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Brand new pneumatic/explosion

A place to ask general spud cannon related questions.
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Brand new pneumatic/explosion

Unread postAuthor: daxspudder » Sun Jun 15, 2008 5:11 pm

Okay, there have been some horrible stories about pneumatics blowing up. This isn't one of those stories. My cannon is all 2" sch40, with a 1" modified sprinkler valve, set to fit all the barrels from my combustions.

Today the cement had finished curing on my new/first pneumatic, so I went out and bought a new BELL brand bike pump. I pumped my gun up twice to 20psi, twice to 40psi, twice to 60psi, it fired a barrel full of water great... then while pumping up to 80, an explosion followed immediately by chest pain. The pump exploded and shot the rammer into my chest knocking the wind out of me. Luckily it was bought at walmart and will be returned asap...

On another note, I'm using a modified sprinkler valve, and whenever I go to recharge, the diaphragm is not resetting easily, it takes fast pumping to 20psi to get it to set correctly. Anyone have any suggestions? ... the spring is in place properly...
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"<I>For dare to be peace, I have to keep at it everyday, da Man doesn't take days off so neither can I</I>" -<B>Bob Marley</B>, day before a performance, a day after being shot in the chest. "<I>If you are the big, big tree, we are the small axe, ready to cut you down!</I>" -Bob again :brave:
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Unread postAuthor: DYI » Sun Jun 15, 2008 5:18 pm

Today the cement had finished curing on my new/first pneumatic, so I went out and bought a new BELL brand bike pump. I pumped my gun up twice to 20psi, twice to 40psi, twice to 60psi, then while pumping up to 80, an explosion followed immediately by chest pain. The pump exploded and shot the rammer into my chest knocking the wind out of me. Luckily it was bought at walmart and will be returned asap...



Roughly the same thing happened to Brian the Brain, but it was with a homemade pump at about 1100 psi... It almost removed a lot of his teeth, if I remember correctly.

I use the El Cheapo (not real name :roll: ) 160psi bike tyre pump from Canadian Tire. Only 15 bucks a pop, and they only fail when you over pressurise them. Considering all the horror stories I've heard about cheap pumps, those things are downright amazing, and worth purchasing if you live in Canada.

You didn't state the chamber volume of your launcher, but I'm assuming that the pressure isn't rising fast enough to seat the diaphragm. Attach another smaller chamber to the back that can be pumped up, and then dumped through a ball valve. This will seat the 'phragm immediately, and you won't have to waste as much air as you are currently.
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Unread postAuthor: D_Hall » Sun Jun 15, 2008 5:24 pm

DYI wrote:You didn't state the chamber volume of your launcher, but I'm assuming that the pressure isn't rising fast enough to seat the diaphragm. Attach another smaller chamber to the back that can be pumped up, and then dumped through a ball valve. This will seat the 'phragm immediately, and you won't have to waste as much air as you are currently.

Or just buy an air compressor. Decent compressors for our purposes can be had for well under $100.

Example: http://www.harborfreight.com/cpi/ctaf/d ... mber=95275
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Unread postAuthor: DYI » Sun Jun 15, 2008 5:39 pm

An air compressor would kill portability though, and a small gun like this is obviously meant to be portable.

Of course, if it's meant to be attached to a vehicle or fired in your back yard, a compressor is a much better long term solution.
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Unread postAuthor: D_Hall » Sun Jun 15, 2008 5:58 pm

DYI wrote:An air compressor would kill portability though, and a small gun like this is obviously meant to be portable.


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Unread postAuthor: potatoflinger » Sun Jun 15, 2008 6:13 pm

Another thing you could do is add a ball valve (same size as your sprinkler valve) between the sprinkler valve and the chamber of your gun. You could just close the ball valve, fill up the cannon's chamber, then open the ball valve so that the air from the chamber seats the valve. Then when you go to fire the gun, you just leave the ball valve all the way open so that it doesn't constrict flow. (This is similar to what DYI said, but a different way of implementing it)
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Unread postAuthor: Fnord » Sun Jun 15, 2008 6:27 pm

Stay away from bell if you can. They weren't that bad until maybe 5 years ago, but after that they started making them cheaper, and I've had so many problems I just stopped buying them. I took a pipe wrench to the last one I had to keep myself from fixing it again (and having it break again 10 mins later).
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Unread postAuthor: pizlo » Sun Jun 15, 2008 7:02 pm

D_hal a pity that reg is 60 bucks... My gun is similar, and my phram would not seal. Try removing the white perforated disc thing on the diaphragm.
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Unread postAuthor: DYI » Sun Jun 15, 2008 8:05 pm

D_hal a pity that reg is 60 bucks... My gun is similar, and my phram would not seal. Try removing the white perforated disc thing on the diaphragm.


Why's it a pity that the rig is amazingly cheap?

I'm not a huge fan of using denser than air gases in pneumatics, but to each his own I guess.
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Unread postAuthor: daxspudder » Sun Jun 15, 2008 10:24 pm

I have no idea my chamber volume yet, but roughly 180ci+some connectors... Im thinking of putting a removable schrader valve on my blowgun so I can pressurize the pilot volume of the diaphragm. Id get a compressor, but Im military and my pay is crap, and with a wife and two kids, spending more than what it takes to make the gun is a pain... so maybe in two more weeks ill pick up a compressor, they had a decent one at home depot for 90usd which is my biweekly "rec fund", usually enough to buy parts and supplies for a cannon, but I do more than just spud guns so kinda SOL for two weeks...

any way to force the diaphragm to seat without pressurizing the pilot volume?
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Unread postAuthor: LikimysCrotchus5 » Sun Jun 15, 2008 10:40 pm

Spring?
(too short)
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Unread postAuthor: daxspudder » Sun Jun 15, 2008 10:48 pm

Yeah, there is a big a55 spring in the sprinkler valve that presses against the diaphragm. When I modded the valve I removed the top plate to avoid accidentally dremeling the diaphragm, I then discovered the spring... here is a pic of the diagram from the valves box... the valve doesnt have the flow adjuster like the diagram shows... see figure D for the spring... and yes it is inside
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Unread postAuthor: psycix » Mon Jun 16, 2008 4:27 pm

Maybe get the spring out, pull at it so it becomes longer, not too hard, but hard enough to deform it permanently a little.
The streched spring will now act out more force when put back in.

But be careful, stretch it too much and it becomes useless.
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Unread postAuthor: daxspudder » Mon Jun 16, 2008 11:05 pm

I tried that, and when it didnt work I assume that my problem is as DYI said in the first reply, I just need to get more pressure in faster... I ordered a threaded schrader valve from bcarms(and a GB barrel!!!) since the valve I have now leaks til 20 psi which sets the inner seal, and due to the rubber exterior it wont take epoxy.
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Unread postAuthor: dongfang » Fri Jun 20, 2008 5:44 am

Hi,

Yeah with all those stories about pumps kicking back (it happened to me too, but the piston and rod stayed connected to the pump), maybe an extra check valve would be a good safety feature.

Regards
Soren
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