GB2089664A - Valved tennis balls - Google Patents

Abstract

A tennis ball (92) has a check valve (66) which may be integrally moulded in the sidewalls thereof, the valve being protected by a gas-permeable fabric covering (90) which extends over the entire surface of the ball, and through which inflation can be effected. The valve is constructed includes tapered sides of elastomeric material such that increased internal pressure wedges the sides increasingly tightly to provide a seal which is resistant to opening upon impact of the ball. The sides are greased and provided with knife edges and a polished surface on the interior to provide leak-free sealing. The valve opening may be further protected by a gauze filter (91) between the opening and the fabric covering. The ball can be pressurized by placing it in a sealed container and then reducing the volume of the container by a fixed amount, thus forcing gas through the covering and valve and into the ball. <IMAGE>

Description

SPECIFICATION Tennis ball Except at the novice level, tennis players are very concerned with the consistency of the playing characteristics of the ball. The typical tennis ball is made of a molded spherical shell of elastomeric material, such as natural or artificial rubber. The shell is prepressurized at the factory, coated with an adhesive, and covered with two interlocking, figure-eight-shaped pieces of fabric disposed over the surface of the tennis ball with a seam between the abutting edges to provide the characteristic tennis ball configuration. Typically, such balls are shipped in metal cans under pressure. When the can is being opened, the ball is subjected to atmospheric pressure. Sometimes, a brand new ball taken from the can will be "dead". That is, it will have insufficient bounce to be useful for play.Also, as a result of varying atmospheric conditions and temperature changes, the internal pressure within a tennis ball van vary an amount such as to cause large differences in the bounce of one tennis ball versus another.

Valves have been put into the sidewalls of inflatable bladder type playing balls for years. Balls such as footballs and basketballs containing large volumes of air and subjected to infrequent andlor low level impacts can be inflated priorto a game to a desired pressure through the valve and will maintain an acceptable level of inflation throughout the game.

Moreover, the pressure within the ball and minor variations thereof are not critical to the playability of the ball.

By contrast, tennis balls have smaller volumes of contained air and are struck repeatedly with high impact forces. As a consequence, even minor leakage through a valve can cause changes in the internal pressure of the ball during play which is sufficient to cause a change in the playing characteristics of the ball.

It is the object of the present invention, therefore, to provide a tennis ball having an integral valve and a method for filling the ball to a constant pressure which is highly resistive to the loss of air during violent game play on the unclean surface of a tennis court.

It is a further object of the present invention to provide a tennis ball having an integral valve and a method for filling the ball to a constant pressure which is adapted to provide constant bounce regard less of the altitude and temperature at the site of play.

It is yet another object of the present invention to provide a method of making a valved tennis ball.

Figures 1-12 are drawings related to the prior art.

Figure 1 depicts a tennis ball having a valve dis posed through the sidewall thereof.

Figure 2 is a cut-away enlarged view through the valve of the ball of Figure 1 in the plane ll-ll.

Figure 3 is an end view of the valve of Figure 2 in the plane Ill-Ill.

Figure 4 is a partially cut-away drawing showing a syringe-type pump being used to inflate the tennis ball of Figures 1-3 through the valve thereof.

Figure 5 is a cut-awayviewthrough a standard duckbill type valve as integrally molded into the sidewall of a gameball.

Figure 6 is a cut-away view through an integrally molded duckbill type valve according to an alternate embodiment.

Figure 7 is a plan view of a portion of the valve of Figure 6.

Figure 8 is a cut-away view through yet another embodiment of a duckbill type valve.

Figure 9 is a plan view of the valve of Figure 8.

Figure 10 is a cut-away view through a duckbill type valve in an unpressurized condition.

Figure 11 is a cut-away view of a duckbill type valve in a pressurized condition.

Figure 12 is an enlarged view of the valve of Figure 11 in the area Xll.

Figure 13 is a drawing depicting the principle of operation of the valve employed in the present invention in its unpressurized state.

Figure 14 is a cut-away view and a simplified drawing of the valve of Figure 13 in a semi-pressurized state showing the beginning of the wedging effect employed therein.

Figure 15 shows the valve of Figures 13 and 14 in its fully wedged and sealed state.

Figure 16 is a cut-away view through the molded rubber shell of a tennis ball according to the present invention.

Figure 17 is an enlarged view of the valve employed in the present invention as contained within Figure 16 in the area XVII.

