Abstract:
The present invention concerns a hydrophone signal limiting shunt switch, electrically associated and physically conjoined with a conventional hydrophone, for limiting hydrophone signal operability to water depths less than a predetermined, proscribed depth. The primary components of the shunt switch are a protected plunging bolt, at least one disk spring and an electrically conducting foot, none of which are ever in direct contact with the ocean environment. Flexure of the disk spring is the sole determinant of switch actuation. Upon sensing a predetermined, proscribed operating depth, the protected plunging bolt forces the electrically conducting foot to shunt the electrical connection between the associated hydrophone and the hydrophone transmission cable, consequently, quenching the hydrophone signal at the proscribed depth.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention concerns generally a hydrostatic actuated electrical circuit limit device. In particular, the present invention is directed to a tamper-proof acoustic hydrophone electrical signal limiting shunt switch; the shunt switch apparatus situated within the body or housing of and connectively conjoined with an associated hydrophone, imperatively quenching and preventing any signal transmission from the associated hydrophone when the hydrostatic pressure of the surrounding environment of the hydrophone exceeds a predetermined value, thereby rendering the hydrophone inoperative at or below a predetermined depth. 
     2. Description of the Related Art 
     There are many instances when it is desired to control the operation and functioning of an apparatus by means of a pressure sensor, such instances typically involving mechanical pressure, air pressure, or hydrostatic pressure. More particularly, in a maritime or aquatic environment, hydrostatic pressure sensors are often used, for example, ignition of a depth charge or the opening of a conduit to a sample bottle to obtain a sample of seawater at a desired depth. Typically, such devices are “single event” devices and do not employ electrical circuitry, that is, once the initial event has occurred the device either explodes or there is no need for a subsequent sampling event. 
     However, there are also numerous instances where hydrostatic switches are employed in conjunction with an electrical circuit. Such switches can be broadly categorized into fluid flow control or operating safety. 
     Hydrostatic flow control switches can be found in water purification and supply systems. For example, U.S. Pat. No. 4,922,067 “Fluid Pressure Switch Having Venting Means For Dispersing Back Pressure” by H. L. West utilizes deformation of laminated conducting and nonconducting materials to detect changes in water pressure. In similar manner, U.S. Pat. No. 4,931,601 by W. J. Lavender also uses a combination of insulating and conducting materials to sense changes in water pressure. Such devices are generally designated for use on land. 
     Safety at sea and on the water is always a prime concern of those who are in any way involved in a maritime environment. Consequently, many devices used on or under the sea incorporate an ancillary safety device for protection. Such pressure sensors often control an electrical circuit, turning the apparatus either on or off, initiating, igniting, or preventing a potentially dangerous function from occurring. 
     For example, U.S. Pat. No. 4,495,849 “Remotely Activated Cable Cutter” by M. W. Cooke et al. includes an electrically connected pressure switch “designed to inactivate the apparatus beyond a preset ocean depth”. A detailed description of the switch is absent; presumably, it is a conventional switch proper. Another example of a hydrostatic pressure switch incorporated in an apparatus intended for use under water is U.S. Pat. No. 4,050,382 “Electrically Detonated Explosive Device” by J. M. Power. In both cases, the hydrostatic actuated electrical limit switch is ancillary to the predominant purpose of the apparatus, that is, either severing an underwater cable or igniting an explosive device. These aforementioned inventions are incorporated herein by reference for purposes of indicating the background of the present invention or illustrating the mature state of the art. 
     In marked contrast to the aforementioned patents, the purpose of the present invention is not ancillary, but a major fail-safe, tamper-proof component of a hydrophone, incorporated therein to nondestructively limit the operating depth of that hydrophone to a predetermined depth. 
