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Piston Valve Questions

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 Valve Questions

Unread postAuthor: CannonCreator » Sat Aug 25, 2007 11:29 pm

I have read up completely on how All the Piston Valves work. In a few days I Plan on going to Home Depot, and getting all the pieces to make a piston valve. I Want to make a Tee-Fitting Barrel Seal piston valve that im am going to Use on my Next Pneumatic Cannon. The size ratios I plan on using for the Next Cannon is going to be 3/4" barrel, and a 2" chamber.

My questions are,

1. What size Tee Fitting should I use (looking at other cannons I have seen mostly 2 1/2" Tees)?

2. What do I use to make the piston head (The part that blocks air from going into the barrel) (End Caps that fit in the tee snugly, or sanded down PVC pipe, so it slides smooth)

That’s it, I know how it works, that im Going to NEED O-rings, I just need help with the materials for making the piston, and recommended size Tee-Fitting. I searched the forum and got nothing.

Thanks,

CannonCreator
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Unread postAuthor: MrCrowley » Sat Aug 25, 2007 11:47 pm

Okay, looks like you have done some research.
My cannon used a 2" chamber with a 2" tee, barrel sealing piston valve.
It works great for launching golf balls up to 380m, so it should work great for your 3/4" barrel.
This is the cannons thread here:
http://www.spudfiles.com/forums/viewtop ... tml#100616

2" tee's are good to use for starters, as there are so many different types of pistons, like deodorant cans fit great(when the tee is sleeved with 2" pipe) and 1 1/4" fittings(like end caps) also fit great.

This is my 2" tee piston made from a deodorant can:
Image
Image

2 1/2" fittings are usually quite rare in the US, I hear. So just go 2", makes it easy and plenty of power.
For the sealing face, neoprene rubber or round rubber gaskets (usually orange or black) found in the plumbing section work great as well, thats what I used on mine.

Hope that helps.
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Unread postAuthor: Marco321 » Sun Aug 26, 2007 12:02 am

I would suggest either hot glue, but it isn't the best thing to use because it naturally has friction. But the plus side is its very easy and very cheap.

A very good thing to use is epoxy to make the piston. I use that putty stuff and i just stuffed it into a pipe and let dry. It is absolutely perfect.

I use 2 layers of inner tube as the sealing face with a large head screw to hold them down. I have never had trouble with sealing, it sealed first time 100%.

My housing was a coaxial, the second is in a T, its about 2" or about 45ishmm ID (from memory), I'm in Aus so we use the good system :P it worked well.
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Unread postAuthor: MrCrowley » Sun Aug 26, 2007 12:10 am

Marco321 wrote:I would suggest either hot glue, but it isn't the best thing to use because it naturally has friction. But the plus side is its very easy and very cheap.

A very good thing to use is epoxy to make the piston. I use that putty stuff and i just stuffed it into a pipe and let dry. It is absolutely perfect.

I use 2 layers of inner tube as the sealing face with a large head screw to hold them down. I have never had trouble with sealing, it sealed first time 100%.

My housing was a coaxial, the second is in a T, its about 2" or about 45ishmm ID (from memory), I'm in Aus so we use the good system :P it worked well.


If you're talking about 2" pipe, its I.D is certainly not 45mm, its about 65mm I think
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Unread postAuthor: CannonCreator » Sun Aug 26, 2007 12:59 am

MrCrowley wrote:Okay, looks like you have done some research.
My cannon used a 2" chamber with a 2" tee, barrel sealing piston valve.
It works great for launching golf balls up to 380m, so it should work great for your 3/4" barrel.
This is the cannons thread here:
http://www.spudfiles.com/forums/viewtop ... tml#100616

2" tee's are good to use for starters, as there are so many different types of pistons, like deodorant cans fit great(when the tee is sleeved with 2" pipe) and 1 1/4" fittings(like end caps) also fit great.

This is my 2" tee piston made from a deodorant can:
Image
Image

2 1/2" fittings are usually quite rare in the US, I hear. So just go 2", makes it easy and plenty of power.
For the sealing face, neoprene rubber or round rubber gaskets (usually orange or black) found in the plumbing section work great as well, thats what I used on mine.

Hope that helps.


That is hte exact kind of answer I was looking for, thanks! Helped A Lot!

And actually I was thinking of making the piston out of hotglue, cuase I recently made a 3/4 rubber sludfor my other cannon, and it is kind of like softer delrin, kinda.
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Unread postAuthor: CannonCreator » Sun Aug 26, 2007 1:43 am

O ya, does anyone perfer using a spring on behind the piston head?
Or is it best no spring?

-AND-

How much room should I have behind the piston, When its Sealing the Barrel?

well, I know It needs to be compltely out of the middle part of the tee were the 3 Sections Meet, But like does it really matter how much room behind the piston as long as theres space for the air to get out of the equilization hole?
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Last edited by CannonCreator on Sun Aug 26, 2007 2:25 am, edited 1 time in total.
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Unread postAuthor: MrCrowley » Sun Aug 26, 2007 1:57 am

It doesn't really matter for what you're doing, no performance increase. They're only really used when you're filling from the chamber.

P.S: I've already told you once, stop double posting, edit your posts.
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Unread postAuthor: Marco321 » Sun Aug 26, 2007 2:02 am

@MrCrowley - Lol yeah my diamter is around 45mm

@CannonCreator
I don't use a spring in my coaxial or barrel sealer. I read that a spring is only really necessary if you fill through the chamber instead of the pilot area. But they don't hurt to have them as long as it is weak. But i could be wrong
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Unread postAuthor: joannaardway » Sun Aug 26, 2007 7:18 am

CannonCreator wrote:O ya, does anyone perfer using a spring on behind the piston head? Or is it best no spring?

How much room should I have behind the piston, When its Sealing the Barrel?

A spring can help lots if you have issues with your sealing pressure. If you're filling from a bike pump, and your sealing pressure is 15 psi, your arms will be worn out even getting it to seal.

The smaller the pilot volume, the better, as long as the piston can move back at least a quarter (ideally a touch more than that to be sure) of the sealing face's diameter.
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Unread postAuthor: noob of noobs » Tue Aug 28, 2007 7:39 am

Wait a second, you need o-rings? I thought those were only necesssary on chamber sealers.
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Unread postAuthor: frankrede » Tue Aug 28, 2007 7:30 pm

http://www.spudfiles.com/forums/barrel- ... t7397.html

Theres my cannon, similar to what you are describing I think,
Heres the tutorial for making the valve.

http://www.bcvids.com/dload.php?action=file&file_id=4
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