Buoyancy Controlling Apparatus and Method

Description

FIELD OF INVENTION

This invention relates to a buoyancy controlling apparatus and to a buoyancy controlling method for controlling buoyancy of a body to be submerged in a liquid.

BACKGROUND TO INVENTION

Various buoyancy control devices have been proposed for controlling a buoyancy of a body, such as a submersible in a body of liquid. These devices suffer from a number of draw backs and disadvantages. One such disadvantage is that energy and power is needed to bring the submersible to the surface after the submersible has reached its required depth of dive. This is disadvantageous and dangerous because if there is a problem with the power supply, motors, pumps, or engines of the submersible, resurfacing may not be possible.

The need exists for objects to travel vertically in water column during changes in external pressure exerted by the fluid. During that vertical travel it may be advantageous that the buoyant force exerted by an apparatus shall be constant and independent of external pressure changes. The displacement of ambient fluid with a less-dense gas in an open-bottom container to create buoyancy has unto now meant that the gas volume changes during vertical travel, changing the buoyant force in a positive feedback loop, moving deeper compresses gas further, accelerating downward movement. Moving shallower decompresses gas further, accelerating upward movement.

It may be desired for an object to remain at a constant depth in a fluid environment. An object, once neutrally-buoyant, has no tendency to move vertically due solely to buoyancy, but may move vertically due to disturbances in fluid currents, changes in salinity and temperature, activities and operations upon and within the object that exert other types of forces (inertia, acceleration, torque and other of the typical mechanical forces). Maintenance of the physical vertical distance from the surface then requires constant small adjustments to the buoyant force, the object may need to become negatively or positively buoyant for a short period to compensate for external forces and move back towards the desired depth, then once again adjust buoyancy in the opposite of the first adjustment to compensate for the inertia of the object motion.

It is advantageous that these adjustments be accomplished using the least amount of energy and consume the least amount of resources such as stored compressed-air supplies, battery power and the like.

Since building pressure vessels to resist the pressures encountered within the bodies of fluid such as the sea is expensive, difficult and dangerous, it is neither economical nor advisable to create a positive pressure at the surface that will still be a positive pressure at depth. Some method of adjusting the gas pressure to keep it positive within a certain range in relation to external ambient without affecting the volume of ambient fluid displaced by the gas volume must be affected.

A need exists for a buoyancy controlling apparatus and method which allows a submersible to surface without energy or power. A need further exists for a buoyancy controlling apparatus and method which allows a submersible to surface even if all electrical, and or other systems of the submersible fails.

In short, a need exists for a buoyancy controlling apparatus which includes a “fail-safe” method of resurfacing in emergency situations, and/or when systems on the submersible are failing and/or non-operational or partially operational.

In this specification, the term “gas” shall be interpreted broadly to mean any gas, such as, for example, air. The term “liquid” shall be interpreted broadly to mean any liquid such as, for example, fresh water, sea water, etc.

SUMMARY OF INVENTION

According to a first aspect of the invention, there is provided a buoyancy controlling apparatus for controlling buoyancy of a body to be submerged in a body of liquid, the buoyancy controlling apparatus including:

• • a gas pressure vessel defining a pressure chamber for holding pressurized gas;
  • a controllable buoyancy pressure vessel defining one or more internal chambers, said one or more internal chambers having an inlet leading into said one or more internal chambers and an outlet leading out of said one or more internal chambers; said one or more internal chambers being configured for holding pressurized gas and/or pressurized liquid introduced therein through the inlet of said one or more internal chambers;
  • a pressure control valve in flow communication with said one or more internal chambers of the controllable buoyancy pressure vessel and with the pressure chamber of the gas pressure vessel, for controlling gas flow between the pressure chamber of the gas pressure vessel and said one or more internal chambers of the controllable buoyancy pressure vessel;
  • a liquid pressurization device for pressurizing liquid, the liquid pressurization device including:
  • (a) a pump having an inlet and an outlet for pumping pressurised liquid out of the pump and into said one or more internal chambers of the controllable buoyancy pressure vessel via the inlet thereof;
  • (b) one or more valves in flow communication with the outlet of the pump for controlling fluid flow between the pump and the inlet of the controllable buoyancy pressure vessel for controlling fluid flow into said one or more internal chambers of the controllable buoyancy pressure vessel via the inlet thereof.

The outlet of said one or more internal chambers of the controllable buoyancy pressure vessel may be operable for releasing liquid from said one or more internal chambers, thereby to control the buoyance of the controllable buoyancy pressure vessel.