     SUMMARY 
     An objective of the present invention is to provide a readily adjustable acoustic hydrophone electrical signal limit switch which nondestructively limits the operation of an associated hydrophone to depths more shallow than a predetermined depth setting. Another objective of the present invention is to provide a tamper-proof acoustic hydrophone electrical signal limit switch which can be readily incorporated with existing commercially available hydrophones. A further objective of the present invention is to provide an acoustic hydrophone electrical signal limit switch which allows the resumption of the normal hydrophone function once the hydrophone is removed upwards above the preset depth limit. Yet another objective of the present invention is to provide an acoustic hydrophone electrical signal limit switch which is not directly exposed to the ocean environment. Yet a further objective of the present invention is to provide an acoustic hydrophone electrical signal limit fail-safe, tamper-proof switch which is environmentally robust and reliably functions at ocean depths up to and in excess of 1000 m. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation half-section view, illustrating a typical commercially available Encapsulated Hydrophone Assembly  34  (not claimed in the present invention), of a generally cylindrical body, the enclosed hydrophone  37  lacking connective conjunction with the present invention, namely, an acoustic hydrophone electrical signal limiting shunt switch. In this illustration, the hydrophone  37  comprises a ceramic element  39 , having a Glass-ceramic upper end piece  35  and a Glass-ceramic lower end piece  36 . Typically, the hydrophone  37  is electrically connected to a hydrophone signal conducting cable  31  by a plurality of hydrophone circuit pins  38 , embedded in the lower end piece  36 , generally, three pins, namely high hydrophone signal potential, low hydrophone signal potential, and ground. Typically, this conventional hydrophone configuration is protected from the ocean environment by Hydrophone Polyurethane Encapsulation  32 . 
         FIG. 2  is an elevation half-section view illustrating an encapsulated hydrophone assembly  12 , of a generally cylindrical body comprising a modified associated hydrophone connectively conjoined with an embodiment of the present invention, namely, an acoustic hydrophone electrical signal limiting shunt switch  10 , Switch  10  capped by Silicone Rubber Boot  13 . Although protective, the primary purpose of the Silicone Rubber Boot  13  is to create and bound the oil-filled cavity which transduces the external ocean pressure into a measurable force impelled onto the plunging bolt. In this instance, the plurality of hydrophone circuit pins  38  is, observing signal polarity, connectively matched to an equivalent plurality of Electrically Conducting Spring-Loaded Pins  19 , the Electrically Conducting Spring-Loaded Pins suitably positioned in Glass-ceramic shunt switch end piece  27 , thereby interposing the depth limiting shunt switch  10  on the hydrophone circuitry. 
         FIG. 3  is an exploded elevation half-section view illustrating each component of a preferred embodiment of the present invention, an acoustic hydrophone electrical Signal Limiting Shunt Switch  10 . Electrical communication between a suitably modified associated conventional hydrophone and Shunt Switch  10  is facilitated by means of the plurality of conjoining Electrically Conducting Spring-Loaded Pins  19 , located in Glass-ceramic Shunt Switch End Piece  27 . 
       Successively viewed upwards from Glass-ceramic Shunt Switch End Piece  27  are components: Foot  18 , Compression Spring  16 , O-Ring B  17 , Base  26 , Disk Springs  25 , Shim Washer  15 , Retaining Ring  24 , freely-moving Protected Plunging Bolt  22 , Shroud  23 , O-Ring A  14 , and Silicone Rubber Boot  13 . The Silicone Rubber Boot  13  provides for an Oil Filled Cavity  21  to communicate external environment hydrostatic pressure to the head of Plunging Bolt  22 . 
         FIG. 4  is an elevation half-section view of an assembled preferred embodiment of Signal Limiting Shunt Switch  10  positioned within Polyurethane Shunt Switch and Hydrophone Encapsulation  12  (the associated hydrophone is not shown in this illustration). 
         FIG. 5  illustrates a top view of Base  26 . This view shows a Base Bore  260  and a Base Upper Surface  261 . 
         FIG. 6  illustrates an elevation center view of Base  26 . This view shows a Base Threaded Collar  262 , a Base O-ring Groove  263 , and a Base Lower Collar  264 . 
         FIG. 7  illustrates a bottom view of Base  26 , displaying a Base Bore  260 , a Base Lower Collar Face  265 , a Base Foot Well  266 , and Base Fixture Holes  267 . Base  26  is an important component of the present invention, interacting with Foot  18 , via the “D”-shaped key way, Disk Springs  25 , O-Ring B  17 , Plunging Bolt  22 , and Shroud  23 . 
         FIG. 8  illustrates a top view of Plunging Bolt  22 . Plunging Bolt  22  is a machined shaft whose upper end is Bolt Head  220 , featuring a Bolt Adjustment Tool Aperture  221 . 
         FIG. 9  illustrates a side, center view of Plunging Bolt  22 , displaying a Primary Bolt Shaft Section  222 , a Secondary Bolt Shaft Section  223 , a Threaded Bolt Shaft Section  224 , Bolt Snap-Ring Groove  225 , and Circumferential Shoulder  226 . 
