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1" piston wont pilot on blowgun.. WTF!?!?

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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1" piston wont pilot on blowgun.. WTF!?!?

Unread postAuthor: c19o » Tue Dec 25, 2007 6:37 pm

I've made 2 other valves exactly like this and they worked fine piloting off a modded blowgun... ( reason I cant use the other valves is because I have a 1" female adapter glued on the chamber port, they where used to pilot a 1.5" piston valve) this one doesn't want to cooperate with me.

Specs:
Housed in a 1" tee
Piston is a .5" coupling sanded down to fit tight but still slide easy
Neoprene rubber sealing face
a rubber cylinder from an old fax machine, grinded down to fit as a bumper
Pilot is a modded blowgun
amount of air to pilot looks around 1 to 2 ci of air
piston travel is .5"

I fill up the gun, hit the trigger and all the air rushes out, I remove the blowgun, cover the hole with my finger, fill up, let go, it fires great...


Here's some pics
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Unread postAuthor: carter » Tue Dec 25, 2007 6:41 pm

to slow opening or maybe a blocked valve?
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Unread postAuthor: c19o » Tue Dec 25, 2007 6:42 pm

I modded it, and flow was much greater, I did check if it was blocked, it wasnt.
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Unread postAuthor: hi » Tue Dec 25, 2007 6:42 pm

I've made 2 other valves exactly like this and they worked fine piloting off a modded blowgun


well obviously they aren't EXACTLY the same, but my only guess is that to much air is leaking around the piston. maybe wrap some tape around it, thats what i do with mine.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 25, 2007 6:42 pm

It looks like it's the blowgun that's the problem, have you tried using a different one on the launcher, or the same one on another launcher?
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Unread postAuthor: c19o » Tue Dec 25, 2007 6:44 pm

I stole the piston from a working valve, so I guessed it would work.
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Unread postAuthor: Killjoy » Tue Dec 25, 2007 6:44 pm

1/4" ball valve?
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Unread postAuthor: c19o » Tue Dec 25, 2007 6:46 pm

Oh yea and I tried that too, it doesnt work :x

Its so good a fit that not even clear tape can go on there, I can seal the valve with my mouth and when i let go i hear the piston come back a little.
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Unread postAuthor: Hotwired » Tue Dec 25, 2007 7:12 pm

Well the obvious has already been posted so howabout stickiness of the sealing point?

I can't imagine when you're using a finger over the port that you're using particularly high pressure, but with a blowgun and the 1/4" ball valve I'm guessing you're using higher pressure.

It might sound unlikely but if the seal of the rubber against the barrel is greater than the force of air at those higher pressures to push it back then the piston won't move.

Feel like humouring me and, I don't know, oiling the rubber sealing face? :wink:
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Unread postAuthor: Killjoy » Tue Dec 25, 2007 7:20 pm

You know hot wired you may be right, Cause the same thing happened to me. The rubber would "cling" to the sealing surface in that as the piston would try and pull back the extra width on the rubber would hold onto the sealing surface until almost all the air was gone.
So I would recommend trying to secure the sealing face's sides down on the piston or trimming it so theres very little excess sticking out arouns the sealing surface.
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Unread postAuthor: c19o » Tue Dec 25, 2007 7:44 pm

O I never thought that could happen, tomorrow I'll try that and report back..
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Unread postAuthor: MrCrowley » Wed Dec 26, 2007 1:28 am

A 1/4" ball valve will give much better performance. If it's struggling to actuate now, even if something could be holding it back a bit, a ball valve would be better.
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Unread postAuthor: Hotwired » Wed Dec 26, 2007 5:57 am

Killjoy wrote:1/4" ball valve?

c19o wrote:Oh yea and I tried that too, it doesnt work :x
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Unread postAuthor: Gunner » Wed Dec 26, 2007 8:45 am

I have almost same problem, but I dissolved it by swapping my blowgun to 1/2" ball valve.
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Unread postAuthor: noob of noobs » Wed Dec 26, 2007 2:39 pm

Dude, I have the same exact problem (my piston's not as clean however :oops: ) I'm trying to lubricate it up a bit. How exactly did you mod your blowgun by the way?
Oh yeah, I also heard from sombody that if you coat the inside of the piston carridge with aluminum from a soda can, it'll make a tighter fit. Might be useful if you still have some clearance between the piston and carridge, but if you can't wrap tape around it, that probably won't help much.
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