BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to prosthetics, and more specifically to a valve system for air release from a limb prosthetic.  
         [0003]     2. Related Art  
         [0004]     Gravitational and other forces tend to cause separation between a prosthetic limb and a residual limb. This happens, for example, during the swing phase of the gait, when a prosthetic leg is additionally subjected to centrifugal forces. The manner in which an artificial limb is suspended and/or attached to the residual limb determines the amount of control an amputee has over the prosthesis. Patients have routinely worn a variety of belts, straps, cuffs and harnesses to prevent the prosthetic limb from separating from the residual limb, but such devices are inconvenient and tend to cause chafing against the patient&#39;s body, giving rise to sores and abrasions.  
         [0005]     It has long been appreciated that differential air pressure or “suction” may be utilized to retain or suspend, or assist in retaining or suspending, a prosthetic limb on a patient&#39;s residual limb. Suction suspension typically involves a hard socket and a cooperating liner positioned between the residual limb and the prosthetic socket. The liner is rolled onto the residual limb for a suction, slight compression, and/or gripping connection of the inner gel layer (or otherwise tacky layer) of the liner to the skin of the residual limb. The liner-covered limb is then inserted into the prosthetic socket, and the outer surface/layer of the liner preferably forms a suction, grip, or other interference fit to the socket to interfere with the socket falling off the limb.  
         [0006]     These socket liners frequently have been called “suction liners,” “gel liners,” “roll-on liners” or “suspension liners” and include the “first generation” of gel-layer-only liners, and also the modern “second generation” liners currently preferred by most wearers of prosthetics. These modern liners comprise a thin textile/fabric outer layer that is fixed to the gel-like inside layer. Thus, the second generation of liners is similar to the first in its connection to the residual limb, but its connection to the socket is modified by the presence of the textile/fabric layer. The term “suction liner” began with the first generation liners, which featured the gel layer contacting both the residual limb (liner&#39;s inner surface) and the socket (liner&#39;s outer surface), and which, therefore, could be used to create a fairly high amount of pressure differential between the inside of the socket (in the “well” of the socket) and the surrounding ambient air. The terms “suction liner” and “suction socket” are still used by many manufacturers, prosthetic technicians, insurance and medicare/medicaid entities, and wearers of prosthetics, even though the modern liners, with their textile/fabric outer layers, typically do not form what would be called “true” or “pure” suction with the socket, as further discussed below. See the discussion of suction liners in Janusson, et al. (U.S. Pat. No. 6,706,364) and Janusson, et al. (U.S. Pat. No. 6,626,952).  
         [0007]     Preferred socket liners are usually fabricated from silicone, urethane, or other gel-like material that grips the limb to such an extent that they need to be rolled-onto the limb from a rolled-up “doughnut” form, rather than pulled on like a sock. When rolled-on, there is little, if any, air remaining between the inner surface of the roll-on liner and the limb, and the roll-on liner is snug against the limb all the way around the circumference of the limb. Also, the inner surface of the roll-on liner is of such material and tacky texture that air will not be able to, or be very unlikely to, enter between the roll-on liner and limb. Thus, the roll-on liner may be said to form a suction fit and/or a slight compression fit with the limb. A distal force on the liner, such as caused by the swing of a gait with a prosthetic leg, may tug on the roll-on liner but typically does not loosen, lower, or remove the liner from the limb.  
         [0008]     The hard socket is usually laminated or otherwise fabricated from polyethylene, polypropylene, or other copolymers, for example, and is donned over the liner and the residual limb. A suction-fit, including a partial-suction fit, as discussed above, may form between the liner-sheathed limb and the interior of the socket. A “true” suction fit (allowing high suction, greater amount of vacuum) will be more likely to form if the liner exterior surface is smooth and flexible enough to conform to the contours of the residual limb, for example, non-air-permeable material such as the silicone, urethane, or other rubbery or gel-like material such as described above for the liner-to-limb connection; if the interior surface of the socket is also smooth and non-air-permeable; and, of course, if the socket has no un-sealed holes or apertures.  
