Abstract:
A pressure equalizer for an underwater vessel can include a pneumatic reservoir and a pressure compensating valve (PCV). The PCV can be in fluid communication with the surrounding underwater environment and the vessel interior, and in selective fluid communication with the reservoir. The PCV can further include a valve body and a valve plug. As the PCV opens, the plug moves within the body to establish a path of fluid communication from the reservoir, through the PCV to the vessel interior, to allow flow of high pressure compressible fluid from the reservoir into the interior to pressurize the vessel interior. As the vessel interior pressure equalizes with the surrounding environment, the plug moves within the body to close the fluid communication path with the reservoir, thereby stopping the flow of compressible fluid into the vessel interior to maintain the equalized pressure.

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     This invention (Navy Case No. 100323) is assigned to the United States Government and is available for licensing for commercial purposes. Licensing and technical inquires may be directed to the Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif. 92152; voice (619) 553-2778; email T2@spawar.navy.mil. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains generally to pressure compensating systems. More particularly, the present invention pertains to an underwater pressure compensating system that uses a pneumatic reservoir to equalize and maintain the pressure between the interior of an underwater system and its surrounding environment with a minimum of moving parts. 
     BACKGROUND OF THE INVENTION 
     Autonomous vehicles are being increasingly used for a variety of underwater applications. Some applications include gathering undersea data pertaining to seafloor mapping, and gathering data for chemical analysis for possible oil field exploration, with an increasing trend towards deep water field developments. The data gathering can be important, particularly in the case of deep water development for oil fields, because there is a much greater potential for larger finds than can be expected in more littoral regions. But to gather data, these autonomous vehicles will often contain components that cannot withstand a large pressure differential, such as onboard electronics, for example. Accordingly, these deep water vehicles will often employ a pressure compensation system for either an electrical subsystem such as a battery, or the complete electrical system, such as in the case of the Navy Advanced Tethered Vehicle. Other deep diving autonomous vehicles have components that must kept dry, in addition to being pressure sensitive. One way to accomplish this is to develop deep diving vehicles where the entire sensor and electrical package is kept dry by enclosing the package within a pressure vessel, which is itself pressure compensated. 
     However, the use of pressure vessels in the traditional way to protect electronic equipment from the undersea environment has its own costs. As pressures increase due to the deeper depths desired for exploration, the size, weight, and cost of pressure vessels required to house the selected vessel components increases as well, and the increase is exponential. One example of this is the comparison between the REMUS 100 and REMUS 6000 autonomous vehicles manufactured by Hydroid®. Both vehicles utilize the same electronics and software. However, to accommodate an increase in depth range from one hundred meters to six thousand meters (100 m to 6000 m), the vessel weight increases from eighty pounds to approximately two thousand pounds (80 lbs to 1950 lbs) to accommodate the stronger pressure vessels needed. Alternately, a combination of exotic material and heavy walled pressure vessels are used. But in addition to being heavy, the exotic materials used to manufacture such pressure vessels add a great deal of cost, which restricts their utility. 
     Still other pressure compensation systems use an inert, non-compressible fluid such as mineral oil, contained in a compressible volume pressure compensation system to protect batteries and electronics from the undersea environment. The advantage of using a liquid is that, there is little volume change as pressure increases. This allows for more compact system designs. Incompressible fluid filled systems are however heavy, require that additional buoyancy be added to the system to offset the mass of the fluid filled vessels in order to maintain neutral buoyancy. This added buoyancy is typically provided by using large quantities of materials which are less dense than water such as ceramic spheres, syntactic foam, or ultra high molecular weight polyethelene. While the added bulk from flotation is not always a drawback, such as in moored instruments, it is in the case of autonomous underwater vehicles that are mobile, where the added weight and bulk increases drag and energy expenditures, resulting in lower endurance. 
     In view of the above, it is an object of the present invention to provide a pressure compensating system that equalizes the pressure between the interior of a vessel and the surrounding underwater environment. Another object of the present invention is to provide a pressure compensating system that uses a compressible fluid to equalize pressure between the vessel interior and the surrounding environment. Yet another object of the present invention is to provide a pressure compensating system that uses pressure rather than volume for pressure equalization, to allow for a maximum packing efficiency of electronics, as significantly less vessel volume must be allocated for pressure equalization. Another object of the present invention is to provide a pressure equalizing system that equalizes pressure between the vessel interior and the surrounding environment as the system descends to its operating depth without requiring the use of exotic ceramic materials for the system components. Yet another object of the present invention is to provide a pressure compensating system for a vessel that uses a balance of forces to prevent implosion of the pressure vessel instead or a complicated arrangement of pressure seals. Yet another object of the present invention is to provide a pressure compensating system for a vessel that can actively reduce the pressure inside of the vessel to prevent explosion of the vessel as ambient pressure decreases. Still another object of the present invention is to provide a pressure compensating system that is easy to manufacture in a cost-efficient manner. 
