EP1625315A2

EP1625315A2 - Linked lading and vent valves for vessels

Info

Publication number: EP1625315A2
Application number: EP04752534A
Authority: EP
Inventors: William J. Jakubowski; Hernando D. Ledesma
Original assignee: Delaware Capital Formation Inc; Capital Formation Inc
Current assignee: Delaware Capital Formation Inc; Capital Formation Inc
Priority date: 2003-05-20
Filing date: 2004-05-18
Publication date: 2006-02-15
Also published as: EP1625315A4; WO2004104456A2; WO2004104456A3

Abstract

Apparatus for effecting substantially tandem operation of first and second valves spaced apart by a variable distance comprises a mechanical coupling mechanism interconnecting the valves and including first and second pivotally interconnected portions respectively coupled to the valves in a configuration which varies with the distance between the valves, the coupling mechanism being responsive to operation of the first valve to effect the corresponding operation of the second valve. The valves may be mounted in a vessel and the coupling mechanism may permit operation of the second valve independently of the first valve and may also automatically disconnect from the second valve in response to a predetermined movement of the second valve without operation thereof.

Description

LINKED LADING AND VENT VALVES FOR VESSELS

RELATED APPLICATION This application claims the benefit of the filing date of copending U.S. Provisional Application No. 60/472,162, filed May 20, 2003, and entitled "Linked Lading and Vent Valves for Rail Tank Cars".

BACKGROUND The present application relates generally to an actuator for valves in a vessel, such as a railway tank car and, more particularly, to operably coupling spaced-apart valves disposed within a vessel to facilitate synchronous movement between closed and opened positions.

Many vessels, such as railway tank cars or semi-trailer tanks, have a lading valve disposed on the bottommost portion of the tank for withdrawing a liquid from the tank or pumping a liquid into the tank. However, when liquid is withdrawn from the tank, under-pressure or vacuum is created within the tank because air is not able to replace the volume of withdrawn liquid. Thus, the flow of the withdrawn liquid is impeded and the tank outer shell may implode due to the pressure difference between the inside and outside of the tank. Conversely, as liquid is pumped into the tank via the valve, air pressure within the tank increases as the remaining volume of available void space decreases and the air cannot escape, again impeding the flow of liquid and possibly causing the tank to explode due to over-pressurization.

It is well known that, to combat this problem, an independent vent valve may be disposed at the top of the tank to allow air/vapor to enter or escape from the tank. The vent valve may be biased into a closed position and automatically moved to an open position when the air pressure within the tank drops below or rises above a predetermined level. For example, when a certain under-pressure has been achieved, the biasing force is overcome and the vent valve is opened to allow air enter the tank, thus allowing proper pressure equalization within the tank and avoiding a vacuum environment. Such a vent valve must be manually opened during filling the tank with liquid to allow air to escape to ensure proper pressure equalization. Conversely, a pressure relief valve would have to be manually opened to prevent under-pressure situations. A limitation of both such valve systems is that, since the lading valve and vent valve are independent, both valves must be independently opened and closed to operate properly. Alternately, it is well known that the lading valve and the vent valve can be opened simultaneously with hydraulic assistance, a flexible cable coupling or sliding vent valve housing. However, limitations of such systems are that each is complex and inherently unreliable. Also, it is known that flexing of vessel walls can occur during loading of liquid into and unloading of liquid from the vessel, which flexing can alter the distance between the lading and vent valves. Prior systems of mechanical coupling of the valves, such as by flexible cable, have not accommodated such changes in tank geometry.

Furthermore, prior arrangements for simultaneous operation of lading and vent valves utilizing mechanical interconnection have been specifically designed for specific tank geometries. It would be advantageous to have a system of coupling valves, wherein the same coupling arrangement could be utilized in any of a number of different sized vessels.

Additionally, changes in tank pressure can occur independently of tank loading or unloading operations, such as because of temperature variations and, therefore, it is necessary that the vent valve be capable of operation independently of the lading valve to correct over-pressure or under-pressure situations which do not result from loading and unloading operations. Prior valve coupling arrangements utilizing mechanical couplings have not accommodated such independent valve operation.

