Abstract:
In one aspect, the invention is directed towards a helicopter-carried firefighting device including a valve. The valve has an outer assembly and an inner assembly in which the outer assembly has a reduced surface area on those surfaces which are disposed normally to a direction of movement. The outer assembly therefore may be less affected by hydrostatic and hydrodynamic forces directed so as to oppose its movement. The valve may be located in a reservoir of fluid, and controlled by a control head operated remotely from the helicopter so as to release fluid from the reservoir over a fire. The valve may be symmetrical about a longitudinal axis of the valve, such that transversely directed fluid flows through the valve may be cancelled, producing a coherent, longitudinal fluid flow. The valve may be opened partially so as to operate as a metering valve. The valve may be closed relatively rapidly to retain fluid in the reservoir so as to permit multiple dumps from a single reservoir if so desired.

Description:
FIELD OF THE INVENTION 
     The invention pertains to a mechanical valve, which may be used to regulate fluid flow, for example in aerial fire fighting equipment. 
     BACKGROUND 
     Helicopter carried dump-buckets are well known for use in fighting forest fires. These buckets, at their simplest, may comprise a rigid or flexible reservoir or body for holding a volume of water, a sling to suspend the reservoir from a helicopter, a valve, and an actuator which is controlled from inside the helicopter to operate the valve to release the water from the reservoir over the fire. 
     In many existing buckets, the valve may consist of a simple flapper valve located on a bottom interior surface of the reservoir and operated by a remotely controlled actuator, for example. A flapper valve typically includes a base plate having an outlet therein, a flat flapper member disposed over-top of the base plate so as to block the outlet, and a hinge connected between an edge of the flapper member and the base plate to hingeably connect the flapper member to the base plate permitting the flapper member to alternately block and expose the outlet. While such a valve is mechanically simple and robust, it may have significant shortcomings. 
     In fire-fighting buckets, it may be desirable to place the valve at the bottom of the reservoir so as to permit the reservoir to be completely drained therethrough. In this location, the force of the full head of water in the reservoir resists the hinging of the flapper member and thereby resists the opening of the flapper valve. The resistive force increases directly as the area of the flapper member. Therefore, if a flapper valve having a reasonably large flapper member is provided, such that the reservoir may be dumped reasonably quickly, a fairly powerful motor may be required to actuate the flapper, resulting in increased weight and power consumption. Furthermore, the operation of the valve may create turbulent flow, causing the water to disperse laterally as it is dumped. As previously stated, one edge of the flapper member may be hingeably connected to the base portion. Therefore, when the flapper valve is opened, water may be blocked by the hinged edge while being permitted to flow to the outlet past the remaining edges. This may create unbalanced flows and turbulence. This effect may be exacerbated if the valve is opened only part way so as to operate as a metering valve. In fire-fighting, lateral dispersal may be undesirable as the water may be more susceptible to evaporation before reaching the ground and also because some of the water may overshoot the desired target. 
     Lastly, a flapper valve may not be adequately controllable to rapidly shut off the flow of water to permit multiple dumps, for example. When the valve is open, hydrostatic forces acting on the flapper member may tend to keep the valve open, canceling some of the hydrodynamic forces caused by the outflow of water which may tend to close the valve. Furthermore, the turbulence caused by the valve, as previously described, may further cancel the hydrodynamic forces. Such cancellations may slow the closure of the valve, causing the operator to dump a larger volume water than necessary, possibly the entire bucket load, in a location regardless of whether or not the full volume of water is required at that location. 
     Some existing buckets may use a butterfly valve in place of the flapper valve. A butterfly valve typically includes a longitudinally extending axle having first and second coplanar plates extending laterally therefrom. The butterfly valve may be connected to a bottom portion of the bucket and located in an opening therein. When closed, the first plate may seal against an interior surface of the bucket while the second plate may seal against an exterior surface of the bucket. The valve may be opened by rotating the first and second plates about the axle and may be fully opened by rotating the plates to a position perpendicular to their closed position. While the butterfly valve is hydrodynamically balanced, it may tend to cause lateral dispersal when operated as a metering valve and may be difficult to seal as one plate may be located inside the bucket and the other plate may be located outside the bucket. 
