CA2820804A1 - Apparatus, system and method for recharging tennis balls - Google Patents

Abstract

An apparatus, system and method for recharging depleted tennis balls that uses pressurized gas is disclosed. A pressure vessel includes a cylindrical shell with a closed end and a spaced apart and opening top connected by a wall to form a charging chamber. The vessel may be pivotally secured to a base. A port in the outer wall, closed end, or top of the vessel permits gas entry and exit for charging. The chamber is filled with an appropriate number of discharged tennis balls and then is sealed and charged with high pressure gas having a molecular weight heavier than air. The chamber is monitored to determine when the tennis balls have reached a desired internal pressure. Once the balls reach the desired internal pressure they are removed.

Description

APPARATUS, SYSTEM AND METHOD FOR RECHARGING TENNIS BALLS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and is a continuation-in-part of currently pending US
Application Serial No. 12/657,032 filed January 12, 2010, which is a continuation-in-part of U.S.
Application Serial No. 11/820,423, filed June 19, 2007, now issued as U.S.
Patent 7,658,211.
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to the field of recharging depleted or exhausted or dead or depressurized tennis balls. In particular, the present invention relates specifically to an apparatus and method for recharging depleted or exhausted or dead or depressurized tennis balls to restore the liveliness and optimum configuration of the individual balls.

2. Description of the Known Art.
Many games use a gas pressurized hollow ball during play (i.e. football, basketball, soccer, tennis, etc.). In the game of tennis, the ball is spherical and of a standard diameter and it is covered with a fibrous nap. Important parameters of the tennis ball are its bounce or liveliness or resiliency and this is a function of the ball's internal gas pressure, its size and spherical configuration and the condition of the fibrous nap. All of these parameters should be maintained constant and uniform from ball to ball and during the useful life of the ball.
Since the reaction of the ball to the impact of the racket and its ground rebound characteristics are functions of the above parameters, any significant change or variation thereof adversely affects the proper playing of the game.

SUBSTITUTE SHEET (RULE 26) As is well known, the resiliency exhibited by tennis balls is due, at least in part, to the pressurization of the tennis balls during manufacturing. To be suitable for tournament play, tennis balls must be able to meet quite rigid specifications regarding their size, the distance to which they rebound when dropped from a standard height, the amount of deformation they exhibit under an applied standard force, and their surface characteristics.
For example, current International Tennis Federation rules require that tennis balls weigh between 56.0 -59.4 grams.
All manufacturers strive to comply with these rigid specifications to insure that the balls they manufacture exhibit the uniformity demanded by serious amateur as well as professional tennis competitors.
Tennis balls are generally packaged and marketed in pressurized hermetically sealed containers to minimize or prevent any outwardly diffusion of the pressurized gas in the ball which would reduce its liveliness and to prevent distortion of the ball from its standard size or shape as a consequence of the ball's high internal pressure. A basic problem with tennis balls presently in use is that, as the balls age, they lose pressure. This pressure loss results from the diffusion through the tennis ball surface of whatever gas may be used to inflate tennis balls during manufacture. Partially to combat this loss of pressure, tennis balls have, for some time, been marketed in pressurized canisters, generally three or four tennis balls to a canister. Of course, once the canister in which the tennis balls have been sold is opened, the tennis balls are removed from their pressurized environment and, as a result of the pressure differential across their surfaces, they begin to deflate and distort thus limiting the useful life of the ball.
As stated previously, with usage and/or the passage of time, the internal pressurization of tennis balls eventually escapes until the internal pressure of the tennis balls drops to atmospheric pressure. At that time, the unpressurized and depleted tennis balls are considered to be dead or flat even though the tennis balls may otherwise be acceptable. Depleted tennis balls are typically discarded. While many of the tennis balls may be retired because their surfaces have become worn beyond acceptable limits, many more tennis balls are retired simply because they have lost their pressurization. Discarding depleted but otherwise acceptable tennis balls can be extremely wasteful, particularly at large tennis clubs and country clubs or tennis instruction academies where the quantity of depleted tennis balls can be high.
Others have proposed solutions to deal with depleted tennis balls, including recharging and/or recycling apparatus and methods. Patents disclosing information relevant to tennis ball pressurization include U.S. Patent No. 4,124,117 issued to Rudy on November 7, 1978; U.S.
Patent No. 1,207,813 issued to Stockton on December 12, 1916; U.S. Patent No.
4,019,629 issued to Dubner et al. on April 26, 1977; U.S. Patent No. 4,020,948 issued to Won on May 3, 1977; U.S. Patent No. 4,046,491 issued to Roeder on September 6, 1977; U.S.
Patent No.
4,073,120 issued to Berggren on February 14, 1978; U.S. Patent No. 4,086,743 issued to Hoopes on May 2, 1978; U.S. Patent No. 4,101,029 issued to Feinberg et al. on July 18, 1978; U.S.
Patent No. 4,161,247 issued to Feinberg et al. on July 17, 1979; U.S. Patent No. 4,165,770 issued to Goldman et al. on August 28, 1979; and U.S. Patent No. 4,372,095 issued to De Satnick on February 8, 1983. Each of these patents are hereby expressly incorporated by reference in their entirety.
Many of the devices discussed in the above patents are either complex and inconvenient to employ or they have been unsatisfactory in that they tended to damage the surface of the ball, thereby adversely affecting the ball's playing properties and otherwise left much to be desired.