Figure 18 is a cut-away view normal to the longitudinal dimension of the valve of Figure 17 showing nominal dimensions thereof in a tested embodiment.

Figure 19 is a cut-away view longitudinally through the valve of Figure 17 showing the dimensions of the tested embodiment thereof.

Figure 20 is a partially cut-away drawing through a portion of a tennis ball depicting the ideal balance characteristics of the valve of the present invention when incorporated in a tennis ball.

Figure 21 is a cut-away view through the inner portion of the valve employed in the present invention in its unpressurized state.

Figure 22 is a cut-away view through the inner portion of the valve employed in the present invention in its pressurized state.

Figure 23 is a cut-away view through a completed tennis ball according to the present invention.

Figure 24 is a view of the outside of a tennis ball according to the present invention in its preferred embodiment.

The insertion of a valve into a tennis ball has been attempted previously by others with only limited success. Such a typical ball is shown with reference to Figures 14. The tennis ball, generally indicated as 10, has a molded rubber shell 12 with a fabric covering 14 adhesively attached as described above and with seams 16 between the edges of the covering 14.

A hole is drilled through the shell 12 and a valve, generally indicated as 18, is inserted in the hole and held in place by an appropriate adhesive. Typically, valve 18 is also made of rubber. The valve 18 comprises an outer portion 20 being cylindrical and adapted for the insertion of the cylindrical filling nib 22 of a small syringe-type pump 24 as shown in Fig ure 4.

Valve 18 has an inner portion 26 which allows the one-way passage of air therethrough. Typically, inner portion 26 has been of the so-called "duckbill" type construction. Various forms of such duckbill valve construction are shown in Figures 2-7. In addi tiontothevalve 18 being inserted through a hole made in the wall of rubber shell 12, it has also been integrally molded as part of the initial molding process of shell 12 as shown in the examples of Figures 5,6,and8.

The principle of operation of a duckbill type valve is similar regardless of the specific construction.

That is, the inner portion 26 terminates in a pair of opposed surfaces 28 having a slit 30 through them.

Internal air pressure in outer portion 20 from pump 24 forces the opposed surfaces 28 apart opening slit 30 to allowthe passage of air through it into the interior of the ball. Upon release of pressure within outer portion 20, the opposed surfaces 28 resume their original position due to the restorative force of the stretched elastomeric material from which they are constructed and then the internal pressure of the ball 10 tends to hold the opposed surfaces 28 tight together. Until my valve all such valves have proved ultimately unsuccessful for use in tennis balls. The reason can be understood with reference to the drawings of Figures 10-12.

In Figure 10, atypical inner portion 26 of a duckbill type valve is shown in its relaxed state. Under internal pressure, it is compressed to the shape shown in Figure 11. As shown in the greatly expanded view of Figure 12, however, the normal method of making such duckbill valves causes an incomplete closure across the entire surface of opposed surfaces 28 creating a small passageway 32 at each side. While the amount of air that can leak through the pair of passageways 32 is small, when the small initial quantity of air filling ball 10 and the number of times the ball is struck during play are considered, the air loss soon becomes large on a relative basis.Also, opposed surfaces 28 are such that during the deformation of shell 12 caused by the high impact of tennis ball 10 against the ground and the tennis racquet, opposed surfaces 28 are not maintained in constant alignment but are "worked" back and forth relative to one another creating microscopic losses along the entire area of opposed surfaces 28.

Until my discovery, the exact nature of and reason for this air loss has not been understood and, therefore, various attempts have been made to solve the problem with incomplete success. In the basic duck bill valve as shown in Figures 2,3, and 5, the opposed surfaces 28 taper inwardly from outer portion 20 to meet in a small area adjacent slit 30. Since the total area of opposed surfaces 28 in contact is minimal in this design, the air loss through the valve is maximum. In the variation of Figures 8 and 9, opposed surfaces 28 are contained within a thin parallel projection 34 having slit 30 at the extreme inner end thereof. A further variation of this general approach is shown in Figures 6 and 7 where the parallel projection 34 has the inner end sealed and small holes 36 provided through the sidewalls of parallel projection 34 to replace the slit 30.If sufficient holes 36 are provided to allow a reasonable filling rate through valve 18, the leakage of the variation of Figures 6 and 7 and that of Figures 8 and 9 is almost identical. Both, however, are better than the basic duckbill valve of Figure 5.

