My understanding is the time it takes to revive balls. Days for C02 or weeks for regular air.
My Tennis Ball Pressurizers
- Thread starter WilsonPlayer101
- Start date
My understanding is the time it takes to revive balls. Days for C02 or weeks for regular air.
WilsonPlayer101
Professional
I never tried CO2 but from what I heard is that CO2 pressurizes the balls in a shorter amount of time.
happyandbob
Legend
why would CO2 pressurize faster than air? CO2 is a bigger, heavier molecule than N2 or O2 (the primary components of air). Pressurized air would penetrate tennis ball rubber faster than CO2, I would think.
Pressure Refresher | Tennis Ball Repressurizer CO2 Charging Kit - 20 LB CO2 Cylinder
This kit includes a freshly reconditioned, hydrostatically tested and painted 20 lb CO2 cylinder and a new dual guage Taprite CO2 regulator with a fill line and a schrader valve fill nozzle for easy pressurizing of our tennis ball repressurizer unit. Kit Includes: 20 lb. CO2 Cylinder - may not...
pressurerefresher.com
happyandbob
Legend
Thanks, but that just seems to be a company selling corny kegs and compressed CO2 tanks. I'm not seeing anything at that link that says CO2 gas pressurizes tennis balls faster than compressed air at the same pressure.Pressure Refresher | Tennis Ball Repressurizer CO2 Charging Kit - 20 LB CO2 Cylinder
This kit includes a freshly reconditioned, hydrostatically tested and painted 20 lb CO2 cylinder and a new dual guage Taprite CO2 regulator with a fill line and a schrader valve fill nozzle for easy pressurizing of our tennis ball repressurizer unit. Kit Includes: 20 lb. CO2 Cylinder - may not...pressurerefresher.com
I think the reason they are selling co2 tanks because I haven't seen anyone selling pressurised air except very small cans. It doesn't make any sense that co2 could revive faster. Under the same pressure, regular air should penetrate the rubber faster as it contains smaller molecules overall as @happyandbob stated.Pressure Refresher | Tennis Ball Repressurizer CO2 Charging Kit - 20 LB CO2 Cylinder
This kit includes a freshly reconditioned, hydrostatically tested and painted 20 lb CO2 cylinder and a new dual guage Taprite CO2 regulator with a fill line and a schrader valve fill nozzle for easy pressurizing of our tennis ball repressurizer unit. Kit Includes: 20 lb. CO2 Cylinder - may not...pressurerefresher.com
Ya, he just says 2-3 days with the CO2. I bought a Pressure Refresher from him and it takes 2-3 weeks to fully refresh balls with air. Notice he says to go to 40 PSI. This is what I found to be about right myself too by trial and error. This is why most other things don't work. They can't get up to 40 PSI (I'm thinking about that long plastic tube thing and other similar ideas). That would be good for "maintaining" pressure. But it's not going to revive balls that have been around for a bit.
But I can't verify how fast CO2 is. I just figured he knew what he was talking about
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happyandbob
Legend
You'll never revive dead balls using 40 psi, no matter what gas you're using. Fully dead balls flatten and invert at around 25 psi. Once they flatten, they won't gain any internal pressure no matter how long you keep it pressurized.
Not sure what his baseline is or how dead the balls were for his 2-3 day claim. You can take a one session used ball and revive with regular air at 25 lbs in just a day or two. There's nothing special about CO2, it's just pressure differential and how quickly the gas penetrates the rubber.
If you have really dead balls, you have to do it in stages. A few weeks at 20-25 PSI. Then a few weeks a bit higher and so on, until you get the bounce you want. But on these, you do have to crank up the pressure to 40 PSI in the final stages, to get them back to normal. Not sure that it's really worth reviving "dog balls", but I've done it.
If you have "old balls" but not "dog balls" (so just somewhat soft), then you go to right around 30 PSI and finish at 40 PSI. But you're right. I've crushed some going too high too soon and ruined them. There's a bit of an "art" to doing all of this. You get to know your ball and know about what PSI you should be using.
If you have balls you just opened and played with today, then they won't be dead at all. Just put those in at 15-20 PSI to maintain. At 20 PSI, they aren't going to get too bouncy or get crushed. You can of course repressurize them too far. They're too bouncy.
The 40 PSI is just what I keep my current use ball machine balls at. You'd think you could keep them at a lower pressure. But 40 PSI does seem to work the best.
I honestly have no idea about CO2. You might be right.
