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Piston - Dont Release Air.

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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Piston - Dont Release Air.

Unread postAuthor: neeewwww » Sat Jul 18, 2009 4:21 pm

Hi,
I have a problem with my piston. It seals perfectly (Barrel Sealer). But when I open t he BV (Exhaust) it dont seat back, so, all the air goes throught the BV instead of barrel. Tried a lot of pressures (20psi or 150psi), even blowing air throught the BV (the piston seals the barrel), but when I blow air throught the chamber side of the "Tee", all the air goes throught the BV.

Any suggestions/solutions?


Specs:
- 3/4in "Tee"
- 1/2in "Barrel"
- 1/2" Ball Valve

Pics:

** The back seat and o-ring. This is a 3/4" to 1/2" reducer.
Image

** At background (inside the Tee), the 1/2" Fitting (Barrel)
Image

** Piston housing (chamber side view).
Image

** Piston Housing "Full View".
Image

** Piston Housing, BV (without handle), fill part.
Image

** Full view, without barrel.
Image
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Unread postAuthor: ralphd » Sat Jul 18, 2009 4:29 pm

I know this one......your pilot valve is too small. I had the same problem and tried a number of things to fix it. The only thing I didn't try was a bigger valve to release the pilot area faster. Someone here recommended it, I did it and vwooshhhh.
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Unread postAuthor: neeewwww » Sat Jul 18, 2009 4:31 pm

@ralphd - Even without the BV, just the Tee and piston housing (the 3/4" to 1/2" reducer), the piston dont seat back...
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Unread postAuthor: Brian the brain » Sat Jul 18, 2009 4:32 pm

I think there is no-or not enough difference in diameter between the sealing face surface and the crosssection of the piston itself.

IOW, the pressure has no surface to push against..
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jrrdw » Sat Jul 18, 2009 4:37 pm

The piston has to meet the barrel in the middle of the tee. Other wise the chambered air just pushs against the side of the piston and not the face. Also, is your piston threaded? or am I seeing things???
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Unread postAuthor: neeewwww » Sat Jul 18, 2009 4:41 pm

@jrrdw - Theres no piston in the picture... I guess what you see is the "Barrel", like this fitting:

http://www.cec.com.br/images/5/53716g.jpg

I screw this fitting, into the Tee (so I have interchangeable barrel).
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Unread postAuthor: jrrdw » Sat Jul 18, 2009 4:43 pm

Ok, but does your piston seal against the barrel in the middle of the tee?
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Unread postAuthor: neeewwww » Sat Jul 18, 2009 4:54 pm

@Jrrdw - Yes it seal... I tried a different shapes (flat, rounded and "conic). And none releases air throught the barrel side, just throught the BV. If I push the piston using my finger (low pressure 15psi), the piston slides back and some air goes throught the barrel. Blowing air throught the BV, the piston seals...

Blowing air throught the chamber side (BV Open), the air goes throught the BV. BV closed, the piston seals against the barrel.

Question:

- The piston travel is too small?
- The "barrel" (1/2") are too large?
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Unread postAuthor: Brian the brain » Sat Jul 18, 2009 5:40 pm

What diameter is your piston and what diameter is the out-port?

The piston must be bigger than the outside diameter of your port in order to actuate.....
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: neeewwww » Sat Jul 18, 2009 7:03 pm

Im not at home... I will draw some schematics with measures asap.

o>
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Unread postAuthor: le_rufus » Sat Jul 18, 2009 8:24 pm

Just to be sure, you're filling through the ball valve side of the piston correct?
Also, your piston may not be the correct diameter for your tee; or if you have an equalization hole in your piston it may be to large.
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Unread postAuthor: neeewwww » Sat Jul 18, 2009 10:51 pm

@le_rufus: Yeah, I´m filling throught the ball valve side. To be correct, through the schrader valve.

I got the dimensions... Here you are:

Image

And I realize, that, my piston MUST be around 2,10cm, and my sealing face around 2,40cm (inner diam. of the Tee).

This will work fine.. Or my barrel side must be smaller?

I have to say, that my piston works fine, like, two or three times... Using a small boucing ball as sealing face, but, it turned into rubber dust after the third shot...

Colours:
- Red: 1/2" Barrel
- Blue: 3/4" Tee
- Purple: 3/4" to 1/2" reducer - Piston Housing
- Gold: O-ring/Bumper.

Thanks o>
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Unread postAuthor: Crna Legija » Sun Jul 19, 2009 2:13 am

maybe your piston is to small for the barrel port it should cover the barrel and still have some hanging over
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Unread postAuthor: jrrdw » Sun Jul 19, 2009 5:58 am

neeewww, your not understanding my question, -_-'s picture describes my question perfectly. In his picture you can see where the barrel and piston seal directly in the middle of the tee. In the middle of the chamber port is best, that gives the piston a assessable surface for the air to push open the piston while the release of the pilot chamber creates a vacuum that pulls on the back of the piston.

The release of the pilot chamber works hand in hand with the chambered air to push and pull open the piston.

Looks to me like your piston meets the barrel at the end of the tee instead of the middle.
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Unread postAuthor: far_cry » Sun Jul 19, 2009 6:35 am

the seat diameter is almost the same of the piston ,thats is your problem

if you but a pictures of the piston and the seat (where the piston face seal) this will provide a clear picture of your problem

see my piston and the seat ,the piston diameter is bigger than the seat diameter
http://www.spudfiles.com/forums/my-first-piston-valve-picture-and-video-t18197.html

and this pic you will see the piston bigger than the seat too

Image
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