In my United States Letters Patent No.4,240,630, issued December 1980, 1 disclosed a valve well suited for use in a game ball. While the valve as shown in that patent works well in a clean environment such as racquetball court, when placed in the sidewall of a tennis ball and inflated with a small handpump as taught therein, the valved tennis ball often began to leak after playing with in on the unclean surface of a tennis court.

My objectives have been met by my tennis ball which comprises a spherical, hollow, rubber shell covered with a pair of generally figu re8-shaped pieces of fabric wherein the fabric is permeable to the passage of air and the one-way check valve of my United States patent is positioned disposed in the sidewall of the shell beneith the fabric to allow the air to pass aforementioned through it into the ball.

In the preferred embodiment, a piece of gauze material is positioned beneath the fabric and over the opening to the valve to filter particles from the fabric which could otherwise enterthe valve and destroy its sealing qualities.

To fill the ball to achieve the repeatable bounce qualities desired, the ball is placed in a canister of a fixed volume at the play site and the canister then sealed and compacted to a lesser volume such that the change in volume subjects the ball to a pressure which will impart the desired bounce.

In making the ball, two hemispheres comprising the shell have the valve in one and are bonded together. Prior to bonding them together, the valve is greased with a silicone grease to prevent valve malfunction.

Specifically, the valve employed my tennis ball works on a combination of wedging action and improved sealing surfaces. The preferred embodiment of my tennis ball employs a minimum diameter, heat bonded valve insert, similar two the one indicated as 42 in the simplified drawing of Figures 13-15, but with the outer surface below the fabric covering. The valve could also be integrally molded.

Valve 42 is shown positioned within a hole 40 provided in the rigid sidewall 38 of a container. Valve 42 is positioned to allow fluid flow in the direction of arrow 44 and to prevent fluid flow in the direction of arrow 46. Valve 42 is of unitary construction and is molded of a soft pliable elastomeric material. Soft natural rubber is preferred. However, any material having the deformation and sealing qualities of soft, natural rubber can be employed. Valve 42 is annular in shape and of such a thickness adjacent the sides of hole 40 that, in combination with the support provided by the sidewalls of hole 40, it resists deformation in the axial direction close adjacent the sidewalls of hole 40.Valve 42, however, tapers radially inward and axially in the direction of desired fluid flow (i.e. in the direction of arrow 44) becoming thinner the further it gets from the sidewalls of hole 40. Valve 42 tapers together becoming oval in cross section and ultimately coming into sealed mating relationship at the opposite end from the end in contact with the sidewalls of hole 40. Being of a deformable elastomeric material, such as soft rubber, and tapering towards increased thinness, valve 42 becomes more readily deformable towards the center of hole 42. As can be seen in Figure 13, with no pressure applied, valve 42 is positioned with the portion at the extreme inner ends labeled 48, in sealed mating contact.Portion 48, therefore, forms a normally closed valve which resists fluid flow in the direction of arrow 46 but which will open to allow the passage of fluid in the direction of arrow 44. Below normally closed portion 48 is a normally open portion 50. That is, the facing inner surfaces 52 of valve 42 in the area 50 are separated to provide a passageway. The balance of valve 42 can be considered as an annular body portion, which has been labeled as54.

Referring now to Figure 14, the action of valve 42 upon the introduction of fluid pressure in the direction of arrow 46 is shown. Fluid (as represented by the arrows 56) is initially prevented from passing through valve 42 by the action of normally closed portion 48. Accordingly, fluid 56 presses on the upper surfaces 58 of valve 42. Valve 42, therefore, begins to deform into hole 42 from the pressure of fluid 56. As previously mentioned, valve 42 is more readily deformable adjacent the center thereof and becomes increasingly less deformable adjacent the sidewalls of hole 40 (i.e. in the area of annular body portion 54). As a result, facing internal surfaces 52 of normally opened portion 50 are first brought into sealed contact as valve 42 assumes the position of Figure 14.

Valve 42 is constructed such that the length at any point about its periphery from the sidewall of hole 40 to the facing internal surfaces 52 (as indicated by the dashed arrow 60) is longer than the radius of the hole 40 at the same point (as indicated by the dashed arrow 62). This being true, as greater internal fluid pressure is created, as indicated by the heavier arrows 56' in Figure 15, valve 42 is tightly wedged into hole 40 as the pressure of fluid 56 is increased.

