'Repressurizing' tennis balls

FranzS

Rookie
Did anyone try to put old, depressurized tennis balls into a pressure vessel or something to restore the original pressure inside them?
Did it work?
How long did it take to fully 'repressurize' them?
 

Injured Again

Hall of Fame
It depends on the ball. Higher quality balls that go flat slower take a longer time to re-pressurize. In any event, you're looking at a week or two before you get any significant re-pressurization. I've once tested some once used Dunlop Championships (third or fourth tier ball) and US Open (top tier ball) at 25 PSI for a week. The Dunlops were noticeably softer than new when I put them under pressure and after a week almost got back to new bounce height. The US Opens were barely softer than new and felt just about like new after a week.

The rubber core of the ball undergoes some degradation when the balls are played. Even a fully re-pressurized ball doesn't feel as supple as a new ball, though they're more than good enough for practice.
 

Tennisist

Semi-Pro
1) I was never able to re-pressurize balls that are "far-gone" to a playable condition.

2) However, I made an interesting discovery recently.

For somewhat used balls, when I put them in the pressurizer, I could never raise the pressure above 20 PSI -- the balls would collapse.
If you keep them like this for a day, and then try to play, they will be "broken" balls.
However, if you keep the pressure at 20 PSI for a day or two, you can come later and add more pressure -- and the balls would not collapse.
Several days later -- add even more pressure. In the course of a week ( we had a heat wave ), I was able to raise the pressure to 35 PSI.

When we tried to play with these balls, they had a bounce noticeably higher than a normal, freshly opened can.
In fact, the bounce was so high, that both I and my partner preferred not to use these "bouncy" balls, and use the normal ones instead.

This is just to show that if you raise the pressure gradually , you can indeed increase the bounce of the old balls, and quite a bit!
 

travlerajm

G.O.A.T.
1) I was never able to re-pressurize balls that are "far-gone" to a playable condition.

2) However, I made an interesting discovery recently.

For somewhat used balls, when I put them in the pressurizer, I could never raise the pressure above 20 PSI -- the balls would collapse.
If you keep them like this for a day, and then try to play, they will be "broken" balls.
However, if you keep the pressure at 20 PSI for a day or two, you can come later and add more pressure -- and the balls would not collapse.
Several days later -- add even more pressure. In the course of a week ( we had a heat wave ), I was able to raise the pressure to 35 PSI.

When we tried to play with these balls, they had a bounce noticeably higher than a normal, freshly opened can.
In fact, the bounce was so high, that both I and my partner preferred not to use these "bouncy" balls, and use the normal ones instead.

This is just to show that if you raise the pressure gradually , you can indeed increase the bounce of the old balls, and quite a bit!
This has been my experience as well. I can get used balls to bounce significantly higher than fresh new balls within a few days by adding volume filler (rings of bungee cord) to a 3-ball screw-down pressurizer can and venting daily to recharge the pressure.

The limiting factor for ball life longevity with my supercharged repressurizer is that the felt wears completely off, even though the pressure is still great.

I still haven’t gotten around to seeing whether I can recharge a fully dead ball to new, because I’ve been using my pressurizer on daily basis for my matches.
 
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Injured Again

Hall of Fame
This has been my experience as well. I can get used balls to bounce significantly higher than fresh new balls within a few days by adding volume filler (rings of bungee cord) to a 3-ball screw-down pressurizer can and venting daily to recharge the pressure.

The limiting factor for ball life longevity with my supercharged repressurizer is that the felt wears completely off, even though the pressure is still great.

I still haven’t gotten around to seeing whether I can recharge a fully dead ball to new, because I’ve been using my pressurizer on daily basis for my matches.
There is no way you can change the pressure inside a ball within a few days by that extent, unless you're using some gas soluable in rubber like CO2. If it were possible to permeate air into a ball that quickly, the balls would also go flat as quickly after opening if they just sat there, and they don't. A few times, I've mistakenly opened a can of balls only to find they weren't needed, and a couple of days later they still bounced like new.

For a used tennis ball, you have to over-pressurize it to get it bounce the same as a new ball. That's because the rubber undergoes elastic strain hardening as it is hit, and that lessens the bounce height for the same internal pressure.

I use a PressureTube, inflated to 25 PSI. For a few days, it basically only works as a pressure maintainer. It is at least a couple of weeks before it makes a noticeable difference in bounce height, and even then the elastic strain hardening means the ball still doesn't play like a new ball, but like I said in my first post, they still work fine for practice.
 
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