the other end thereof.

3,344,555 Patented Oct. 3, 1567 The lever means is preferably a two-armed lever having a shorter and a longer arm including an acute angle with each other.

Separate locking means for the door become therefore unnecessary, and in addition thereto the door will make during opening and closing thereof a harmonic motion.

The aforementioned arrangement may be constructed either in such a manner that the elongated guide means is connected by means of a length adjustable linkage to the door and this arrangement is especially advantageous if the drive means have to be installed on an already existing door whereby the adjustable linkage permits to adapt the drive arrangement in a convenient manner to the available space and to the existing structural arrangement.

On the other hand, the guide means may be arranged with respect to the door in such a manner that the tilting axis of the guide means coincides with the turning axis of the door and in this arrangement the one end of the guide means is fixedly connected to the door in the region of the turning axis of the latter.

An especially compact arrangement is derived when the support means includes an elongated substantially rectangular support plate on which the guide means and the two-armed lever are respectively pivotally mounted in the region of diagonally opposite corners of the plate and in 'which the cylinder member, likewise mounted on the plate, has an axis which includes with a diagonal connecting the pivot points of the guide means and the lever an acute angle.

According to a further feature of the present invention the means for feeding the fluid under pressure into the cylinder preferably include a pump, a pair of conduits connecting the pump to opposite ends of the cylinder member, an electromotor operatively connected to the pump for driving the same, means for starting and stopping the motor and including an electrical time delay so adjusted that after the motor is started it will be automatically shut off by the time relay after a time period slightly longer than that necessary to move the door between the end positions thereof. Preferably, an adjustable pressure release valve is provided in each of the conduits.

Due to this arrangement it is possible to arrest the door in any position without the danger of damaging the drive motor or any of the connecting elements. This arrangement makes also separate stop switches engaged by the door in either of the end positions thereof and in circuit with the motor for disconnecting the same when the door reaches either of its end positions unnecessary, and the door may be simply stopped in either of its end positions by mechanical means provided for instance at opposite ends of the guide means. This arrangement has also the advantage that, if movement of the door should be stopped by any resistance before it reaches its end position, for instance by accumulated snow, the pressure fluid fed by the pump into the cylinder will be discharged through the adjustable pressure relief valve and after a predetermined time the motor will be stopped by the time relay so that further feeding of pressure fluid to the cylinder will likewise stop.

Since the pressure relief valves are individually adjustable it is possible to adjust the maximum force exerted by the drive means on the door during the closing movement of the latter in a manner slightly different from the maximum force exerted by the drive means on the door during the opening movement of the same. Preferably the arrangement includes also adjustable regulating means in each of the counduits connecting the pump to the opposite ends of the cylinder member constructed and arranged in such a manner for letting fluid freely pass from the pump to the cylinder member and for adjustably regulating flow of fluid from the cylinder member to the pump. This makes it possible to regulate the speed of the door closing movement in a manner different from that of the door opening movement. This arrangement in which the flow of the pressure fluid from the pump to the cylinder member is not throttled in any way, so that the full pressure produced by the pump will be maintained in the conduits, has also the advantage that underpressure or inclusion of air in the conduits will be avoided, which could otherwise be produced when extraneous forces, for instance wind pressure, act on the door tending to move the door with a speed greater than that produced by the drive means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a partial top view of one modification of the arrangement according to the present invention in which the means for feeding pressure fluid into and out of the cylinder member are only schematically illustrated; and

FIG. 2 is a partial top view of another embodiment of the arrangement according to the present invention, drawn to a smaller scale than FIG. 1, and wherein the pressure fluid feeding means are omitted.

The arrangement illustrated in FIG. 1 includes a door T mounted on a bracket fixed to a pillar 2 of a building construction and turnable in the bracket between an open end position, shown in full lines in FIG. 1, and a closed end position, shown in dash-dotted lines, about a turning axis 3 extending along one side edge of the door. The means for turning the door T between the end positions are mounted on an elongated substantially rectangular support plate 1 which may be connected in any known manner to the rear side of the pillar 2. These means include a cylinder member 8 pivotally mounted at 9 in the region of a closed end thereof on the plate 1. A piston member, now shown in the drawing, is slidably mounted in the cylinder member 8 and the piston member includes a piston rod 18 projecting beyond the other end of the cylinder member. A two-