Also, safety regulations in certain countries require that means be provided for preventing vent valves from opening during drastic changes in transportation vessel geometry of the type which could occur during an accident. Accordingly, it is desirable that any technique utilized for effecting tandem operation of vent and lading valves be able to satisfy such regulations.

SUMMARY The present application discloses a method and apparatus of operably coupling two valves spaced apart by a variable distance.

In an embodiment, there is provided an apparatus having a wall structure defining a storage compartment and having first and second apertures therein respectively having first and second axes and spaced apart by a variable distance, first and second valves mounted on the wall structure and respectively associated with the first and second apertures, each valve being operable between a closed condition closing the associated aperture and an open condition opening the associated aperture, and a mechanical coupling mechanism interconnecting the first and second valves, the coupling mechanism including first and second pivotally interconnected portions respectively coupled to the first and second valves and disposed in a configuration which varies with the distance between the apertures, the coupling mechanism being responsive to operation of the first valve between the open and closed conditions for effecting a corresponding operation of the second valve between its open and closed conditions.

In an embodiment, the valves may be respectively associated with apertures in a vessel wall structure. In an embodiment, each of the portions of the coupling mechanism may include a parallelogram linkage.

In an embodiment, the second portion of the coupling mechanism may include structure which permits operation of the second valve between open and closed conditions independently of the first valve. In an embodiment, the coupling mechanism may include disconnect mechanism responsive to a predetermined movement of the second valve without operation of the second valve for disconnecting the coupling mechanism from the second valve.

BRIEF DESCRIPTION OF THE DRAWINGS For the purpose of facilitating an understanding of the subject matter sought to be protected, there is illustrated in the accompanying drawings an embodiment thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. FIGS. 1A-1C are side elevational views of a coupling mechanism operably coupling a vent valve to a lading valve in three different sizes of a liquid holding vessel;

FIG. 2 is an enlarged, fragmentary view in partial section of the circled portion designated 2 in FIG. IB, with portions broken away; FIG. 3 is a fragmentary isometric view of the portion illustrated in FIG. 2, with a portion broken away;

FIG. 4 is an enlarged, fragmentary, side elevational view, in partial section, of the circled portion designated 4 in FIG. IB, with portions broken away; FIG. 5 is a fragmentary, isometric view, in partial section, of the portion illustrated in FIG. 4; and

FIG. 6 is an enlarged, fragmentary, side elevational view, with portion broken away, of the circled portion designated 6 in FIG. IB.

DETAILED DESCRIPTION Referring to FIG. 1, there is disclosed a portion of the wall structure 5 of a vessel, such as a railway tank car or semi-truck tank trailer, having apertures 6 and 7 therein, respectively at the top and bottom of the vessel and substantially in vertical alignment. While a tank car or trailer has been described herein, that is simply for illustrative purposes, and it will be appreciated that the principles described in the present application apply to any type of vessel. The apertures 6 and 7 are respectively provided with a lading valve 10 and a vent valve 20 for controlling the opening and closing of the apertures. The valves 10 and 20 are of known construction and only so much thereof as is necessary to understand the subject matter to be protected will be described herein. While the valves 10 and 20 are illustrated in substantially vertical alignment with each other, it will be understood that this need not necessarily be the case.

Referring also to FIGS. 2 and 3, the lading valve 10 includes a poppet guide 11 having a plurality of downwardly extending legs 12 and defining a poppet travel way 12a. Each leg 12 may be coupled to the inner bottom wall 13 of the vessel in a known manner. A poppet 14 is disposed within the poppet travelway 12a and is axially moveable between opened and closed positions relative to the aperture 6. The poppet 14 is sized and configured to be in substantial liquid-tight sealing engagement with a cooperating poppet seat 15 circumferentially disposed about the aperture 6 when the poppet 14 is in the closed position. A poppet stem 16 extends coaxially upwardly from the poppet 14. When the poppet 14 is moved to the opened position, the poppet 14 is upwardly spaced from the poppet seat 15, thereby allowing liquid to pass through the aperture 6. It will be appreciated that the poppet travelway 12a provides a plurality of opened sections 12b that allow communication between the lading compartment of the vessel and the aperture 6. Movement of the poppet 14 between the opened and closed positions is typically caused by a lever or handle accessible from outside of the tank (not shown). Such a valve is well-known.