         FIG. 10  illustrates a bottom view of Plunging Bolt  22 , displaying a Primary Bolt Shaft Section  222 , Secondary Bolt Shaft Section  223 , Threaded Bolt Shaft Section  224 . and Circumferential Shoulder  226 . 
         FIG. 11  illustrates a top view of Foot  18 . Foot  18  is a truncated disk featuring a Threaded Bore  180 , a Foot Upper Face  181 , and a Foot Truncated Face  183 . 
         FIG. 12  illustrates a side view of Foot  18 . This depiction demonstrates Foot Upper Face  181  and Foot Lower Face  182  are two planar surfaces, parallel to each other, and Foot Truncated Face  183  is a planar surface normal to both Upper Face  181  and Lower Face  182 . 
         FIG. 13  illustrates a top view of Shroud  23 , having a Shroud Bore  230  and a Threaded Shroud Collar  231 . 
         FIG. 14  illustrates an elevation view of Shroud  23 . Here can be seen Threaded Shroud Collar  231 , Shroud Adjustment Shoulder  232 , and Shroud Outer Surface  233 . Shroud Adjustment Shoulder  232  comprises two parallel shoulders, formed on the upper portion of Shroud  23 , flanking Threaded Shroud Collar  231 . The shoulders on Shroud  23  are wrench flats used to receive a crescent wrench to rotate Shroud  23 . The shoulders are used for turning Shroud  23  in order to thread Shroud  23  onto Base  26 . The shoulders are also used to adjust the pre-load on the Disk Springs  25 . Both of these tasks are accomplished by rotating Shroud  23  with a wrench. 
       During the assembly process of threading Shroud  23  onto Base  26 , Base  26  is held in place with pins that protrude from an assembly jig. These pins engage the Base Fixture Holes and prevent Base  26  from rotating while Shroud  23  is threaded onto Base  26  with a wrench using the shoulders on Shroud  23 . 
         FIG. 15  illustrates a bottom view of Shroud  23 , showing Shroud Bore  230 , Shroud Base Well  235 , and Shroud Base Well Threaded Surface  234 . 
         FIG. 16  depicts an electrical circuit schematic  11 , demonstrating the electrical connectivity between Shunt Switch  10  and a Conventional Hydrophone  37 , and further illustrating how impelling actuation of Foot  18  provides a short circuiting of the hydrophone signal circuitry. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Ordinarily, hydrophones are designed to function over the widest possible range of operating conditions, including a wide range of operating depth. However, there are some special circumstances where it is imperative to limit the operating depth of a hydrophone to no more than a predetermined set limit. The distinguishing embodiment of the present invention addresses one of these special instances. 
     The present invention solves a particular problem, namely, preventing the operation of a hydrophone below a certain predetermined ocean depth. As hydrostatic pressure is a function of depth, consequently, it is possible to utilize hydrostatic pressure as a means for controlling the operability of the hydrophone. The present invention involves use of a freely-moving Protected Plunging Bolt  22 , one end responsive to the hydrostatic pressure of the ocean environment, and the opposite end attached to an electrically conductive shunt which effectively short-circuits the hydrophone circuitry at or exceeding a predetermined hydrostatic pressure, thereby, preventing operation. If the hydrophone is raised to a depth more shallow than the predetermined ocean depth, the Plunging Bolt  22 , responding to the lessened hydrostatic pressure, retracts the shunt, permitting the hydrophone to once again operate in a normal manner. 
     The present invention, Switch  10 , is intended to function in cooperative conjunction with a commercially available hydrophone  37  (not claimed in the present invention). 
     As illustrated in  FIG. 1 , a conventional hydrophone typically comprises ceramic element assembly  39 , supported on its upper end by a Glass-ceramic (commercially available material) upper end piece  35 , and supported on its lower end by a similar Glass-ceramic lower end piece  36 , the lower end piece  36  pierced by a plurality of electrically conducting pins  38 . The electrically conducting pins  38 , typically high potential, low potential, and ground, connect the hydrophone signal to a conducting transmission cable  31 . A portion of the conducting cable  31  and the entire hydrophone  37  are protected from the intended operating environment by a polyurethane encapsulation  32 , effectively shielding the hydrophone and its conducting circuitry from any moisture leakage or inundation. 