     Furthermore, both butterfly valves and flapper valves may tend to provide relatively poor seals as they may use flat gaskets which may only resist fluid flow directed normally to a plane of the gasket and which may permit fluid leakage directed parallel the plane of the gasket. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a valve having an outer assembly and an inner assembly in which the outer assembly is moveable between open and closed positions, and the outer assembly has a reduced surface area on those surfaces which are disposed normally to a direction of movement. The outer assembly is thereby adapted to be less affected by hydrostatic and hydrodynamic forces directed so as to oppose its movement. 
     In accordance with one aspect of the invention there is provided a valve which may be housed in a fluid reservoir. The valve may include an inner assembly having a spaced apart top plate and base plate, and a substantially open side portion. The valve may also include an outer assembly with solid side walls that are complementary to the inner assembly. The outer assembly may be movable with respect to the inner assembly between an open position and a closed position so that an upper portion of the solid side walls sealably cooperate with the top plate only when the outer assembly is in the closed position, and a lower portion of the solid side walls sealably cooperate with the base plate only when the outer assembly is in the closed position. In the open position, flow through the valve is permitted through the open side portion and the outlet of the inner assembly. In the closed position, flow through the valve is prevented by sealing engagement between the solid side walls of the outer assembly and the top plate and by sealing engagement between the solid side walls and the base plate of the inner assembly. 
     In one embodiment of the invention, the valve may be used in a fire fighting device which may be carried to the site of a forest fire by a helicopter. In this embodiment, an operator, located inside the helicopter may send a command to a control head, instructing the control head to open, or partially open, the valve, thereby releasing water from the reservoir onto the fire. In the open and partially opened positions, the valve may be hydrodynamically balanced such that the flow of water may be a coherent stream. Before the reservoir is emptied, the operator may also instruct the control head to close the valve, retaining water in the reservoir for use elsewhere, thus permitting partial dumps. 
     The following detailed disclosure and drawings disclose several embodiments of the invention, which is capable of expression in structures other than those particularly described and illustrated. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation of a fire-fighting bucket, suspended from a helicopter, according to one aspect of the invention; 
     FIG. 2 is a simplified section of the front elevation of the bucket of FIG. 1 showing a valve and a control head; 
     FIG. 3 is a simplified section of the front elevation of the valve of FIG. 2, in a closed position; 
     FIG. 4 is a simplified section of the front elevation of the valve of FIG. 2 in a fully opened position; 
     FIG. 5 is a simplified top plan view of the valve of FIG. 2; 
     FIG. 6 is a simplified bottom plan view of the valve of FIG. 2; 
     FIG. 7 is a simplified section of a front elevation of the control head of FIG. 2; and 
     FIG. 8 is a simplified section of a front elevation of an alternative control head employing a chain and sprocket to actuate the valve. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, a fire-fighting apparatus according to one aspect of the invention is shown generally as  10 . The apparatus  10  may include a reservoir  12  for containing a volume of fluid  30 . The reservoir  12  may include a bottom interior surface  13  having a valve  18  thereon for controllably releasing a stream  24  of fluid over a fire, for example. The reservoir  12  may be suspended from a control head  26  by support cables  15  and the control head  26  may be suspended from cargo hook  20  of helicopter  22  by support cable  14 . A control cable  16  may be connected between the helicopter  22  and the control head  26  to transmit instructions from an operator to the control head  26 . The control cable  16  may be an electrical cable, a hydraulic hose, or a pneumatic hose, for example. An actuator cable  28  may be connected between the control head  26  and the valve  18  to enable the control head  26  to open and close the valve  18  in response to operator commands. 