The liquid pressurization device of the buoyancy controlling apparatus may further include, in addition to the pump, and one or more valves, (c) a pressure storage and return device in flow communication with the outlet of the of the one or more internal chambers of the controllable buoyancy pressure vessel, the pressure storage and return device being configured, in use, for storing pressure exerted by the fluid as it is driven from said one or more internal chambers of the controllable buoyancy pressure vessel by the expansion of the gas. As such, the pressure storage and return device may also be in flow communication with the outlet of said one or more internal chambers of the controllable buoyancy pressure vessel for returning stored pressure, stored, in use, to the inlet of the pump, thereby to reduce the differential head-pressure between the pump inlet and the pressure of the internal chambers of the controllable buoyancy pressure vessel, when required.

More particularly, the pressure storage and return device may be in the form of a spring-loaded piston-cylinder mechanism arranged such that pressurized liquid from the outlet of said one or more internal chambers of the controllable buoyancy pressure vessel loads a spring of the spring-loaded piston-cylinder mechanism, in use. In use, the loaded spring of the spring-loaded piston-cylinder mechanism of the pressure storage and return device may be used to unload potential energy build up in the spring-loaded piston-cylinder mechanism, for assisting the pump, when required, in use.

In another embodiment, the pressure storage and return device may be in the form of one or more elastomeric balloon-type expandible enclosures for resiliently expanding when pressurized fluid from the outlet of the internal chamber fills the elastomeric balloon-type expandible enclosures. In use, the one or more elastomeric balloon-type expandible enclosures may be used to unload potential energy build up by expansion of the one or more elastomeric balloon-type in a manner similar to that described in the case of the spring-loaded piston-cylinder mechanism 38. expandible enclosures.

The valves of the pressure storage and return device may further include a one-way valve having an inlet and an outlet, the inlet being in flow communication with the body of liquid, in use, and the outlet of the one-way valve leading into the inlet of the pump. As such, in use, liquid supplied by the pump is drawn from the body of liquid in which the apparatus is submerged and through the one-way valve of the pressure storage and return device.

The liquid pressurization device may further include a liquid flow controlling arrangement for controlling flow of liquid into and out of the inlet of said one or more internal chambers of the controllable buoyancy pressure vessel.

More specifically, the liquid flow controlling arrangement may be displaceable between:

• • a liquid emptying configuration in which liquid is emptied from said one or more internal chambers of the controllable buoyancy pressure vessel, thereby to increase the buoyancy of the controllable buoyancy pressure vessel; and
  • a liquid filling configuration wherein liquid flows into said one or more internal chambers of the controllable buoyancy pressure vessel thereby to decrease the buoyancy of the controllable buoyancy pressure vessel.

More specifically, when in the liquid emptying configuration, the liquid flow controlling arrangement permits liquid to flow out of the outlet of said one or more internal chambers of the controllable buoyancy pressure vessel, said outflow being driven by gas pressure in said one or more internal chambers of the controllable buoyancy pressure vessel.

When in the liquid filling configuration, the liquid flow controlling arrangement permits liquid to be pumped into said one or more internal chambers of the controllable buoyancy pressure vessel under action of the pump and against the gas pressure in said one or more internal chambers of the controllable buoyancy pressure vessel.

In a particular embodiment, the liquid flow controlling arrangement may include one or more stop valves, that are held in a valve closed position, when an external ambient fluid pressure of the body of water exterior and adjacent the apparatus approaches a pre-determined differential pressure in said one or more internal chambers of the controllable buoyancy pressure vessel.

Said valve may be configured to operate entirely on physical principles of pressure vs area over a diaphragm or piston and require no external activation trigger nor any energy source. The energy for remaining closed against a pressure differential coming from the overpressure condition itself.

As such, the buoyancy controlling apparatus may include a “fail safe” mechanism for returning the buoyancy controlling apparatus to the surface of the body of liquid, in use, whereby, if the apparatus descends such that the internal pressure of said one or more internal chambers of the controllable buoyancy pressure vessel approaches a minimum positive-differential pressure to the external ambient fluid pressure of the body of water exterior and adjacent the apparatus, said one or more stop valves will displace into an open position, said open position constituting the liquid emptying configuration of the liquid flow controlling arrangement, wherein liquid is emptied from said one or more internal chambers of the controllable buoyancy pressure vessel, thereby to increase the buoyancy of the controllable buoyancy pressure vessel.