Another significant drawback of the prior art is that such prior art contemplates pressurization of a very small number of tennis balls, typically, three tennis balls in a container of a configuration similar to the containers in which tennis balls are marketed.
The increasing popularity of tennis and the resultant growth in the offering of group tennis lessons, as well as the burgeoning tennis club industry, have resulted in the use of far more tennis balls than such prior art apparatus can economically preserve. For example, it is not uncommon for a tennis club in a large metropolitan area to use 10,000 or more tennis balls in a year. To address the large quantities of balls, some have proposed "batch"
systems to repressurize balls. "Batch" processing of tennis balls can be a real and immediate solution that may result in significant economy, particularly for users of large numbers of tennis balls. As used by many, batch processing refers to the processing of, for example, 50 or more tennis balls at one time. U.S. Patent No. 4,101,029 issued to Feinberg et al. on July 18, 1978, entitled Tennis Ball Rejuvenator and Maintainer and U.S. Patent No. 4,046,491 issued to Roeder on September 6, 1977, entitled Tennis Ball Preserver are examples of such batch systems.
The known art fails to address many perceived shortcomings in the industry.
For example, a desirable improvement in the art would be the introduction of a system adapted to quickly recharge depleted tennis balls economically and efficiently while also providing the ability to store tennis balls indefinitely. What is needed then is an improved apparatus and method for quickly recharging large quantities of depleted tennis balls in an efficient and economical manner while also providing the ability to store them indefinitely.

SUMMARY OF THE INVENTION
The present invention is directed to an improved apparatus and method for quickly recharging large quantities of depleted tennis balls (i.e., between 50 and several hundred) in an efficient and economical manner. In accordance with one exemplary embodiment of the present invention, a method and apparatus for recharging depleted tennis balls is provided that uses compressed gas. Many different types of gases may be used but gases having a molecular weight heavier than air are preferred. Carbon dioxide is a preferred gas due to its molecular weight, performance, price, and availability.
Of particular note is the invention's ability to quickly and economically recharge tennis balls. One exemplary embodiment of the invention is a method of recharging tennis balls. In the method according to the invention a pressure vessel, specifically the hollow interior charging chamber of the pressure vessel, is filled with a plurality of discharged tennis balls while the vessel is at ambient pressure. The phrase "discharged tennis balls" as used herein means tennis balls that no longer exhibit the "bounce" required for tournament play. More specifically, the phrase includes balls that no longer meet sanctioning body specifications regarding size, the distance that balls must rebound when dropped from a standard height, the amount of deformation exhibited under an applied standard force, and/or their surface characteristics.
The pressure vessel is sealed and the charging chamber is charged with a quantity of gas having a molecular weight heavier than air thereby increasing the internal pressure of the vessel.
Carbon dioxide is a preferred gas. Preferably the internal pressure of the vessel is increased to about 40 psi to 70 psi (275 kPa to 482 kPa), preferably around 60 psi (413 kPa). The balls are then maintained within the charging chamber for a period of time that is sufficient for the balls to reach a desired internal pressure. One way of determining if a sufficient amount of time has passed is to monitor the pressure within the vessel. As the pressure within the vessel drops there is an increase in the internal pressure of the balls.
Within 1 to 10 days, usually between 2.5 to days depending on the pressure and gas combination used, the balls become fully pressurized and the pressure may be released and the recharged balls removed from the vessel.