Since valve 42 is of a deformable elastomeric material, such as rubber, internal compression forces as indicated by arrows 64 are created within valve 42 between the sidewalls of hole 40 acting on the facing internal surfaces 52 of both normally closed portion 48 and normally open (now closed) portion 50 tending to hold valve 42 tightly closed in the presence of shocks and forces.

Referring nowto Figures 16 through 19, the fore- going operation can be seen as it is applied to the preferred embodiment of a valve to be employed in my tennis ball, being molded as an integral valve in the rubber shell 12' of the tennis ball. In this embodiment, the valve, generally indicated as 66, is in the form of an inwardly projecting, flattened tubular nipple 68, having rounded edges (as shown in Figures 21 and 22) and flat sides 70 and 72 which are separated by an internal cavity 74. The cavity 74 becomes bell-shaped as it approaches and opens to the exterior of the ball's rubber shell 12. That is, the cavity smoothly curves from being about normal to the surface of the shell 12 on the inner end to being tangential to the shell's surface at the exterior end.

At its inner end, the nipple 68 is molded with a solid closed end, which is then lanced through with a sharp blade, leaving a slit 76 that is held closed by the elasticity of the rubber but which can be spread apart when the air pressure in the cavity 74 is greater than the pressure inside the ball.

The construction of the cavity 94 in combination with the wedging action makes my tennis ball virtually leak-proof even in high-shock game play. The cavity 74 is formed by molding itwith a male mold piece having knife edges and a mirror-smooth polished surface for the portion forming at least the inner half of cavity 74. As a result, the formed cavity 74, for at least the inner half of its length, is a laterally-elongated narrow slit having slightly spaced mirror-smooth facing surfaces 78 and 80.

The slit tapers to the lateral knife edges shown in Figure 21.

By employing the polished surfaces and knife edges the previously unrecognized leakage paths of prior art game ball check valves as discussed above are eliminated. As a result, when the nipple 68 is collapsed by air pressure within the ball, a portion of the cavity 74 is closed and sealed airtight. In this collapsed or closed condition, coupled with the wedging action, the valve 66 is tightly sealed against leakage and no air escapes from the ball even during the most violent game play.

The relationship of the valve 66 to the wedging action just described in simplified form with reference to Figures 13-15, can best be understood with reference to Figure 17 where valve 66 is shown in superimposed normal and pressurized states. The normal position is shown with the ghosted lines and the pressurized state is shown in the solid lines. As can be seen, the area of nipple 68 containing the lanced slit 76 comprises the normally closed portion.

In like manner, the area of nipple 68 having flat sides 70 and 72 separated by internal cavity 74 (with the knife edges and polished surfaces) comprises the normally opened portion. The area of rubber of the shell bounded by the dashed lines 82 is the passageway (hole) and is, therefore, labeled 40' for relation to the previous discussion relative to Figures 13-15. Valve 66 as shown in the ghosted position of Figure 17 corresponds to simplified valve 42 of Figure 13. Thus, in corresponding fashion, when the ball is being inflated from no or very low internal pressure, the lanced slit 76 serves as an initial seal to prevent air from leaking out before enough pressure can be built up within the ball to collapse the sidewalls of the nipple 68.

As air pressure builds up, the nipple 68 collapses from the lateral pressure forces and the polished surfaces 66, 80 close against one another to form the secondary airtight seal which is capable of holding the relatively high shock load pressures that are cre ated when a fully inflated ball is hit hard by a racquet. Then, as internal pressure (indicated by the arrows 84) continues to increase, the valves 66 is deformed increasingly into wedged contact with the sidewalls of the integral hole 40'. Since the length of the nipple 68 from the boundary line 82 at any point is longer than the radius of the passageway 40' at that point (in the same manner as described in relation to Figure 14), the internal compressive sealing forces indicated by the arrows 56' are created in the same fashion as previously described with relation to Figure 15.

The design of the valve 66 is such that when constructed of substantially similar material to the ball, the total volume of rubber in the nipple 68 is almost exactly the same as the airspace volume of the cavity 74. Additionally, as shown in Figure 20, the valve 66 is distributed along a radius line such that its slightly heavierweight (as shown by the arrow 86) acts through the radial distanced2 which is slightly shorterthan the distance d, through which the weight opposite (shown by arrow 88) acts such that the rotational forces on the ball are equal and opposite making the ball dynamically balanced. As a result, the valve 66 has no appreciable effect on the balance of my tennis ball.

Figures 18 and 19 show the dimensions (in inches) of such a valve as actually constructed and tested in a playing ball.