         [0009]     A “partial” suction fit (allowing lower suction, low amount of vacuum) is more likely to form if one of these conditions is not met, for example, if the outside of the liner is the thin fabric or other woven material bonded to a rubbery/gel-like interior layer of the liner, for example, as described above for “second generation” liners. In such a case, some air will tend to leak through or past the fabric layer of the modern liners into the well of the socket, that is, between the liner and the socket interior surface, so that there is typically not a true air-tight seal between the two. However, the air leaks fairly slowly because of the preferred close fit between the contour of the liner-cover limb and the contour of the internal surface of the socket. This slow air leakage and close fit typically allow their to be a “partial” suction fit between the socket and the liner outer surface, and this “partial” suction fit tends to be more comfortable for many wearers that a “true” or “full” suction fit. In other words, a textile/fabric-covered liner and the resulting “partial” suction tends to be more comfortable than the stronger “tugging” on the residual limb created by the “full” suction of first generation, gel-layer-only liner. The air that slowly leaks into space(s) in between the socket and the liner tends to be expelled with each step due to the force of the residual limb pushing into the socket. This way, modern, fabric-covered roll-on liners still tend to create some pressure differential between the well of the socket and the ambient air.  
         [0010]     Therefore, many of skill in the field of prosthetics still apply the term “suction” to a fit or suspension of the prosthetic to the limb ranging from excellent suction (with a “true” seal, large resistance to equalization of pressure between the inside and the outside of the socket) to slight suction (with a “partial” seal, small resistance to said equalization such as in many popular liners). Therefore, the terms “suction,” “suction-fit,” and “suction suspension” herein are therefore not limiting to a particular amount of pressure differential, but to the general process known well in this field of providing a “roll-on” liner or other “interference” liner that helps keep a socket on a residual limb while creating at least a small amount of blockage/hindrance to air freely moving in and out of the socket well past the residual limb.  
         [0011]     Therefore, it may be said that any region or amount of negative pressure in the space(s) between the liner-sheathed stump and the interior of the socket, relative to ambient (outside of the socket), may help to hold the prosthesis upon the limb during use. Certainly, more suction is more secure than slight suction, but there may be comfort sacrifices that result from more suction, for example, chaffing or pulling on the limb. A high-suction prosthesis suspension system may cause the user a discomforting disturbance of circulation in the limb on which the prosthesis is worn, due to the build up of a high degree of partial vacuum during walking, particularly in warm humid weather. Therefore, a very popular conventional roll-on liner is one such as the Ohio Willow Wood Alpha™ liner, which has multiple layers, that is, a rubbery/gel-like inner layer and a thin fabric outer layer bonded to the inner layer, so as to moderate the suction to a reasonably effective amount without allowing the great forces on the limb that can result from a high amount of suction. A “suction liner” or “roll-on liner” suspension, even in moderate range of suction provided by the preferred liners, gives the patient the ability to better control the prosthesis and provides for useful sensory or proprioceptive feedback. This is because there is a more intimate connection between the limb and the prosthetic, over much of the surface area of the limb, compared to old-fashioned waist belts, distal locks, or other methods. Suction or roll-on liner suspension also make a prosthesis feel lighter as compared to other forms of suspension.  
         [0012]     A valve system may be used in combination with a suction/roll-on suspension system in order to regulate the air pressure in the socket, so that undesirable pressure differentials do not prevent or complicate the donning and doffing of the socket. Conventional valves aim at relieving buildup of pressure when the lined limb is inserted into the socket, which is typically a snug fit by design, to prevent a positive pressure inside the socket relative to outside of the socket (ambient air) and therefore to allow donning.  
         [0013]     Because the typical valve system is a one-way valve, or “check valve,” it is intended to maintain a slight negative pressure (slight, partial suction) relative to ambient once the socket has been fitted on the residual limb and used. The process of walking and other weight-bearing will tend to push the limb further into the socket, but the swing of the gait will tend to pull the socket off the limb. The pushing of the limb further into the socket may cause the valve to allow air to be expelled, and the pulling of the socket during the swing will tend to create suction in the socket because the valve will not allow air to enter through the valve.  
