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Piston length ?

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: Technician1002 » Mon May 17, 2010 10:06 am

Just a quick note on using vegie oil. It will go bad. It is OK to use but plan on fully cleaning all the parts after a week or so of shooting. I used to use it in my ABS Cellular Core Cannon. I switched after a few times the oil became very rancid when it was not used for a few weeks.
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Unread postAuthor: TheLostOtter » Mon May 17, 2010 12:35 pm

The stuff I'm using must be different because it doesn't really start to stink, but it seems to "disappear" after a while.

I saw someone say Vaseline, that's petroleum based, but is it safe for this application?
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Unread postAuthor: mark.f » Mon May 17, 2010 8:08 pm

White lithium grease seemed to work wonders in all of my cannons.
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Unread postAuthor: c9d » Mon May 17, 2010 8:38 pm

I went and got a nice tube of white lithium grease.. thanks for the advice.

@Gipetto I should have those pics soon. I would love for you to look it over before I use it.
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Unread postAuthor: c9d » Tue May 18, 2010 8:18 pm

@Gipetto... here are the pics. criticism and advice welcome

barrel face up
Image

Bumper face up
Image
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Unread postAuthor: Gippeto » Wed May 19, 2010 12:02 am

My .02 then;

Spool shape for weight reduction...that's good.

As far as the bumper is concerned, it'd work better turned around. Doing so, will aid in controlling air flow through the valve..ie... it'll act as a check valve...air allowed into the chamber easily...air from the chamber not allowed back into the pilot volume under piloting.

The sealing face looks to be the same part as the bumper??

I prefer to use harder or at least thinner sealing faces. Harder seals, break contact (stop sealing) more abruptly, and offer a performance enhancement. Call it a theory if you wish. :)

Looks like a lot of give in that for a sealing face...might give you trouble with it cutting from contact with the barrel.

If it were me,(and the other components will allow the changes) I'd remove that sealing face, and use contact cement to attach a thin neoprene gasket. Then add the typical bolted fender washer as reinforcement.

Be certain that the bolt is sealed inside the piston as well. A common cause of problems.

Been a long day...that's all I have for now.

Later
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Unread postAuthor: c9d » Fri May 28, 2010 9:56 pm

@Gipetto... or anyone with constructive criticism...
I took your advice and turned the bumper around, and replaced the sealing face gasket with a 1/8" rubber type gasket material cut to size. I got all the leaks worked out and fixed. Now the problem I am facing is that the piston hangs up right when I release the pilot volume. I will take some pics and post them shortly.

Image
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Unread postAuthor: Gippeto » Sat May 29, 2010 12:15 am

Looks like the bumper end of the spool is on the small side. This might allow the spool to shift off axis, and could be the cause of the jams.

I'll suggest that the front and rear plastic pieces (hdpe?) should both be nearly the same size as the id of the chamber to keep it tracking true.

Fender washer could be a bit bigger too. Ideally, only slightly smaller than bore size.

Does the bumper make contact before the bolt and washer?
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Unread postAuthor: c9d » Sat May 29, 2010 1:37 am

I ended up taking a second HDPE circle, like the one under the barrel seal, and putting it behind the bumper/seal. Now since their was now no bumper, I cut 1/3 off of a tennis ball, drilled a hole in the other side, and installed that as the new bumper. Wouldn't you know... the darn thing works now... no hang ups. Almost put that nerf vortex thru the drywall in my garage. I will post pics of my cannon after this weekend. I will be putting her thru the paces in WI shooting at APCs...
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Unread postAuthor: c9d » Thu Jun 10, 2010 9:15 pm

@Gipetto

Well... took the thing to event and was turned away because it was too powerful. Launched that Nerf pocket vortex at 220 fps.

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Unread postAuthor: jackssmirkingrevenge » Fri Jun 11, 2010 12:36 am

shame, couldn't you have turned down the pressure?
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Unread postAuthor: c9d » Fri Jun 11, 2010 12:58 am

Well... since the power source was a whole 12g CO2 cartridge, I would have had to rebuild the whole thing longer. But on the bright side, I have already lined up some parts to regulate and monitor chamber pressure. I will be able to use it next year.
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Unread postAuthor: Gippeto » Fri Jun 11, 2010 2:09 am

Bunch 'o chickens! :lol:

Maybe time to consider a regulated co2 setup w/ remote tank?

Glad you got it working though, looks good! :D
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Unread postAuthor: c9d » Fri Jun 11, 2010 10:49 am

since I am limited to 12g cylinders, i was thinking of a dual 12g adapter, a low pressure regulator, pressure gauge, and either a simple push button valve or electric solenoid to fill the chamber. The push button would be cheaper, but i have room for a switch battery and wiring for a solenoid.
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