     Referring to FIGS. 3,  5  and  6 , valve  18  may have a flat circular base plate  40  having a central circular outlet  42  extending therethrough. A perimeter portion  44  of the base plate  40 , which may be L-shaped in cross-section, defines a seat to receive an edge portion of the reservoir  12 . A flat annular clamping member  46  may be fastened to the perimeter portion  44  by a plurality of bolts  48 , clamping the received edge of the reservoir  12  therebetween to create a substantially waterproof seal between the valve and the reservoir. 
     A plurality of support members  50  may extend rigidly and perpendicularly from an interior surface  41  of the base plate  40 . A top plate  54 , which in one embodiment of the invention defines a circular perimeter, may be rigidly connected to distal ends of the support members  50  so as to be substantially parallel to the base plate  40 , thereby defining an open-sided cylinder therewith. A guide post  55  may extend from an outer surface  53  of top plate  54 , the guide post preferably being hollow and being connected substantially perpendicularly thereto by flange  56  disposed about an opening  59  in top plate  54 . 
     Base plate  40  and top plate  54  may together define an inner assembly  100  of the valve  18 , which may further include support members  50 , guide post  55  and flange  56 . 
     An outer assembly  90  comprises solid side walls  60  having first and second open ends  63  and  65 . Side walls  60  may be cylindrical and may be disposed substantially concentrically about top plate  54 . The outer assembly is movable with respect to the inner assembly between an open position shown in FIG. 4, and a closed position shown in FIG.  3 . An upper portion  75  of solid side walls  60  may be adapted to sealably cooperate with top plate  54  only when outer assembly  90  is in the closed position (FIG.  3 ). A lower portion  61  of solid side walls  60  may be adapted to sealably cooperate with base plate  40  only when the outer assembly is in the closed position. In the open position (FIG. 4) flow through valve  18  is permitted through open side portions  49  and outlet  42  of inner assembly  100 . In the closed position (FIG. 3) fluid flow through valve  18  is prevented by sealing engagement between solid side walls  60  of outer assembly  90  and top plate  54  and base plate  40  of inner assembly  100 . Annular collar  58  may be slidably located around guide post  55  and rigidly connected to side walls  60  by diametrically aligned spacer arms  70 . A plurality of spacer arms  70  may be connected to the inner assembly  100  by constant force tension springs  74 . The tension springs  74  may assist in closing the valve when the reservoir  12  is empty as will be further described. When the reservoir  12  contains fluid, the hydrodynamic pressure from the outflow stream  24  may be sufficient to close the valve. It will be appreciated that alternative means may be provided to urge the outer assembly into the closed position with respect to the inner assembly, such as a variety of resilient members or springs connecting the outer assembly and the inner assembly. 
     To adapt lower portion  61  of side walls  60  to sealably cooperate with base plate  40 , a lower O-ring  62  may be disposed around an outer perimeter of the lower portion  61  of side walls  60 . Engagement between lower O-ring  62  and perimeter portion  44  of base plate  40  provides a substantially waterproof seal between the side walls  60  and base plate  40  when the valve is closed. A first hoop fastener  66  which may be L-shaped in cross-section, may be disposed around the outer perimeter of the lower portion  61  of side walls  60  to fasten lower O-ring  62  thereto. The shape of first hoop fastener  66  may be adapted to protect lower O-ring  62  from damage. 
     To adapt upper portion  75  of side walls  60  to sealably cooperate with top plate  54 , upper O-ring  64  may be disposed around an inner perimeter of the upper portion  75  of side walls  60 . Engagement between upper O-ring  64  and top plate  54  provides a substantially waterproof seal between side walls  60  and top plate  54  when the valve is closed (FIG.  3 ). A second hoop fastener  68  which may be L-shaped in cross-section, may be disposed around the inner perimeter of the upper portion  75  of side walls  60  to fasten upper O-ring  64  thereto, and to protect the upper O-ring  64  from damage. The distance between first and second O-rings  62  and  64  may be selected to be substantially equal to the distance between base plate  40  and top plate  54  to permit both O-rings to form respective seals substantially simultaneously when valve  18  is closed. In some embodiments, O-rings  62  and  64  do not bear on any surface when valve  18  is opened, so that wear on O-rings  62  and  64  is reduced. 