More specifically, the initial starting gas pressure of said one or more internal chambers of the controllable buoyancy pressure vessel before addition of any fluid, and the volume/pressure of fluid pumped into said one or more internal chambers of the controllable buoyancy pressure vessel may be predetermined for a predetermined depth of descent into the body of water, such that when the apparatus descends such that the internal pressure of said one or more internal chambers of the controllable buoyancy pressure vessel approaches a predetermined positive differential to the external ambient fluid pressure of the body of water exterior and adjacent the apparatus, said one or more stop valves will displace into the open position constituting the liquid emptying configuration of the liquid flow controlling arrangement, the remaining gas pressure differential in said one or more internal chambers of the controllable buoyancy pressure vessel will be sufficient to expel all liquid or sufficient liquid from said one or more internal chambers of the controllable buoyancy pressure vessel such that the apparatus surfaces.

In one embodiment, said one or more internal chambers of the controllable buoyancy pressure vessel, may comprise two separate chambers, including a separate liquid chamber and a separate gas chamber. As such the liquid chamber may have an inlet and an outlet. The gas chamber may also have an inlet and an outlet. In a particular embodiment, a single orifice may serve as both the inlet and the outlet.

In one embodiment, the controllable buoyancy pressure vessel may have a flexible diaphragm separating the liquid chamber and the gas chamber. The flexible diaphragm may be gas and liquid impermeable. In one embodiment, the controllable buoyancy pressure vessel may comprise only a single chamber in which the liquid and the gas is contained.

In one embodiment, the controllable buoyancy pressure vessel may include a single chamber and may have a flexible pressure bladder located inside the internal chamber for holding one of the liquid and the gas with the other one of the liquid and the gas being contained external the bladder and within the single chamber of the controllable buoyancy pressure vessel. The bladder may be gas and liquid impermeable.

According to a second aspect of the invention, there is provided a buoyancy controlling method for controlling buoyancy of a body to be submerged in a body of liquid, the buoyancy controlling method including:

• • providing a source of pressurized gas to replenish the pressure differential to ambient as ambient pressure increases;
  • providing a source of pressurised liquid;
  • providing one or more controllable buoyancy pressure vessels; and
  • controlling the buoyancy of said one or more controllable buoyancy pressure vessels by filling said one or more controllable buoyancy pressure vessels with a desired mixture of pressurized gas and pressurized liquid.

The method may include increasing the buoyancy of said one or more controllable buoyancy pressure vessels by releasing liquid from said one or more controllable buoyancy pressure vessels.

The method may include decreasing the buoyancy of said one or more controllable buoyancy pressure vessels by adding liquid to said one or more controllable buoyancy pressure vessels.

Since the liquid is denser than the gas, increasing the proportion of liquid in said one or more controllable buoyancy pressure vessels increases the density and therefore decreases the buoyancy. Conversely, decreasing the proportion of liquid in said one or more controllable buoyancy pressure vessels decreases the density and therefore increases the buoyancy.

The inventor has advantageously found that since the liquid is incompressible, it's volume and density remains constant at any pressure. Since the gas is compressible, if it is allowed to expand or compress in relation to the external ambient pressure, the buoyancy will change in a positive feedback loop with the direction of vertical travel. Keeping the gas at a positive pressure to the external ambient fluid, but restraining it with a pressure vessel breaks that feedback loop. The method may include filling said one or more controllable buoyancy pressure vessels with sufficient gas such that, for a predetermined depth of descent into the body of water, the gas pressure shall be sufficient to eject sufficient liquid from said one or more controllable buoyancy pressure vessels, so as to reduce the buoyancy of the apparatus sufficient so as to cause the apparatus to re-surface.

Providing the source of pressurized gas may be achieved by providing a gas pressure vessel containing pressurized gas. Providing the source of pressurised liquid may be achieved by providing a pump for pressurizing liquid obtained from the body of liquid. In a particular embodiment, providing a pressurised liquid may further include providing means for temporarily storing energy from the pressurized liquid and return said stored energy when desired to supplement the force supplied by the pump when pumping liquid into said one or more controllable buoyancy pressure vessels. Providing means for temporarily storing energy may comprise providing a spring-loaded piston-cylinder mechanism for storing and returning the energy.

BRIEF DESCRIPTION OF DRAWINGS

Further features of the invention are described hereinafter by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying schematic drawings. In the drawings:

FIG. 1 shows a schematic view of a buoyancy controlling apparatus in accordance with a first aspect of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A buoyancy controlling apparatus in accordance with a first aspect of the invention is designated generally by the reference numeral 10. The apparatus 10 is configured for controlling buoyancy of a body to be submerged in a body of liquid, such as, for example, a submersible to which the apparatus 10 is connected which is submersed in the ocean. It will be understood that reference to liquid in this context means sea-water, however, the submersible, could be submersed in any liquid medium.

