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Coaxial problem

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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Coaxial problem

Unread postAuthor: Demon » Thu Sep 11, 2008 3:29 pm

I have a big problem:


My coaxial is 2 feets long, have a 3inch chamber and 1 1/2 inch barrel.

My piston is a 2 inch pvc endcap wraped in a little bit in duct tape and with a piece of neoprene for the sealing surface.

I am able to make seal the barrel after 2 bikes pump and there is no problem with any parts

ECXEPT

The air escape system(to make the piston going back)




When i am ready to fire and press on the blowgun its makes pCHHHHHHHH until there is no more pressure in the gun

Is the fault to the blowgun?(because they have a very low air flow)

Will putting a brass 1/4 ball valve will make it work?

Thanks to answer(and i dont want any reply like"I dont know")
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Last edited by Demon on Sat Sep 13, 2008 4:52 pm, edited 2 times in total.
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Unread postAuthor: POLAND_SPUD » Thu Sep 11, 2008 3:38 pm

hmmm I don't know :D





why don't you use a 1/2" BV instead... you know just to be sure ?

ohh one more thing ? is the piston a tight fit ? too much air might be leaking from chamber to pilot side when you pilot it...

most likely it is both casued by the piloting valve and air leaking past the piston..
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Unread postAuthor: Demon » Thu Sep 11, 2008 3:44 pm

I am able to make move the piston just by blowing on it.

And a interesting fact:

I blowed with my mouth trough a 1 inch long 6mm barrel: lot of air
getting trough

I blowed with my mouth trough a 1/4 blowgun(opened, of course!):aprox. nothing camed trough.

So if you plan on making a coaxial, never use a blowgun, use a ball valve.
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Unread postAuthor: blind909 » Thu Sep 11, 2008 5:19 pm

Ball Valves do work excelent, but your gun is too big for a measly blowgun. If you have a 1 1/2 inch or less that A blowgun will pilot the gun excelently. But your chamber is too big.
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Unread postAuthor: mark.f » Thu Sep 11, 2008 5:32 pm

Like the others said, a little 1/8" blowgun will not actuate that size launcher effectively.

First off, address the piston's fit. Wrap it in duct tape until it slides in with no wiggle and with a tiny bit of resistance. Once you have done that, coat the piston in a heavy lubricant (grease, petroleum jelly, etc.), and insert it, then close the valve up.

For the pilot valve, I would suggest AT LEAST a 1/4" quick-exhaust. This would probably work, but you may want to get some insurance and buy a 1/2" just the same. You can get these from McMaster-Carr, and they make very good pilot valves.

If this fails, you can vent this piston valve with an even smaller piston valve (based in a tee). I've seen it done before, but I've yet to find the link.
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Unread postAuthor: Demon » Thu Sep 11, 2008 5:38 pm

I can only use a 1/4 inch ball valve because i use the tit i used for the
blowgun. i will soon post a pic of it( i cuted it in two 'cause of a stupid mistake with a o ring and hot glue) when i will had finished my homeworks( i am 13 years old).
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Unread postAuthor: frankrede » Thu Sep 11, 2008 5:45 pm

A 1 1/4" cap for a 3" chamber??
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Unread postAuthor: Demon » Thu Sep 11, 2008 5:57 pm

No a 2 inch cap
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Unread postAuthor: psycix » Fri Sep 12, 2008 1:32 pm

Trying to pilot a 3" piston with a blowgun will not give you what you want unless you are using well applied O-rings.
Install a larger pilot valve.
As big as possible :)
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Unread postAuthor: Demon » Fri Sep 12, 2008 4:38 pm

YAY!!! I founded an other problem and fixed it: my piston was not well wrapped in duct and was not perfectly circle... i passed 30 minutes to slowly and precisely wrap it again and the results are over all my hopes!
i am able to pilot it with a blowgun! a 3 inch chamber piloted by an blowgun(i will put a ball valve anyway)!


But was is sad is then i have to wait until the end of the month to buy some missing parts( i cuted my coaxial in two to fix a stupid mistake with an o-ring).
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Unread postAuthor: MaxuS the 2nd » Fri Sep 12, 2008 5:36 pm

Is english your first language?
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Unread postAuthor: Demon » Sat Sep 13, 2008 10:46 am

No I am a french canadian.

Why?

and if its to tell then my english sucks i know.
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Unread postAuthor: Demon » Sat Sep 13, 2008 10:52 am

HO HO!

I am now very stressed because i just see on an other topic then piston valves guns needs lubrications... and mine is glued with pvc cement.

will it stop to work after i shooted a lot of time with it because i can no more lubricate it?

Arghhh! i can wait having my answer!
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