     Lifting member  82  may be disposed across an interior diameter of the side walls  60 , connected to interior faces of side walls  60 , preferably at the lower portion  61  of side walls  60 . Lifting member  82  may define a plurality of openings therethrough having guide bushings  86  therein. Guide bushings  86  may be disposed coaxially about respective support members  50  and slidably connected thereto. A cable connection  84 , which may comprise a screw-threaded cable adjuster/connection, may be disposed on lifting member  82 . In a cylindrical embodiment of valve  18 , cable connection  84  may be at a centre-point on lifting member  82  and may be concentric with cylindrical side walls  60 . A first end of actuator cable  28  may be connected to cable connection  84  and the actuator cable disposed to extend therefrom through an opening  59  in top plate  54  and through guide post  55 , a second end of the actuator cable  28  being connected to control head  26  as will be further described. 
     The side walls  60 , the annular collar  58 , the spacer arms  70 , the O-rings  62  and  64 , the hoop fasteners  66  and  68  and the lifting member  82  comprise the outer assembly  90  of the apparatus. 
     Referring to FIGS. 2 and 3, the valve  18  is shown in a closed position, such that the lower portion  61 of side wall  60  is adjacent the base plate  40  and the upper portion  75  of the side wall is adjacent the top plate  54 . In this position, lower O-ring  62  may be held in close contact with the interior surface  41  of base plate  40  to form a substantially fluid-tight seal therewith about the whole of the outside perimeter of lower portion  61 . Similarly, upper O-ring  64  may be held in close contact with the outer surface  53  of top plate  54  to form a substantially fluid-tight seal therewith about the whole of the inside perimeter of upper portion  75  of side wall  60 . Furthermore, the constant force tension springs  74  may exert forces which urge outer assembly  90  towards inner assembly  100 , thereby forcing the upper and lower O-rings  62 ,  64  into close contact respectively with top plate  54  and the base plate  40 , thereby creating improved waterproof seals. 
     Referring to FIGS. 1 and 7 the control head is shown generally at  26 . The control head may include an attachment portion  110  whereby the control head may be connected to support cable  14 . A control-head-plate  112  may extend from the attachment portion  110  to locate components of the control head as will be herein described. A DC electric motor  114  and reduction gear  116  may be rigidly connected to the control-head-plate  112 . The DC motor  114  may be electrically connected to a motor control unit  135  located on the control-head-plate  112  to receive electrical power therefrom as will be further described. A rotor shaft  113  of the motor  114  may be connected to a collinearly disposed input shaft  111  of the reduction gear  116  so as to drive input shaft  111 . A cable pull arm  118  may be connected to a high torque output shaft  115  of the reduction gear  116  to produce rotary motion of a distal end of the cable pull arm  118  in response to rotation of the high torque output shaft  115 . A cable connector  120  may be pivotally connected to the distal end of cable pull arm  118  and connected to the second end of actuator cable  28  whereby the second end of the actuator cable  28  may be made to rotate with the cable pull arm  118  about the output shaft  115 . A pair of rollers  131  may be located adjacent the actuator cable  28  to limit lateral movement of the actuator cable and to produce substantially linear motion of a length of actuator cable  28  extending between said rollers  131  and said lifting member  82  in response to rotational motion of the cable pull arm  118 . A plurality of positional sensors  122 . 1 ,  122 . 2 ,  122 . 3 ,  122 . 4 ,  122 . 5  may be located adjacent the cable pull arm  118  to sense the relative position thereof. In one embodiment of the invention, the positional sensors comprise micro-switches which are operable by a cam  119  connected to the cable pull arm  118 . Alternatively, the positional sensors may be reed switches, Hall effect sensors, photo transistors, magnetic sensors or any of the other sensors which are known in the art. Motor control unit  135  may be connected to control cable  16  to receive DC power from a remote power source (not shown) located in helicopter  22  and to receive operator instructions. Motor control unit  135  may also be connected to positional sensors  122 . 1 ,  122 . 2 ,  122 . 3 ,  122 . 4  and  122 . 5  to obtain positional feedback therefrom. The motor control unit  135  may be connected to DC motor  114  to provide controlled DC power thereto so as to control the rotation thereof in response to the operator instructions and the positional feedback from the positional sensors. The waterproof housing  27  may be disposed to enclose the components of the control head to permit the control head  26  to be immersed in water, such that the control cable  16  and the actuator cable  28  enter the housing through waterpoof seals. 