The buoyancy controlling apparatus 10 includes a controllable buoyancy gas pressure vessel 12 defining an internal pressure chamber 14 for holding pressurized gas, a controllable buoyancy pressure vessel 16, a pressure control valve 18, a liquid pressurization device 20 for pressurizing liquid, as will be explained in more detail hereinbelow, conduits for connecting the various components to one another as shown in FIG. 1 of the drawings; and a fail-safe mechanism for returning the buoyancy controlling apparatus 10 to the surface of the body of liquid, in use.

The gas pressure vessel 12 which defines the internal pressure chamber 14 may be made of metal, for example, a standard SCUBA tank or similar.

The controllable buoyancy pressure vessel 16 comprises a single internal chamber 22, although other arrangements are possible as will be explained in more detail hereinbelow. The internal chamber 22 includes a gas inlet/outlet 24 leading into and out of the internal chamber 22 and a liquid inlet/outlet 26 leading into and out of the internal chamber 22. The internal chamber 22 is configured for holding pressurized gas and pressurized liquid introduced through inlets 24, 26 respectively. The controllable buoyancy pressure vessel 16 includes a safety pressure release valve 27 for releasing excess pressure in the internal chamber 22. The safety pressure release valve 27 is set above maximum allowable working pressure (MAWP), but below material failure.

The pressure control valve 18 is in flow communication with the internal chamber 22 of the controllable buoyancy pressure vessel 16 and with the pressure chamber 14 of the gas pressure vessel 12 and is configured for controlling gas flow between the pressure chamber 14 of the gas pressure vessel 12 and the internal chamber 22 of the controllable buoyancy pressure vessel 16. In a particular embodiment, valve 18 may be so configured to maintain the pressure within 16 within a range of predetermined positive-pressure differential to the ambient fluid.

The liquid pressurization device 20 is configured for pressurizing liquid and includes a pump 28, valves 30.1,30.2,30.3, and 30.4, and a pressure storage and return device 32.

The pump 28 has an inlet 34 and an outlet 36 for pumping pressurised liquid out of the pump 28 and into the internal chamber 22 of the controllable buoyancy pressure vessel 16 via the inlet 26 thereof.

The pressure storage and return device 32 is in flow communication with the outlet of valve 30.4, and is configured, in use, for storing pressure exerted by the gas within the internal chamber 22 of the controllable buoyancy pressure vessel 16 when liquid flows out of valve 30.4. As such, the pressure storage and return device 32 is in flow communication with the inlet 34 of the pump 28 for returning stored pressure, stored, in use, to the inlet 34 of the pump 28, thereby to assist the pump 28 by lowering differential head pressure across the pump, when required.

More particularly, the pressure storage and return device 32 is in the form of a spring-loaded piston-cylinder mechanism 38 or some other tensile enclosure arranged such that pressurized liquid via valve 30.4 from the outlet 26 of vessel 22 loads a spring of the spring-loaded piston-cylinder mechanism 38, in use. In use, the loaded spring of the spring-loaded piston-cylinder mechanism 38 of the pressure storage and return device 32 is used to unload potential energy build up in the spring-loaded piston-cylinder mechanism 38, for assisting the pump 28, when required to make minor increments to the level of liquid in the internal chamber 22 with minimum energy input/with assistance from the spring-loaded piston-cylinder mechanism 38.

The valve 30.1 of the pressure storage and return device 32 is in the form of a one-way valve having an inlet and an outlet, the inlet being in flow communication with the body of liquid, in use, and the outlet of the one-way valve 30.1 leading into the inlet 34 of the pump 28. As such, in use, liquid supplied by the pump 28 is drawn from the body of liquid in which the apparatus 10 is submerged and through the one-way valve 30.1 of the pressure storage and return device 32.

The liquid pressurization device 20 further includes a liquid flow controlling arrangement for controlling flow of liquid into and out of the inlet/outlet 26 of the internal chamber 22 of the controllable buoyancy pressure vessel 16.

More specifically, the liquid flow controlling arrangement is displaceable between:

• • a liquid emptying configuration in which liquid is emptied from the internal chamber 22 of the controllable buoyancy pressure vessel 16, thereby to increase the buoyancy of the controllable buoyancy pressure vessel 16; and
  • a liquid filling configuration wherein liquid flows into the internal chamber 22 of the controllable buoyancy pressure vessel 16 thereby to decrease the buoyancy of the 315 controllable buoyancy pressure vessel 16.