Referring also to FIGS. 4 and 5, the vent valve 20 is preferably coupled to inner upper wall 13a of the vessel and is configured to seal the vent aperture 7 that allows air to egress or ingress the tank, thereby providing proper tank air pressure equalization. In an embodiment, the vent valve 20 is disposed in substantially coaxial vertical alignment with the lading valve 10, as illustrated in FIG. 1. In another embodiment, the vent valve 20 may be disposed in substantial longitudinal alignment with the lading valve 10 relative to the longitudinal axis of the vessel. The vent aperture 7 may communicate with a vapor duct 21 that may be in operable communication with a vapor recovery mechanism (not shown). The vent valve 20 includes a depending, substantially cylindrical housing 23 with a stem guide 24 disposed therein for axially guiding a poppet 25 having a poppet stem 26 extending therethrough, wherein the poppet stem 26 is slideably disposed through an aperture on the stem guide 24. The poppet 25 cooperates with a complementary poppet seat 27 to provide a substantially air-tight seal when the poppet 25 is disposed upwardly into a closed position. The poppet 25 may be upwardly biased to the closed position by a biasing structure, such as a spring 28, that is circumferentially disposed around the poppet stem 26 and operably coupled to the poppet 25. When the poppet 25 is axially moved to an opened position, the poppet 25 is spaced downwardly from the poppet seat 27, thereby allowing air/vapor egress or ingress. Further, as a safety mechanism, the poppet 25 may automatically move to the opened position if the under-pressure within the tank overcomes the biasing force of the spring 28, thereby ensuring that under-pressurization in the tank is minimized. Such a vent valve is well known.

Referring again to FIGS. 2 and 3, the poppet stem 16 of the lading valve 10 is provided with a limited-motion universal joint 30, which includes a generally cup- shaped frame 31 having a circular opening or hole 32 in the bottom wall thereof through which the upper end of the poppet stem 16 projects, the poppet stem 16 being pivotally coupled to the frame 31 by a pivot pin 33 which extends diametrically through both. Disposed in the upper end of the frame 31 is a relatively thick coupling disk 34 which is pivotally coupled to the frame 31 by a pivot pin 35 which extends diametrically through both. The pivot axes defined by the pivot pins 33 and 35 are arranged orthogonally to provide a universal-type coupling, although it will be appreciated that a fairly narrow range of movement is permitted because of the relatively small clearances between the frame 31 and the poppet stem 16 and the disk 34. A stud 36 projects coaxially upwardly from the disk 34 and is provided with a lock nut 37, the stud being threaded into the lower end of an internally threaded bore extending axially through an elongated rectangular post 38. Referring to FIGS. IB and 6, the lading valve 10 is operably coupled to the vent valve 20 with a coupling mechanism 40 (FIG. IB) to facilitate synchronous operation of the valves 10, 20. The coupling mechanism 40 includes an upper portion or arm assembly 41 and lower portion or arm assembly 42 pivotally coupled to each other at a junction 40a approximately midway between the valves 10, 20. In an embodiment, the upper arm assembly 41 includes an upper control link 43 and an upper stabilizer link 44. In an embodiment, the lower arm assembly 42 includes a lower control link 45 and a lower stabilizer link 46. Each control link 43, 45 and each stabilizer link 44, 46 has upper and lower ends. A pair of pivot plates 47 is provided to pivotally couple the respective lower and upper ends of the upper and lower control links 43, 45 and the respective lower and upper ends of the upper and lower stabilizer links 44, 46, thereby pivotally coupling the upper and lower arm assemblies 41, 42 to each other. In an embodiment, each pivot plate 47 may be generally in the shape of an equilateral triangle, having pivot apertures formed therethrough respectively adjacent to the corners of the triangle, and may have a large central lightning aperture formed therethrough. In an embodiment, the coupled ends of the links 43-46 are disposed between the plates 47, which are arranged in parallel congruent relationship. Referring to FIG. 6, the upper control link 43 is pivotally coupled to the pivot plates 47 via a pivot pin 47a disposed through the pivot apertures at a first corner, the lower control link 45 is pivotally coupled to the pivot plates 47 via a pivot pin 47b disposed through the pivot apertures at a second corner, and the upper and lower stabilizing links 44, 46 are pivotally coupled to the pivot plates 47 via a shared pivot pin 47c disposed through pivot apertures at a third corner. In an embodiment, each of the pivot pins 47a-47c may be held in place with a cotter pin, retaining ring, C-clip or the like and suitable washers and/or spacer bushings may be provided to maintain proper spacing and inhibit frictional contact between adjacent pivotally coupled parts, all in a known manner.