     Referring to FIG. 8, an alternative control head is shown generally at  26 . 1  In this embodiment, cable pull arm  118  has been replaced with a chain-sprocket  200 . The sprocket  200  may be circular and may be mounted eccentrically about reduction gear output shaft  115 . 1 . A connecting chain  204  may be connected to the sprocket  200  and disposed to extend over a partial perimeter of the sprocket so as to engage sprocket teeth . A distal end of the chain  204  may be connected to actuator cable  28  to transmit force to the actuator cable and the outer portion of the valve as previously described. The eccentric sprocket may be mounted so as to provide greater leverage when the valve is in a fully closed position, and less leverage as the valve is opened, an arrangement which corresponds to the water-loads which must be overcome to open the valve. A circular plate  202 , having a diameter larger than the sprocket  200  may be mounted eccentrically on output shaft  115 . 1  so as to describe a substantially identical path as sprocket  200  and may serve as a chain guard to keep the chain on the sprocket. A cam  205  mounted concentric with the shaft may serve to actuate positional sensors disposed as previously described. 
     OPERATION 
     Referring to FIGS. 1,  2  and  3  the helicopter may carry a reservoir containing volume of water  30  to the site of a fire, the volume of water being retained in the reservoir by valve  18  which may be maintained in a closed position to prevent water from reaching outlet  42 . 
     The design of the valve and the use of O-rings in place of flat gaskets may provide improved seals reducing water losses. When the valve is in a closed position, the top plate  54 , the base plate  40  and the side walls  60  may define a closed-sided cylindrical chamber  57  which may be in communication with the surrounding environment through outlet  42 , but which is separated from the reservoir by fluid-tight seals. The reservoir  12  may be open at the top such that when the reservoir contains water, hydrostatic pressure in the reservoir is greater than atmospheric pressure by an amount equal to the head of water in the reservoir. The cylindrical chamber  57  may be in communication with the atmosphere through outlet  42  and therefore may be at atmospheric pressure. Therefore, the pressure in the reservoir may be higher than the pressure in cylindrical chamber  57  and may tend to urge O-rings  62  and  64  into respective openings between the outer and inner assemblies  90  and  100  of the valve, creating improved waterproof seals therebetween. 
     Referring to FIGS. 1 and 7, a signal may be sent from the helicopter  22  to the control head  26  along control cable  16  to instruct the control head to open valve  18 . The signal, which may include DC electrical power, may be sent to motor control unit  135  to control DC motor  114  to produce rotary motion of shaft rotor  113 . The rotary motion of the rotor shaft  113  may be used to drive input shaft  111  of the reduction gear  116 . The reduction gear may convert the high speed, low torque output of the DC motor  114  into a low speed, high torque output at its output shaft. The cable pull arm  118  connected to the output shaft  115  of the reduction gear  116  may thereby be made to rotate at reduced RPM with respect to the rotor shaft  113  of DC motor  114 . By controlling the rotation of the DC motor  114 , the distal end of cable pull arm  118  may be moved from a point of minimum distance  124  from the valve  18  to a point of maximum distance  126  from the valve by causing the cable pull arm to rotate through an angle of 180 degrees. A distance  128  between these points  124  and  126  corresponds to a maximum linear travel of the cable connector  120  and actuator cable  28  which are pivotally connected to the cable pull arm  118 . In one embodiment of the invention, the distal end of the cable pull arm describes a circle having a diameter of approximately 9 inches so as to permit a maximum linear travel of the actuator cable  28  of approximately 9 inches. 