armed lever

6, 19 is pivotally mounted between the ends thereof at 7 on the support plate 1 and the short arm 19 of the two-armed lever, which includes an acute angle with the longer arm 6 thereof, is pivotally connected at the free ends thereof to the free outer end of the piston rod 18. Engaging means project from the free end of the longer arm 6 and these engaging means may include a pivot pin 10 projecting in substantial normal direction from the free end of the arm 6 and a roller 11 turnably mounted on the pivot pin 10. The

engaging means

10, 11 project upwardly and engage in a groove formed in an elongated substantially straight guide means 4 pivotally connected at one end thereof at to the support plate 1 so that the roller 11 is slidably guided in the groove of the guide means 4 and so that during tilting of the two-

armed lever

6, 19 about its pivot axis 7 the elongated guide means 4 is likewise tilted about its pivot axis 5. The opposite ends of the groove in the elongated guide means 4 are closed and the end opposite to the end at which the elongated guide means 4 is pivoted is closed by a connecting member 12 fixedly connected to this end of the guide means, for instance by welding. The connecting member 12 extends transverse to the axis of the elongated guide means 4 and is provided at the opposite ends thereof with a pair of bores 13 and 14 and an elongated linkage means 15 is pivotally connected at one end thereof to the bore 13 of the connecting member 12. The other bore 14 of the connecting member 12 may be used for connecting the linkage means 15 thereto in an arrangement in which the drive means are located on the side of the door opposite from 4 the side thereof shown in FIG. 1. The other end of the linkage means 15 is pivotally connected to a connecting bracket 16 fixedly connected in any convenient manner to one side face of the door T spaced from the pivot axis 3 thereof. The linkage means 15 are preferably adjustable in length and these linkage means may include a rod 15 provided at opposite ends with an external right hand and left hand thread, respectively, which are respectively engaged into sleeve members 15" provided with correspondingly directed internal threads and respectively pivotally connected to the connecting member 12 and to the bracket 16 so that during turning of the rod 15 about its axis the length of the linkage means 15 and therewith the angular position of the door T with respect to the elongated guide means 4 may be adjusted. The rod 15' may be provided with a bore therethrough to facilitate turning of the same about its axis. The end of the support plate 1 adjacent to the pillar 2 is preferably provided with a cutout in which the closed end of the cylinder 8 is pivotally mounted and the arrangement is made in such a manner that the elongated guide means 4, the linkage means 15 and the double-

armed lever

6, 19 are mounted as close as possible above the cylinder member 8. The elongated guide means 4 and the

lever

6, 19 are respectively pivotally mounted in the region of diagonally opposite corners of the support plate 1, whereas the axis of the cylinder member 8 extends substantially in longitudinal direction of the elongated support plate 1 so that the axis of the cylinder member 8 and the piston rod 18 aligned therewith includes an acute angle with a diagonal connecting the

pivot points

5 and 7 of the guide means 4 and the two-

armed lever

6, 19, respectively. This provides for a very compact construction of the arrangement.

The means for feeding pressure fluid, preferably pressure oil, into opposite ends of the cylinder 8 and for discharging the pressure fluid therefrom comprise a pair of

conduits

21 and 22 each flexibly connected at one end thereof to the respective end of the cylinder memoer 8 and each communicating over a one-way suction valve 24 with the interior of a container B filled with oil. The

conduits

21 and 22 communicate intermediate the ends thereof with opposite ends of a reversible pump 23, which may be in the form of a gear pump, and which may be driven by means of a reversible electromotor M connected to the gear pump 23 in any convenient manner for rotating the same. Communicating with each of the

conduits

21 and 22 is also an adjustable pressure release valve 25 by means of which the pressure of the pressure oil furnished from the pump 23 to the cylinder member 8 may be adjusted. The arrangement includes also adjustable regulating means 26 and 27 respectively arranged in the

conduits

21 and 22 intermediate the ends thereof. The adjustable regulating means 26 includes a bypass 28 provided with a one-way valve through which oil under pressure may flow freely from the pump 23 to the one end of the cylinder 8 and an adjustable throttle passage 30 through which flow from the aforementioned end of the cylinder 8 to the pump 23 may be throttled. The regulating means 27 include also a bypass 29 with a oneway valve permitting free flow from the pump 23 to the other end of the cylinder member and an adjustable throttle passage 31 for the return flow of the fluid from the other end of the cylinder member 8 to the pump 23. The

throttle passages

30 and 31 may be individually adjusted, whereby movement of the piston in the cylinder in the one or the other direction may be individually adjusted for adjusting the opening and closing time of the door.