In an embodiment, the upper stabilizer link 44 is integrally coupled to a pair of upper stabilizer link end plates 48 which, in turn, are pivotally coupled to the pivot plates 47 by pivot pin 47c. The plates 48 may have an oblong shape and could be provided with plural openings therethrough so as to be usable for length adjustment.

Referring again to FIGS. 2 and 3, the coupling mechanism 40 includes a lower lever assembly 50 which connects the links 45 and 46 to the lading valve 10. More specifically, the lower lever assembly 50 includes a pair of upstanding angle brackets

51 fixedly secured by suitable means to the top of the housing of the lading valve 10, and respectively having plates 52 arranged in parallel spaced-apart relationship. A pair of parallel crank arms 53 are disposed between the plates 52 of the angle brackets 51, each crank arm 53 being in the form of an elongated, dogleg-shaped member, with a plurality of apertures 54 therethrough. At one end of the crank arms 53, they straddle the post 38 of the lading valve 10 and are pivotally connected to the post 38 by a pivot pin 55 which extends through complementary openings in the post 38 and the crank anus 53. A pair of oblong link end plates 56 are respectively fixed to opposite sides of the lower end of the stabilizer link 46, the lower ends of the link end plates 56 extending between the crank arms 53 at the midpoints thereof and being pivotally coupled thereto and to the angle bracket plates 52 by a pivot pin 57. The distal ends of the crank arms 53 straddle the lower end of the control link 45 and are pivotally coupled thereto by a pivot pin 58. It will be appreciated that the link end plates 56 may have plural openings therein and could be used for length adjustment. It can be seen that the portion of the crank arms 53 between the pivot pins 57 and 58 cooperate with the link end plates 56, the links 45 and 46 and the portions of the pivot plates 47 extending between the pivot pins 47b and 47c to form a parallelogram linkage. Referring now again to FIGS. 4 and 5, the coupling mechanism 40 also includes an upper lever assembly 60 which couples to the vent valve 20. More specifically the vent valve 20 is provided with a depending cylindrical extension 61 having a wide slot 62 formed diametrically therethrough, the slot 62 having substantial axial and circumferential extent. Fixedly secured to the outer surface of the cylindrical extension 61 adjacent to the lower edge of the slot at one end of the slot is an angle iron 63, while an angle iron 64 spans the opposite end of the slot 62 just above the lower edge thereof. Extending diametrically through the slot 62 are a pair of spaced-apart, elongated support arms 65, which are joined adjacent to one end thereof by a stop pin 66 which is disposed for engagement with the angle iron 64 to prevent the support arms 65 from being pulled out of the slot 62. A pair of crank arms 67 are disposed between the other ends of the support arms 65, the crank arms 67 being similar to the crank arms 53 of the lower lever assembly 50, except having the dogleg angle opening upwardly instead of downwardly. The crank arms 67 are positioned so that their midpoints are disposed between the distal ends of the support arms 65, the crank arms 67 straddling the upper end of the control link 43 at one end thereof and being pivotally coupled thereto by a pivot pin 68. A T-shaped fulcrum 70 is fixed, as by welding, adjacent to the upper end of the stabilizer link 44, the fulcrum 70 having a crossbar 71 disposed beneath the distal ends of the support arms 65. The link 44 extends through the fulcrum 70 and projects upwardly between the crank arms 67, being pivotally connected to the midpoints of the crank arms 67 and to the support arms 65 by a pivot pin 73.