More specifically, when in the liquid emptying configuration, the liquid flow controlling arrangement permits liquid to flow out of the inlet/outlet 26 of the internal chamber 22 of the controllable buoyancy pressure vessel 16, said outflow being driven by gas pressure in the internal chamber 22 of the controllable buoyancy pressure vessel 16.

When in the liquid filling configuration, the liquid flow controlling arrangement permits liquid to be pumped into the internal chamber 22 of the controllable buoyancy pressure vessel 16 under action of the pump 28 and increasing the gas pressure in the internal chamber 22 of the controllable buoyancy pressure vessel 26.

The inventor has found it particularly advantageous that the liquid flow controlling arrangement specifically includes stop valves 30.3 and 30.4, that are held in a valve closed position, when an external ambient fluid pressure of the body of water exterior and adjacent the apparatus 10 is less than a pressure in the internal chamber 22 of the controllable buoyancy pressure vessel 16. This arrangement constitutes the “fail safe” mechanism which is configured intentionally for returning the buoyancy controlling apparatus 10 to the surface of the body of liquid, in use. More specifically, if the apparatus 10 descends such that the internal pressure of the internal chamber 22 of the controllable buoyancy pressure vessel 16 approaches the minimum positive differential pressure in comparison to the external ambient fluid pressure of the body of water exterior and adjacent the apparatus 10, the stop valves 30.3 and 30.4 will be displaced into an open position, said open position constituting the liquid emptying configuration of the liquid flow controlling arrangement, wherein liquid is emptied from the internal chamber 22 of the controllable buoyancy pressure vessel 16, thereby to increase the buoyancy of the controllable buoyancy pressure vessel 16.

More specifically, when the internal chamber 22 is empty of fluid, gas is introduced into chamber 22 from gas pressure vessel 12, pre-loading it with pressurized gas to a pre-determined value and the apparatus 10 is ready for operations. In this condition the buoyancy of the internal chamber is at it's maximum. Subsequently, fluid is pumped into the internal chamber 22 via port 26, reducing the available volume for the gas and compressing it. More fluid compresses the gas further. When sufficient fluid has entered internal chamber 22 for the desired buoyant force, no further fluid is added. The apparatus 10 may be allowed to descend through the ambient fluid. During this descent, as long as a positive pressure differential exists between the volume of the gas in 22 and the ambient fluid, the displacement volume of the gas in chamber 22 does not vary, so the buoyancy does not change. If the apparatus 10 descends until the positive pressure differential reduces beyond a pre-determined minimum value, then the opening of valve 30.4 & 30.3 allows the positive pressure differential of the gas in vessel 22 forces the fluid out, allowing expansion of the gas, increasing the buoyancy and returning the apparatus 10 to the surface.

It will be understood that this fail safe will become activated if the pressure pressure control valve 18 fails in it's function of maintaining the pressure differential into the internal chamber 22 of the controllable buoyancy pressure vessel 16, as the apparatus descends. As such, any failure in the pressure control valve 18, conduits, etc. will result in the activation of the fail safe and the resurfacing of the apparatus 10 without any additional energy being required and without the use of drop-weights or other configuration changes. The inventor envisages that this constitutes a substantial improvement over known arrangements.

For a better understanding of the invention, an example shall be provided below with reference to specific details and some illustrative figures.

The inventor envisages that the buoyancy in the apparatus 10 is created by the difference in total density of the controllable buoyancy pressure vessel 16 (including gas, liquid and structure) and the same volume of ambient liquid which is displaced in which the apparatus 10 is submerged. For the purposes of this example, we shall assume that when the level of the incompressible liquid in internal chamber 22 of the controllable buoyancy pressure vessel 16 is at a maximum design level and conversely the gas volume is at it's smallest, most compressed volume, the small volume of air in the internal chamber 22 of the controllable buoyancy pressure vessel 16 will displace the least amount of ambient fluid with less-dense gas and therefore produce the least buoyant force. That buoyancy may be exceeded by the weight of the physical structure and the load intended to be supported when in use, meaning the apparatus 10 might be negatively buoyant (would sink in the ambient fluid). Negative buoyancy is sometimes desirable to allow objects to descend to the desired depth. Repeatable reversibility of the buoyancy is also a desired function, whereby the buoyancy may be negative, then neutral, then positive, then negative again and so on and so on.

When the liquid level in the internal chamber 22 of the controllable buoyancy pressure vessel 16 is at its minimum design level the air shall be at maximum volume, so buoyancy shall be referred to as 100% (i.e., maximum buoyancy which the apparatus can deliver).

For this example, the pressure rating of the internal chamber 22 of the controllable buoyancy pressure vessel 16 in bar over bottom pressure (the pressure of the external environment) shall be at least 3 barG but may be more.

