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.

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.

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 61of 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 1/3, 1/2, and 2/3 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.