The other ends of the crank arms 67 are joined by a pivot pin 74, which is coupled to a transfer lever 75. More specifically, the transfer lever 75 has a substantially rectangular top plate 76, provided with an elongated slot 77 therein centrally of the upper end thereof for receiving the lower end of the poppet stem 26, being retained in place thereon by a retainer 78. Depending from the opposite side edges of the top plate 76 are rectangular side flanges 79, each of which is provided at its lower end with an elongated slot 80 in which the pivot pin 74 is disposed. The transfer lever 75 extends upwardly through the adjacent end the slot 62 in the cylindrical extension 61 above the angle iron 63 between the support arms 65, the upper ends of the side flanges 79 being pivotally coupled to the support arms 65 by a pivot pin 81.

It can be seen that the portions of the crank arms 67 between the pivot pins 68 and 73 cooperate with the links 43 and 44, the link end plates 48 and the portions of the pivot plates 47 between the pivot pins 47a and 47c to form a parallelogram linkage.

It will be appreciated that, as was described above in connection with the pivot plates 47, all of the pivot pins 55, 57, 58, 68, 73, 74 and 81 may be retained in place by cotter pins, C-clips, retaining rings or the like and may be provided with washers and/or spacer bushings, as needed, to maintain appropriate spacing of the coupled parts and to prevent direct frictional engagement between pivotally connected members, all in a known manner. Also, while in the illustrated embodiment, the pivot plates 47, the link end plates 48 and 56, the angle brackets 51, the crank arms 53 and 67 and the support arms 65 are provided in pairs to afford added stability, these parts could also be provided singly, and the coupling mechanism 40 could still operate effectively.

Referring again to FIGS. IB and 2-6, in operation during opening of the lading valve 10, the raising of the poppet stem 16 causes an upward movement of the post

38, which pivots the crank arms 53 in a counterclockwise direction, as viewed in FIG. 2, about the axis of the pivot pin 57. This pulls the control link 45 downwardly which, in turn, pivots the pivot plates 47 in a counterclockwise direction about the axis of the pivot pin 47c. This pulls the control link 43 downwardly which, in turn, pivots the crank arms 67 in a counterclockwise direction about the axis of the pivot pin 73, as viewed in FIG. 4. This causes the pivot pin 74 to pivot the transfer lever 75 about the axis of the pivot pin 81 in a clockwise direction, thereby pulling down the poppet stem 26 and opening the vent valve 20. Thus, it can be seen that the combination of the two parallelogram linkages formed by the upper and lower arm assemblies 41 and 42 function as an orientation-following linkage, with the opposite ends of each parallelogram linkage always remaining parallel to each other. Thus, similarly, when the lading valve 10 is closed, the lowering of the poppet stem 16 pivots the crank arms 53, the pivot plates 47 and the crank arms 67 in a clockwise direction, thereby pivoting the transfer lever 75 in a counterclockwise direction for reclosing the vent valve 20. Accordingly, the operation of the vent valve 20 follows the operation of the lading valve 10.

During the above-described operation of the coupling mechanism 40, it will be appreciated that the stabilizer links 44 and 46 do not move, being provided simply to afford stability to the mechanism. However, they may move in the event of a change in geometry of the vessel as a result of flexing of the vessel wall, of the type which could occur during loading or unloading operations. Thus, during such vertical flexing the distance between the valves 10 and 20 may change, and the orientation of the coupling mechanism 40 changes accordingly to accommodate this motion. An exaggerated illustration of this change in orientation can be seen by comparison of the

FIGS. 1A, IB and lC. Thus, with the change in distance between the valves, the angles formed between the upper and lower arm assemblies 41 and 42 and the axes of the valves 10 and 20 changes, but the orientations of the crank arms 53 and 67 do not change, so that the operating conditions of the valves do not change. As can be seen from FIGS. 1A-1C, this adaptability of the coupling mechanism 40 also permits it to be installed in different size vessels with significantly different spacings between the valves.

