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Problems with coaxial

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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Problems with coaxial

Unread postAuthor: hotknife ralphie » Tue Jan 15, 2008 3:07 am

Evening,
The problem I seem to be having is that when the piston has sealed against the barrel and the gun has been pumped up, all the air within the gun is going out the sprinkler valve outlet.
i.e- No air is going out the barrel.
I thought it may be because no air was getting past the piston and into the chamber, however, on other shots the piston will seal but only till about 30 psi at which the piston slides back and lets the air out the barrel without me venting the pilot, i.e I am not venting and the piston still opens.

The barrel is 1m long the pipe is 15mm, the chamber is 50cm and the pipe is 25mm, and it is vented by a modified sprinkler valve. I'm not sure of the pilot volume, it is approx. 10 cm long and 25mm pipe Any input as to why my gun is not working would be helpful.

Thankyou.

Here are some pictures...I hope.
Image

Image

Image
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Last edited by hotknife ralphie on Tue Jan 15, 2008 5:18 am, edited 1 time in total.

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Unread postAuthor: Novacastrian » Tue Jan 15, 2008 3:12 am

Your description is good but vague-oxymoron i know, any more details about the cannon? Pics would be good.

Edit: Did you put the sprinkler valve on the "right" way?
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Unread postAuthor: dongfang » Tue Jan 15, 2008 4:06 am

Hi,

I guess you had better invest in a pressure gauge, so you can know what you have in your chamber. You will be using it later anyway.

Regards
Soren
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Unread postAuthor: psycix » Tue Jan 15, 2008 5:45 am

dongfang wrote:Hi,

I guess you had better invest in a pressure gauge, so you can know what you have in your chamber. You will be using it later anyway.

Regards
Soren


He did know wha pressure he used since he told us something about 30psi...
Maybe he got a pressure gauge on his pump/compressor/air source like I also do :)


But to your problem:
As Nova said:
Is the sprinkler not backwards? Did you forgot to seal some hole?
I definitely is the sprinkler that not O.K.

You could try disassembling the sprinkler, making it dust-free etc. and then putting it back together.
There may be some dust or stuff making the diaphragm not seal well.
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Unread postAuthor: hotknife ralphie » Tue Jan 15, 2008 5:49 am

When I tried it the sprinkler valve was definately on the 'right way'. I thought it could be the problem also, so I unscrewed it and screwed a ball valve on to make sure if it wasen't holding the air or venting properly, however i still had the same problems with the ball valve. I am completely stumped.
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Unread postAuthor: dewey-1 » Tue Jan 15, 2008 10:30 am

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Last edited by dewey-1 on Sun Apr 20, 2008 2:27 pm, edited 1 time in total.
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Unread postAuthor: psycix » Tue Jan 15, 2008 10:56 am

If you got the same problems with a ball valve, then there is weird stuff going on.
Find out where it exactly leaks.
Put it underwater to do that :)

-Maybe it leaks at the threads, do you use teflon tape or similar?
-Maybe you glued it wrong.
Did you twist it 90 degrees after pushing the fittings together?
-Maybe it leaks at the schrader valve (or other inlet I dont know what it is)
or even at your pump or air supply.
You are filling from the pilot side right?
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Unread postAuthor: Carlman » Tue Jan 15, 2008 11:30 am

have you got an equilisation hole?, if so how big?

Is the piston tight or loose in the chamber?

PS: ur aussie aye? (commonwealth bank statement on counter lol)
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Unread postAuthor: spudy buddy » Tue Jan 15, 2008 5:23 pm

ya i noticed that the valve is on the wrong way to caus it's like that on my gun but it leads to the barrel and the chamber is on the free side in the pic but if it does that with a ball valve then it's not the problem
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Unread postAuthor: BigGrib » Tue Jan 15, 2008 5:45 pm

dewey-1 wrote:In the second picture, a close up of the sprinkler valve, I notice that the valve is in backwards.
It took a long time of staring until I noticed it because of the poor quality of the image.
I referenced the angular part of valve bottom to see its orientation.
Does any body else see this or is it just my poor eye sight?


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Unread postAuthor: MrCrowley » Tue Jan 15, 2008 5:51 pm

dewey-1 wrote:In the second picture, a close up of the sprinkler valve, I notice that the valve is in backwards.
It took a long time of staring until I noticed it because of the poor quality of the image.
I referenced the angular part of valve bottom to see its orientation.
Does any body else see this or is it just my poor eye sight?


I think you're right.

I can see the 'angular' curve on the side facing the wrong way, the curve always leads to the chamber side.
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Unread postAuthor: BigJon » Tue Jan 15, 2008 5:54 pm

Are you saying that when you pilot the valve it all goes out the back instead of the barrel? If so then its most likely a piston problem like carlman was leading towards.
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Unread postAuthor: Carlman » Tue Jan 15, 2008 6:07 pm

i have the same valve on my first gun:

Image

so the 'slope' should lead to the pressure and this is the way with his coaxil. The valve is not the problem unless it leaks.
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Unread postAuthor: dewey-1 » Tue Jan 15, 2008 6:09 pm

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Last edited by dewey-1 on Sun Apr 20, 2008 2:28 pm, edited 1 time in total.
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Unread postAuthor: hotknife ralphie » Thu Jan 17, 2008 4:30 am

Thanks for everyones reply. I took a look at the piston today and have decided to make one that fits a bit more snug. I bought some Araldite(epoxy stuff?) and some hot glue. Which would be better overall to be a piston?
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