Keep your Tennis balls bouncing

The annoying issue with Tennis balls is, that after only a few days they start to lose their bounce. I was annoyed and intrigued this and used a modified pressure canner to reverse the process to revive old balls and keep them bouncing. The final result can store around 60 Tennis balls and keep them bouncing forever (or at least until the felt is completely worn off). In the following I will describe some specs of my homemade tennis ball pressurizer. 

Tennis balls are pressurized and over time air escapes from the inside and the pressure drops. That results is poorly bouncing balls and finally, us buying new balls.  If we can store the balls at a higher pressure, this process can be slowed and even reversed! That is what all this is about.

Some more background

The internal pressure of Tennis balls is about 14psi or 1 bar. If the ball hits the ground, the internal air is further compressed and acts as a spring leading to nicely bouncing balls. The problem is that the balls are not perfectly airtight – this means over time that internal pressure drops. This process is independent of us playing with the balls. It just happens. That is the reason why the ball canisters are pressurized, that way that pressure drop is prevented (until we open that can).

The bottom line is that even without us playing, the Tennis balls will get bad or dead after some time. That is in particular frustrating, as in most cases the felt of the balls is still quite good. It feels to be a waste to have to buy new balls even if the old ones still seem to be in decent shape.

So what if that process can be reversed?

As a matter of fact you can revitalize dead balls. The only thing you have to do is to increase the internal air pressure to a level as if they were new. Some internet research leads you to companies selling such devices. The Pressure Ball is one of those and I took the risk and bought it. It works really well, but I was annoyed by the process of fiddling balls in and out of the tube all the time. In particular if you have many balls this is really annoying. There are other products out there, that allow to pressurize many balls at once in a larger vessel. One of them is the Ball Charger, but the price is also much higher.

Inspired by the principle and that it actually works, I started out to build my DIY tennis ball pressurizer…

This shows how many balls fit in there.

What I am going to present in the following involves handling larger amounts of compressed air. That is potentially very dangerous and I do not guarantee that anything what I present is actually safe to do so. Proceed at your own risk. 

 The pressure vessel

The main problem for such a Do-it-yourself project is, to get a decent pressure vessel. The good thing is, that the pressure the Tennis balls require is relatively low.  They are stored at ca. 14 psi and Pressure Ball recommends to increase the pressure up to 20 psi in order to restore balls. So that is the basic requirement, an airtight container that can withstand up to 20+ psi and it is large enough to fit a decent amount of tennis balls. As it turns out getting a proper container is not that simple. There are pressure pots for painting, but they tend to be very expensive.

So I opted for another option, a 23 quart pressure canner from Amazon.


There are four holes in the lid of the canner that have to be prepared and finally make airtight. At first place they are closed by some plugs, but they are not built to be completely airtight. Therefore one has to tweak some of them a little…

1) The center hole is easy. Just screw in the pressure gauge and you are done. I was afraid that this one might not be airtight, but it is.

2) The air vent: This one should actually seal when there is internal pressure, but for me it did not. A quick fix was to add a layer of soft latex (I just cut a little bit of the Thera Band Exercise Band I had lying around), and added it as a sealing. That just works fine. In case that would not have worked, I would have just sealed that hole using silicone or something.

3) The vent pipe: This one provides a nice nozzle on which I put a pipe and a valve. I use this valve to depressurize the container.

4) The overpressure plug hole: This one is just too small to fit a quarter inch thread for the valve. I used a knive to scrape off some material to make it fit. This is really a matter of just a little bit until the valve went in. I used lots of teflon tape and a counter nut to fix and seal the valve. On this side I connect the bicycle pump. As the pump is not completely airtight, I have to close the valve once the pressurizing is complete.

see text for a description of the numbers

In the end it was pretty straightforward and as far as I can tell, having just used it overnight, the pressure vessel seems to be airtight.

Some more about safety

By doing this, there is nothing left to prevent overpressure. The only think that is between you and an exploding tank is your brains. When increasing the pressure watch the pressure gauge closely and do not put too much pressure in it. Be sure that the gauge is working properly. Even with a bicycle pump you can reach dangerous pressure levels! I cannot recommend you any pressure you can put into the tank safely. In the end that will depend on the pressure tank you use and how large you want the safety margin to be.  You will have to decide that yourself and I do not want to be held responsible for any exploding tanks.

If you test your device, fill it up with water as high as possible, that way the amount of compressed air is reduced and you might have less severe injuries if something blows up.

Do not, or if so super cautious, use a compressor to pressurize the vessel. By doing so you can easily increase the pressure to dangerous levels. They can easily produce super high pressures.

