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Troubleshooting Issues

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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Troubleshooting Issues

Unread postAuthor: coryS » Thu Jan 14, 2010 8:29 pm

Hi guy's, well I just about finished my cannon for my senior project. It's a two inch barrel sealing piston valve. It's piloted by a 3/4 inch ball valve (I had a sprinkler valve on it but it wasn't working at all, I just want it to fire now and worry about that later.) I've been having some issues with it.
I'll fill it up to around 30 psi and it will vent until it hits around 10 psi than it will actuate barley. If i fill to sixty it will actuate around 20. I was hoping for some better performance than this. I think the issue might be to much dead space but I am not sure. My Piston is made of some unknown UHMW (that's what the label said on it lol). It is a very good fit and is lubricated with some silicon lube from boeing. If anyone can tell me what they think the problem is that would be awesome. I'll post some pictures if anyone asks. Thank you in advance.
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Last edited by coryS on Fri Jan 15, 2010 1:48 am, edited 1 time in total.
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Unread postAuthor: spudkpi » Thu Jan 14, 2010 8:32 pm

I want to help but cannot really understand what you are getting at. Just list the specs of the cannon
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Unread postAuthor: coryS » Thu Jan 14, 2010 8:36 pm

That was fast. Can you list the specs you want because thats a very general question.
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Unread postAuthor: MrCrowley » Thu Jan 14, 2010 9:31 pm

Actually it would help if you post pictures of the cannon, the piston and the piston housing.

Then just give us these specs:
Chamber diameter and length
Barrel diameter and length
Piston housing diameter (diameter of the piston)

They're not essential, but it helps put things in perspective.
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Unread postAuthor: twizi » Thu Jan 14, 2010 10:08 pm

whats the sealing face sound like my old cannon the sealing face was bad and leaked so it acuated very low psi
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Unread postAuthor: coryS » Thu Jan 14, 2010 10:21 pm

chamber aprox 70 inches long x
piston 4.8 cm x 7.6 cm
piston housing aprox 4.88 cm x 13

I have not used the barrel but it is a tennis ball barrel. It is 5ft long

Image


Image


Image[/img]
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Unread postAuthor: MrCrowley » Thu Jan 14, 2010 10:28 pm

Where have I seen that design before? :P

Can you get a picture of the inside of the piston housing?
Do you use o-rings on your piston because the picture only shows the o-ring grooves.
In your end cap, is there a bumper that restricts the air flow to the pilot setup?

Your pilot volume is pretty big but I would expect a 3/4" ball valve could still handle it.
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Unread postAuthor: coryS » Thu Jan 14, 2010 10:45 pm

Have you seen this design before? I thought it was pretty original but I guess not. My piston does not have orings the thought was that the increases surface would help with opening times (mentor/uncles crazy engineering idea)

Actually yes there is a very small hole in my bumper becuase i though it looked "clean" that way. Never would have thought that could make a difference.

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Image
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Unread postAuthor: MrCrowley » Fri Jan 15, 2010 12:08 am

Have you seen this design before? I thought it was pretty original but I guess not.

http://www.spudfiles.com/forums/viewtop ... tml#100616

:D

My piston does not have orings the thought was that the increases surface would help with opening times

Highly doubt it. You may as well chuck o-rings on there now that you have the grooves, that could help with your problem.

Try making the hole in the bumper a lot bigger, an inch diameter or so will do, but bigger is always better. That flow restriction coupled with your large pilot volume is probably your problem as far as I see it.
Assuming your piston is a nice fit, which if it's not, can be fixed with some o-rings.

If you put o-rings on your piston, make sure to drill a small equalisation hole through the piston (not through the sealing face, drill a hole from the bottom of the piston about 3/4 of the piston length, and the drill a hole in the side of the piston to meet this hole). A 1/16" drill bit is what I hear is best for equalisation holes.
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Last edited by MrCrowley on Fri Jan 15, 2010 12:42 am, edited 1 time in total.
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Unread postAuthor: coryS » Fri Jan 15, 2010 12:26 am

That's pretty awesome that we came up with the same idea :P. I thought I was being original oh well. I just drilled out the hole i'll get back to you tomorrow after some test fires.

PS. Thank you so much for the help MrCrowley. Wouldn't expect some one with that name to be so nice :wink:
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Unread postAuthor: MrCrowley » Fri Jan 15, 2010 12:28 am

PS. Thank you so much for the help MrCrowley. Wouldn't expect some one with that name to be so nice

At least you spell my name right, tell that to the other dingbats around here :D
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Unread postAuthor: inonickname » Fri Jan 15, 2010 12:38 am

MrCrowley wrote:
PS. Thank you so much for the help MrCrowley. Wouldn't expect some one with that name to be so nice

At least you spell my name right, tell that to the other dingbats around here :D

What was that McCrowley?

Looks like you're off to a very good start (nice piston as well). As Crowley mentioned, the problem with the valve opening is most likely due to the low flow through the bumper hole. Try making it larger without preventing it from slowing the piston down.
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Unread postAuthor: coryS » Fri Jan 15, 2010 1:23 am

Thank you for the kind words :D I'll post the finished product when i'm done. That is if you guy's want me to.
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Unread postAuthor: inonickname » Fri Jan 15, 2010 1:28 am

Course we'd like to see it. Let us know what your going to do with it (or ask if you need ideas).

By the way how did you cut the rubber on the piston? It's extremely neat..even when I turn down 6mm rubber sheet on the lathe and take my time it still ends up a little messy.
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Unread postAuthor: coryS » Fri Jan 15, 2010 1:35 am

For the black rubber it's just a neoprene washer from the store. The brownish orange rubber I cut from a sheet with scissors. Than i glued them down and took a sanding disk that attaches to a drill clamped the drill down than I turned the drill on at a constant speed and spun the sealing face at an even speed. Real high tech I know :roll:
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