     The positional sensors  122 . 1 ,  122 . 2 ,  122 . 3 ,  122 . 4 ,  122 . 5  may be located to detect predetermined positions of the cable pull arm. For example, the sensor  122 . 1  may be located to detect when the cable pull arm is at the point of minimum distance  124 ; sensor  122 . 5  may be positioned to detect when the cable pull arm is at the point of maximum distance  126 ; and sensors  122 . 2 ,  122 . 3 ,  122 . 4  may be positioned to detect when the cable pull arm is at positions ⅓, ½, and ⅔ of the distance therebetween, respectively. This positional information may be used as feedback by the motor control unit  135  to control the rotation of DC motor  114  and may be transmitted to the helicopter  22  along control cable  16  to provide such positional information to the operator. 
     Referring to FIGS. 4 and 7, the cable pull arm may be rotated from point  124  to point  126  so as to move the cable connector  120  and actuator cable  28  upwardly by the maximum linear travel. The first end of the actuator cable  28  may be connected to the lifting bar  82 , such that the upward motion of the actuator cable  28  is transmitted to the lifting bar  82  and thereby to the outer assembly  90  of the valve. Therefore, the positional information about the cable pull arm  118  may correspond to linear positional information about the cable connector  120 , the actuator cable  28  and the outer assembly  90 . The operator may therefore use the positional information provided by the positional sensors  122 . 1 ,  122 . 2 ,  122 . 3 ,  122 . 4 ,  122 . 5  to control the DC motor  114  so as to stop the outer assembly  90  at a position intermediate fully closed and fully opened positions, whereby the valve may be controlled to permit a reduced or partial flow of fluid from the reservoir. 
     The valve may be designed to reduce forces which oppose movement of the outer assembly. For example, the outer assembly  90  may be slideably mounted on support members  50  and guide post  55  and guided by bushings  86  and collar  58  such that the outer assembly  90  may slide under the influence of the actuator cable without undue friction or racking. The spacer arms  70  and the lifting member  82  may be essentially the only parts of the outer assembly  90  which may be disposed generally perpendicularly to the direction of travel of the outer assembly  90 . Therefore, hydrostatic and hydrodynamic forces acting on the surfaces of these portions may be the only hydrostatic and hydrodynamic forces tending to resist the movement of the outer assembly. The lifting member  82  and connector arms  70  may have substantially reduced surface areas, as compared to a flapper valve for example, such that hydrostatic and hydrodynamic forces thereon will be correspondingly reduced. An increase in the size of the outlet  42  and a corresponding increase in the size of the valve may produce a relatively small increase in the surface areas of lifting member  82  and connector arms  70 . Because the hydrostatic and hydrodynamic forces resisting movement of the outer assembly may be relatively small, the DC motor  114  may therefore be relatively small, permitting a reduction in weight and power requirements. 
     In one embodiment, the valve  18  may be substantially symmetrical about a vertically extending central axis  150  extending through the centre of outlet  42  such that water may flow transversely towards the outlet  42  from all directions equally. Therefore, the transverse or horizontal components of respective flows may substantially cancel one another, reducing turbulence and producing an output stream  24  which may be substantially coherent and vertically directed. Turbulence may be further reduced due to the fact that in an open or partially open position, there may be few obstructions to block water flow. The support members  50  may have relatively small cross-sections and correspondingly small surface areas. Additionally, the support members may have rounded profiles to reduce turbulence. 