In manufacturing mytennis balls, two hemispherical core sections are first molded. One contains the integral valve and one is without a valve. The two hemispherical core segments are then bonded together under heat and pressure to form a spherical core having an integral valve in its sidewalls. The fabric covering is then bonded to the surface to complete the tennis ball.

Because of the pressures involved and the materials required to achieve the complete sealing of the valve, it was found that an unexpected problem can occur. That is, in order to achieve the desired sealing the valve used in my tennis ball is of soft natural rubber or a material having the qualities of soft natural rubber. Also, the mating surface are formed in a mirror-smooth mold such that the surfaces themselves are mirror-smooth. When subjected to internal pressure the valve is forced into a wedging state wherein the mating surfaces are wedged into a firm sealing relationship. Employing conventional manufacturing techniques causes such a sealing arrangement to be affected as a result of the molding and joining process of the spherical core.The manufacturing process itself creates a hollow spherical core containing an internal pressure which can force the soft rubber surfaces into a wedged relationship sufficient to create a virtual diffusion welding or bonding of the mating surfaces. Later, when the ball is placed within the pressurized container, the diffe rential pressure between the outside desired pressure and the pre-established internal pressure in the ball is insufficient to break the diffusion bond. The ball is merely deformed and the correct pressurization is not achieved.

I have found that coating the internal, mating surfaces of the valve with a light coating of silicone grease or the like prior to the joining of the two hemispherical core segments results in an elimination of this problem. The internal pressure still occurs as part of the manufacturing process, but the sealing of the valve is a normal sealing without the diffusion surface bonding which previously occurred sometimes.

It is important when employing this procedure that the grease employed by a silicone-based grease, or the like, which does not attack the soft natural rubber as would be the case with normal petroleum-based greases. The term "grease" as employed herein includes any material which would provide the desired surface coating action without causing deterioration thereof.

Turning now to Figures 23 and 24, having thus prepared the molded rubber shell 12' with valve 66 in it shell 12' is covered in the usual mannerwith a pair of generally figure-8-shaped pieces of felt fabric 90 as shown in Figure 24 to form the classic tennis ball covering. Fabric 90 for my tennis ball should be of an air-permeable material and is placed, as shown in Figure 24, with the fabric 90 covering the opening to valve 66. Fabric 90 is adhesively attached to rubber shell 12' in the usual manner but care must be taken to prevent the adhesive from entry into the opening of valve 66.

Also, it is preferred to further separate the opening to valve 66 from any possible contamination by first covering it with a disc or patch 91 of gauze material.

In tested balls without the gauze material, the objectives of preventing the dirt and contamination of the playing environment were met, but, after a time, the balls unexpectedly leaked. It was finally determined that a single fiber dislodged from the surface of the felt fabric used to cover my tennis ball was sufficient to enter the valve 66 and destroy its unique sealing qualities. The gauze filter patch 91, being free of loose fibers, filters the opening of valve 66 and keeps it in good sealing condition. While other materials could be used, the gauze is preferred since it is thin and practically weightless in the size required so that the weight and balance of the ball is not affected by it.

The tennis ball 92 thus formed can be pressurized by placing the ball 92 into any of a number of containers presently available for shipping and/or storing tennis balls under pressure. In this regard, the fabric covering 90 serves two functions. Being permeable, it allows the air to pass therethrough and through valve 66 to the interior of ball 92.

Moreover, since the sealing qualities of valve 65 depend upon the firm mating of the mirror-smooth sidewalls to achieve the desired pressure retention results, fabric 90 serves as a filter to prevent the entry of small foreign particles into valve 66 which would cause valve 66 to lose its pressure-retention capabilities as discussed above.

It is very important to note that if ratherthan prepressurizing the tennis ball as is the usual custom, my tennis ball is pressurized at the play site by placing it in one of the available containers which subject it to on-site change of volume pressurization rather than pressurizing itto a fixed gauge pressure, my tennis ball will be pressurized in a manner which compensates completely for altitude and temperature variations. It is therefore pressurized in a manner which imparts the same bounce characteristics regardless of the altitude and temperature of the site.