The arrangement is illustrated in full lines in FIG. 1 in a position in which the door T is fully open. In this one end position of the door, the double-

armed lever

6, 19 is also in one of its end positions and the

engaging means

10, 11 on the free end of the longer lever arm 6 are at one end of the groove in the elongated guide means 4 abutting against the connecting member 12 afiixed to the one end of the guide means 4. As shown in FIG. 1; in this end position of the

lever

6, 19 the longer arm 6 thereof includes an angle beta of substantially 90 with the axis of the elongated guide means 4 and in this position of the elongated guide means 4 and the arm 6 of the two-armed lever any forces tending to turn the elongated guide means about the pivot axis 5 thereof will be taken up by the arm 6 so that turning of the elongated guide means 4 or the door connected thereto by extraneous forces, for instance wind forces acting on the door, will not be possible. The door T will therefore be locked in the open position and can be moved only by feeding pressure fluid into one end of the cylinder 8 and simultaneously discharging pressure fluid from the other end thereof. 4

A time relay 31 and a switch 32 are arranged in circuit with the motor M, as schematically shown in FIG. 1. The switch 32 is constructed and arranged in a known manner in circuit with the time relays 31 and the motor M so that during each closing of the switch 32 the time relay 31 is started and the direction of the motor M is reversed. The time relay 31 is adjusted in such a manner so as to shut off the motor M again after passing of a time period which is slightly longer than necessary to move the door normally between the end positions thereof.

The arrangement above described will operate as follows:

If the door T is to be moved from the open position shown in full lines in FIG. 1 to the closed position thereof shown'in dash-dotted lines, the switch 32 is closed, starting thereby the time relay 31 and the electromotor M which will drive the gear pump 23 in the direction as indicated by the arrow A to pump thereby pressure oil through the bypass 29 of the conduit 22 into the end of the cylinder member 8 which is opposite the end thereof at which the cylinder member 8 is pivotally mounted on the support plate 1. The piston rod 18 is thereby retracted into the cylinder member 8, turning thereby the two-

armedlever

6, 19 in counterclockwise direction so that the

engaging means

10, 11 fixed to the free end of the longer arm 6 of the two-armed lever will move along the groove in the elongated guide means 4 to turn the latter in clockwise direction about the pivot axis 5 thereof whereby this turning movement of the elongated guide means 4 will be gradually accelerated and subsequently thereto gradually decelerated until the guide means is moved to the end position as shown in dash-dotted lines in FIG. 1. Turning of the elongated guide means 4 about its pivot axis 5 will'be transmitted over the

linkage

12, 15 and 16 to the door '1 which will bemoved thereby from the open position, shown in the full lines, to the closed position, shown -in dashdotted lines, in which further movement of the door will be stopped, since in this end position of the door T and the elongated guide means 4 the axis of the elongated guide means extends also normal to the longer arm 6 of the double armed lever due to the fact that the length of the arm 6 is chosen substantially identical to that of the groove in the elongated guide means 4. In the closed position of the door T the latter will be also held in fixed position by the linkage connected thereto. When the door reaches its closed position, the pump will still be operated for a short time until the time relay 31 shuts off the motor M. During this time pressure fluid pumped by the pump 23 will be discharged through the pressure relief valve 25 connected to the conduit 22.

The pressure oil which during the closing movement of the door will be discharged from the cylinder passes from the latter through the conduit 21 and has to flow through the throttled passage 30 in this conduit whereby the adjusted open cross section of the throttled passage 30 will determine the maximum speed of the closing movement of the door. The above described sequence of operations will be reversed during reopening of the door.

If the above described arrangement is to be used on a 6. door having two wings, then two drive units as above described are used, whereby the cylinder members 8 of the two units are preferably supplied with pressure fluid from a common pump connected by two conduits as described above to the cylinder of each drive unit, each of the conduits provided with adjustable regulating means in the manner as described above.

As mentioned above, the provision of the time relay makes separate electrical stop switches, engaged by the door in the end positions thereof, unnecessary. The described arrangement is thereby considerably improved over arrangements known in the art since such stop switches which are mounted in the open are liable to fail, especially during snow or rain. A separate overload switch for protecting the motor is also not necessary since the running time of the motor determined by the time relay will be usually shorter than the operating time of an overload switch.