     At any time, the operator may signal the motor control unit  135  to close the valve. The motor control unit may close the valve by reversing the polarity of the DC power thereby reversing the direction of rotation of DC motor  114 , the reduction gear and cable pull arm  118  and reversing the direction of linear travel of the cable connector  120  and actuator cable  28 . Alternatively, the cable pull arm may be permitted to describe a full circle, thereby returning to the point of minimum distance  124 , the cable connector  120  and actuator cable  28  automatically reversing their direction of travel as the cable pull arm moves from the point of maximum distance  126  back towards the point of minimum distance  124 . If the cable pull arm is permitted to describe a complete circle, additional positional sensors may be required to detect the position of the cable pull arm over the entire circle so described. Regardless of control method, when the actuator cable  28  reverses direction, it may stop exerting a force on lifting member  82 , permitting the outer assembly  90  to return relatively quickly to the closed position under the influence of its own weight and the spring force generated by the constant force tension springs  74 . Hydrostatic and hydrodynamic forces acting to resist movement of the outer assembly may be minimal, being mostly directed normally to the direction of travel such normal forces being cancelled by equal and oppositely directed normal forces due to the substantially symmetrical design of the valve. By closing the valve  18  before the reservoir is empty, the operator may use the apparatus to perform controlled partial dumps whereby only a portion of the total volume of water  30  is dropped in a location, the remained being used elsewhere. By partially closing the valve  18 , the operator may control the valve to permit reduced fluid flows, as required. 
     The operator may control the valve to permit the apparatus to be refilled at a lake or river, for example, by opening the valve of the now empty reservoir and lowering the reservoir into the lake. The apparatus will tend to sink under its own weight and will thereby force water into the reservoir. When the reservoir is sufficiently full, the operator may signal the motor control unit  135  to close the valve, thereby sealing the water into the reservoir. The helicopter may then lift the apparatus out of the lake and repeat the dump/fill cycle as needed. When filly immersed, water will fill both the reservoir  12  and the cylindrical chamber  57  such that forces on the outer assembly  90  may be balanced such that there is insufficient downward pressure on the outer assembly to form a good seal with the inner assembly  100 . For this reason, tension springs  74  may be included to apply a biasing force between the inner assembly  100  and outer assembly  90 . As the apparatus is lifted clear of the lake, the fluid in chamber  57  will drain out through outlet  42 , creating an unbalanced hydrostatic force on the outer assembly  90  which may tend to further seal the outer assembly to the inner assembly. 
     ALTERNATIVES 
     While a specific embodiment and application of the invention has been disclosed, the invention encompasses many alternative embodiments and applications. For example, while an embodiment of valve  18  is cylindrical in shape, other shapes may be used. The valve may be made of metal plate welded into a cube or prism, for example. In such a valve, the base plate  40  and top plate  54  may define square plates separated by support members  50  to define an open-sided cube, for example. The side walls  60  of such a valve may be in an open ended box configuration. The valve may be further modified by making the base plate  40  funnel-shaped or in the shape of an inverted pyramid, for example. Alternative shapes may be useful to adapt the valve of the invention for alternative uses, such as for regulating the flow of particulate solids in railway hopper cars or agricultural hoppers, for example. The tension springs and actuator cable may be replaced with a hydraulic or pneumatic cylinder where an appropriate hydraulic or pressurized air supply is available. Support members  50  may be extended beyond top plate  54  to act as guide rods for the outer assembly  90  and may thereby replace guide post  55  and flange  56 . Alternatively, a plurality of U-channel tracks may be disposed to extend between top and base plates  54  and  40  respectively, and complementary guide rollers attached to an inner surface of side walls  60  such that the guide rollers may act as a roller bearing to facilitate the movement of the outer portion  90  with respect to the inner portion  100  while the U-channel tracks may provide alignment and prevent racking. Further mechanical equivalents will be apparent in which elements of the valve are replaced by parts that perform substantially the same function in substantially the same way to achieve substantially the same result, and such equivalents are within the scope of the present invention.