However, as was indicated above, it is also important that the vent valve 20 be permitted to operate independently of the lading valve 10 to correct excessive pressure differential conditions which could occur irrespective of operation of the lading valve 10. In this regard, the poppet stem 26 and the transfer lever 75 are constrained against relative vertical movement in only one direction by the retainer 78. Thus, if the vent valve 20 opens when the pressure differential across the valve poppet 25 exceeds the resistance of the poppet spring 28, the poppet stem 26 can move downwardly through the slot 77 in the transfer lever 75 without moving the transfer lever, and can similarly return to its closed position without moving the transfer lever.

It is a significant aspect of the coupling mechanism 40 that it is designed to disconnect in the event of a catastrophic tank failure, of the type which may occur in an accident. In one possible failure mode, such as in a side impact, the vessel may be squeezed laterally, causing the upper wall and the vent valve 20 carried thereby to move upwardly relative to the lading valve 10. This will tend to straighten out the parallelogram linkages of the coupling mechanism 40, as explained above, until they reach a limit point, similar to the position illustrated in FIG. 1C, wherein the upper and lower parallelogram linkages are substantially vertically aligned with each other. At this point, the continued upward force exerted by the support arms 65 will cause the pivot pin 73 to shear, the pin having shear points designed therein for this purpose, thereby disconnecting the support arms 65 from the upper parallelogram linkage. When this occurs the upper and lower arm assemblies 41 and 42 will fall back toward the position illustrated in FIG. IB, pulling the pivot pin 74 out of the slots on the transfer lever 75, completing the disconnection before the upward movement of the vent valve can cause it to open.

In another failure mode, there might be a vertical collapse of the vessel, causing the vent valve 20 to move downwardly relative to the lading valve 10. In this event, the upper and lower arm assemblies 41 and 42 will move from the FIG. IB position toward the FIG. 1 A position until, ultimately, they reach a limit point, wherein the links 45 and 46 of the lower arm assembly 42 contact each other, preventing any further folding of the parallelogram linkages. At this point, the continued downward movement of the vent valve 20 will cause the support arms 65 to contact the fulcrum crossbar 71, effecting a strong lever action which will again cause the pivot pin 73 to shear, this leverage being effected by the large mechanical advantage resulting from the fact that the lower pivot point 47c of the stabilizer link 44 is much further from the fulcrum point than is the upper pivot point 73. From the foregoing, it can be seen that there has been provided an improved valve operating mechanism whereby the operation of one valve is caused to follow the operation of another, but wherein the one valve is still permitted to operate independently of the other. The coupling mechanism between the valves can accommodate changes in distance between the valves in use and may be mountable in different-sized vessels on which the valves may be disposed, and is automatically disconnectable from one of the valves in the event of a catastrophic failure of the vessel in which the valves are mounted.

The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants' contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.

Claims

WHAT IS CLAIMED IS:

1. A vessel having a wall structure defining a storage compartment and having first and second apertures therein respectively having first and second axes and spaced apart by a variable distance, first and second valves mounted on the wall structure and respectively associated with the first and second apertures, each valve being operable between a closed condition closing the associated aperture and an open condition opening the associated aperture, and a mechanical coupling mechanism interconnecting the first and second valves, the coupling mechanism including first and second pivotally interconnected portions respectively coupled to the first and second valves and disposed in a configuration which varies with the distance between the apertures, the coupling mechanism being responsive to operation of the first valve between the open and closed conditions for effecting a corresponding operation of the second valve between its open and closed conditions.

2. The vessel of claim 1, wherein the first and second portions are respectively inclined at predetermined non-zero angles to the first and second axes.

