To those of you who repressurize tennis balls - which settings do you use?

[FatHead250]

For fresh balls to lose about half of its pressure it takes at least over than a month, maybe even two. If airfill speed has linear dependency on pressure difference, it means that to repressurise a ball at 1.4 atm pressure in a 1.8 atm (fresh ball pressure) tank its going to take more than 3 or 6 months. It seems barely viable.

What is your experience, how long does it take?

When setting the tank to more than 1.8 atm, you risk ripping the balls. Does anybody do higher than 1.8 atms? What are you pressure-time observations?

 

[travlerajm]

https://tt.tennis-warehouse.com/index.php?threads/supercharged-3-ball-tennis-ball-pressurizer.670729/

 

[socallefty]

Even if the repressurized ball is bouncy, isn’t it much harder to control them with topspin as their felt is gone compared to new balls? Sometimes when the hard court I play on is very dirty on a windy day, the fluff gets chewed up by all the grit within 3-4 games. After that the ball plays weird as it is bouncy like a new ball, but doesn’t take spin well because of the loss of felt. Is that what these repressurized balls play like?

 

[FatHead250]

Even if the repressurized ball is bouncy, isn’t it much harder to control them with topspin as their felt is gone compared to new balls? Sometimes when the hard court I play on is very dirty on a windy day, the fluff gets chewed up by all the grit within 3-4 games. After that the ball plays weird as it is bouncy like a new ball, but doesn’t take spin well because of the loss of felt. Is that what these repressurized balls play like?

Im going to repressurise balls with good felt on them. I dont play on coarse hard courts

 

[travlerajm]

Even if the repressurized ball is bouncy, isn’t it much harder to control them with topspin as their felt is gone compared to new balls? Sometimes when the hard court I play on is very dirty on a windy day, the fluff gets chewed up by all the grit within 3-4 games. After that the ball plays weird as it is bouncy like a new ball, but doesn’t take spin well because of the loss of felt. Is that what these repressurized balls play like?

When using Penn heavy duty, they go thru a cycle:

Phase 1. Play like new for first 20 minute.

Phase 2. The felt initially fluffs up more, which creates more air drag, so the spin rate slows down in the air more. The net result is less bend in the air and slower ball flight. Points are longer because it’s harder to hit winners.

Phase 3. The felt wears back down to the initial roughness height. The balls play more similarly to a new ball at this stage, but the rotational moment of inertia is a little lower, so spin rate still slightly less than brand new.

Phase 4. The felt is pretty much gone, with patches of crispy glue layer showing. The balls fly much faster thru the air, and play much more lively than new. Spin rate similar to new because lower air drag compensates for lower moi. Much easier to hit winners.

 

[Injured Again]

For fresh balls to lose about half of its pressure it takes at least over than a month, maybe even two. If airfill speed has linear dependency on pressure difference, it means that to repressurise a ball at 1.4 atm pressure in a 1.8 atm (fresh ball pressure) tank its going to take more than 3 or 6 months. It seems barely viable.

What is your experience, how long does it take?

When setting the tank to more than 1.8 atm, you risk ripping the balls. Does anybody do higher than 1.8 atms? What are you pressure-time observations?

It takes a couple of weeks to revive noticeably low bouncing balls to near-new height using 32 PSI over atmospheric pressure. Some balls revive more quickly than others, but strangely those balls also seem to retain their bounce more. I've got both US Open and Dunlop Championship balls in a corny keg right now and the US Open balls regain their normal bounce in about 10-12 days, while the Dunlop balls take about a week longer. But, the US Open balls also lose pressure more slowly in play so I'm not sure the mechanism for this.

32 PSI is about as high as can be used. I've gone a bit higher and can hear some balls collapsing. I've also tried lower pressures, like around 20 PSI over atmospheric, and all that happens is the existing bounce is retained and only barely improves even after a couple of weeks.

Even though the balls have the same level of bounce when dropped straight down, used repressurized balls play more slowly. I believe the repeated hitting of the ball work hardens the rubber so it's energentically more lossy and especially more lossy the more the ball is deformed. You have to swing harder to get the same ball speed off the strings, and the forward bounce doesn't carry as far. This is perfect as a proxy for playing on slower courts, and this is the primary reason I repressurize balls. Our club's courts are on the faster side and I need to get used to much slower courts like are used for age group tournaments in warmer weather areas.

