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Need a simpler solution to piston valve problem

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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Unread postAuthor: MrCrowley » Sat Sep 27, 2008 4:59 pm

Is that a clean out cap on the cannon? (second to last picture top right)

As far as I am aware, you can't buy those pressure rated. Feel free to correct me anyone but I'm pretty certain.

Some of your fittings also have the 'DWV look' but you can buy pressure rated fittings that look like DWV fittings so as long as they have NSF-PW on them they should be fine.

Apart from that, nice cannon, quite unorthodox but judging by the damage it can unleash, no one's complaining :D
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Unread postAuthor: Velocity » Sat Sep 27, 2008 6:47 pm

jackssmirkingrevenge wrote:
PotatoNick wrote:Where I disagree with you is the reason for having lift of up to .50d(or any value greater than .25d) . I don't believe that much, if any, piston bounce occurs during the time a projectile is in the barrel because you have so much force constantly being applied from the pressure pushing the piston backwards I would think that it would more than cancel out any opposing force from the very low spring rate of PVC.


I used to agree religiously with that view, however my change of heart is explained in reasonable detail here.


I think that it is important to note that you were using pressures well above 125 PSI (you used a high of 400 PSI to prove your point), which is usually the standard maximum pressure to be used in a PVC pneumatic. Your figures at 100 PSI, while not completely convincing (considering the disparity between the greatly upscaled size of your larger launcher and the relatively low gains), seem to show that piston bounce is not a huge factor at lower pressures. Besides, there must be some other mitigating factors when you compare a spudgun of one size to a spudgun of another, especially in this case, where the weight of the piston probably exceeds the weight of your entire gun :wink:

EDIT: Just some more thoughts

clide wrote:To reduce bounce you would want to decrease the size of the piston relative to the barrel...Which also has the benefit of making the gun more efficient.


Also, considering that piston bounce was related to the "honking" of a sprinkler valve in that thread that you provided, it would suggest that a larger pilot valve was needed. However...I don't think that is the case in this situation (piston valve being actuated by a piston valve being actuated by a sprinkler valve).

...I can't believe I needed to look up how to fix "honking" in a sprinkler valve...man it has been a LONG time since I used one.
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Unread postAuthor: McThunderThighs » Sat Sep 27, 2008 8:48 pm

Yes that is a cleanout cap, on the back of the barrel.

The 4" fittings are PW, no worries.

We were shooting tennis balls straight up today on one valve again (one of the gaskets on a piston came off). We were getting about 9 to 12 second hang times (about 200 ft/s muzzle velocity) discounting air resistance. Thats heights of about 600 ft. Not too impressive, but I can't wait to sync the pistons and then see what we can do!

[youtube]http://www.youtube.com/watch?v=Omh38105h0w[/youtube]

Thanks!
-MTT
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Unread postAuthor: starman » Sat Sep 27, 2008 11:11 pm

I'm thinking that even if you do get the valves syncing perfectly, You aren't going to realize significant if any power increase shooting tennis balls.

I do question the wisdom of shooting this thing in plain sight suburbialand.
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Unread postAuthor: McThunderThighs » Sat Sep 27, 2008 11:18 pm

We just have to make it work with tennis balls, that wont be what we shoot for fun. In fact some 2 kilo shots are curing tonight. I expect that the additional time the 2 kilo cans are going to see in the barrel is going to let that second valve do some work.

3 of 4 cardinal neighbors are FBI (no joke, we couldn't even think of having a party here). They all came out in turn and had a good laugh. One donated a cucumber for play time later. I'm not to worried about pissing anyone off, or a cop driving up, this far out of the city and you don't see any black and whites.
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Unread postAuthor: frankrede » Sun Sep 28, 2008 12:05 am

McThunderThighs wrote:One donated a cucumber for play time later
*snickers*
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Unread postAuthor: starman » Sun Sep 28, 2008 12:39 am

McThunderThighs wrote:3 of 4 cardinal neighbors are FBI (no joke, we couldn't even think of having a party here). They all came out in turn and had a good laugh. One donated a cucumber for play time later. I'm not to worried about pissing anyone off, or a cop driving up, this far out of the city and you don't see any black and whites.


All it takes is for a busy body neighbor to call you in, and they will have to investigate. Just be careful.

Yeah I'm with Frank....what the heck you got going on with the cucumber anyway? 8)
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Unread postAuthor: mark.f » Sun Sep 28, 2008 8:54 am

[blunt]
That's a bad practice. Could get an infection.
[/blunt]

I love this launcher except for the DWV, but that topics been thrashed dead and gone so let's forget it. Nice cannon!
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