         [0014]     In applications wherein the multi-layer roll-on liner allows air to slowly leak into the socket well, or wherein a seam, connection, lock or other aperture in the socket allows air to leak into the socket, weight-bearing steps will tend to expel air from inside the socket through the valve and then said leaking will tend to replace at least some of it (especially on the swing of the gait). Therefore, there may be frequent opening and closing of the valve, perhaps for each, or for many, of the user&#39;s steps. Many conventional valves for these applications are known to either not work very well, to plug easily, or to make embarrassing noise with each step.  
         [0015]     There are many valve systems in use in the market. Typical valve systems use an inner base that passes from the inside of the socket to the outside of the socket. The outer housing and the valve are then threaded onto the inner base or threaded to the socket wall in an attempt to create an air-tight seal. Such systems requires a generally flat socket wall surface for installing the valve and outer base to prevent air from leaking out of the socket around the valve structure instead of being expelled through the valve at the desired air pressure.  
         [0016]     Issued patents and patent publications relating to valve systems are listed as follows: Underwood (U.S. Pat. No. 1,586,015), Catranis (U.S. Pat. No. 2,530,285), Sharp et al. (U.S. Pat. No. 2,533,404), Hauser (U.S. Pat. No. 2,790,180), Edwards (U.S. Pat. No. 4,010,052), Carrow (U.S. Pat. No. 4,106,745), Greene (U.S. Pat. No. 5,201,774), Hill (U.S. Pat. No. 5,490,537), Hill (U.S. Pat. No. 5,709,017), Slemker et al. (U.S. Pat. No. 6,287,345), Perkins (U.S. Pat. No. 6,334,876), Hoerner (U.S. Pat. No. 6,361,568), Caspers (U.S. Pat. No. 6,508,842), Laghi (U.S. Pat. No. 6,544,292), Caspers (U.S. Pat. No. 6,761,742), Abrogast et al. (U.S. Pat. No. 6,797,008), Caspers (U.S. Publication No. 2004/0181290), and Patterson et al. (U.S. Publication No. 2004/0260403).  
       SUMMARY OF THE INVENTION  
       [0017]     The present invention is a valve system for helping to regulate the air pressure in the space(s) between a residual limb, or liner-covered limb, and a hard socket of a prosthetic limb. The preferred valve is an externally-mounted “one-way” or “check” valve, with a valve stem that “pops” or otherwise opens consistently and quietly at a small differential pressure, for example, a pressure inside the socket (in the space(s) between said socket and the limb or liner-covered limb) that is ≦3 psi pressure above ambient pressure (outside the socket). The valve may be adhesively mounted on the outside of the socket, and is easier to mount than conventional valves due to this preferred adhesive mounting and due to preferably no part of the valve being installed from the inside of the socket. The preferred valve has no threaded attachment to the socket, and no portion that extends into the hard socket. The valve stem may have a polygonal side wall, or have other recesses or grooves in its side wall(s) to create passages through which air may flow quietly. Alternatively, the valve stem may be cylindrical and the channel in which the valve stem slides (the valve housing bore) may be polygonal or have recesses or grooves in its wall(s), to create passage through which air may flow quietly. Or, both valve stem and the housing bore may be non-cylindrical. The low profile of the valve, and the quieter action of, and quieter air flow from, the valve may result in a less intrusive and less noticeable apparatus that is more acceptable and less embarrassing to wearers.  
         [0018]     The valve system includes a base having an opening for receiving a valve assembly. The base may be installed on or near the outside surface of the hard socket, preferably without threaded connection between the base and the socket. A hole is drilled in the hard socket from the outside surface of the socket to the inside surface of the socket, to align the hole in the socket with the bores/passages in the valve system. A valve housing holding the valve operating mechanism is then received in the opening in the base.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a schematic view of a hard socket and liner combination, wherein one embodiment of the invented valve is shown attached to the outside of the hard socket. In this view, the liner is shown as spaced from the socket, but it will be understood from the foregoing discussion, that the liner and socket will tend to be in close contact for at least part of the length along the socket and preferably all around the circumference of the liner and socket at or near the top of the socket. Some space between the liner-covered limb and the socket interior surface is normally present, so that the limb does not reach all the way to the distal end of the well of the socket.  
