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piston not opening.

A place to ask general spud cannon related questions.
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piston not opening.

Unread postAuthor: )DEMON( » Sat Jul 01, 2006 1:48 am

I have finally got my piston to close and seal but now when I exhaust all the air from behind it with my sprinkler valve it dosn't open and the chamber empties.I don't understand why it isn't opening :?

Below is an accurate picture of my piston.
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piston not opening.JPG
The piston and what it sits inside can be removed from the T .
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Unread postAuthor: SpudStuff » Sat Jul 01, 2006 2:15 am

I had the same prob. make the sides of the piston concave
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Unread postAuthor: Benny » Sat Jul 01, 2006 2:19 am

does the piston slide through the chamber smoothly?
do you have a very strong spring in there?
and, how wide is your pilot hole?
i made the pilot hole too big on my piston cannon, (now dissasembled) and it was doing the exact same thing your describing.
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Unread postAuthor: )DEMON( » Sat Jul 01, 2006 2:43 am

Concave?how would that help? This piston slide easily through everything and I don't use a spring in it,all I do is point the gun down and start pumping air into it and it seals. I use a sprinkler valve to exhaust the piston and a special system(can't be discussed right now) which is mush faster than a blowgun to exhaust the sprinkler valve.
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Like this?
concave.JPG (14.16 KiB) Viewed 588 times
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Unread postAuthor: Benny » Sat Jul 01, 2006 2:51 am

Hmm, how big is your pilot valve. :?:
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Unread postAuthor: )DEMON( » Sat Jul 01, 2006 2:56 am

I tried it with the blowgun from the HK1 and it still isn't working.I think the problem is the piston itself,does it need any O-rings or something? The problem shouldn't be related to the pilot valve and I am not sure of the volume of the pilot valve.
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Unread postAuthor: Benny » Sat Jul 01, 2006 3:01 am

AAAAAAAAAHHHHHHHHHHH CRAP! Sorry, not pilot valve, i meant Equalizization hole, OH god, what have i been smoking?
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Unread postAuthor: )DEMON( » Sat Jul 01, 2006 3:04 am

I didn't make one because the piston is not perfectly sealed in the slightly larger pvc it sits in.There is about a 1mm gap.

*I got some pics up of my piston.
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piston-and-other.jpg
This is the piston and the larger piece of pvc it sits in.I took the adapter off because it was causing problems.
piston-and-other.jpg (11.17 KiB) Viewed 566 times
old-adapter.jpg
This is the adapter,40mm to 20mm
old-adapter.jpg (12.25 KiB) Viewed 566 times
back-of-T.jpg
The set up goes in the back of this T
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Unread postAuthor: noname » Sat Jul 01, 2006 10:26 am

Try making the piston longer so that when it seals more of it is sticking back into the other pipe.
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Unread postAuthor: djt » Sat Jul 01, 2006 12:08 pm

i had the same problem. i just made the piston fit a little tighter and glued it back together yesterday. if it still doesnt work im scrapping it. all i can say is lubricate it really well and make it fit pretty tight.
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Unread postAuthor: )DEMON( » Sun Jul 02, 2006 12:44 pm

I think I will have to make the largest piston that will fit in there.I am not having any luck with the current piston.The overall design will have to change slightly but I am sure I will have to only make slight changes.
How small does the equilization hole have to be?What will happen if it is too big?
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Unread postAuthor: djt » Sun Jul 02, 2006 1:23 pm

if its too big probably not too much. it will just let a tiny bit more air out of the pilot valve. i would still keep it small though, the more efficient the better!
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Unread postAuthor: )DEMON( » Sun Jul 02, 2006 3:02 pm

So when you exhuast the air from behind the piston the air forcing it to seal is going to push the piston back,right?Thats the theory anyway.But what I think is happening is the air is still keeping the piston sealed but escaping past the piston and out the pilot valve.OF COURSE!!!,have you seen the type of piston that will only let air into the chamber but not back OUT! yes! that will work,I must just make some sort of one way valve. Someone has made this befor, but I can't remember where :? What do you think?

Can someone help find a link.
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Unread postAuthor: djt » Sun Jul 02, 2006 3:18 pm

make the piston seal perfectly, drill an equilizaiton hole and put a flap of rubber or plastic on the side of the side of the hole opposite of the exaust valve. this way the pressure will be equil on both sides when you fill it, but when you open the pilot valve no air from the chamber can come out of it, only the air behind the piston can.

ps: click on the picture.
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piston.JPG
piston.JPG (14.32 KiB) Viewed 516 times

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Unread postAuthor: )DEMON( » Sun Jul 02, 2006 3:28 pm

That seems a little flimsy to me,I will think about it in the morning.YAWN!
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