3. The vessel of claim 2, wherein the coupling mechanism includes a control portion which transmits pivotal movement from one end of the coupling mechanism to the other and a stabilizing portion which prevents a change in the predetermined angles in response to operation of the valves.

4. The vessel of claim 3, wherein each of the first and second portions includes a control link and a stabilizing link.

5. The vessel of claim 1 , wherein each of the first and second portions includes an adjusting link.

6. The vessel of claim 1, wherein the first and second valves are vertically spaced apart.

7. The vessel of claim 6, wherein the second portion includes disconnect mechanism responsive to a predetermined movement of the second valve without operation of the second valve for disconnecting the coupling mechanism.

8. The vessel of claim 7, wherein the disconnect mechanism includes structure responsive to movement of the second valve in a first direction without operation of the second valve for disconnecting the coupling mechanism in a first mode.

9. The vessel of claim 8, wherein the disconnect mechanism includes structure responsive to movement of the second valve in a second direction without operation of the second valve for disconnecting the coupling mechanism in a second mode.

10. The vessel of claim 1 , wherein the second portion includes a coupling to the second valve so as to permit operation of the second valve between open and closed conditions independently of the first valve.

11. A vessel having a wall structure defining a storage compartment and having first and second spaced-apart apertures therein, first and second valves mounted on the wall structure and respectively associated with the first and second apertures, each valve being operable between a closed condition closing the associated aperture and an open condition opening the associated aperture, and a mechanical coupling mechanism interconnecting the first and second valves, the coupling mechanism including first and second pivotally interconnected portions respectively pivotally coupled to the first and second valves with each portion including a parallelogram linkage, the coupling mechanism being responsive to operation of the first valve between the open and closed conditions for effecting a corresponding operation of the second valve between its open and closed conditions.

12. The vessel of claim 11, wherein the coupling mechanism includes a common link member pivotally connected to the first and second portions so that the orientation of the common link member remains substantially constant in use.

13. The vessel of claim 11 , wherein each of the first and second portions includes an adjustable section.

14. The vessel of claim 11 , wherein each of the first and second portions includes a crank arm.

15. The vessel of claim 11 , wherein the first and second valves are spaced apart by a variable distance.

16. The vessel of claim 15, wherein each of the first and second portions includes a crank arm, the orientation of the crank arms remaining substantially constant despite variations in the distance between the valves.

17. The vessel of claim 15, wherein the first and second valves are vertically spaced apart.

18. Apparatus for effecting substantially tandem operation of first and second valves spaced apart by a variable distance, comprising: a mechanical coupling mechanism interconnecting the first and second valves, the coupling mechanism including first and second pivotally interconnected portions respectively coupled to the first and second valves and disposed in a configuration which varies with the distance between the valves, the coupling mechanism being responsive to operation of the first valve between open and closed conditions for effecting a corresponding operation of the second valve.

19. The apparatus of claim 18, wherein the coupling mechanism includes a coupling to the second valve so as to permit operation of the second valve between open and closed conditions without effecting a corresponding movement of the first valve.

20. The apparatus of claim 18, wherein each of the first and second portions includes a parallelogram linkage.

21. The apparatus of claim 18, wherein each of the first and second portions includes a crank arm disposed in an orientation which does not change in response to variation in the distance between the first and second valves.

22. A method of controlling operation of first and second valves disposed in a vessel wall structure and spaced apart by a variable distance, the method comprising: connecting a first orientation-following mechanical linkage to the first valve, connecting a second orientation-following mechanical linkage to the second valve, pivotally interconnecting the first and second mechanical linkages to create an orientation-following coupling mechanism, and operating the first valve between open and closed positions to cause the coupling mechanism to effect a corresponding operation of the second valve.

23. The method of claim 22, wherein the first and second valves are vertically spaced apart.

24. The method of claim 22, and further comprising varying the distance between the valves without effecting an operation of the valves.

25. The method of claim 22, and further comprising permitting operation of the second valve without operation of the first valve.

26. The method of claim 22, and further comprising disconnecting the coupling mechanism in response to a sudden predetermined movement of the second valve without operation of the second valve.