     SUMMARY OF THE INVENTION 
     A pressure equalizer for an underwater vessel, and methods for manufacture and use therefor, can include a pneumatic reservoir and a pressure compensating valve (PCV). The PCV can also be in fluid communication with the surrounding underwater environment, as well as with the vessel interior. The reservoir and PCV can be in selective fluid communication with each other. In some embodiments, the PCV and reservoir can be located within the vessel interior. In other embodiments, the PCV and reservoir can be external to the vessel. 
     The PCV can further include a valve body and a valve plug. The valve body can be formed with an interior orifice, a pneumatic inlet orifice, a backflow orifice and an environment orifice. The valve plug can be positioned within the valve body, and the valve plug can be formed with a longitudinal conduit that extends from the end of the plug closest to the interior orifice partially into the plug. The longitudinal conduit can merge into at least one transverse duct that extends completely across the body and that is in fluid communication with said conduit. A spring or similar type of resilient member can be positioned between the plug and the portion of the valve body that is proximate the interior orifice. 
     The PCV can alternately move between an open position and a closed position to equalize pressure between the vessel interior and the surrounding underwater environments. In the open position the surrounding underwater pressure is greater than the pressure in the vessel interior plus the compressive force of the spring, and the spring can be fully compressed. This moves the plug towards the end of the valve body having the interior orifice, which establishes a path of fluid communication from the reservoir, through the pneumatic inlet orifice, into the duct, through the conduit and the interior orifice, and into the vessel interior. This allows flow of a high pressure gas into the interior to pressurize the vessel interior. 
     Once the pressure in the vessel interior plus the force of the spring is approximately equal to the pressure of the surrounding underwater environment, the PCV closes. In the closed position, the spring is relaxed, which moves the plug away from the interior orifice. This establishes a path of fluid communication from the vessel interior and through the interior orifice, through the conduit and duct, and out of the valve body through the backflow orifice. At the same time, the aforementioned path of fluid communication from the reservoir into the vessel interior becomes closed. While the PCV is in the closed configuration, high pressure gas cannot flow into the vessel interior due to the pneumatic inlet orifice being isolated between two seals. Furthermore, the PCV is stable in this configuration due to the balance of opposing forces on the seals which isolate the pneumatic inlet orifice. The system can further include backflow piping and backflow check valves. The backflow piping establishes a path of fluid from communication from backflow orifice to the external environment, while the check valves prevent water from flowing in the opposite direction, from the environment into the PCV valve body. With this configuration, compressible gas from the vessel interior can bleed (flow) out of the vessel interior, out of the backflow orifice through the backflow piping and out of the system when the vessel interior pressure is greater than the ambient underwater pressure. This arrangement effectively prevents over-pressurization of the vessel interior and maintains an equal pressure between the vessel interior and the surrounding underwater environment as the vessel and system surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the present invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similarly-referenced characters refer to similarly-referenced parts, and in which: 
         FIG. 1  is a side elevational view of the pressure equalizer according to several embodiments of the present invention; 
         FIG. 2  is side elevational view of an alternative embodiment of the pressure compensating valve (PCV) for the equalizer of  FIG. 1 , with the PCV plug shown in phantom; 
         FIG. 3  is an exploded side elevational view of the PCV of the equalizer of  FIG. 1 , with portions of the valve body removed for clarity; 
         FIG. 4  is a cross-sectional view of the plug for the PCV taken along line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 1 , with the PCV in an open position; and, 
         FIG. 6  is the same view as  FIG. 5 , but with the PCV in an open position. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring initially to  FIGS. 1 and 2 , a pressure compensating system in accordance with several embodiments of the present invention can be shown and generally designated by reference character  10 . As shown, system  10  can include a high pressure reservoir  12  that is connected with a pressure compensating valve (PCV)  14  via piping  16 . PCV  14  can be positioned within the interior  18  of underwater vessel  20  (shown in phantom in  FIG. 1 ) so that it can be in fluid communication with interior  18  via interior orifice  40 , and the PCV can be in fluid communication with the surrounding underwater environment via environment orifice  34  (environment orifice  34  can be seen in  FIG. 3 ) and fitting  24 . The system  10  uses air or other similar type of compressible fluid at a high pressure and at a controlled rate from reservoir  12  to dispense air or other similar type of compressible fluid at a controlled rate into the vessel  20 . The amount of air/compressible fluid to be dispensed can be controlled through comparison of the surrounding ambient environment pressure through fitting  24 , with the pressure in interior  18  of vessel  20 , as described more fully below. 
     Reservoir  12  can be made of any lightweight rigid material that can maintain its shape at increased water depths. Reservoir  12  in  FIG. 1  is shown with a spherical shape and can be formed with a rigid material, which establishes a constant volume of compressible fluid for operation of system  10 . It should be appreciated that reservoir  12  could be formed with any shape that is convenient to the user, such as cylindrical, cubic, and the like. Similarly, PCV  14  could be made of various materials and shaped according to the user&#39;s needs; for example, PCV could have a substantially cylindrical shape, as shown in  FIG. 2 . It should also be appreciated that the system  10  could also be located outside of vessel  20  and connected to vessel  20 . In these embodiments, the PCV would be in fluid communication with the surrounding underwater environment via orifice  40 , and in fluid communication with interior  18  via orifice  34 . 