Hulger
Semi-Pro
We just bought an 18-liter keg with my friends. Attaching the ball-lock connector and further attaching it to the bike valve extension hose was a breeze. We pumped it all the way up to 35 psi using a bike pump, and some of the balls seemed to collapse judging by the sounds, but I reckon most of the 60 balls will come out intact and firm. Still waiting on the results of the 2-week incubation. 
Hulger
Semi-Pro
We still haven’t taken out those aforementioned balls, but even 20 psi obtained by a different ball pressurizer seemed to revive balls used for 4 hours, which were previously unplayably soft and didn’t allow much shaping of the trajectory. They are still a tad softer than new balls but bounce at least as well. Also, interestingly, they don’t lose their bounciness after a couple of serves like new balls tend to do.We just bought an 18-liter keg with my friends. Attaching the ball-lock connector and further attaching it to the bike valve extension hose was a breeze. We pumped it all the way up to 35 psi using a bike pump, and some of the balls seemed to collapse judging by the sounds, but I reckon most of the 60 balls will come out intact and firm. Still waiting on the results of the 2-week incubation.
Some dough and environmental savings ahead!!!
austintennis2005
Professional
What about all the felt wearing off? Seems if you like tennis $3 for a can of new balls is not very much to pay
For me, I play on dirty outdoor courts. So even new balls with new felt gets dirty and old pretty fast. New balls aren't new for very long.
I still open a can of balls for playing even semi-serious tennis. But I don't mind repressurized balls for rally practice.
WilsonPlayer101
Professional
You are correct, once the felt is worn off the balls are no good. $3 plus take I can afford but I suppose if I can get more life out of a ball, say the initial use and pump them up 2 more times then the $3.30 balls cost $1.10. I think the felt is good for two times in the pressurizer. So yeah tennis balls I can easily afford but I like to get more use.
WilsonPlayer101
Professional
At Costco they have air filling stations for you to pump up your tires. My understanding is they use CO2. I may bring my water filter pressurizer and try to see if I can fill it with CO2. I am a Costco member and spend tons of money there, buy tires there also, so I think filling my tennis ball pressurizer there is not unreasonable, especially since I don't ever pump my tires there but use my air compressor at home, so to fill a ball pressuriizer makes up for not filling my tires there. I'll pump to about 24. Usually I do 34 but at Costco I'll try 24.
I think Costco uses Nitrogen
austintennis2005
Professional
Dirty balls with all their felt are different than having all the felt worn off, to me.
If you buy the premium usopen or the top of the line Penn the pressure and felt will last much longer
WilsonPlayer101
Professional
Thanks. Now that you mention it that sounds right what you say.
stapletonj
Hall of Fame
With Wilson US Opens at $110. per case plus shipping, repressurizers are feasible
110 plus 10 is 120,
sales tax of say $10. 130.
130 divided by 24 is $5.41 per can, or $1.80 per ball
110 plus 10 is 120,
sales tax of say $10. 130.
130 divided by 24 is $5.41 per can, or $1.80 per ball
travlerajm
Talk Tennis Guru
Once I solved the pressure problem with my juiced-up, void-filled 3-ball saver, I found I could get 3x x 2h singles sparring sessions with my regular hitting buddy before the felt got bald enough that it was time for different balls.
But instead of switching to new, I would switch to pressure-rejuvenated old balls that still had perfectly good felt.
$$ savings that covid 2020 season when I played a lot of tennis was great.
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WilsonPlayer101
Professional
Good point.
So if I use the balls three times by using the initial opening, then pump them up two times I get to use them at 60 cents per ball or $1.80 per can if you look at it as a can after each use. Then if the felt is bad after the third use, at least I paid only $1.80 per can.
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Injured Again
Hall of Fame
Back to the question from a few weeks back about CO2 - it perfumes into and out of the ball faster because CO2 is more soluble than Nitrogen or Oxygen. If you’ve ever used a CO2 inflator for a bicycle tire, it will lose probably a third of its pressure overnight. Regular air probably loses only 5% overnight.
Repressurized balls bounce forward slower than a new ball even if they have the same bounce height. This is great for us northern tier players who typically play on faster hard court surfaces than the outdoors courts in the south, as playing with repressurized balls helps getting acclimated to slower surfaces.
i typically open two cans of USO extra duty balls and can play three 90 minute sessions of drill/hitting and sets before the felt is too worn. I played at Indian Wells a couple of years ago and the felt was history after two hours. There’s no way that ball was playable after that time even if it bounced fine.
Repressurized balls bounce forward slower than a new ball even if they have the same bounce height. This is great for us northern tier players who typically play on faster hard court surfaces than the outdoors courts in the south, as playing with repressurized balls helps getting acclimated to slower surfaces.
i typically open two cans of USO extra duty balls and can play three 90 minute sessions of drill/hitting and sets before the felt is too worn. I played at Indian Wells a couple of years ago and the felt was history after two hours. There’s no way that ball was playable after that time even if it bounced fine.
travlerajm
Talk Tennis Guru
Yes. And nitrogen leaks slower than air.