         [0020]      FIG. 1A  is a schematic view of a hard socket holding a residual limb with second generation roll-on liner, with one embodiment of the invented valve system installed on the hard socket distal portion. This view illustrates more accurately the preferred relationship of residual limb, roll-on liner, socket and valve.  
         [0021]      FIG. 1C  is a schematic cross-section detail view of a two-layer liner on a residual limb RL, such as in  FIG. 1B , wherein the liner has an inner gal-layer G and an outer fabric layer F.  
         [0022]      FIG. 2  is a front perspective view of the valve embodiment of  FIG. 1 .  
         [0023]      FIG. 3  is a front view of the valve embodiment shown in  FIGS. 1 and 2 , with a front o-ring/gasket removed to better show internals of the valve.  
         [0024]      FIG. 4  is a side view of the valve embodiment shown in  FIGS. 1-3 .  
         [0025]      FIG. 5  is a cross-sectional side view of the embodiment shown in  FIGS. 1-4 , wherein the valve is shown in the closed position.  
         [0026]      FIG. 6  is a cross-sectional side view of the embodiment shown in  FIGS. 1-5 , wherein the valve is shown in the open position.  
         [0027]      FIG. 7  is an exploded perspective view of the valve embodiment shown in  FIGS. 1-6 .  
         [0028]      FIG. 8  is an alternative embodiment of a valve stem that has an o-ring in its end surface.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     In the Figures, there are shown several, but not the only, embodiments of the preferred valve system for prosthetics.  
         [0030]     As will be understood by one of skill in the art after reading this application and viewing the drawings, once the air pressure inside the hard socket (relative to the ambient pressure outside the socket) exceeds the crack pressure of the valve, the invented “check” valve or “one-way” valve opens and air is expelled out through the valve. This is useful during donning of the socket, as the insertion of the limb, or liner-covered limb, increases pressure in the socket well; the valve system opens to generally equalize the ambient pressure and the pressure inside the socket in order to allow the donning.  
         [0031]     After donning, when the wearer takes each step, pressure is exerted downward on the limb, that is, toward the bottom of the socket well, and this also increases the pressure inside the socket well. Again, the preferred valve will “crack” or “pop” to relieve this pressure, and then close when the pressure is generally equalized by cessation of the downward pressure of the step, and/or when the swing phase of the gait suspends the prosthetic from the residual limb/liner and a slight suction/vacuum tends to be created in the socket. The preferred valve is designed with a “crack pressure” in the range of ≦3 psi differential, and more preferably 1-3 psi, or most preferably 1-2 psi, differential, so that, with this slight suction/vacuum, and preferably with any pressure differential below the “set-point” (selected from the range of 1-3, or 1-2, psi positive pressure inside the socket well), the valve will close to not allow air into the socket through the valve.  
         [0032]     The valve system  10  is adapted to cooperate with a suspension system  100  for prosthetics, which, as discussed in the Related Art section, includes a liner that provides at least some blockage/hindrance to air passing between the socket and the liner. As shown in  FIG. 1 , the suspension system  100  comprises a liner  103  received on a residual limb, and a hard socket  105  adapted to fit over the liner  103  and residual limb. The hard socket  105  comprises a sidewall  110  defining an interior space  1 , wherein the sidewall  110  comprises an outer surface  115  and an inner surface  120 .  
         [0033]     The liner  103  is preferably a roll-on liner, and may be of various types, as discussed in the Related Art section, which provide varying amounts of “suction.” Modern liners comprising both an inner gel layer and a textile/fabric outer layer are preferred, and the preferred valve system of the invention cooperates well with these liners; the valve system is specially adapted to allow air to be expelled quietly and consistently, even as often as every step, as may be desired with the amounts of air “leakage” experienced with fabric-covered liners.  