 

[Injured Again]

Even if the repressurized ball is bouncy, isn’t it much harder to control them with topspin as their felt is gone compared to new balls? Sometimes when the hard court I play on is very dirty on a windy day, the fluff gets chewed up by all the grit within 3-4 games. After that the ball plays weird as it is bouncy like a new ball, but doesn’t take spin well because of the loss of felt. Is that what these repressurized balls play like?

On the indoor and outdoor courts we have up here in the Pacific NW, the surface isn't gritty enough to really wear down the felt on the higher quality balls. For most balls, it takes usually about four to six hours to really chew up the felt to the point where just the imprinting is haggard looking. The balls after a hard 90 minute session aren't really that worn.

Many folks from my club spend the winters down in the palm desert area. One guy in particular who almost never wears out shoes up here says he's gone through two or three pairs in four months. I can believe it - I've only once had the opportunity to play when I was down at Indian Wells and any of the courts down there are like sandpaper.

 

[socallefty]

With me the effect is opposite and similar to playing with poly. While poly has a lower launch angle and offers more control compared to soft strings, it allows me to swing out more and keep the ball in the court - I end up hitting with more pace as a result. The SnapBack effect that allows more spin also helps me to swing out harder and keep the ball in the court.

Similarly, I prefer when the ball fluffs up slightly as I can swing freely and keep the ball in the court - this leads to harder shots/serves and more winners for me. When the ball is brand new or old with the felt gone, it flies out more easily and I have to control my swing - so, I play more conservatively and end up hitting less winners and being less aggressive.

That‘s why I don’t like balls after they lose their fluff. I play with ED ProPenn, Penn Tour or rarely Dunlop AO - I prefer them to the lighter Penn Championship balls with lighter felt. I’ve noticed that players who slice a lot and use finesse prefer lighter balls while heavy spin hitters like premium balls with more felt.

 

[travlerajm]

It takes a couple of weeks to revive noticeably low bouncing balls to near-new height using 32 PSI over atmospheric pressure. Some balls revive more quickly than others, but strangely those balls also seem to retain their bounce more. I've got both US Open and Dunlop Championship balls in a corny keg right now and the US Open balls regain their normal bounce in about 10-12 days, while the Dunlop balls take about a week longer. But, the US Open balls also lose pressure more slowly in play so I'm not sure the mechanism for this.

32 PSI is about as high as can be used. I've gone a bit higher and can hear some balls collapsing. I've also tried lower pressures, like around 20 PSI over atmospheric, and all that happens is the existing bounce is retained and only barely improves even after a couple of weeks.

Even though the balls have the same level of bounce when dropped straight down, used repressurized balls play more slowly. I believe the repeated hitting of the ball work hardens the rubber so it's energentically more lossy and especially more lossy the more the ball is deformed. You have to swing harder to get the same ball speed off the strings, and the forward bounce doesn't carry as far. This is perfect as a proxy for playing on slower courts, and this is the primary reason I repressurize balls. Our club's courts are on the faster side and I need to get used to much slower courts like are used for age group tournaments in warmer weather areas.

Interesting observations. But the explanation that the rubber gets more lossy would defy the laws of physics. The energy return of rubbers goes up, not down, with repeated stress cycling.

More likely, the balls get softer, so that more of the collision energy at impact goes into ball flattening. Since balls have lower energy return than the strings, the ball impact is less energy efficient. In addition to lower power level, a softer ball will make it easier to apply spin. So spin to power ratio should increase.

 

[J011yroger]

Man, I just grab a handful out of the teaching cart and start playing. If one breaks I throw it out.

J

 

[FatHead250]

It takes a couple of weeks to revive noticeably low bouncing balls to near-new height using 32 PSI over atmospheric pressure. Some balls revive more quickly than others, but strangely those balls also seem to retain their bounce more. I've got both US Open and Dunlop Championship balls in a corny keg right now and the US Open balls regain their normal bounce in about 10-12 days, while the Dunlop balls take about a week longer. But, the US Open balls also lose pressure more slowly in play so I'm not sure the mechanism for this.