The ideal would be a ball filled with 70% sulfur hexafluoride 30% air, but this won't happen soon for a variety of reasons:
A very simple way to pressurize balls is to:
1. Take a premade ball saver
2. Drill a hole and insert a schrader valve
3. Use a hand pump with a pressure gauge to pump it up
This is also convenient because you can use the cap of the schrader valve to release the pressure and it's easy to open the can safely. Minimal equipment and space needed - I keep it all in my bag. FYI, apparently my tennis ball saver was only doing ~8psi, not the advertised 14psi... now I pump it up to 20psi right after a session and it only drops 1psi every few days (I don't know what the can is rated for, especially with a hole drilled into it, so I'm uncomfortable going beyond 20psi).
A very simple way to pressurize balls is to:
1. Take a premade ball saver
2. Drill a hole and insert a schrader valve
3. Use a hand pump with a pressure gauge to pump it up
This is also convenient because you can use the cap of the schrader valve to release the pressure and it's easy to open the can safely. Minimal equipment and space needed - I keep it all in my bag. FYI, apparently my tennis ball saver was only doing ~8psi, not the advertised 14psi... now I pump it up to 20psi right after a session and it only drops 1psi every few days (I don't know what the can is rated for, especially with a hole drilled into it, so I'm uncomfortable going beyond 20psi).
WilsonPlayer101
Professional
For my water filter pressurizers I put in about 38 and it seems to work. It still takes two weeks. My Korny Keg I don't use much but 38 to 40 also is the way to go. I still want to try Nitrogen in mine.
travlerajm
Talk Tennis Guru
Have you tried accelerating the process by venting often?
The pressure on the gauge outside the chamber will be staying at 38 psi, but the driving pressure (ie, the difference in pressure between the void space outside the balls, and the pressure inside the balls, quickly drops to very poor efficiency within a few minutes unless you vent it to reset).
By venting every couple of minutes at stoplights on the way to my tennis session, I can turn a 2-week repressurization into 20-minute one.
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travlerajm
Talk Tennis Guru
When doing my iterative venting, the first several vestings release a strong hiss of the vacuum being released.
When I get closer to fully pressurized, the hiss goes away.
WilsonPlayer101
Professional
No, I was not aware of this method. Great idea. Thanks for the hack.
I don't quite understand how to do it. Can you please give me step by step instructions how to do this? Thanks!
WilsonPlayer101
Professional
WilsonPlayer101
Professional
WilsonPlayer101
Professional
travlerajm
Talk Tennis Guru
With my can, I simply unscrew it (to vent) and then screw it back down to repressurize. For your Korny Keg device, I assume you can open and reclose it similarly.
Since, the balls are compressible, the balls shrink smaller under the pressure, so the pressure inside the balls is only slightly less than the 40 psi pressure in the void space outside them, with that difference roughly equal to the compressive stress in the rubber. As the air leaks across the rubber ball wall from outside to insure, the balls grow in size, causing the small pressure difference to drop to almost nothing (and the stress in the rubber also relaxing) within a few minutes.
By venting repeatedly, you can recharge the pressure difference to maintain the strong enough driving pressure to compress the ball size back down.
In theory, you might be able to accomplish the same thing by simply stepping up the pressure gradually to maintain driving pressure without collapsing the balls.
WilsonPlayer101
Professional
Went to Costco to try to fill my water filter ball pressurizer with nitrogen at the self service tire inflation kiosk. It didn't work. I set the pressure for 34 and attached the "chuck" to the inflation valve but the compressor didn't kick on. So it was no bueno and I went home to inflate it with my air compressor which worked. Was using my clear purple pressurizer and put it up to 40 yet no balls collapsed. 40 is a bit much, 34 is all I need, but I did 40 nonetheless. I play once a week so next week my friend will bring a new can and we will use those and I will pressurize those in the white pressurizer and the following week and use the balls I am pressurizing now.
I once tried to inflate bike tires at Costco and the machine didn't kick in. Not sure why but it just doesn't work for anything other than car tires.
I once tried to inflate bike tires at Costco and the machine didn't kick in. Not sure why but it just doesn't work for anything other than car tires.
Injured Again
Hall of Fame
The tennis balls do not compress down to equalize their internal pressure with the external pressure. If they did as you suggest, you would easily visibly see the balls expand in size when you open a new can of balls in the tubes with are pressurized to 12-14 PSI over atmospheric pressure.