         [0034]     As shown in  FIGS. 2-7 , the valve system  10  comprises a base  20  having an internally threaded circular bore  22  extending through the base  20 . The base  20  is generally cylindrical in shape and is preferably fabricated from a durable polymeric material or “plastic.” Alternatively, the base  20  may not comprise threads, but may instead have other adaptation for joining to the valve assembly that is inserted and secured to the base. For example, a bayonet or other latching mechanism that anchors or secures the valve assembly into the base may be used.  
         [0035]     The base  20  has a generally flat bottom portion  24  and a slightly curved or rounded top portion  26  (see  FIG. 4 ). The bottom  24  of the base  20  may be slightly concave to mimic the contour of the outer surface  115  of the socket in the preferred distal installation area D on the socket (see Distal Area D on  FIG. 1 ). This allows the valve system  10  to be placed on the distal portion/area D of the hard socket  105  so that it is discreet when covered by clothing and so it does not protrude (as it would from a more proximal side of the socket) to catch on clothing or other items.  
         [0036]     After the base  20  is attached to the hard socket  105 , preferably by adhesive, a hole  125  is drilled through the sidewall  110  of the hard socket  105  via the bore  22  in the base  20 , so that the hole  125  generally aligns with the interior bore  22 , and bore  32  and opening  62  discussed below, for fluid communication between the socket well, hole  125 , bores  22 ,  32  and opening  62  to vent air out of the socket interior I.  
         [0037]     One may see from the drawings that the preferred valve  10  has base  20 , o-ring  40 , valve housing  30 , stem  50  and ring  60  all being coaxial, creating a passageway or “exit path” for air to pass through when the valve opens. In use, when the air pressure inside the hard socket  105  (between the liner-covered residual limb and the socket interior surface) exceeds the desired air pressure, as further discussed below, the air will force the valve stem  50  to move away from the opening  125  in the hard socket  105 , compressing the spring  55  against the ring  60 . This movement of the stem  50  unseats the end  54  of the stem from the sealing surface  38 , allowing air to flow around the end  54  and along the sides of the stem to the opening  60  of the ring, and out to the ambient air.  
         [0038]     The valve system  10  comprises the valve assembly  11  that is inserted into the base  20 , which valve assembly  11  comprises a valve housing  30  having an internal circular bore  32  with a conical sealing surface  38  and an external threaded portion  34 . The threaded portion  34  on the valve housing  30  has a slightly smaller diameter than the threaded bore  22  in the base  20 , so that it may cooperate with the threaded bore  22  in the base  20 . As explained above for the base  20 , the valve housing  30  may be otherwise adapted for connecting/securing to the base. For example, the valve housing may not have any threads and may instead have bayonets that are received in slots in the base when the valve housing is inserted into and rotated in the base.  
         [0039]     The exterior of the valve housing  30  is shown as “hex-shaped,” but other shapes may be used, such as a other polygonal shapes or such as a cylindrical shape. The hex-shape is preferable as it may allow the technician to easily install and tighten the valve housing or the entire assembly in the base. Also, because the hex-shape provides a good surface to grip, it may allow the user to manually open the valve, in effect by disassembling the valve (removing the valve assembly from the base), if necessary, prior to the user removing his/her residual limb from the hard socket  105 .  
         [0040]     An o-ring  40  or other seal is placed in a recess in the base  20  between the base  20  and the valve housing  30 . Once the valve housing  30  is threadably or otherwise received and secured in the base  20 , an air tight seal is created between the base  20  and the housing  30 .  
         [0041]     The valve assembly  11  further comprises a valve stem  50  received in the bore  32  of the housing  30 . The valve stem  50  slides axially inside the bore  32  to seat against the sealing surface  38  of the housing, when the valve is closed, and to move away from and unseat from the sealing surface  38  when the valve is open. A spring  55  biases the valve stem  50  into the closed, seated position to close the valve except when a differential air pressure overcomes the spring  55  bias and pushes the valve stem  50  away from the sealing surface. Spring  55  is preferably a cylindrical coil compression spring, the design of which is the main determining factor in the crack pressure of the valve.  