With my tennis ball 92 incorporating valve 66, if it should be necessary to reduce the inflation pressure, all that is necessary is to insert a toothpick, paper clip, or the like into the valve opening so as to spread the sealing lips apart and break the seal. It has been foundthatthe adjusted pressure can be set to an accuracy of plus or minus a fraction of a milimeter of mercury. It has been found that changes in the altitude of play or temperature variations can cause a necessity for the release of excess pressure within the ball and subsequent repressurization to a desired new pressure to provide proper bounce. To this end, in the preferred embodiment as shown in Figure 24, fabric cover 90 is provided with an indicia 94 over the location of valve 66 so that a toothpick, paper clip, or the like can be passed through the fabric 90 to open valve 66 in the above-described manner to relieve the pressure within ball 92. Indicia 94 is conveniently in the form of a dot or circle of ink applied to fabric 90 at the proper location.

Claims (16)

1. In a tennis ball having a spherical, hollow, rubber shell (12) covered with a pair of generally figure-8-shaped pieces of fabric (90), the improvement characterized by the fabric (90) being permeable to the passage of airtherethrough and by a one-way check valve (66) being disposed in the sidewall of the shell (12) beneath the fabric (90) for allowing air to pass therethrough into the ball.

2. Atennis ball comprising: a) a spherical, hollow, rubber shell (12) having a bore through the sidewall thereof; b) a unitary check valve (66) disposed in the bore (40) for sealing the bore (40) to allow pressurized fluid to flow axially through the bore (40) in one direction and prevent pressurized fluid from flowing axially through the bore (40) in the opposite direction, said valve (66) comprising, by) an annular body portion (54) carried coaxially within the bore (40), said body portion (54) being thick enough in the axial direction adjacent the outer edges of the bore (40) that in combination with the support provided by the material defining the bore (40) said portion (54) is substantially non-deformable in the axial direction, and, b2) a sealing nipple portion (58) carried within said body portion (54) tapering radially inward and axially in the direction of desired fluid flow from said body portion (54) on one end to meet in sealed contact adjacent the opposite end, the thickness of said sealing nipple portion (68) in the axial direction becoming increasingly thinner and correspondingly increasingly deformable in the axial direction radially inward from said one end whereby the application of fluid under pressure to said valve (66) in the direction opposite desired fluid flow causes said nipple portion (68) to be deformed axially into said body portion (54) in a wedging action increasingly sealing the bore as increased fluid pressure is applied, said taper being a smooth curve extending from a point on a line substantially normal to the axis of the bore (40) on said one end to a point on a line substantially parallel to the axis of the bore (40) on said other end whereby fluid pressure within the bore (40) tending to move fluid through the bore (40) in a non-desired direction acts normal to the axis on said nipple portion (68) adjacent said other end to initially prevent fluid passage therethrough as it also acts axially on the rest of said nipple portion (68) to deform said nipple portion (68) in said wedging action into said body portion (54), said nipple portion (68) being of a material having the deformation and sealing qualities of soft natural rubber, the surfaces (78, 80) of said nipple portion (68) that meet during said wedging deformation into said body portion having a finish produced by a mirror-smooth mold; and, c) a pairofgenerallyfigure-8-shaped pieces of fabric (90) bonded to the outer surface of said shell with narrow seams between the abutting edges thereof, said fabric (90) being permeable to the pressurizing fluid and covering the outer opening to said valve.

3. The tennis ball of claim 2 wherein: the length of said nipple portion (68) from said one end to said other end is sufficiently long in relation to the deformability thereof that said other end remains in sealed contact and said nipple portion (68) still deformably wedges into said body portion (54) when said body portion (54) is deformed radially outward by expansion of the material defining the bore (40).

4. The tennis ball of claim 2 wherein: said mirror-smooth inner surfaces (78, 80) that are pressed together in fluid-tight sealing engagement come together in knife edges.

5. The tennis ball of claim 2 and additionally comprising: filter means (91) disposed over the outer opening of said check valve (66) and under said fabric (90) for filtering out fibers from said fabric (90) which would otherwise, if dislodged, enter said check valve (66) and deminish its sealing qualities.