For this example, the internal chamber 22 shall be assumed to begin operations empty of water, empty of gas, collapsed, the apparatus 10 shall be assumed to be at sea level and not submerged. The gas pressure in chamber 22 shall be raised to 1 barG by setting the pressure control valve 18 to 1 barG over atmospheric pressure, equivalent to 2 barA. The internal chamber is now pressurized to 2 barA, one barG, the internal chamber 22 is 100% filled with air or gas without any water.

Throughout the example below until noted in the process, no additional gas is admitted from pressure vessel 12 into buoyancy tank 22.

Water is now pumped into the internal chamber 22 via suction through valve 30.1, Pump 28, outlet 36 and valve 30.4. Note that at the first moment, the pump 28 must operate against one barG head-pressure. Let us assume that the operator operates the pump until the liquid level is 50% of the total internal volume of chamber 22.

When the liquid level in the internal chamber 22 of the controllable buoyancy pressure vessel 16, in this example, is 50%, the pressure of the air/gas in the internal chamber 22 of the controllable buoyancy pressure vessel 16 shall be at least 3 barg. 1 barG=2 barA*2=4 barA=3 barG P1*V1=P2*V2 must be calculated in absolute pressures.

In this example at this point, the overall buoyancy of the assembly is 50% of maximum. Note at the end of this pumping operation, the pump 28 must cause water flow against 3 barG of head pressure.

If the load carried by the buoyancy device is equal to 50% of the total buoyancy, the total average density of the device is equal to the total average density of the same volume of displaced water/fluid, and the device+load are now at equilibrium, defined in the art as “neutral buoyancy”. At this buoyancy the apparatus 10 will have neither a tendency to rise nor to fall in the water column, but will stay at the current depth, whatever that might be unless disturbed by external forces.

Note that since the pressure of the gas and water inside internal chamber 22 is now 3 bar G differential between the interior and the pressure of the atmosphere at sea level, the interior will be overpressurized in differential to an external seawater environment at all depths between the surface to 30 meters (where the environmental pressure is also 3 barG). Since it is undesirable to allow the differential pressure to be completely equal to the exterior, the minimum differential shall then be set at 1 barG, equivalent to 10 meters.

Therefore the apparatus 10 can move freely between the surface and 20 meters of depth while the buoyancy remains constant, equivalent pressure at 20 meters being 2 BarG at 20 meters, internal chamber 22 shall be overpressurized to the environment by 1 barG. At this depth, if valve 30.4 and 30.3 are opened, then without any additional energy being expended, internal chamber 22 will completely emptied solely by the expansion of the gas within.

If in this example, additional water pumped in beyond 50% of the total. In this example, if water is pumped in until the water level in internal chamber 22 is 60% of total, the internal pressure will be 4 bar G and the buoyancy will be 40% of total. At this internal pressure of 4 barG, the apparatus 10 could travel anywhere within the first 30 meters below the surface and the buoyancy would remain constant. At 30 meters, opening valves 30.4 & 30.3 are opened, the expansion of the gas within internal chamber 22 would expel all water without any additional energy.

This constant-buoyancy while moving vertically in the water column feature is one claim

This is so the pressure after expansion of one or more volumes (from afore mentioned 50% level to aforementioned 100% level will be at least 1 bar over bottom pressure.

The internal chamber 22 of the controllable buoyancy pressure vessel 16 will be designed for at least 3 bar over bottom pressure, but it may be more. If only 4 bar overpressure, then the maximum liquid level shall be approximately 60% of the total volume, given the least buoyancy in operation is 40% of total volume. This allows the air/gas currently entrapped to expel all the liquid from the chamber 22 until the apparatus 10 is at maximum buoyancy, solely by opening the valves 30.3 and 30.4, without the addition of any new air/gas from the pressure vessel 12. Accordingly, this is a fail-safe arrangement. More specifically, when the valves 30.3 and 30.4 are opened, the buoyancy will return to 100% with no added energy or stored gas.

The inventor envisages that the pressurised gas in the pressure vessel 12 will only be used during descent into the water column beyond the point at which the internal pressure of tank 22 is less than 1 barG differential over the ambient pressure at depth. As the external ambient pressure rises due to descent, additional air/gas must be added to the internal chamber 22 of the controllable buoyancy pressure vessel 16. However, this is only added during the descent to maintain the overpressure differential of the gas in chamber 22. The inventor envisages that if there are any problems with the air/gas supply, the descent can be stopped safely, automatically by the opening of valve 30.4 & 30.3 and releasing the pressurized contents of internal chamber 22 and allowing the gas to expand, increasing the buoyancy and returning the apparatus 10 to the surface, before an unsafe, unrecoverable situation would be reached.

