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Squash Ball Piston?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Squash Ball Piston?

Unread postAuthor: kydavies » Tue Mar 13, 2012 11:38 pm

I was reading a thread about lapped pistons and for some reason it occured to me that a squash ball (racket ball) fits very nicely inside 1.5" sch 40 PVC and might make a decent piston. If I remember correctly from the last time I used squash balls as ammo there was about 0.5mm gap between the PVC and the ball. So why not take advantage of that and make a small piston gun that requires next to no machining or time (not that it takes much but some of us are fairly tool and time restricted) to get up and running.


EDIT: the only problems I see is the piston compressing due to external pressure and maybe a bit of frictional loss.
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Unread postAuthor: dewey-1 » Wed Mar 14, 2012 7:51 am

A racketball has OD of 2.25 inches.
A squash ball has OD of 40mm +/- .5mm. (1.555 to 1.594 in)

!.5 inch SCH 40 ID is 1.590 in (1.558 to 1.622 in)
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Unread postAuthor: pneumaticcannons » Wed Mar 14, 2012 8:11 am

The ball would get a lot smaller under the pressure's you would be using... The question is weather it would re-inflate quick enough after the pilot is vented as to permit a ton of piston blow-by. :? I'd try it if I lived in pvc land( the states) which I don't. Maybe you could make a small scale model with $5 worth of pvc
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Unread postAuthor: evanmcorleytv » Wed Mar 14, 2012 8:39 am

pneumaticcannons wrote:The ball would get a lot smaller under the pressure's you would be using... The question is weather it would re-inflate quick enough after the pilot is vented as to permit a ton of piston blow-by. :? I'd try it if I lived in pvc land( the states) which I don't. Maybe you could make a small scale model with $5 worth of pvc


I'd like you to come to PVC land.. It's magical haha
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Unread postAuthor: cfb_rolley » Wed Mar 14, 2012 8:43 am

I guess you could try it, but I also think it'll deform out of shape under pressure. A solid rubber ball may actually work though.
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Unread postAuthor: kydavies » Wed Mar 14, 2012 12:41 pm

I've never played racket ball... When the squash ball deforms under pressure it will flatten and it's diameter expand on the z and y axis and shrink in the x axis because the sealing face (I know the whole thing is a sealing face but I'm referring to the part sealing against the barrel at the time) is not under pressure (not trying to squish the ball). Il give this a try with some spare parts and "free" PVC




EDIT: I could fill the squash ball with water but I was hoping for a light piston
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Unread postAuthor: Crna Legija » Thu Mar 15, 2012 1:01 am

I don't know anything about them balls but if hollow or cellular the hole dia will shrink
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Unread postAuthor: Insomniac » Thu Mar 15, 2012 4:11 am

They are hollow. I get the feeling it will deform and attempt to squeeze into the barrel.
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Unread postAuthor: Gun Freak » Thu Mar 15, 2012 10:13 am

You could poke a hole in it so it equalizes :lol:
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Unread postAuthor: cfb_rolley » Fri Mar 16, 2012 6:38 am

Gun Freak wrote:You could poke a hole in it so it equalizes :lol:


good point, but it'd have to be a decent hole otherwise it won't drop pressure as quickly as the pilot chamber, and then expand due to the lower external pressure and jam itself in there until it does equalize.

...long story short it's probably a better/easier idea to just make a proper piston.
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Unread postAuthor: Gun Freak » Fri Mar 16, 2012 6:24 pm

If the hole is the perfect size the ball may act as a check valve piston, expanding enough upon piloting to prevent backflow :D
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