It is possible to recharge balls at a pressure as low as 20 psi (137 kPa), but such a lower pressure increases the charging time. Similarly, higher pressures decrease the charging time but use of higher pressures increase apparatus cost and increase safety risks.
Thus, pressures around 60 psi (413 kPa) have been used as a suitable compromise between time, cost, and safety.
Another exemplary embodiment is a system for recharging depleted tennis balls.
The system includes a pressure vessel with a closed bottom and a spaced apart top with an integral, rigid wall extending between the closed bottom and top. The top may be selectively opened to permit access to the vessel's hollow interior charging chamber. The top may be secured by several threaded bolts spaced about the vessel periphery or by other known means of safely securing tops to pressure vessels. The top may be pivotally secured to the vessel by an arm that permits the top to open upwardly and swing outwardly from the vessel.
The system also includes a gas port that is in fluid communication with the charging chamber of the pressure vessel and a gas supply that is in fluid communication with the gas port and with the charging chamber.
The preceding system is sufficient to accomplish the goal of recharging tennis balls so that the used balls regain sufficient rebound height to satisfy applicable regulations. It should also be noted that balls can be recharged in the system multiple times.
Typically excessive wear of the felt covering of the tennis balls is the factor that ultimately results in balls being discarded.

It is thus an object of the present invention to provide a system and process that can be economically operated to process tennis balls to restore a desirable internal pressurization, thereby significantly increasing the useful life of the tennis balls.
An additional object of the present invention is to provide a system for storing tennis balls in a pressurized environment to preserve their pressurization wherein the system is proportioned and designed for bulk processing of tennis balls and sufficient to maintain constant pressure for such batch processing.
A related object of the present invention is to provide an apparatus that may be selectively pivoted when recharging tennis balls.
Another object of the present invention is to provide a method and system for increasing the internal pressure of depleted tennis balls to a desired pressure.
These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent by reviewing the following detailed description of the invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views:
Figure 1 is a schematic view of a recharging system in accordance with an exemplary embodiment of the invention;
Figure 2 is a partially fragmented perspective view of a recharging vessel showing several tennis balls being recharged therein;