     Referring now to  FIGS. 2-4 , the structure of the PCV  14  is shown in greater detail. PCV can include a valve body  26  and a valve plug  28  that can be slidably positioned within the valve body  26 . Valve body  26  can be formed with a pneumatic inlet orifice  30 , a backflow orifice  32  and an environment orifice  34 . Environment orifice  34  provides a path for fluid communication with surrounding underwater environment. PCV  14  also included an end cap  36  that can be formed with a seat  38  that merges into an interior orifice  40 . A spring  42  or similar type of resilient member can be positioned with one end of spring  42  in seat  38  and the other end contacting valve plug  28 . 
     Plug  28  includes a plurality of grooves  44  (grooves  44   a - d  are shown in  FIGS. 3 and 4 ) and a plurality of seals  46   a - d  can be correspondingly placed in grooves  44   a - d . The materials and structure of the seals  46  (as well as the machined tolerances between body  26  and plug  28 ) can be chosen according to the desired application of the system  10 . In some deep-water, high-pressure embodiments, seals  46  can be high pressure seals. For lower pressure applications, a lower quality, more inexpensive seals of different can be used. As shown in  FIGS. 3 and 4 , plug  28  can also be formed with a conduit  48  that extends longitudinally from one end partially into plug  28 . Longitudinal conduit  48  merges into a transverse duct  50  that can be formed in plug  28 . Duct  50  can extend radially completely across plug  28 . Conduit  48  and duct  50  can cooperate with orifices  30 ,  32 ,  34  and  40  to form selective paths of fluid communication through PCV  14  in a manner more fully described below. 
     Referring now to  FIGS. 5-6 , the operation of the pressuring compensating system  10  is shown in greater detail.  FIG. 5  depicts a condition in which the pressure P I  inside the vessel  20  acting on plug  28 , combined with the force of spring  42  (F SPRING ) acting on plug  28 , is less than the ambient undersea pressure P A  outside of vessel  20 , which is acting on plug  28  in the opposite direction of P I  and F SPRING . More specifically, water from the surrounding underwater environment enters PCV  14  through environment orifice  34  and pushes against plug  28  (seal  46   d  prevents intrusion of water past plug  28 ). Similarly, the fluid (air, water, etc.) from the interior  18  of vessel  20  enters PCV  14  through interior orifice  40  and pushes against the end of valve plug  28  proximate end cap  36 . Because P A &gt;(P I +F SPRING ) as described above, spring  42  compresses. As spring  42  compresses, plug  28  moves toward end cap  36  until it contacts end cap. The movement of plug  28  in this manner aligns pneumatic orifice  30  between seals  46   b  and  46   c . As pneumatic orifice becomes aligned between seals  46   b  and  46   c , a path of fluid communication becomes established from reservoir  12 , through piping  16 , inlet orifice  30 , duct  50 , conduit  48 , interior orifice  40  and into interior  18 . This allows flow of high pressure compressible fluid from constant volume  56  of reservoir  12  into interior  18  of vessel  20 . Compressible fluid continues to flow into interior  18  until the interior pressure begins to equalize with the surrounding underwater pressure at the vessel  20  and system  10  depth. 
       FIG. 6  depicts the PCS in the condition in which the pressure on the inside of the system combined with the spring force acting on by plug  28  is greater than the ambient undersea pressure acting on plug  28  in the opposite direction (P I +F SPRING )&gt;P A . Once this occurs, spring  42  will begin to relax. The PCV plug  28  begins to move away from end cap  36  into its normally closed position, as depicted in  FIG. 6 . Once the valve is in its normally closed position, the reservoir  12  becomes disconnected from interior  18 , because pneumatic orifice  30  becomes closed off from duct  50  and from vessel interior  18  by seals  46   a  and  46   b.    
     Additionally, when PCV  14  is shut, a backflow path of communication can be established. More specifically, a path of fluid communication can be established from interior  18  through interior orifice  40 , longitudinal conduit  48  and transverse duct  50 . As compressible gas exits duct  50 , seals  46   b  and  46   c  establish a seal on both sides of backflow orifice  32  and prevent compressible fluid from leaving valve body other than through backflow orifice  32 . As compressible gas exits backflow orifice  32 , it passes through check valves  52  (which prevent flow in seawater into PCV  14 ) and backflow piping  54  and exits the system through fitting  24 , as shown in  FIG. 6 . In this manner, system  10  allows the interior of the undersea vessel  20  can be coupled to the ambient environment to discharge excess compressible fluid, which decompresses vessel  20  and system  10  if the operator raises vessel  20  and system  10  to the water surface. 
     The use of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of any ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.