         [0042]     The valve assembly, including the bias spring  55 , are adapted so that a differential pressure selected from the range of 1-3 psi, and more preferably the range of 1-2 psi, will “crack” or “pop” open the valve. In other words, the valve assembly and particularly the spring  55  are preferably designed so that, when the pressure on the “inner side” of the valve (to the left in  FIGS. 5 and 6 , and typically on the inside of the socket between the liner-covered limb and the interior surface of the socket) is a certain amount above the pressure on the “outer side” of the valve (to the right in  FIGS. 5 and 6 , and typically outside the socket), then the valve will open. This “certain amount” is preferably in the range of 1-3 psi, and more preferably in the range of 1-2 psi. As soon as the differential pressure drops (that is, as soon as the inner pressure is less than the preferred 1-3 psi or 1-2 psi higher than the outer pressure) the spring  55  will again bias the valve stem  50  to the closed, seated position. Thus, as discussed above, the valve will open, if necessary, with each step, to allow air to vent from the socket well, and then quickly close after the air has been vented and/or when the swing portion of the gait lowers the pressure inside the socket well.  
         [0043]     The valve stem  50  preferably has an internal bore  52  (or other hollow or recessed end or cavity that opens to the housing bore preferably at the spring-end of the valve) that may receive air that is flowing out of the valve in the “exit path” comprising passing around the stem, through or around the spring, and out through the outer end of the valve (at ring  60 ). Internal bore  52  may provide extra space for this flowing air, as it passes around or through the spring to exit the valve, thus helping prevent unpleasant noise or venting sounds that might occur with too-narrow portions of the exit path. Further, various embodiments of the bore  52  may be advantageous during the molding or machining process, for weight reduction, and/or for cooperating with or connecting to a spring or other bias member. The preferred location of the spring  55  is that is received between the flat face  53  of the valve stem  50  and the inner face  63  of the ring  60 , and held there securely enough that it may be repeatedly compressed between those surfaces and then released, when the valve opens and closes, respectively, without significantly shifting from its preferred radially-centered position.  
         [0044]     Further, as shown in  FIG. 8 , there may be an o-ring  58  or other material on the generally conical end  54  of the stem  50 , which o-ring  58  or other material is preferably a softer or more flexible material, compared to the preferred brass valve stem  50 , for enhancing the seal between the stem  50  and the sealing surface  38 . Alternatively, the entire stem  50 , the conical end  54  of the stem, or another portion of the stem may be made of a softer plastic or other material with enhanced sealing performance.  
         [0045]     Retaining ring  60  is a generally thin disc that is friction-fit or otherwise secured and anchored into the bore  32  of the housing  30  to retain the spring  55  and the stem  50  in their proper positions inside the housing. The ring  60  is preferably secured to the housing, on ledge  39 , in such a way that it will not normally come out of the housing, but that a prosthetics technician could pry or otherwise remove it to clean the valve assembly  11  and/or replace parts of the valve assembly  11 . Ring  60  has an opening  62  through which the air is expelled. Alternative ways of retaining the valve stem, spring, and/or other parts as may be desired, in the housings of the valve may be used.  