Figure 3 is an elevational view of another exemplary embodiment of the invention taken generally from the side and with the opposite side being a mirror image thereof;
Figure 4 is an elevational view of the embodiment of Figure 3 with dashed lines showing movement;
Figure 5 is a top plan view of the embodiment of Figure 3;
Figure 6 is an elevation view of the embodiment of Figure 3 taken generally from the front side;
Figure 7 is top view of an alternative embodiment of a recharging vessel.
Figure 8 is an elevation view of the embodiment of Figure 7 taken generally from the front side; and Figure 9 is an elevation view of the embodiment of Figure 7 taken generally from the side and showing the top in an open position.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figures 1 and 2 of the drawings, one exemplary embodiment of the present invention is generally designated by reference numeral 20. The present invention employs a pressure vessel 22 with a hollow internal charging chamber 24 that is essentially impermeable when sealed. The charging chamber 24 is formed from the hollow pressure vessel interior bounded between a closed end 26 and a spaced apart removable end or top 27 with a wall 28 extending therebetween. The removable top 27 may include the entire cylinder end as shown in Figure 9 or a portion thereof as shown in Figure 2. A gas charging port 29 penetrates vessel 22 proximate removable end 27. The gas charging port 29 permits the entry and removal of gasses from the charging chamber 24. A pressure gauge 30 may penetrate the pressure vessel 22 adjacent port 29 or alternatively a removable pressure gauge may be placed on port 29 during tennis ball charging to measure the internal pressure in the charging chamber 24.
In another exemplary embodiment shown in Figures 3-6, the pressure vessel 22 includes a removable end or top 27 that may be selectively opened to permit substantially unobstructed access interior charging chamber 24 defined by the bottom 26, top 27, and wall 28. The top 27 may be secured by several threaded bolts 41 equidistantly spaced about the vessel periphery.
Alternatively, the top 27 may be secured by any other known means of securing tops to pressure vessels. Those skilled in the art will know how to adapt such means for use with the present invention. The top 27 may be pivotally secured to the vessel by an arm 40 that permits the top to open upwardly and swing outwardly from the vessel 22 as shown in Figure 9.
When the top 27 is open it is possible for the interior charging chamber of the pressure vessel to receive tennis balls that are to be recharged.
A gas charging port 29 penetrates vessel 22 proximate the selectively open top 27. The gas charging port 29 may be placed in the wall 28 of the pressure vessel 22 or it may be placed in the top 27 or bottom 26. The primary requirement for the gas charging port 29 is that it be in fluid communication with the hollow interior charging chamber 24 of the pressure vessel 22.
The gas charging port 29 permits the entry and removal of gasses from the charging chamber 24.
A pressure gauge 30 may penetrate vessel 22 adjacent port 29 or it may be placed at any desired and suitable position along the outer surface of the pressure vessel.
Alternatively a removable pressure gauge may be placed on port 29 during tennis ball charging to thereby measure the internal pressure in chamber 24.
The top 27 is secured to the vessel 22 by the arm 40. The arm 46 includes a pivot 42 that permits the top 27 to swing upwardly to open and downwardly to be closed. A
convenient handle 45 mounted opposite the arm 40 facilitates user movement of the top 27.
When closed, the top 27 is secured to the pressure vessel 22 by bolts 41.
In this embodiment, the pressure vessel 22 is pivotally secured to a base 50 that permits the vessel to pivot in each direction. The base 50 has supporting arms 52 that each have a triangular outline although other shapes are possible so long as they provide a stable support for the pressure vessel 22 and permit its pivoting movement. The base 50 includes pivoting pins 55 (Figures 5 & 6) secured to the pressure vessel 22 and pivotally mounted to the base. The base 50 includes a flat floor 54 supporting the spaced apart and parallel arms 52 on the ground or other support surface. The arms 52 include a reinforcing gusset 53 spanning between the arms 52 that further stabilizes the arms 52 to maintain their spaced relationship.
A handle 60 secured to the vessel 22 and protruding outwardly facilitates pivoting movement by a user. In a preferred embodiment, the handle 60 is a component of a spring loaded locking mechanism comprising a spring 61 (Figure 6) and a rotating wheel 62 (Figure 3) having two or more spaced apart notches 63 along its perimeter that engage with the handle 60.
When the pressure vessel 22 is in an upright position, the spring 61 places tension on the handle 60 facilitating engagement of the handle 60 with a notch 63 in the wheel 62 to secure the orientation of the pressure vessel 22. Pivoting of the pressure vessel 22 is accomplished by grasping the handle 60 and pulling the handle 60 out away from the vessel (against the tension of the spring 61) thereby disengaging the handle 60 from the notch 63 associated with upright positioning. The user may then pivot the vessel 22 in either direction. The degree of pivot can be established based on the preference of the user. Prototypes of the invention employed notches 63 at positions along the wheel allowing for 100 of rotation in each direction (i.e., 200 of total rotation). The amount of rotation may be adjusted by the user but 100 of rotation is recommended to facilitate easy removal of balls and movement of the vessel.
Alternatively, the handle 60 and locking mechanism may be secured to another movement source for automated movement, which connections and sources are well-known in the art.