Therefore, it is envisaged that the pressure control valve 18 should be set to maintain a positive differential pressure, which might be at least 1 BarG over current ambient pressure but could be other positive values. In one embodiment pressure control valve 18 would be high-hysteresis, set to flow only when the differential pressure reduces near to 1 barG, but to flow thereafter until the pressure differential reaches 3 barG. This allows another 30 meters of free vertical descent & ascent movement with no additional gas utilized.

Note that the volume of water in chamber 22 is what controls the buoyancy. During the actions of descending, ascending, adding gas, as water is incompressible, it's volume does not change, and if the water volume and the internal volume of tank 22 do not change, neither does the volume of the water displaced by the air, even though it's compressible, if no water is allowed to flow outward through valves 30.4 or 30.3, the buoyancy of the apparatus 10 remains the same. In this case, the added density of air compressed by adding gas is considered de-minumus. In other words, doubling an air density of 1.022 kg/m3 to 2.044 kg/m3 is lost as water is 1000 times denser.

If controllability and the safety of energy-free return to maximum buoyancy is desired, the internal chamber 22 of the controllable buoyancy pressure vessel 16 can simply be designed for pressure exceeding 3 bar. If the internal chamber 22 of the controllable buoyancy pressure vessel 16 has a maximum allowable working pressure (MAWP) of 4 barG, the liquid level in the internal chamber 22 of the controllable buoyancy pressure vessel 16 can be 66% of the total volume and the air/gas will still expand under its own pressure to completely fill the internal chamber 22 to maximum buoyancy and have a 1 bar overpressure at the moment the last of the water has been expelled.

Number	Bar G				Free
on	internal	Gas	Fluid	Buoyant	vertical
drwg.	pressure	Volume	volume	Force	travel

39	1 Bar G	100%	Nil	21.2 kG	Nil
40	2 Bar G	66%	33%	14.3 kG	10 meters
42	3 Bar G	50%	50%	10.6 kG	20 meters
44	4 Bar G	33%	66%	8.48 kG	30 meters
46	5 Bar G	25%	75%	7.07 kG	40 meters

With reference to the above table, FIG. 1 shows the liquid levels at 0% indicated by reference numeral 39, 33% indicated by 40, 50% indicated by reference numeral 42, at 66% indicated by reference numeral 44, at 75% indicated by reference numeral 46.

According to a second aspect of the invention, the invention extends to a buoyancy controlling method for controlling buoyancy of a body to be submerged in a body of liquid, the buoyancy controlling method including:

• • providing a source of pressurized gas in the form of providing the gas pressure vessel 12 defining the internal pressure chamber 14 for holding pressurized gas;
  • providing a source of pressurised liquid in the form of providing the liquid pressurization device 20 including pump 28;
  • providing one or more controllable buoyancy pressure vessels in the form of providing the internal chamber 22 of the controllable buoyancy pressure vessel 16; and
  • controlling the buoyancy of the internal chamber 22 of the controllable buoyancy pressure vessel 16 by filling the internal chamber 22 of the controllable buoyancy pressure vessel 16 with a desired initial pre-charge of gas, then further pressurizing the gas with addition of liquid until the desired buoyant force is achieved.

The method includes increasing the buoyancy of the internal chamber 22 of the controllable buoyancy pressure vessel 16 by releasing liquid from the internal chamber 22 of the controllable buoyancy pressure vessel 16. The liquid will flow naturally under the influence of the gas expansion, without use of additional gas or energy.

The method includes decreasing the buoyancy of the internal chamber 22 of the controllable buoyancy pressure vessel 16 by adding liquid to the internal chamber 22 of the controllable buoyancy pressure vessel 16. This requires added energy via the pump 28 only when intending to descend further into the water.

Since the liquid is denser than the gas, increasing the proportion of liquid in the internal chamber 22 of the controllable buoyancy pressure vessel 16 increases the density and therefore decreases the buoyancy. Conversely, decreasing the proportion of liquid in the internal chamber 22 of the controllable buoyancy pressure vessel 16, decreases the density and therefore increases the buoyancy.

The method includes filling the internal chamber 22 of the controllable buoyancy pressure vessel 16 with a pre-charge of sufficient gas such that, for a predetermined depth of descent into the body of water, the gas pressure alone shall be sufficient to eject sufficient liquid from the internal chamber 22 of the controllable buoyancy pressure vessel 16, so as to reduce the buoyancy of the apparatus 10 sufficient so as to cause the apparatus to re-surface, including complete evacuation of fluid from the internal chamber 22 by expansion of the gas already contained within 22. No additional gas is anticipated to be required.

