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A place to ask general spud cannon related questions.
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Unread postAuthor: saefroch » Tue Oct 26, 2010 2:32 pm

No doubt on his credentials, it's just one of those things that's generally accepted as dangerous, except for those who are involved in it.... Like spudgunning :D

And to note, I'm referring to rapping, not his knowledge of pneumatic propulsion.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 26, 2010 6:21 pm

saefroch wrote:No doubt on his credentials, it's just one of those things that's generally accepted as dangerous, except for those who are involved in it.... Like spudgunning :D

And to note, I'm referring to rapping, not his knowledge of pneumatic propulsion.


He was reporting the words of Dennis Quackenbush who certainly makes better air riflesthan the vast majority of spudguns on this site, so I wouldn't dismiss the advice out of hand.

My point is if you're going to be doing this on a regular basis, you might want to consider a more efficient multi-stage design like spudamine's excellent creation - but they're your wrists, if it's comfortable for you then don't let me tell you what you should or shouldn't do ;)
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Unread postAuthor: saefroch » Tue Oct 26, 2010 7:14 pm

The hands and wrists still work perfectly fine, I can assure you. Some people work out by doing "clappers" instead of push-ups, which ought to apply a much greater load to the wrists, but I've never seen anyone say anything about damage to the wrists from that.

Yeah, now go find a link and prove me wrong. :roll:

With all due respect, I don't see any advantage of spudanime's creation over mine. He's feeding lower pressure air into the second stage, and the second stage has a larger diameter.

Likely the greatest advantage he has over me is weight. :P
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 26, 2010 7:19 pm

saefroch wrote:With all due respect, I don't see any advantage of spudanime's creation over mine. He's feeding lower pressure air into the second stage, and the second stage has a larger diameter.


You've got it backwards, his animation shows the stroke cycle quite clearly - both cylinders pressurise the air initially on the upstroke, then the smaller cylinder pressurises this air further on the downstroke.
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Unread postAuthor: saefroch » Tue Oct 26, 2010 7:52 pm

No, I don't have it backwards, and I did read the thread and stare at that animated gif for a while. I get his design. My comparison was from his to mine. Let me remedy this:

With all due respect, I don't see any advantage of spudamine's creation over mine. He's feeding lower pressure air than I am into the second stage of his pump, and the second stage in his pump has a larger diameter than the second stage in mine.

Unless my calculations are vastly wrong.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 26, 2010 8:12 pm

Thanks for rephrasing, I hadn't realised you were now injecting compressed air into your pump.

It would be interesting to see to what extent the upstroke pressurises the air in spudamine's design.
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Unread postAuthor: Technician1002 » Tue Oct 26, 2010 8:12 pm

To me, it looks like the second stage is getting >4 Bar at the end of the upstroke.. I need to do the math to find out how much greater it is than one bar.

At the bottom of the stoke the inlet to the second stage is indeed near 1 bar. It is considerably higher at the end of the upstroke.
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Unread postAuthor: saefroch » Wed Oct 27, 2010 6:47 am

I estimated that he has a compression ratio, entirely based on the diameters of his pipes, of 22:15, which gives an approximated 22psi from the first stage which seems incredibly low, considering I use on average 75psi.

I did notice that he used two o-rings the top of his pump to seal, I'll try adding another and see if I get a 100% reliable seal there.

This should all really be in the comments of this thread. Feel free to comment there instead of here. Or a mod could merge the threads.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 27, 2010 6:57 am

saefroch wrote:I estimated that he has a compression ratio, entirely based on the diameters of his pipes, of 22:15, which gives an approximated 22psi from the first stage which seems incredibly low, considering I use on average 75psi


I figure that's incorrect in as much as the ratio should be based on volume and therefore the ratio is more like 12:5 so the pressure from the first stage should be more like 45 psi, still low compared to your injection pressure but higher than 22 psi.
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Unread postAuthor: saefroch » Wed Oct 27, 2010 4:44 pm

Wow I'm a dunce. Yeah, r^2 not d. :oops:
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Unread postAuthor: Hotwired » Thu Jan 20, 2011 9:14 pm

jackssmirkingrevenge wrote:
saefroch wrote:I would say Tom Gaylord is somewhat unqualified to be writing about such.


In spite of his uninspiring family name *chuckle* he's actuallyquite an authority on the subject.


The only bit of that page I found interesting was the notion that airguns lose power when you charge the reservoir too high.

That's entirely the reverse of how a dump valve as used in pneumatics here works but hammer valves are only intended to open against a certain chamber pressure.
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 20, 2011 11:54 pm

Hotwired wrote:The only bit of that page I found interesting was the notion that airguns lose power when you charge the reservoir too high.


Somewhat off-topic and an old post, but pretty much what we were saying here ;)
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