PV=nrT says that pressure and volume are linearly and inversely related, such that when you double the pressure, the volume halves since the right side of that equation doesn’t change. There is no way the volume of the ball halves, much less decrease even 5%, when you double the external pressure on the ball.
Injured Again
Hall of Fame
During the worst of the ball shortage about 18 months ago, I purchased some of those terrible Penn Championship balls. When I was able to shortly after buy my usual Wilson USO balls, these sat on the shelf. I recently opened up a can and found they had only about 70% of the bounce of a USO ball so I threw them in my Corny Keg and kept it under 30 PSI for about three weeks. That seemed to do the trick. They bounced as high as a USO ball but still had less forward bounce distance. Still, it made them playable for a full 90 minute practice session.
I had some more cans so I did the same, but instead used more pressure hoping to get the balls pressurized faster. I put 40 PSI and checked after two weeks but they still didn’t have the same bounce as the ones with three weeks at 30 PSI. After another week at 40 PSI, they felt just like the first batch that saw 30 PSI. So it seems both 30 and 40 PSI produced the same effect after three weeks. Since permeability of air through rubber depends on the pressure, the ball’s internal pressure should be higher when under 40 PSI so maybe higher internal ball pressures have diminishing returns after some point.
I still have a few cans of the Penn Champ balls so maybe I’ll see if 2 1/2 weeks at 40 PSI works.
travlerajm
Talk Tennis Guru
Your Saturday afternoon physics equation is forgetting a key element of the pressure balance.
Injured Again
Hall of Fame
Your Saturday afternoon physics equation is forgetting a key element of the pressure balance.
Always willing to learn. What is “pressure balance”? A google search brings up pressure measurement devices and shower heads.
Hulger
Semi-Pro
If you had a 14 psi ball in an enviroment where the pressure is the same, the ball would feel ”pressureless.”
Injured Again
Hall of Fame
I’m pretty sure that’s not what @travlerajm is getting at because his contention is that tennis balls change their size to equalizer internal and external pressure, and that’s why his “venting” method can repressurize a ball within an hour whereas a tennis ball pressurizer takes two weeks.
My understanding is that if a ball is going to change volume to equalize pressure, it would obey PV=nrT And since the nrT side is constant, the pressure and volume linearly and inversely must change. The volume of a sphere is 4/3*pi*r^3 so even releasing the pressure from a new tube of balls should result in a visible size change. That’s when @travlerajm brought up “pressure balance”.
I’m all for finding a faster way to repressurize balls since I only have one corny keg and using it for two weeks puts it out of commission for daily use unless I want to constantly be pumping it up, and my laziness won’t let me do that.
Hulger
Semi-Pro
Here’s how I would see the process:
The repressurization in the vessel occurs slowly through the wall of the ball due to the porous nature of rubber, while they flatten due to external pressure as long as there's a pressure difference remaining and equilibrium isn't reached. In practice, the external pressure needs to be over 27 psi for balls to ever reach their original pressure, and the process may benefit from re-pumping the vessel, as depending on the balls' initial pressure, some of the vessel's pressurized air moves slowly into the balls, decreasing the vessel's air pressure. In pressurization, theoretically, these small pores collapse inward under significant pressure differentials, further flattening the balls and possibly preventing air from entering the balls. Thus, gradually increasing the vessel's pressure might be the most efficient. However, there must also be theoretical limits on how much pressure a ball can withstand when the external pressure is returned to atmospheric pressure because the stretching of the wall increases the rubber's permeability to air. Finally, the increase in ball size does not occur in the pressure vessel until the pressure is released, and I interpreted this enlargement of repressurized balls as simply related to the balls wearing out and losing their elastic properties when subjected to stress associated with large pressure differentials, especially during impacts of the gameplay.
The repressurization in the vessel occurs slowly through the wall of the ball due to the porous nature of rubber, while they flatten due to external pressure as long as there's a pressure difference remaining and equilibrium isn't reached. In practice, the external pressure needs to be over 27 psi for balls to ever reach their original pressure, and the process may benefit from re-pumping the vessel, as depending on the balls' initial pressure, some of the vessel's pressurized air moves slowly into the balls, decreasing the vessel's air pressure. In pressurization, theoretically, these small pores collapse inward under significant pressure differentials, further flattening the balls and possibly preventing air from entering the balls. Thus, gradually increasing the vessel's pressure might be the most efficient. However, there must also be theoretical limits on how much pressure a ball can withstand when the external pressure is returned to atmospheric pressure because the stretching of the wall increases the rubber's permeability to air. Finally, the increase in ball size does not occur in the pressure vessel until the pressure is released, and I interpreted this enlargement of repressurized balls as simply related to the balls wearing out and losing their elastic properties when subjected to stress associated with large pressure differentials, especially during impacts of the gameplay.
travlerajm
Talk Tennis Guru
This is a fun math problem, and it’s not trivial to solve. It’s in the wheelhouse of my technical background.