         [0046]     The preferred stem  50  is a hexagonal, or other polygonal shape, so that it has multiple flat or generally flat sides  56 . Therefore, the air may flow along the end  54  of the stem and through the bore  32  of the housing in between the housing inner surface and one or more of the flat sides  56 . This provides multiple passages for the air, with each preferably being a relatively wide passage (that is, radially wider than if the stem where cylindrical inside a cylindrical housing bore), which is believed to be important for reducing air-venting noise. These passages may be said to be “spaced gaps” between the stem and the housing, in that they are spaced apart (separated) by the edges  57  of the stem, which contact, or come very close to, contacting the bore  32  surface. These gaps, therefore, may also be called non-annular gaps or non-annular spaces, as the gap/space between the stem and the bore of the housing is preferably not simply a continuous, annular space around the entire stem, but rather multiple axial passageways that are separated/spaced apart by the edges  57  that are close to, or that contact, the bore  32 . It may also be said that, because the stem and the housing bore are not the same shape (and particularly not the same circumferential shape), there are multiple gaps between the stem and the housing bore created by this difference in shape. This also places the stem  50  in the housing in a slidable arrangement, where it slides axially in the housing bore  32 , with contact being between the edges  57  of the sides  56  and the bore  32  surface, but not all the way around the circumference of the stem. This may be important for keeping the stem freely slidable in the bore  32  and less prone to plugging, seizing-up, and/becoming fouled to an extent that the valve would make more noise.  
         [0047]     The preferred combination of an axially-sliding stem, and a polygonal or other stem shape, that provides multiple air passages along the sides of the stem (which are relatively wide by being flat, recessed, or otherwise spaced from the preferably cylindrical housing bore wall) are believed to be at least part of the reason for the quiet, consistent, and effective operation of the valve. Also, the preferred low crack pressure that is achievable with the preferred valve with repeated, consistent operation, is believed to be important and beneficial for quiet operation and effective prosthetic suspension without large swings in socket pressure.  
         [0048]     Preferably, the base  20 , valve housing  30 , and retaining ring  60  are fabricated from a light-weight durable material, for example, Delrin™ plastic; however, other materials may be used such as aluminum, titanium, nylon or other plastics. Additionally, the stem  50  may be brass, but also may be manufactured from other materials, for example, including other metals, plastics, or combinations thereof.  
         [0049]     The preferred valve system  10  is adapted to be fitted on the outside surface  115  of the hard socket  105 , and most preferably only to the outside surface  115 . The valve system  10  is preferably attached with adhesive, by applying adhesive of types known in the field of prosthetic sockets to the bottom  24  of the base and/or to the outer surface  115 . Other securement means may be used, but adhesive is preferred as it has been found to be reliable, easy to use, and not requiring any other fasteners or complex or protruding parts. Preferably, no portion of the valve system  10  extends through the socket wall, or into the interior space I of the hard socket  105 , or contacts the inside surface  120  of the hard socket  105 . The opening/hole  125  in the socket wall is made by drilling or otherwise cutting through the socket wall, and this step preferably does not include any threading or other shaping or preparing of the socket or the hole therein. Thus, the preferred valve and attachment of the valve may be used effectively with modern thin-walled, light-weight sockets. The valve system  10 , in the preferred but not all embodiments, consists essentially only of, and may consist only of, a base, a valve housing, an o-ring or other seal, a stem with or without supplemental sealing member or portion, a spring and a retainer ring or other closure or cover. This simple design is effective in terms of manufacture, installation, and operation, and has many benefits over prior art valves, including over the prior art valves that are more complicated, prone to plug-up, prone to make venting noise, that include ball-and-spring systems, and/or that screws/threads into the socket wall and/or that resides on both sides of the socket wall. In the preferred embodiment of the invented valve system, only the base, and more preferably only its bottom surface ( 24 ) or portions of the bottom surface ( 24 ), is in contact with the hard socket.  