More pictures and the conclusion

So far I am happy with the result. The container is airtight and the handling seems to be good. The nice thing, compared to the Pressure Ball pipes, is that you just put in the balls and pressurize. No fiddling with balls in and out. I can even keep them in a bag, so I just grab the bag and I am good to go. To  pressurize the canner I need about 60 strokes of my bike pump. Not too bad. It takes some time, but is not crazy long.

And finally, the rest of the pictures:

27 thoughts on “Tennis Ball Pressurizer

  1. Hi, I would like to build this but I don’t know what kind of valve you used or how to find one like it. What is it called, and where can they be purchased?

    1. Hey,
      they are basically regular valves I bought from Home Depot or Lowes. Those are for actually for water piping, but are apparently also airproof. I guess that they are rated for much higher pressures which helps to make them airtight at those low pressures.

  2. Good article. For those who wants a ball-keeper than ball-repressurize, a sprayer from home depot or sears ($7-$9) would work and it’s safe:
    Since it leaks slowly, you may want to pump it every a few days if you really want to repressurize it. Depends on what type of sprayer you have, you may want a hollow, cylindrical spacer to keep the ball from blocking the pump handle pathway (it comes with its own simple pump).

  3. Hi
    Nice work. I also feel weird when discarding apparently good tennis balls but with no pressure. I’m also thinking to make a re-pressurizer like yours.
    Do you have any tips like what is the optimal pressure and how long it takes to repressurize one batch of balls?

    Thanks in advance

    1. Hey,
      so in terms of pressure – regular balls stored at +1 atmosphere, thas is 12 psi or so. I would roughly shoot for that.

      Repressurizing is a completely different story and I do not have quite an experience in that respect. I mainly used it to avoid losing pressure over time. But you I would expect it to take a couple of weeks, probably a similar time it would take new balls to lose pressure.


  4. Hi Tommi,

    Great project, that was in my mind recently after my friend bought a Gexco Tennis Ball Saver, it does not help much to keep more than 3 and it lost pressure.

    Your project seems great, I wish to build one too, but there is another question in my mind, will we over charge the ball pressure more than 1 psi? If that happen it might screw up your consistency of your tennis game right?

    Have you tested the ball with ATP regulation as following?
    Wiki: A ball is tested for bounce by dropping it from a height of 254 cm (100 inches) onto concrete; a bounce between 135 and 147 cm (53–58 inches) is acceptable

    let us know if you have the exact psi we should put on the tank, that’s will be a very good info, 20 psi as you suggest?


    1. Hey Andy,

      though I had already answered your comment, but apparently that was lost….

      In terms of consistency of the balls I did not care too much. I had this more to store my training balls and they are all kinds of brands and different levels of wear. Therefore they are already different to start with, so the difference due to slight pressure differences should be small.

      In terms of pressure, I would go with the pressure that is usually in a tennis ball. It seems that this is around 1 athosphere (14 psi if I am correct) but please check yourself. I never went far above that.

      One thing that I noted is that sometimes the tank is not 100% proof and will loose pressure over the course of some days. Sometimes this happens stronger, sometimes not at all. I suspect that the seal is sometimes not 100% right or something. Overall the tank was not made to be really airtight over long periods of time.

      Hope this helps,

  5. wish hole do you attach the bike pump to and how would I go about putting silicone on the one you talked about. As far as the vent pipe goes where do you get it and how much does it cost


  6. Hello.
    I would like to know, how many time I must to keep the ball with the 14 psi pressure?

    Best Regards!

    1. You mean for how long? That depends on the pressure level you have already in the balls, but it is rather a matter of days or weeks. Pretty much as quickly as the balls would loose pressure.

  7. Hello,
    Can you specify the fixation of the valve?
    How did you make to airtightness ?
    Best Regards!

  8. Hi

    I am definately going to make one of these as I have tried before with a plastic food storage barrel but the lid wouldnt hold 5psi without leeking.

    My question for you is, what size in litres is the pressure cooker you are using or the depth dimesions and how many balls does it hold?

    Thanks for your reply in advance

  9. Used the same pressure canner and left the overpressure plug in it’s place for the obvious overpressure protection and hose clamped a foot of 45 psi hose to the vent tube / pipe to a shut off / on valve , a dual tire inflator on the other end of the off / on valve & connected to a quick coupler attachment and used air compressor pressurized the can @ 21 psi. test all connection with soapy water it is a go

    it has been a few hours 12:24pm PST 6.3.2015 so far, so good and it is holding pressure


      1. Oh interesting. My feeling was that the overpressure plug would leak. Much better of you can keep it. How long does it take to get to 21 psi? And the safety plug is still in there at this pressure?