     In the configuration of  FIG. 1 , a conventional encapsulated hydrophone  34  will function at any depth within its design parameters; however, there are certain circumstances wherein the hydrophone should not be operational at any depth beyond a proscribed limit. This is the purpose of the present invention. 
     When incorporated within the polyurethane switch and hydrophone encapsulation  12 , as illustrated in  FIG. 2 , (and schematically in  FIG. 16 ) the hydrophone hydrostatic shunt switch  10 , interposed upon the circuitry of hydrophone  37 , by means of a hydrostatic pressure actuated shunt, effectively denies operation of hydrophone  37  below a proscribed operational depth limit. 
     As illustrated in  FIG. 2 , the preferred embodiment of the present invention distinguishingly modifies the conventional hydrophone  37  by replacing Glass-ceramic Upper End Piece  35  with Glass-ceramic Switch End Piece  27 . This new configuration, Schematic  11 , depicted in  FIG. 16 , demonstrates how each of a plurality of pins  38 , associated with Hydrophone  37 , is singularly electrically conjoined with an associated pin from an equivalent plurality of Electrically Conducting Spring-Loaded Pins  19 . 
     In this configuration, Hydrophone  37  will operate normally at depths shallower than a proscribed limit. If Hydrophone  37  descends to or below a proscribed depth, the increased hydrostatic pressure will actuate Shunt Switch  10 , impelling Foot  18  (shown in  FIG. 3 ), comprising an electrically conducting material, upon each and every pin, of the plurality of Electrically Conducting Spring-Loaded Pins  19 , effectively imposing a short circuit across all pins of the plurality of hydrophone pins  38 , and consequently, forming a short circuit across all signals present on Transmission Cable  31 . 
     The pin configuration is not important in the functional sense of Shunt Switch  10 . Practically, due to the cylindrical nature of the shunt switch, the pins are arranged symmetrically around the center point. Any number of pins can be used for different variations of the switch, (space permitting), and each number of pins could have a different arrangement. The preferred embodiment of the present invention utilizes three pins arranged around the center of the switch, offset 120° from each other for a three terminal device. 
       FIG. 3  is a half-section, exploded view depicting the various components comprising the preferred embodiment of the present invention;  FIG. 4  is a half-section view illustrating the various components when assembled. There are three important aspects distinguishing the components which affect the operation of the preferred embodiment; first, communicating the ambient hydrostatic pressure that actuates Foot  18 , via impelling Protected Plunging Bolt  22 , second, adjusting the preferred embodiment of the present invention to actuate the Shunt Switch  10  at a predetermined pressure setting, and third, protecting the Shunt Switch  10  from the external environment of the ocean. 
     Upon Shunt Switch  10  actuation, impelled Foot  18  enables and establishes a short circuit across all hydrophone signal circuitry (See  FIG. 16 , Schematic of Shunt Switch and Hydrophone Circuitry). Foot  18 , depicted in  FIG. 11  (top view) and  FIG. 12  (side view), is fabricated from an electrically conducting material, and is in the form of a truncated disk, having Threaded Bore  180 , a Foot Upper Face  181 , a Foot Lower Face  182 , and a Foot Truncated Face  183 . The Foot Upper Face  181  and Foot Lower Face  182  are each planar and parallel to each other; the Foot Truncated Face  183  is also planar and normal to both Upper Face  181  and Lower Face  182 . The diameter of Foot  18  is sufficient to encompass all of the plurality of Electrically Conducting Spring-Loaded Pins  19  positioned in Glass-ceramic Switch End Piece  27 . 
     Foot  18  is keyed and fits the keyed Base Foot Well  266  (Shown in  FIG. 7 ) in Base  26 . A “D” key is used (not shown). The Foot  18  is essentially a disk with a truncated flattened side and the keyway in the Base  26  is a corresponding “D” shaped cavity. There is no separate key that binds the Foot  18  and the Base  26 . The geometry of the Foot  18  and the “D” shaped cavity of Base Foot Well  266  in the Base  26  prevents the Foot  18  from rotating. 
     In the center of the disc-like Foot  18 , is a Threaded Bore  180  (Shown in  FIG. 11 ), for threaded communication with Threaded Bolt Shaft Section  224  of impelling Plunging Bolt  22 . 