         [0050]     Preferred embodiments may be described as a pressure-control system for a prosthetic hard socket, wherein the prosthetic socket comprises a wall having an outer surface and an interior surface defining a well for receiving a residual limb, and said wall has a hole extending from said outer surface to said interior surface; and wherein the valve system comprises: a base connected to said outer surface and having a base bore positioned over said hole in the wall; and the valve housing being connected to said base and extending into said base bore and having a housing bore generally coaxially aligned with said base bore and in fluid communication with said hole in the socket wall, said valve housing having a sealing surface; a valve stem received in said housing bore and slidable into a first, sealed position wherein a portion of said valve stem (preferably a sealing end) seals against said sealing surface and into a second, unsealed position away from the sealing surface; and a spring biasing the valve stem into the first, sealed position until said air pressure inside the prosthetic socket well is at a differential pressure in the range of 1-3 psi greater than ambient pressure outside the socket, at which time the valve stem is pushed by said differential pressure into said second, unsealed position so that air leaves the socket well by flowing through the hole and through the valve system. Alternatively, or in addition, the valve stem circumference may be not the same shape as the housing bore circumference (preferably one of the two being non-circular) so that, when the valve stem is in the second, unsealed position, air flows around the valve stem through axial gaps between the valve stem and the housing. Preferably, this difference in circumference/shape occurs along the stem side portion, which is the side portion of the stem not adapted to contact the sealing surface. The axial gaps are preferably different from simply an annular space all the way around the stem, and, instead, are axial passages separated by edges that come close to, or touch the housing bore. These edges&#39; proximity to the housing bore wall keeps the valve stem generally centered in the housing bore, while air flows freely past the valve stem through said axial gaps. Thus, the valve stem may be described as being shaped so that multiple axial gaps between the stem and a stem housing extend along the length of the valve stem to receive air flow when the valve stem is in the second, open position, and so that said multiple axial gaps are separated by axial edges of the valve stem that contact or come close to said stem housing and keep said valve stem generally centered in said housing. In many embodiments, said valve stem further has a hollow end with an opening near said spring, wherein said opening is in communication with the air passageway(s) through the valve, providing additional space for air to flow or reside, further reducing air venting noise. The venting of air sooner (at lower differential) and with less-restricted flow, compared to prior art vents is believed to be instrumental in reducing or eliminating the sudden, louder pop, squeak, or sputtering sounds of prior art devices.  
         [0051]     The invention may also comprise the methods of installing and using such a valve system. For example, some embodiments of the invention may comprise:  
         [0052]     A method of installing a pressure-relief valve in a prosthetic socket, the method comprising: providing a hard socket; providing a one-way air valve comprising a base with a base bore, a removable valve stem housing with a housing bore, valve stem, and a spring;  
         [0053]     adhesively attaching said base to the outside of the socket;  
         [0054]     drilling a hole through the socket by inserting a drill bit through said base bore and drilling through the socket to make a hole in the wall generally coaxially aligned with said bore in the base;  
         [0055]     inserting and securing said housing into the base so that the housing bore is generally coaxially aligned with said base bore and said hole in the wall;  
         [0056]     inserting the valve stem and spring into the housing bore so that said valve stem slides in the housing bore to a closed position and an open position to allow venting of air out of the socket well when pressure builds in the socket to a differential pressure that is greater than ambient pressure.  
         [0057]     Preferably, the method comprises no insertion of any part of the air valve into the socket well, and no part of the air valve extends through the socket wall to reach the well. Preferably, the only attachment of the air valve to the socket is adhesive connection of the base to the outer surface of the socket, and, preferably, there is no threaded attachment of the air valve to the socket.  
         [0058]     Although this invention has been described above with reference to particular means, materials and embodiments, it is to be understood that the invention is not limited to these disclosed particulars, but extends instead to all equivalents within the broad scope of the following claims.
A valve system may attach to the distal area of the outer surface of a prosthetic hard socket without leaks in spite of the high amount of curvature of the distal area. The preferred valve stem is biased to slide inside the valve housing(s) to a closed position sealing with a sealing surface. The stem preferably has a non-cylindrical outer side surface, or other outer side surface that does not seal or mate closely with the surface in which the stem slides, creating one or more wide passageways for air to flow out of the valve. A polygonal stem is especially effective, as its generally flat sides allow air to flow past the stem and out of the valve with minimal noise and minimal occurrence of plugging of the valve. The valve system is adapted for a low "crack" or "pop" pressure, which gives repeated, consistent, and quiet performance, which helps prevent uncomfortable and/or high-noise-producing swings in the pressure inside the socket well. Preferably no portion of the valve system extends through the wall of the socket or resides inside the socket, and no part need be installed from inside the socket. The preferred valve system preferably has a wide base that is adhesively attached to the outside of the socket, and may be installed on thin-walled sockets.