One potential use for this device is for an object to remain at a constant depth for extended periods of time. A neutrally buoyant object has no intrinsic tendency to depart from an assigned depth, with the exception of external forces such as the forces of subsurface currents, upwellings, salinity changes and the like. Facility for temporarily and reversibly counteracting said disturbances using the least amount of energy or consumable resources is advantageous. Providing the source of pressurised liquid further includes providing means for temporarily storing energy from the pressurized liquid upon discharge from internal chamber 22 and returning said stored energy when desired to supplement the forces supplied by the pump when pumping liquid into the controllable buoyancy pressure vessel. Providing means for temporarily storing energy comprises providing the spring-loaded piston-cylinder mechanism 38 for storing and returning the energy.

This specification has been described with reference to embodiments of the invention. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. For example, while the internal chamber 22 as described above is a single chamber, other arrangements are possible and beneficial. For example, in one embodiment (not shown), the internal chamber of the controllable buoyancy pressure vessel, may comprise multiple separate chambers, including a separate liquid chamber(s) and a separate gas chamber(s). As such the liquid chamber may have an inlet and an outlet. The gas chamber may also have an inlet and an outlet. In a particular embodiment, a single orifice may serve as both the inlet and the outlet.

In one embodiment (not shown) the controllable buoyancy pressure vessel may have a flexible diaphragm separating the liquid chamber and the gas chamber. The flexible diaphragm may be gas and liquid impermeable. In one embodiment, the controllable buoyancy pressure vessel may comprise only a single chamber in which the liquid and the gas is contained.

In one embodiment (not shown) the controllable buoyancy pressure vessel may include single chamber and may have a flexible pressure bladder located inside the internal chamber for holding one of the liquid and the gas with the other one of the liquid and the gas being contained external the bladder and within the single chamber of the controllable buoyancy pressure vessel. The bladder may be gas and liquid impermeable.

In one embodiment (not shown) the function of spring-loaded piston-cylinder mechanism 38 may be provided with one or more elastomeric balloon-type expandible enclosures for resiliently expanding when pressurized fluid from the outlet of the internal chamber fills the elastomeric balloon-type expandible enclosures. In use, the one or more elastomeric balloon-type expandible enclosures may be used to capture potential energy via expansion of the one or more elastomeric balloon-type expandible enclosures, in a manner similar to that described in the case of the spring-loaded piston-cylinder mechanism 38.

that the inventor has found that it is highly advantageous that the volume of the liquid-displacing gas should not change with pressure. The inventor has found a novel solution is to provide a pressure vessel 16 that is designed for just some small maximum differential, but keep that differential within a positive range as the apparatus 10 descends. Even, for example, at the bottom of the Marianas Trench, 11,000 meters depth, 1,100 BarG, 16,170 psig, if the pressure vessel 16 is maintained at only one atmosphere above that ambient pressure, so the external pressure is 1,100 BarG but the internal pressure is 1,101 BarG, the buoyancy will remain constant because the fluid is incompressible, and if the valve 26 is opened, the air pressure inside will still drive all the water out and the device will ascend. The pressure vessel 16 only needs to be designed in this case for 1 BarG internal pressure. And the pump 28 only needs to drive against one bar head pressure to return the apparatus 10, at the bottom of the Marianas to neutral or negative buoyancy.

The inventor has advantageously found that it is a key principle that as the gas in the controllable buoyancy pressure vessel 16 expands and displaces internal fluid, that fluid, which is at the same pressure as the gas, then moves out of the pressure vessel 16, but stays under some positive differential pressure relative to the external environment. As fluid flows from the controllable buoyancy pressure vessel 16, it will displace ambient fluid. But since both are of the same density, this causes no net change in buoyancy. The only change in buoyancy is due to the expansion of the gas volume in the controllable buoyancy pressure vessel 16. Some part of the energy of that expansion is captured by the pressure storage and return device 32 and lowers the energy needed to pump fluid from the ambient pressure into the controllable buoyancy pressure vessel 16.

The applicant has found that it is highly advantageous that the chamber 22 on the interior of vessel 16 is at a greater pressure than ambient at all times. This positive differential, the pressure in chamber 22 greater than ambient, is a key point, and is created by having some small positive gas pressure in chamber 22 before ANY water is pumped in. Every liter of fluid volume pumping in increases that differential. Releasing the fluid, the gas expands, pushing the fluid out. Release all of the fluid, and the pressure is exactly at the initial positive pressure value you had before any fluid was introduced