6. The tennis ball of claim 5 wherein: said filter means (91) comprises a piece of gauze material.

7. Atennis ball comprising: a) a molded, spherical, hollow, rubber shell (12) having a unitary check valve (66) of elastomeric material integrally molded into the sidewall thereof, said valve (66) comprising a substantially flattened tubular nipple portion (68) having external rounded edges and generally flat sides defining an internal cavity (74) with an elongated axis, said cavity (74) smoothly curving from a point on a line normal to said axis at the entrance end of said nipple portion (68) to a point on a line parallel to said axis as it approaches and opens to the interior end of said nipple portion (68), said nipple portion (68) having an inner end defining an inner extremity of said cavity, said inner end being a solid closed end having a thin slit (76) therethrough which communicates with said cavity (74), said slit (76) being normally held closed by the elasticity of the elastomeric material, said cavity (74) being configured for at least an inner half of its length in the form of a laterally elongated narrow slit having spaced walls (78,80) produced from a mirror-smooth mold, said walls (778,80) tapering down to lateral knife edges, said cavity (74) being further configured at its inner end adjacent said solid end of said nipple portion (68) by its tapering down to a knife edge adjacent and communicating with said thin-slit opening (76); and, b) a pair of generally figure-8-shaped pieces of fabric (90) bonded to the outer surface of said shell (12)with narrow seams between the abutting edges thereof, said fabric (90) being permeable to the pressurizing fluid and covering the outer opening to said valve (66).

8. The tennis ball of claim 7 and additionally comprising: filter means (91) disposed over the outer opening of said check valve 66) and under said fabric (90) for filtering out fibers from said fabric (90) which would otherwise, if dislodged, enter said check valve (66) and deminish its sealing qualities.

9. The tennis ball of claim 8wherein: said filter means (91) comprises a piece of gauze material.

10. The method of producing a tennis ball having predictable and repeatable bounce characteristics at different altitudes and temperatures comprising the steps of: a) producing a spherical, hollow, rubber shell having a bore through the sidewall thereof which bore contains a unitary check valve for sealing the bore to allow pressurized fluid to flow axially through the bore in one direction and prevent pressurized fluid from flowing axially through the bore in the opposite direction, said valve comprising, al) an annular body portion carried coaxially within the bore, said body portion being thick enough in the axial direction adjacent the outer edges of the bore that in combination with the support provided by the material defining the bore said portion is substantially non-deformable in the axial direction, and, a2) a sealing nipple portion carried within said body portion tapering radially inward and axially in the direction of desired fluid flow from said body portion on one end to meet in sealed contact adjacent the opposite end, the thickness of said sealing nipple portion in the axial direction becoming increasingly thinner and correspondingly increasingly deformable in the axial direction radially inward from said one end whereby the application of fluid under pressure to said valve in the direction opposite desired fluid flow causes said nipple portion to be deformed axially into said body portion in a wedging action increasingly sealing the passageway as increased fluid pressure is applied, said taper being a smooth curve extending from a point on a line substantially normal to the axis of the bore on said one end to a point on a line substantially parallel to the axis of the bore on said other end whereby fluid pressure within the bore tending to move fluid through the bore in a non-desired direction acts normal to the axis on said nipple portion adjacent said other end to initially prevent fluid passage therethrough as it also acts axially on the rest of said nipple portion to deform said nipple portion in said wedging action into said body portion, said nipple portion being of a material having the deformation and sealing qualities of soft natural rubber, the surfaces of said nipple portion that meet during said wedging deformation into said body portion having a finish produced by a mirror-smooth mold;; b) bonding a pair of generally figurn8-shaped pieces of fabric to the outer surface of said shell with narrow seams between the abutting edges thereof, said fabric being permeable to the pressurizing fluid and covering the outer opening to said valve; and, c) at the altitude and temperature whereat the tennis ball is to be used for play, placing the tennis ball being of a given volume VI into a collapsable container having a given internal volume V2, sealing the container and compressing the container to a second given internal volume V3 wherein the change in volume (V3-V2) is sufficient to place the tennis ball under a pressure which will impart the desired bounce characteristics to it.

11. The method of claim 10 wherein said step of producing a spherical, hollow, rubber shell comprises the steps of: a) forming a first hemispherical core segment having the integral valve with mating, sealing surfaces in the sidewall thereof; b) forming a second hemispherical core segment; c) disposing a material between the mating, sealing surfaces which will prevent the surfaces from sticking together as a result of the pressure and temperature conditions of the bonding step which follows without attacking the material of the surfaces; and, d) bonding the first and second core segments together to form a spherical shell.

12. The improvement of claim 11 wherein: said disposing step comprises applying a coating to the surfaces.

13. The improvement of claim 12 wherein: said coating is a grease.

14. The improvement of claim 13 wherein: said grease is a silicone grease.

15. Atennis ball substantially as described herein with reference to Figures 13 to 24 of the accompanying drawings.

16. A method of manufacturing a tennis ball substantially as described herein with reference to Figures 13 to 24.