32 PSI is about as high as can be used. I've gone a bit higher and can hear some balls collapsing. I've also tried lower pressures, like around 20 PSI over atmospheric, and all that happens is the existing bounce is retained and only barely improves even after a couple of weeks.

Even though the balls have the same level of bounce when dropped straight down, used repressurized balls play more slowly. I believe the repeated hitting of the ball work hardens the rubber so it's energentically more lossy and especially more lossy the more the ball is deformed. You have to swing harder to get the same ball speed off the strings, and the forward bounce doesn't carry as far. This is perfect as a proxy for playing on slower courts, and this is the primary reason I repressurize balls. Our club's courts are on the faster side and I need to get used to much slower courts like are used for age group tournaments in warmer weather areas.

If you leave balls for too long in 32 PSI above atm, do they burst?

Also, im not sure how it is that in 20 psi the balls only retain bounce, when the pressure in a fresh ball is 12 psi. So, surely, 12 psi should be enough to retain and slowly regain bounce.

Are you sure your manometer is working properly?

 

[Nate7-5]

I use 2 tubes at pressureball.com to keep 8 hard court and 8 clay balls at 15psi during the summer and use them for maybe 6-8 hours over a few weeks - pretty cost effective at that point if you buy a case of balls. Reviving flat balls seems difficult but it would be nice to use them to fill up a crate for practicing serves.

 

[Injured Again]

Interesting observations. But the explanation that the rubber gets more lossy would defy the laws of physics. The energy return of rubbers goes up, not down, with repeated stress cycling.

I'd love a citation for this. In every field that I've been involved in where I've had to the opportunity to read peer reviewed research, such as in track cycling's hour record, rolling resistance increases over time due to work hardening of the rubber as the tire rolls. The rubber gets stiffer as it strain hardens, meaning for the same force, the material deforms less. But restitution is also affected because that restitution must now work against a stiffer material. So energy losses increase.

More likely, the balls get softer, so that more of the collision energy at impact goes into ball flattening. Since balls have lower energy return than the strings, the ball impact is less energy efficient. In addition to lower power level, a softer ball will make it easier to apply spin. So spin to power ratio should increase.

No, the balls aren't softer. They bounce equally as high as new balls, and probably have a slightly greater internal pressure, but they come off the strings and off the court much slower than new balls. I've experienced this multiple times, when we've used both freshly repressurized and brand new balls at the same time. They bounce the same for a drop test but they play significantly differently.

 

[Injured Again]

If you leave balls for too long in 32 PSI above atm, do they burst?

Also, im not sure how it is that in 20 psi the balls only retain bounce, when the pressure in a fresh ball is 12 psi. So, surely, 12 psi should be enough to retain and slowly regain bounce.

Are you sure your manometer is working properly?

No, the balls don't burst. If you left a ball under 32 PSI over atmospheric for a couple of months, it would have significantly higher internal pressure than a new ball and probably bounce much higher.

The rubber in a tennis ball is a few mm thick. This means that there is some resistance to perfusion that takes a significant over-pressure to overcome in the time frames we're talking about. If you had a year, probably even a couple of PSI over the internal pressure would equalize, but who wants to take a year?

The pressure gauge on the corny keg I bought is very accurate. I have multiple tire pressure gauges certified accurate to within 0.5 PSI and the corny keg's gauge is accurate to within that margin up to 35 PSI.

 

[travlerajm]

I'd love a citation for this. In every field that I've been involved in where I've had to the opportunity to read peer reviewed research, such as in track cycling's hour record, rolling resistance increases over time due to work hardening of the rubber as the tire rolls. The rubber gets stiffer as it strain hardens, meaning for the same force, the material deforms less. But restitution is also affected because that restitution must now work against a stiffer material. So energy losses increase.



No, the balls aren't softer. They bounce equally as high as new balls, and probably have a slightly greater internal pressure, but they come off the strings and off the court much slower than new balls. I've experienced this multiple times, when we've used both freshly repressurized and brand new balls at the same time. They bounce the same for a drop test but they play significantly differently.

Here is an example of how repeated impacts on an elastomeric polymer results in a material with increased energy return. All elastomeric materials have reduced hysteresis in the stress-strain curve with cycled stress.

http://twu.tennis-warehouse.com/learning_center/deadstringsPart2.php