     As depicted in  FIGS. 5  (top view),  6  (side view), and  7  (bottom view), Base  26  comprises Base Bore  260 , Base Upper Surface  261 , Base Threaded Collar  262 , Base O-Ring Groove  263 , Base Lower Collar  264 , Base Lower Collar Face  265 , Base Foot Well  266 , Base Fixture Holes  267 . 
     The small Base Fixture Holes  267  depicted on the bottom surface of Base  26  are used for assembly purposes only (not claimed in the present invention). They are shallow free-fit dowel pin holes that are used in conjunction with an assembly jig to prevent Base  26  from rotating as Shroud  23  is screwed onto Base  26 . The assembly jig has two dowel pins that project about a flat surface. The Base  26  is placed over the dowel pins such that the two holes on the bottom of the base engage the protruding dowel pins on the jig. This mechanically prevents Base  26  from rotating during assembly. After Shroud  23  is conjoined to Base  26  these holes are no longer utilized and are sealed with epoxy in the contiguous surface between Glass-ceramic Switch End Piece  27  and Base  26  during later assembly steps. 
     There is a keyway machined into Base  26  that receives Foot  18  preventing Foot  18  from rotating relative to the rotation of Plunging Bolt  22 . 
     As illustrated in  FIGS. 13  (top view),  14  (side view), and  15  (bottom view), Shroud  23  features Shroud Bore  230 , Threaded Shroud Collar  231 , Shroud Adjustment Shoulder  232 , Shroud Outer Surface  233 , Shroud Base Well Threaded Surface  234 , and Shroud Base Well  235 . Shroud Adjustment Shoulder  232 , (not claimed in the present invention), one each, flanking Threaded Shroud Collar  231  is used in conjunction with a jig, for assembly purposes. Shroud Outer Surface  233  is approximately the same diameter as the outer diameter of Silicone Rubber Boot  13 , and of sufficient diameter to permit Shroud Base Well  235  to adequately receive Base  26 . 
     Upon assembly, Foot  18  fits within Base Foot Well  266  (Shown in  FIG. 7 ) of Base  26 ; in turn, Base  26  fits within Shroud Base Well  235  (Shown in  FIG. 15 ), conjoined by threads of Base Threaded Collar  262  and threads of Shroud Base Well Threaded Surface  234 . This fabrication includes freely-moving Protected Plunging Bolt  22 ; threadingly conjoined by Threaded Bolt Shaft Section  224  and Threaded Bore  180  to Foot  18 ; Secondary Bolt Shaft Section  223  movably contained within Base Bore  260  of Base  26 ; Primary Bolt Shaft Section  222  movably contained within Shroud Bore  230  of Shroud  23 . 
     Actuation of Shunt Switch  10  depends upon uninterrupted impelling motion of Plunging Bolt  22 , conforming to restraints established by a hydrostatically sensitive spring mechanism. Motion of Plunging Bolt  22  is maintained by containing the movement of Secondary Bolt Shaft Section  223  (Shown in  FIG. 9 ) of Plunging Bolt  22  within Base Bore  260  of Base  26  and Primary Bolt Shaft Section  222  within Shroud Bore  230  of Shroud  23 . 
     As illustrated in  FIGS. 8  (top view),  9  (side view), and  10  (bottom view), Plunging Bolt  22  comprises Bolt Head  220 , featuring Bolt Adjustment Tool Aperture  221 , Primary Bolt Shaft Section  222 , Secondary Bolt Shaft Section  223 , Threaded Bolt Shaft Section  224 , and Bolt Snap-Ring Groove  225 . Plunging Bolt  22  is free to move longitudinally through Shroud Bore  230  of Shroud  23  and Base Bore  260  of Base  26 . 
     At a proscribed depth, Bolt Head  220 , responding to external hydrostatic pressure, motivates Plunging Bolt  22  against a hydrostatically sensitive spring mechanism. If the adjustment of the hydrostatically sensitive spring mechanism is equal or less than the equivalent environmental hydrostatic pressure, Plunging Bolt  22 , in communication with Foot  18 , via Threaded Bolt Shaft Section  224  in conjunction with Threaded Bore  180  of Foot  18 , impels Foot  18  upon Electrically Conducting Spring-Loaded Pins  19 , shorting the hydrophone circuitry. Conversely, if the adjustment of the hydrostatically sensitive spring mechanism is greater than the equivalent environmental hydrostatic pressure, Plunging Bolt  22  remains stationary and the hydrophone is able to perform normally. 