The invention may include a series of storage vessels 23 (Figure 1) that are virtually identical to pressure vessel 22. The storage vessels may be appropriately plumbed to reuse gas released from the charging vessel 22 or they may be supplied with gas separately as appropriate.
Such storage vessels may be used to store recharged tennis balls at a desired pressure indefinitely. Normally balls are stored between 17- 22 psi (117-152 kPa) but could be stored at pressures anywhere from slightly above atmospheric to the limits of the pressure vessel.
Another embodiment of the invention is shown in Figures 7-9. This embodiment is similar to the embodiments shown in Figures 3-6. The primary difference between the two embodiments is that the pressure vessel 22 shown in Figures 7-9 does not pivot. Instead it is secured to a fixed base 72 and utilizes additional bolts 41 to secure the top 27.
Both the pivoting and stationary embodiments of the apparatus according to the invention are connected to a compressed gas supply 70, schematically represented in Figure 1. The gas supply 70 provides gas to the hollow interior charging chamber of the pressure vessel 22 and thus must be in at least intermittent fluid communication with the gas port 29 and the charging chamber of the pressure vessel 22. Preferably the gas supply 70 provides gas that has a molecular weight heavier than air (e.g., carbon dioxide) as discussed in more detail below.
Another benefit of the claimed system for recharging depleted tennis balls is the prevention of warping of recharged tennis balls. As noted in the background section above, other devices and methods for recharging depleted tennis balls are known.
However, those that attempt to recharge balls using bulk, batch processes (i.e., batches that typically include 50 or more tennis balls) often have the problem of producing warped tennis balls. In other words, the tennis balls leaving the process have one or more flat spots on them which make them unsuitable for further use as tennis balls.
At present it is believed that the warping is caused by at least two factors.
First, the initial compression of the balls upon the application of increased pressure causes the outer diameter of the balls to shrink which allows them to pack more tightly in the initial phase of the recharge cycle. As they regain pressure they return to their full shape which forces some balls against the edge of the wall where they develop flat spots. Second, it is also believed that the weight of the balls becomes a factor when large numbers of balls are recharged. In other words, when large numbers of balls are recharged the balls at the bottom of a large recharging chamber are flattened by the weight of the balls above.
Early prototypes of the current invention also experienced this problem. In these early prototypes the problem was overcome by agitating the balls at least once during the course of a recharging cycle. However, agitation adds another step to the recharging cycle so other means for preventing warping were explored. Accordingly, the system for recharging depleted tennis balls according to the invention also comprises various means for preventing warping of tennis balls during a recharging cycle.
One means of preventing warping of tennis balls in the system according to the invention is the previously described base 50 which pivotally supports the pressure vessel 22. Pivoting the pressure vessel (usually by about 45 ) during a recharging cycle has been shown to eliminate warping. This means of preventing warping is particularly applicable to large recharging systems (i.e., those systems capable of handling 3000 or more balls) because it transfers a portion of the overall weight of the ball load to the sides of the vessel rather than placing all of the weight on the balls at the bottom of the vessel. In addition, pivoting the vessel greatly aids in the removal of balls from the vessel by simply dumping them out.
Another means of preventing warping of tennis balls in the system according to the invention was developed by noticing a relationship between the diameter of the early prototypes and the amount of warping. Two early prototypes were built. The first pressure vessel had a 9 inch (22.86 cm) diameter and 18 inch (45.72 cm) height. The second vessel had a 12 inch (30.48 cm) diameter and 24 inch (60.96) height. Both produced warped tennis balls.
However, it was noticed that the degree of warping in the 12 inch (30.48 cm) diameter vessel was less than that seen in the 9 inch (22.86 cm) diameter vessel. Therefore a third prototype was built using a pressure vessel with a 20 inch (50.8 cm) diameter and a 36 inch (91.44 cm) height. The recharged balls from this prototype did not show signs of warping even when filled to capacity and in the absence of agitation. Thus there is a relationship between the diameter and/or height of the charging chamber of the pressure vessel and the degree of warping seen in recharged balls.
Accordingly, one means of preventing warping in the claimed system for recharging tennis balls is to design the pressure vessel 22 such that its hollow interior charging chamber possesses a diameter sufficient and a height sufficient to allow the tennis balls to recharge without warping.
Lastly, agitation, either through shaking, pivoting, or internal stiffing of the balls (using either automated or manual means known to those in the art) is a further means of preventing warping of tennis balls during a recharging cycle.
Turning now more toward the method according to the invention, of particular relevance to the present invention is Dalton's law. It says the total pressure of a gas is equal to the sum of the partial pressures of each of the component gases:

