Pressurized Air tank - bag

September 10, 2007 10:33 AM

I want to put tennis balls in a tank/bag that I can pressurize to about ~20-30 psi (perhaps more). Do you know where I can find such a tank(or what it would be called) for a reasonable price (less than $50) ? It should be able to hold at least 30 balls. Used would be fine.
posted by tallpaul to sports, hobbies, & recreation (10 comments total)

30 balls sounds like quite a volume, and most air tanks aren't going to have an opening that big. I suggest you look at surplus yards for old autoclaves. They are big and very heavy, but that's good whenever you're dealing with pressure. Also, they usually have a large door/opening since they are meant to hold objects not just air.

Plan B would be to make something yourself out of some shedule 80 PVC.
posted by Rhomboid at 11:10 AM on September 10, 2007

Uhm, what in god's name are you going to do with this contraption? I mean, just curious, and it would help to know why you want to pressurize the balls.

8" Sch 80, with cleanouts and caps, drill and tap a hole in one cleanout cap for a scrader adapter, and one of those cigar-lighter tire pumps ought to do it.
posted by notsnot at 11:17 AM on September 10, 2007

Yeah I was going to say PVC as well. You could get some SCH40 in 4" dia and cement on some endcaps and a cleanout (might have to search to find a cleanout that's actually SCH40 and not drainwater) and you should be able to pressurize that. Just don't stand too close.

If you do find an autoclave -- paricularly one of the older stovetop types -- make sure it's one that can do high-temperature sterilization. A high-temperature autoclave, according to Wikipedia, gets up to 134C, which corresponds to a pressure of 3.0 bar (44 psia). That's 30 psig, just barely.

Unfortunately I don't think that a regular kitchen pressure cooker will do the trick; most of them are only designed to take about 125C/15psig. I'm not sure I'd want to overpressure one to find out what sort of safety margin they were engineered with.

The only other thing that came to mind is the filter tank on a pool filtering system. Some of the ones for large pools may be built to withstand significant pressure. On a small above-ground pool, I know mine has a gauge that reads to 15psi. Maybe if you hunt you can find one that's designed for 20 or 30...?

Regardless of what you choose, before you compress it with air or steam, I encourage you to pressure test it using water first. (Fill the vessel completely full with water and then pressurize that from an external source to somewhere above your redline.) Something bursting from water is a lot more pleasant / less deadly than one with steam or air behind it. (Particularly steam, but I'm figuring you're not going to be using that.)
posted by Kadin2048 at 11:33 AM on September 10, 2007

You can get 30psi easy in a tire mounted on a wheel. A 16.5" wheel doesn't have an inner bead so it's really easy to break loose (essentially just let the air out). And they often have a deep profile so you should be able to squeeze the balls between the unmounted tire and rim. Lots of 16.5" truck tires will handle 65psi.
posted by Mitheral at 12:20 PM on September 10, 2007 [1 favorite has favorites]

I too am curious as to the purpose of exposing tennis balls to 20-30 psi.

If the goal is merely to see what happens to them, then one might consider taking them to a lake and sinking them in 60 feet of water.
posted by rlk at 2:01 PM on September 10, 2007

Basically, I want to use this "contraption" to "repressurize" my practice tennis balls. Standard pressure for a tennis ball is 14.7 psi (twice sea level). If I put them in at 20 psi, they should be go to go in about 3-4 days.
posted by tallpaul at 2:23 PM on September 10, 2007

Is the volume of 30 tennis balls less than 4.5 gallons? If so, go to a homebrew shop and get a used soda keg. I got mine for $25. It's made to withstand higher pressures than 30psi and has an easy to close, easy to seal lid with an aperture that will easily accomodate a tennis ball.
posted by plinth at 5:19 PM on September 10, 2007

Mitheral - that's the kind of genius I love. I wish I could favorite that twice. A couple of truck tires. So obvious, but... not.
posted by ctmf at 8:18 PM on September 10, 2007

Do you need to repressurize all 30 balls simultaneously? If you're fine with 3 balls at a time, you can get a gadget from some tennis shops that will do the job. You fill one half with the tennis balls, then screw the other half on. There's an airtight seal and the pressure goes up as you screw it down.

I don't remember what this gadget is called. Ask around, but not all shops will carry them or tell you about them since obviously it's in their interest to carry on selling you more balls.
posted by randomstriker at 6:46 PM on September 11, 2007

Thanks for all the advice. The soda thing sounded interesting, but the hole seems to be too small (at least from what one vendor told me).

The PVC solution was also very interesting, but pricing it out it became more expensive than my final solution.

The tire thing, it seemed would not work as while that may exert 30+ PSI on the balls it seems that it would not push air into the balls, or maybe it just did not understand the concept. A tire would take up a lot of room in my apartment.

By putting the tennis balls in an environment with an air pressure of 20-30 psi the air gradually seeps back into the balls, thus restoring their bounce.

My final solution was to buy a 2+ gallon weed sprayer with a built in hand pump for $30. I'll probably add a schrader valve for faster filling. It pumps up to about 20 psi.

The gadget from the tennis stores only pressurizes to 14.7 psi, and it only holds 3 balls. It actually does a very poor job of rejuvenating the balls.

I did not checkout autoclaves too extensively,
posted by tallpaul at 8:16 PM on September 17, 2007