I’ll tackle in more detail when I have some free time.
I’ll tackle in more detail when I have some free time.
travlerajm
Talk Tennis Guru
Not going to try to solve it now, but my goal in solving is to show from the analytical modeling side why I have empirically observed that a bungee-cord stuffed 3-ball saver can rejuvenate a half-dead set of balls within 20 minutes by venting iteratively, when the process requires several days without the iterative venting, and requires 6-8 weeks without the bungee stuffers.
Key Considerations:
The cylindrical 3-ball vessel is made from deformable hard plastic, probably polycarbonate. Its volume expands upon pressurization. In fact, the ends of the cylinder visibly deflect multiple mm, so that the vessel teeters on the bulged end when stood upright.
The balls are made from deformable rubber, probably polybutadiene. The wall thickness starts out about 5mm, too thick for thin-wall assumptions. The diameter of the ball changes with the pressure gradient across the wall. And the wall thickness can also change, and the stress condition within the wall can in turn impact the permeability.
Even though the volume of the tennis balls probably isn’t changing all that much (because the rubber has high modulus), the ratio of the volumes outside:inside the balls can be very different at different steps, going from:
1. open unscrewed config.
2. Freshly screwed in config.
3. quasi-equilibrated config several minutes after venting.
This means the driving pressure maybe can change several fold rapidly, amplifying the impact of the iterative venting.
The spherical balls are not perfect spheres, so the critical buckling pressure under external pressure comes into play. The fact that I was unable to revive completely dead balls on my one attempt all but proves this. Fully dead balls would need to be revived in stages, and it should be possible to calculate the optimal protocol for that.
Key Considerations:
The cylindrical 3-ball vessel is made from deformable hard plastic, probably polycarbonate. Its volume expands upon pressurization. In fact, the ends of the cylinder visibly deflect multiple mm, so that the vessel teeters on the bulged end when stood upright.
The balls are made from deformable rubber, probably polybutadiene. The wall thickness starts out about 5mm, too thick for thin-wall assumptions. The diameter of the ball changes with the pressure gradient across the wall. And the wall thickness can also change, and the stress condition within the wall can in turn impact the permeability.
Even though the volume of the tennis balls probably isn’t changing all that much (because the rubber has high modulus), the ratio of the volumes outside:inside the balls can be very different at different steps, going from:
1. open unscrewed config.
2. Freshly screwed in config.
3. quasi-equilibrated config several minutes after venting.
This means the driving pressure maybe can change several fold rapidly, amplifying the impact of the iterative venting.
The spherical balls are not perfect spheres, so the critical buckling pressure under external pressure comes into play. The fact that I was unable to revive completely dead balls on my one attempt all but proves this. Fully dead balls would need to be revived in stages, and it should be possible to calculate the optimal protocol for that.
I have a case of "Costco Penns" that I can't get repressurized. I bought them from someone for 50 cents a can because they didn't bounce and he didn't want them. I've had them in my Pressure Refresher for many, many weeks trying different pressures from 30 lbs to 50 lbs. I've only had 1 break under pressure. But none of them have repressurized at all. They all bounce like rocks. Any ideas on what to try?
Incidentally, I've always maintained that "Costco Penns" can't be different from anything else (how could they). But I've had dead Costco Penns like this before and I've never seen dead balls like this from anywhere else. I can't imagine why this could be the case.
travlerajm
Talk Tennis Guru
In addition to the analytical math fun, I want to find some fresh bungee material and do some tests to see if I can go from 100% dead to fully revived in my saver can.
I suspect the key is that you have to ramp up the external pressure from zero extremely gradually to avoid buckling the ball shells.
Let me know what you find out
I have the exact same experience with Penn Championships I have lying around from the pandemic. They've lost pressure but repressurize at 30-40 lbs in my Pressure Refresher.
But not the Costco Penns. Funny thing is, they feel very pressurized (in fact, over pressurized). But they don't bounce. I don't understand it.
I don't understand the part when you say nrT is constant. If you are talking about the pressure and volume inside ball, nrT cannot be constant because when the pressure is higher outside the ball, air keeps going inside the ball nrT will keep increasing with the volume.
travlerajm
Talk Tennis Guru
Both n and T are changing.
I would assume the temperature change negligible though.