Ptotal = P1 P2 P3 = = = Pn If we consider air, this means the total atmospheric pressure of 1.013 bars (14.7 pounds per square inch absolute or 101 kPa) is the sum of the partial pressures of all its constituents:
nitrogen, oxygen, water vapor, argon, carbon dioxide, and various other gases in trace amounts.
In particular, air contains roughly 78% nitrogen, 21% oxygen, 0.93% argon, 0.04% carbon dioxide, and trace amounts of other gases, in addition to variable quantities of water vapor, which normally approximates 3%. The two most dominant components in dry air are Oxygen and Nitrogen. Oxygen has an atomic unit mass of 16 and Nitrogen has an atomic unit mass of 14.
Since both of these elements are diatomic in air - 02 and N2, the molecular mass of Oxygen is 32 and the molecular mass of Nitrogen is 28. Since air is a mixture of gases the total mass can be estimated by adding the weight of all major components as shown below:
Volume Ratio iMolecular Mass -Components in Molecular Mass in compared to Dry IM
Dry Air Air Air 1(kg/kmol) Oxygen 0.2095 32.00 16.704 1Nitrogen 0.7809 128.02 21.88 ,Carbon Dioxide 0.0003 144.01 10.013 1Hydrogen 0.0000005 12.02 0 lArgon 0.00933 139.94 0.373 1Neon 0.000018 120.18 0 iHelium 0.000005 14.00 0 1Krypton 0.000001 183.8 0 1Xenon 0.09 10-6 1131.29 0 1Tota1 Molecular Mass of dry Air 28.97 Water vapor H20 is composed of one Oxygen atom and two Hydrogen atoms.
Hydrogen is the lightest element at 1 atomic unit while Oxygen is 16 atomic units. Thus water vapor molecules have an atomic mass of 18 atomic units. At 18 atomic units, water vapor is lighter than diatomic Oxygen with 32 units and diatomic Nitrogen with 28 units. Thus, it is important to note that water vapor in air will replace other gases and reduce the total density of the mixture and hence dry air is more dense than humid air. Carbon dioxide (CO2) on the other hand has an atomic mass of 44.01, which is more dense than dry air at 28.97.
In the pressure vessel 22, carbon dioxide is preferably kept at about 60 psi (413 kPa) during charging. The introduction of multiple depleted tennis balls 30 introduces a quantity of air at atmospheric pressure (i.e. air at approximately 14.7 psi or 101 kPa).
The total quantity is dependent upon the number of tennis balls introduced but can be expected to be the number of tennis balls multiplied by the internal volume of each ball, which can be calculated based upon the formula: sphere volume = 4/3 = it = r3 = (it =d3)/6. The acceptable measurements for the external diameter of tennis balls according to the International Tennis Federation is 2.575 inches (6.54 cm) to 2.700 inches (6.858 cm) with the outer covering and internal rubber core having a thickness of approximated 0.125 inches (0.3175 cm). Thus, the appropriate diameter is approximately 2.7 inches (6.86 cm) and the internal volume of each ball is approximately 8.17 cubic inches (133.882 cm3). Fifty such balls would have an internal volume of about 408.5 cubic inches (6694 cm3). The pressure vessel volume is much larger.