FIG. 2 illustrates another embodiment of the present invention at a smaller scale. The arrangement shown in FIG. 2 differs from the arrangement shown in FIG. 1 mainly in that the pivot axis of the elongated guide means 4 in this arrangement coincides with the turning axis 3 of the door T and in that the elongated guide means is fixedly connected to the door T in the region of the tuming axis of the latter. A

separate linkage arrangement

12, 15, and 16, as shown in FIG. 1, between one end of the elongated guide means and the door becomes therefore unnecessary in the arrangement shown in FIG. 2. Otherwise, the arrangement shown in FIG. 2 is substantially identical with that shown in FIG. 1 and elements of the arrangement shown in FIG. 2 performing the same function as the corresponding elements illustrated in FIG. 1 are therefore designated with the same reference numeral. It is to be understood that the

conduits

21 and 22 schematically and only partly indicated in FIG. 2 are provided with the same devices and furnished with pressure fluid in the same manner as described in connection with FIG. 1.

While in FIG. 2 the elongated guide means 4 are shown to be connected to the door T to be substantially aligned with the same, it is obvious that this arrangement may be modified if necessitated by the construction of the pillar 2 or for some other reasons in such a manner that the elongated guide means 4, while fixedly connected to the door T, may include an angle of less than with the latter.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of hydraulic drive means for turning a door dilfering from the types described above.

' While the invention has been illustrated and described as embodied in an hydraulic drive means for turning a door in which the drive means is constructed to lock the door in opposite end positions thereof, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An arrangement of the character described, comprising in combination, support means; a door mounted on said support means turnably between two end positions about a turning axis; a cylinder member; a piston member movable in said cylinder member between opposite ends thereof and including a piston rod projecting with one end thereof beyond said cylinder member, one of said two members being pivotally mounted at one end thereof to said support means; means for feeding a fluid under pressure into one end of said cylinder member and for discharging the fluid from the opposite end thereof and vice versa for reciprocating said piston member in said cylinder member; lever means mounted on said support means pivotable about a pivot axis and pivotally connected at a portion thereof to that end of the other of said two members which is farthest from the end at which said one member is pivotally mounted on said support to be moved between two end positions during movement of said piston member between the ends of said cylinder member; elongated substantially straight guide means pivotally connected at one end thereof to said support means for pivoting movement about a tilting axis, said guide means having a length at least equal to the distance between said pivot axis and a free end of said lever means and being operatively connected to said door for turning the latter about said turning axis during tilting movement of said guide means; and engaging means projecting from said free end of said lever means and engaging said guide means for tilting the latter about said tilting axis during pivotal movement of said lever means, said lever means and guide means being arranged with respect to each other and to said door in such a manner that in either end position of said lever means said door is in a corresponding end position and the portion of said lever means between said pivot axis and said free end thereof includes an angle of substantially 90 with said guide means, whereby said door will be fixedly held in either end position and can be moved only by feeding pressure fluid into one end of said cylinder member and discharging pressure fluid from the other end thereof.

2. An arrangement as set forth in claim 1, wherein said cylinder member is the said member pivotally mounted at one end thereof on said support means and wherein said piston rod is the other said member that projects beyond the other end of said cylinder member and is pivotally connected at the free end thereof to said lever means.

3. An arrangement as set forth in claim 2, wherein said lever means is a two-armed lever, having a longer and a shorter arm, said engaging means projecting from the free end of said longer arm, and said free end of said piston rod being pivotally connected to the free end of said shorter arm.

4. An arrangement as set forth in claim 3, wherein said two arms of said lever includes an acute angle with each other.

5. An arrangement as set forth in claim 4, and said operative connection including linkage means pivotally connected at opposite ends thereof to said door and to the other end of said guide means.

6. An arrangement as set forth in claim 5, wherein the length of said linkage means is adjustable.

7. An arrangement as set forth in claim 4, wherein said support means includes an elongated substantially rectangular support plate, said guide means and said twoarmed lever are respectively pivotally mounted in the region of diagonally opposite corners of said plate, and said cylinder member, likewise mounted on said plate, having an axis including with the diagonal connecting the pivot points of said guide means and said lever an acute angle.

8. An arrangement as set forth in claim 1, wherein said turning axis of said door coincides with said tilting axis of said guide means and wherein said one end of said guide means is fixedly connected to said door in the region of said turning axis.

9. An arrangement as set forth in claim 1, wherein said means for feeding the fluid under pressure into said cylinder member include a pump, a pair of conduits conmeeting said pump to opposite ends of said cylinder member, a motor operatively connected to said pump for driving the same, means for starting and stopping said motor and including timer means so adjusted that after the motor is started it will be automatically shut off by said timer means after a time period slightly longer than that necessary to move said door between said end positions thereof.

