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| Wave Rider |
 Posted: 05/12/2008 17:55 PM Post subject: My first spud gun (and problems) |
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Private
Joined: 12 May 2008
Posts: 1
10.00 Spud Bux
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I just discovered this place a couple of days ago, and I am amazed at the amount of new technology that has become available though this forum, especially the wealth of information about piston valves.
Naturally I set out right away to construct a small prototype coaxial launcher. Failing to find any pressure rated PVC in the shops around here I decided to go with what I had in my junk box, so I made this fairly run of the mill coax using a cast epoxy piston with a piece of bike tire for the seal. The chamber is from a desoldering sucker, the copper pipe is 1cm (3/8") inner diameter and the "end caps / bushings" are made from 5mm acrylic I cut to shape and glued in place with a generous amount of epoxy. I don't expect this to hold a lot of pressure, but it's just a prototype after all.
Trouble is: Even though nothing is leaking, and the piston definitely gives a good seal, nothing happens when I pump up the chamber and then trigger the valve. The pilot volume empties with a small whoosh of air, but nothing comes out the front. I am wondering if either the main chamber is not filled up at all (piston forming too tight a seal), or if all the air from the chamber exits through the pilot valve (piston too loose).
The fit seems about right, the piston moves easily and if I blow hard with my mouth I can get a little air past it. I guess I could just mold a few more pistons, since it's easy enough, but maybe I am just overlooking something very simple since I am new to this?
Any help would be appreciated!
| Description: |
| Schrader valved end cap, coaxial assembly and greased up piston |
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28.25 KB |
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139 Time(s) |
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| bigbob12345 |
| Posted: 05/12/2008 18:27 PM Post subject: |
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Experienced n00b
Joined: 01 Dec 2007
Posts: 1514
362.74 Spud Bux
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Your problem is that your pilot is not suffecient, i would reccomend a presta valve rater than a schrader.
Or you could deacrease your pilot volume.
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| starman |
| Posted: 05/12/2008 18:32 PM Post subject: |
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Big Daddio
Joined: 12 Dec 2007
Posts: 977
1398.91 Spud Bux
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| Your piston may not be fitting close enough either...needs to be just close enough without catching the cylinder walls. In looking at your piston cylinder, the hole does not look round, rather a little out-of-round. That could be enough to let the air just slip on by without engaging the piston much or at all.
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| Davidvaini |
| Posted: 05/12/2008 18:45 PM Post subject: |
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Colonel
Joined: 29 May 2007
Posts: 541
1192.70 Spud Bux
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| Edit: Suggestion already noted..
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| Pyro Ninja |
| Posted: 05/13/2008 2:30 AM Post subject: |
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Captain
Joined: 09 Oct 2006
Posts: 320
173.62 Spud Bux
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First of all nice build. I'm glad you did the research. 
1-As you noted, a likely problem could be that there is not a sufficient seal around the piston.
2- (Already said) may need a more efficient pilot valve
3- Id say opt for a smaller barrel, this would give you more chamber volume, which usually equals more power
| Description: |
| This pretty much had no power, little puff of air out the barrel. |
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| psycix |
| Posted: 05/13/2008 4:59 AM Post subject: |
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Major General
Joined: 25 Jun 2007
Posts: 1424
386.81 Spud Bux
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Exept for the piston and the pilot valve, you could also try higher pressures.
What pressure are you on now?
More pressure -> faster acting piston.
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| MaxuS the 2nd |
| Posted: 05/13/2008 10:22 AM Post subject: |
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Lieutenant Colonel
Joined: 19 Jan 2008
Posts: 498
568.68 Spud Bux
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| Copper is pressure rated...Which you seem to have.
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