The volume of a cylinder can be calculated using the formula: Volume = it = r2 = height = 1/4 = n = d2 = height. In one exemplary embodiment, the charging chamber 24 of a pressure vessel 22 has a radius of approximately 6 inches (15.24 cm) and a height of approximately 30 inches (76.2 cm). Thus, the volume of the charging chamber would be approximately 3391 cubic inches (i.e. 3.14 x 62 x 30) or 55568 cm3. Such a charging chamber can hold 50 or more tennis balls. These dimensions can be scaled to create larger systems. For example, a commercial model of the system according to the invention utilizing a pressure vessel approximately 6 feet (1.82 m) tall and 3 feet (0.91 m) in diameter can process around 5000 tennis balls per batch. Those skilled in the art will know the mathematical calculations necessary to design charging chambers of other sizes therefore they will not be demonstrated here.
Introducing fifty flat tennis balls 32 at atmospheric pressure into the charging chamber does not change the pressure or gas concentrations inside the chamber, which is already at ambient room conditions. After the balls are added, the pressure in the charging chamber 24 is increased to 60 psi (413 kPa) by introducing an appropriate quantity of pressurized carbon dioxide. As noted previously, the pressure within the chamber can be adjusted up or down depending on cost, time, and safety factors.
The added carbon dioxide initially fills the charging chamber 24, increasing the pressure throughout the charging chamber. Each of the tennis balls 32 acts as a small pressure vessel with permeable walls that the pressurized carbon dioxide gas must permeate over time. The internal pressure of each depleted tennis ball is usually around 14.7 psi (i.e. 1 atm or 101 kPa) but over time the pressurized carbon dioxide at 60 psi (413 kPa) will penetrate the tennis ball 32 exterior as well as the semi-permeable rubber core or internal wall and begin equalizing the internal tennis ball pressure with the chamber internal pressure. As the tennis ball internal pressure increases, the chamber pressure decreases accordingly. Over time (usually about 3 days at 60 psi), the internal tennis ball pressures will have risen from about 14 psi (96 kPa) to about 17 psi (117 kPa) while the chamber pressure will have decreased from 60 psi (413 kPa) to 57 psi (393 kPa). Thus, it is possible to monitor the status of the charging tennis balls by monitoring the decreasing pressure of the charging chamber 24 over time to determine when the balls are recharged.
It is also possible to monitor the amount of time that it takes an individual pressure vessel to recharge a number of balls. Since the invention may be practiced using multiple styles and shapes of pressure vessels the exact pressures and times used for one vessel may not be the optimum pressure and time for another vessel. Some vessels may have small leaks or the temperature of operation may change depending on where the vessel is located.
Accordingly, those skilled in the art will recognize that for any particular vessel at any given pressure and temperature there will likely be a period of time that is optimum for recharging balls to a desired internal pressure. For such circumstances the practitioner will likely rely on time within the vessel as the main factor for determining when to remove the balls.
It has been found that the number of tennis balls being recharged is not especially important in that 3 balls can be recharged in essentially the same time frame as 30 balls.
The steps for implementing the method according to the present invention include the following. The pressure vessel charging chamber 24 is empty and open and at ambient atmospheric condition. Several depleted tennis balls are then introduced into the charging chamber 24 through the opened removable top 27. Top 27 is closed and the chamber sealed. A
gas, preferably having a molecular weight heavier than air, and most preferentially carbon dioxide, is introduced into the charging chamber 24 through gas port 29. As additional gas is introduced, the pressure inside chamber 24 rises above 14 psi (96 kPa) (or whatever the ambient pressure is) and then above 17 psi (117 kPa). While feasible to operate at lower pressures, it has been determined through experimentation that practicable time periods (i.e.
less than 10 days) requires a chamber pressure of at least 40 psi (275 kPa) and more preferentially 60 psi (413 kPa).
Once the pressure chamber 24 is pressurized to the desired pressure (i.e. 60 psi or 413 kPa), the chamber may be subjected to a ball warping reducing step if needed.
For example, the pressure vessel 22 may be agitated to jostle the balls 30 inside the chamber.
Alternatively, the pressure vessel 22 may be pivoted. Through experimentation it was found that pivoting large pressure vessels (such as a 6 foot tall (1.8 m) by 3 foot (0.91 m) diameter commercial prototype) by about 45 degrees during a recharging cycle prevents warping of the balls.
The chamber pressure is monitored with a pressure gauge, which may be a permanent part of the pressure vessel 22 or used in conjunction with a gas port 29. As the chamber pressure decreases, the pressure inside the balls will increase correspondingly. Once a desirable pressure decrease has occurred (i.e. 3 psi (21 kPa) drop in the chamber pressure) a corresponding pressure increase in the balls will occur as well. Thus, for balls entering the chamber at 14 psi (96 kPa), once the chamber pressure drops 3 psi (21 kPa) the internal ball pressure should have increased from about 14 psi (96 kPa) to about 17 psi (117 kPa). Similarly, if the chamber pressure drops by 8 psi (55 kPa) the internal ball pressure should have increased to about 22 psi (152 kPa). The pressure and/or time inside the charging chamber is monitored until the balls reach the desired internal pressure. In most instances the balls will remain in the chamber until they have reached an internal pressure between about 17 psi (117 kPa) and 22 psi (152 kPa).

