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piston weight

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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piston weight

Unread postAuthor: no-limit » Sat May 24, 2008 6:50 pm

I'm making a new piston now but it's just under 8oz, is that to much? If so what is the ideal weight.
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Unread postAuthor: LikimysCrotchus5 » Sat May 24, 2008 6:59 pm

The lighter, the better, because its easier to actuate.
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Unread postAuthor: no-limit » Sat May 24, 2008 8:01 pm

So does that mean mine is to heavy, or to light?
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Unread postAuthor: jrrdw » Sat May 24, 2008 8:12 pm

no-limit wrote:So does that mean mine is to heavy, or to light?


Ether, or. If it works well, it's not to heavy in theory, but perhaps could be lighter. Unless there is a specific reason for it to be a certin weight, I wouldn't worry about it.
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Unread postAuthor: benstern » Sat May 24, 2008 8:13 pm

Depends on the size. What are the dimensions of your piston? If you can, please include a rough graphic of the piston and it's sizes.

Lighter objects require less energy to move them.
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Unread postAuthor: MrCrowley » Sat May 24, 2008 8:35 pm

Also the heavier the piston, the more force it will have when slamming into your bumper.
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Unread postAuthor: koolaidman » Sat May 24, 2008 8:39 pm

MrCrowley wrote:Also the heavier the piston, the more force it will have when slamming into your bumper.


Not neccesarily mr crowley, it will most likely have the same momentum.
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Unread postAuthor: bigbob12345 » Sat May 24, 2008 8:48 pm

koolaidman wrote:
MrCrowley wrote:Also the heavier the piston, the more force it will have when slamming into your bumper.


Not neccesarily mr crowley, it will most likely have the same momentum.


not true
It will have a good bit less momentum if the weight is less
Its like firing heavy ammo out of a cannon, it gets more ftlbs but it goes slower.
You see what Im getting at :wink:

I may be totally utterly wrong so correct me if I am.
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Unread postAuthor: koolaidman » Sat May 24, 2008 9:06 pm

[quote="bigbob12345] It will have a good bit less momentum if the weight is less
[/quote]

Well, momentum is Mass times velocity. So, if you are imparting the same force times time on the piston, which should remain somewhat consistent independent of "heaviness," then it will have the same momentum. So, when you say there will be less momentum because the weight is less, the velocity is actually going up because it is directly proportional. Muzzle energy is a little different
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Unread postAuthor: no-limit » Sat May 24, 2008 9:39 pm

It's for a 2" piston valve.
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Unread postAuthor: psycix » Sun May 25, 2008 6:29 am

koolaidman wrote:[quote="bigbob12345] It will have a good bit less momentum if the weight is less
[/quote]

Well, momentum is Mass times velocity. So, if you are imparting the same force times time on the piston, which should remain somewhat consistent independent of "heaviness," then it will have the same momentum. So, when you say there will be less momentum because the weight is less, the velocity is actually going up because it is directly proportional. Muzzle energy is a little different[/quote]


Because the heavier piston accelerates slower (same force on it, more mass to move) the pressure works on it for a longer time. It is indeed slower then a lighter one, but because of it takes force over a longer time, it gains more energy and slams in harder.
When m goes up, v goes down, but because of the longer t, the terminal velocity doesnt go down by much and it slams in hard.



Back on topic:
no-limit, that piston looks a bit long and thus heavy, but it will work just fine.
If you really are going for optimum performance:
Cant you cut it in half?
And if that makes you have too much pilot volume, either fix that by cutting off pipe, shoving in the seating pipe further or adding a bumper that takes up volume.
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Unread postAuthor: no-limit » Sun May 25, 2008 6:18 pm

I don't think I can cut it in half because it will not be long enough to stay in the pvc that I put in to join the T with the end piece. If I drill out the T more so that the piece goes in farther in the T it will start cutting off the chamber part. I could extend the barrel father in to go about half way into the T but didn't think that was good to do.

So again, 8 oz is to much. So if I do get it down to half in size that should make it about 4 oz, is that best?
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Unread postAuthor: jrrdw » Sun May 25, 2008 9:15 pm

The barrel is sapossed to be half way into the tee.
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Unread postAuthor: clide » Sun May 25, 2008 9:40 pm

I wouldn't worry too much about your piston weight. Unless you are making it out of solid lead it probably won't produce a measurable change in performance.
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Unread postAuthor: no-limit » Sun May 25, 2008 9:55 pm

Supposed to be half way into the tee. Now that's an answer.

Don't worry about the weight? Could it be possible that's correct? Hope so.

Now how about 8 oz and loose fitting?!!
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