  10. Hi, A lot of people talk about their home made ball re-pressurizers loosing pressure over time!
    This is probably NOT the case!
    The pressure in the chamber surrounding the balls might be 20psi, the pressure in the quantity of used balls may be 10psi, the pressure between the chamber and balls is trying to balance out. As the ball pressure increases the chamber pressure decreases until equilibrium is achieved. Its a ratio of volume of air within the balls to volume of higher pressure outside!
    Hope this helps!

  11. Brilliant idea using a large canner. However, I made one much simpler. No modifications needed except to swap out the “air vent cover” with a basic stem valve for car tires. Cost me $11 for set of 4 on Amazon (only need one). Simply unscrew the vent and screw on the car stem valve. Step 2. You need to duct tape the inside and outside of the pressure relief value since it will release the pressure beyond 15 lbs/sq inch. Basically your covering up all the vent holes. The already supplied “pressure relief valve” seems to hold up so I’m not changing it. The pressure gauge measure only to 20lb+ but my bike pump has a pressure gauge so I’m not changing that either. Theoretically, the ideal pressure to pump is at the pressure just before the ball begins to cave in. This will minimize the time needed to repressurize the ball. If the ball collapeses, then it will never repressurize. So ideally, its best to repressurize balls in groups with the same flatness. Guideline is 24 hours at 30lbs/inch for fairly new balls. Completely dead balls at 15-18lbs and slowly increase pressure over time. May take a week to 2 months. Remember to group like balls otherwise, the caved in ones wont recover. Maintain correctly pressurized balls at 15lb. New balls come pressurized at 14lbs.

  12. Update. The canner was losing 2-3lbs of pressure per day. I added neoprene washers to the pressure gauge. I replaced the “pressure release” button with a 1/8″ Air Compressor SAFETY RELIEF POP OFF VALVE I purchased on Ebay. I used 3/8″ neoprene washers and attached them with a 7/16″-20 nut. Lastly I plugged up the other hole (pressure relief value) with neoprene washers using a screw and nut.
    Remember, I did no damage to the cover. No drilling bigger holes. Nothing. I can simply put back the original parts and sell as “like new”.
    However, it still leaked about 2lbs per day, so I added Vaseline to the large rubber gasket in the interior the cover. Its been 2 days at 21lbs. No pressure loss so far.
    So perhaps, just try to use Vaseline on the gasket and see if that solves any leakage by itself. Maybe it wasn’t not necessary for me to use the new parts. IDK, I already done everything so no need to experiment any futher. Let me know you experience.

    1. Hey,
      thanks for the update. I think I had similar problems of pressure loss. It kind of happened not always, but I think depended on how I put on the lid. Also added Vaseline and for sure was not a bad thing 🙂

      The last step, I never got around to do, would have been to add a compressor that just monitors pressure and turns on if needed. Using the bike pump got annoying over time. But never found a compressor that would stop at those pressures. If not you might build a bomb when the compressor overfills….

    2. Oh and one more thought: depending on the balls you had in, the pressure drop could also be going into the balls, repressurising them!

  13. Thanks so much for this guys. All I had to do was buy the tire valve stem from my local auto parts store (autozone), remove the vent cover, pull the tire valve stem through the vent cover opening, cover all the other openings that leaks air, and pump in 35psi (not recommended since that’s over the maximum limit by 15psi). I honestly think these canner can hold much more…but I’m not going to risk an explosion in my house..and I’m sure it would make the balls way too bouncy. While pumping to the 20-25psi, I can hear some of my old dead tennis balls pop like popcorn 🙂 I’m only pumping pass the 20psi mark because the canner gradually leak air…so until I find the proper fix….I have to keep pumping 25-30psi. It’ll last me a couple of hours before dropping to 10psi. My arms are looking GREAT for tennis with all this pumping haha

  14. I believe that tennis ball makers intentionally manufacture leaky balls so you have to continually buy new ones. There is no reason why a tennis ball should not have a storage life of 5+ years in a normal home at 1 bar. I have found that this “natural” leakage can be easily remedied by injecting new balls with starch, then removing the needle and sealing the hole with superglue, then shaking the balls to evenly distribute the starch. The starch finds its way to the microcracks, and seals them. Other safe chemicals may work just as well, such as baby oil. Any others? You can also inject dead balls with just air to bring them up to pressure, then seal the hole as above.

  15. I took an old aluminum pressure cooker and sealed all the valves. I bought a replacement tire valve an auto store and put it in one of the holes that was close to the diameter of the valve. Unfortunately the p cooker’s rubber seal didn’t seal enough for the pressure I needed. I had to bend the tabs on the pot at an angle so when I turned the lid on it would seal very tight. Also had to sand down the contacting surface where the rubber seal touch to a very smooth surface as to ensure the best seal. After trial and error I got the perfect seal. So to repressurize dead balls it must be at 30 to 35 psi and for 2 weeks. After they are back to correct pressure all you will need is to keep them at about 14 psi for storage.

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