     Shown in  FIG. 8 , in the preferred embodiment of the present invention, Bolt Adjustment Tool Aperture  221  in the head portion of freely-moving Plunging Bolt  22  is a screwdriver slot. Prior to installation of Silicone Rubber Boot  13 , and subsequent Polyurethane Switch and Hydrophone Encapsulation  12 , this slot enables Plunging Bolt  22  to be rotated easily with a screwdriver and the relative position of Foot  18  can be adjusted. This tool aperture is important as it is associated with the means for setting Shunt Switch  10  to actuate at a predetermined hydrostatic pressure. The actual shape of the Tool Aperture providing means for adjusting Shunt Switch  10  is not critical; it could be a hex head, Phillips head, socket head, etc. 
     In operation, Primary Bolt Shaft Section  222  rests within Shroud Bore  230  and Secondary Bolt Shaft Section  223  rests partially within Base Bore  260  of Base  26 . Disk Springs  25  is disposed atop Base Upper Surface  261  of Base  26 , the outer circumference of Disk Springs  25  stationed upon Base Upper Surface  261 , forming a circumferential locus of Base Bore  260 ; conversely, the inner circumference of Disk Springs  25 , somewhat elevated from the outer circumference, forms a circumferential locus of Secondary Bolt Shaft Section  223  of Plunging Bolt  22 . Under compression, Disk Springs  25  pushes upwards against Shim Washer  15 , which in turn, pushes upwards against Retaining Ring  24 . Retaining Ring  24  (Shown in  FIG. 3 ) is secured to Plunging Bolt  22 , by means of engagement of Retaining Ring  24  in Bolt Snap-Ring Groove  225 . 
     Disk Springs  25  may comprise one or more individual disc springs to achieve its intended purpose; it alone senses and responds to the force applied by Protected Plunging Bolt  22  and snaps to its full fully deflected position when a predetermined force is exceeded. Plunging Bolt  22 , Foot  18 , and Compression Spring  16  all move with Disk Springs  25  as it deflects. Disk Springs  25  (singular or plural) is matched in such a way to have a nonlinear force response causing the switching action at a predetermined applied force. 
     Compression Spring  16  does not act in opposition to the Disc Springs  25 ; it is placed under Secondary Bolt Shaft Section  223 , and around Threaded Bolt Shaft Section  224 . Subsequently, Foot  18  is then threaded onto Threaded Bolt Shaft Section  224 . Compression Spring  16  exerts force between Circumferential Shoulder  226 , the shoulder under Secondary Bolt Shaft Section  223 , and Foot Upper Face  181  of Foot  18 . The purpose of Compression Spring  16  is to exert a force on to Foot  18  so that Foot  18  resists unintended movement while threaded onto Plunging Bolt  22 . Thus, Compression Spring  16  is isolated from the forces exerted on and by the Disc Springs  25 . 
     Shunt Switch  10  is responsive to the external hydrostatic pressure, communicated from the external environment to Bolt Head  220  of Plunging Bolt  22  by means of Oil Filled Cavity  21  within Silicone Rubber Boot  13  (Shown in  FIG. 2 ), Boot  13  suitably threaded and conjoined with Threaded Shroud Collar  231  of Shroud  23 . 
     O-Ring A  14 , seated in a female O-Ring gland located within Shroud Bore  230 , seals the Oil Filled Cavity  21  from leaking through the seam between Shroud Bore  230  and Primary Bolt Shaft Section  222 . O-Ring A  14  is part of the boundary of the sealed Oil Filled Cavity  21 . Oil Filled Cavity  21  is bounded by Silicone Rubber Boot  13 , O-Ring A  14 , Shroud  23 , and freely-moving Plunging Bolt  22 . 
     O-Ring B  17 , positioned in Base O-Ring Groove  263  (Shown in  FIG. 6 ) of Base  26 , seals the seam between Base  26  and Shroud  23 , preventing liquid polyurethane intrusion into Hydrophone Hydrostatic Switch  10  during the encapsulation process. Polyurethane encapsulation, once cured, provides the watertight integrity of the entire Polyurethane Switch and Hydrophone Encapsulation  12 . 
     Although only a few exemplary embodiments of the invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-functions clauses are intended to cover the structures described herein as performing the recited functions and not only structural equivalence but also equivalent structures.