The pressure in the charging chamber 22 is then bled off through gas port 29 or another suitable port until at an acceptable level (i.e. 17-22 psi (117-152 kPa) for storage or atmospheric pressure if the chamber is to be opened).
From the foregoing, it will be seen that this invention well adapted to obtain all the ends and objects herein set forth, together with other advantages which are inherent to the structure. It will also be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Many possible embodiments may be made of the invention without departing from the scope thereof. Therefore, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention.

Claims (18)

1. A system for recharging depleted tennis balls, the system comprising:
a pressure vessel with a closed bottom and a spaced apart, selectively open top with an integral rigid wall extending therebetween and having a charging chamber adapted to receive tennis balls to be recharged through the top when open;
a gas port that is in fluid communication with the charging chamber; and a gas supply in fluid communication with the charging chamber wherein said gas has a molecular weight heavier than air.

2. A system according to claim 1 further comprising means for preventing warping of said tennis balls during a recharging cycle.

3. A system according to claim 2 wherein said means for preventing warping of said tennis balls comprises a base pivotally supporting the pressure vessel, said base including at least two spaced apart arms extending upwardly from the base and pivotally secured to the vessel above the base to permit pivotal movement of the vessel relative to the base; and a handle secured to the vessel and adapted to facilitate user pivotal movement of the vessel.

4. A system according to claim 2 wherein said means for preventing warping of said tennis balls comprises a charging chamber having a diameter sufficient and height sufficient to allow said tennis balls to recharge under pressure without warping.

5. A system according to claim 2 wherein said means for preventing warping of said tennis balls comprises means for agitating said tennis balls while they are within said hollow interior.

6. A system according to claim 1 wherein said pressure vessel further comprises a pressure gauge adapted to display vessel pressure.

7. A system according to claim 1 wherein said selectively open top is secured in a closed position by multiple bolts.

8. A system according to claim 1 wherein said charging chamber is capable of receiving at least 50 tennis balls.

9. A system according to claim 1 wherein said gas is carbon dioxide.

10. A method of recharging depleted tennis balls comprising the steps of :
filling a pressure vessel charging chamber by introducing a plurality of discharged tennis balls into the charging chamber while said chamber remains at ambient pressure;
charging said chamber by sealing said chamber and then increasing the internal pressure of said chamber by introducing a quantity of gas with a molecular weight heavier than air;
maintaining said balls within said chamber for a time sufficient for said balls to achieve a desired internal pressure; and relieving the internal pressure of said chamber after said balls reach the desired internal pressure.

11. The method of claim 10 further including the step of agitating the recharging tennis balls at least once while recharging.

12. The method of claim 10 further including the step of pivoting the pressure chamber while recharging the tennis balls.

13. The method of claim 10 wherein the gas is carbon dioxide.

14. The method of claim 10 wherein the pressure within the pressure vessel charging chamber is sufficient to raise the internal pressure of a recharging tennis ball to between 117 kPa and 152 kPa.

15. The method of claim 14 wherein the pressure is at least 413 kPa.

16. The method of claim 10 wherein said process is completed in less than 10 days.

17. The method of claim 10 wherein at least 50 tennis balls are introduced into said pressure vessel charging chamber.

18. A recharged tennis ball produced in accordance with the process of claim 10.