10. An arrangement as set forth in claim 9, wherein said motor is a reversible electric motor, and wherein said timer means is an electrical time relay.

11. An arrangement as set forth in claim 10 and including an adjustable pressure relief valve in each of said pair of conduits.

12. An arrangement as set forth in claim 11 and including adjustable regulating means in each of said conduits constructed and arranged for letting fluid freely pass from said pump to said cylinder member and for adjustably regulating flow of fluid from said cylinder member to said pump.

References Cited UNITED STATES PATENTS 1,716,567 6/ 1929 Shonnard 49137 2,550,349 4/1951 HelZ 49-340 3,244,415 4/ 1966 Lunenschloss et a1. 52 X 3,301,313 1/1967 Schurink 188 3,302,330 2/1967 Loftus 49137 X DAVID J. WILLIAMOWSKY, Primary Examiner.

J. K. BELL, Assistant Examiner.

Claims

1. AN ARRANGEMENT OF THE CHARACTER DESCRIBED, COMPRISING IN COMBINATION, SUPPORT MEANS; A DOOR MOUNTED ON SAID SUPPORT MEANS TURNABLY BETWEEN TWO END POSITIONS ABOUT A TURNING AXIS; A CYLINDER MEMBER; A PISTON MEMBER MOVABLE IN SAID CYLINDER MEMBER BETWEEN OPPOSITE ENDS THEREOF AND INCLUDING A PISTON ROD PROJECTING WITH ONE END THEREOF BEYOND SAID CYLINDER MEMBER, ONE OF SAID TWO MEMBERS BEING PIVOTALLY MOUNTED AT ONE END THEREOF TO SAID SUPPORT MEANS; MEANS FOR FEEDING FLUID UNDER PRESSURE INTO ONE END OF SAID CYLINDER MEMBER AND FOR DISCHARGING THE FLUID FROM THE OPPOSITE END THEREOF AND VICE VERSA FOR RECIPROCATING SAID PISTON MEMBER IN SAID CYLINDER MEMBER; LEVER MEANS MOUNTED ON SAID SUPPORT MEANS PIVOTABLE ABOUT A PIVOT AXIS AND PIVOTALLY CONNECTED AT A PORTIONS THEREOF TO THAT END OF THE OTHER OF SAID TWO MEMBERS WHICH IS FARTHEST FROM THE END AT WHICH SAID ONE MEMBER IS PIVOTALLY MOUNTED ON SAID SUPPORT TO BE MOVED BETWEEN TWO END POSITIONS DURING MOVEMENT OF SAID PISTON MEMBER BETWEEN THE ENDS OF SAID CYLINDER MEMBER; ELONGATED SUBSTANTIALLY STRAIGHT GUIDE MEANS PIVOTALLY CONNECTED AT ONE END THEREOF TO SAID SUPPORT MEANS FOR PIVOTING MOVEMENT ABOUT A TILTING AXIS, SAID GUIDE MEANS HAVING A LENGTH AT LEAST EQUAL TO THE DISTANCE BETWEEN SAID PIVOT AXIS AND A FREE END OF SAID LEVER MEANS AND BEING OPERATIVELY CONNECTED TO SAID DOOR FOR TURNING THE LATTER ABOUT SAID TURNING AXIS DURING TILTING MOVEMENT OF SAID GUIDE MEANS; AND ENGAGING MEANS PROJECTING FROM SAID FREE END OF SAID LEVER MEANS AND ENGAGING SAID GUIDE MEANS FOR TILTING THE LATTER ABOUT SAID TILTING AXIS DURING PIVOTAL MOVEMENT OF SAID LEVER MEANS, SAID LEVER MEANS AND GUIDE MEANS BEING ARRANGED WITH RESPECT TO EACH OTHER AND TO SAID DOOR IN SUCH A MANNER THAT IN EITHER END POSITION OF SAID LEVER MEANS SAID DOOR IS IN A CORRESPONDING END POSITION AND THE PORTION OF SAID LEVER MEANS BETWEEN SAID PIVOT AXIS AND SAID FREE END THEREOF INCLUDES AND ANGLE OF SUBSTANTIALLY 90* WITH SAID GUIDE MEANS, WHEREBY SAID DOOR WILL BE FIXEDLY HELD IN EITHER END POSITION AND CAN BE MOVED ONLY BY FEEDING PRESSURE FLUID INTO ONE END OF SAID CYLINDER MEMBER AND DISCHARGING PRESSURE FLUID FROM THE OTHER END THEREOF.