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1/2 inch piston help

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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1/2 inch piston help

Unread postAuthor: Benjg555 » Fri Oct 15, 2010 3:03 pm

Hey you guys currently I have a regular plain are cannon with changeable barrels and pressure gauge. What I would like to do is get a .5 inch barrel with a T valve also .5 inches. Then put a .5 inch piston in the T valve. But then I can change to say a regular 2 inch barrel :idea:. Also on the making of the piston I'm thinking of using a foam block use a drill press with a .5 inch bit to drill the hole. Then insert the washer and nut I am going to use for it. I'm thinking of molding the little guy out of epoxy. Oh and also I'm working on swithchin the 1 inch ball valve that's metal to a 1 inch modded rain bird sprinkler valve. Should give it more power :D
Thanks :)



http://i.pgu.me/PAH0LvaE_original.jpg
sketch of my cannon (sorry its not very good, I didn't put some of the reducers in the drawing eather :?)

Would this sprinkler valve work? It's 1 inch with the solenoid directly in the center
http://i.pgu.me/BkaW+kjE_original.jpg


http://i.pgu.me/R8RUj2Fi_original.jpg
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Last edited by Benjg555 on Fri Oct 15, 2010 7:01 pm, edited 4 times in total.
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Unread postAuthor: MrCrowley » Fri Oct 15, 2010 3:38 pm

I can't really see much of your design at all except that your chamber is behind the piston in the pilot area? :?

I think you're trying to build one cannon for all your needs, a 1/2" piston and a 2" barrel wont be great in terms of performance. You should specialise your cannons, figure out what you want the most and stick to it. If you want a cannon with a 2" barrel, build a cannon that is suited for 2" barrels.

Try make a design in MSPaint or something and could you give us more details about it in your post?
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 3:55 pm

Alright sorry bout that :(

Well I'm thinking about a multi purpose barrel so it's an interchangeable piston barrel. The .5 inch piston would only go in the .5 barrel with the .5 inch T to release the air. The .5" would not go into the 2" barrel

Ya sure I'll try Microsoft paint. Details about? :?
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Unread postAuthor: Technician1002 » Fri Oct 15, 2010 4:29 pm

I found the range of barrel sizes that work best with a valve size is a large valve and small barrel is good. Barrel and valve port the same size is excellent, and larger barrels than the port by about 1.5 times works quite well. For example a golf ball barrel works good on the Marshmallow Cannon, but the 2 inch valve will out shoot the Marshmallow cannon by a huge margin. The 2 inch will toss a golf ball further on 50 PSI than the 1 inch can at 100 PSI.

You mentioned a 1/2 inch piston. Is this the valve seat port diameter or the piston diameter? My above references are the size of the air opening into the barrel. For a 1/2 inch barrel you may want a larger diameter piston with at least a 1/2 inch diameter valve seat opening.

I have a tutorial on how to make them on a drill press.
Look in the stickies in the How To section.
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Unread postAuthor: MrCrowley » Fri Oct 15, 2010 4:37 pm

The .5 inch piston would only go in the .5 barrel with the .5 inch T to release the air. The .5" would not go into the 2" barrel

I don't follow.

You want a separate valve for the 2" barrel? The 0.5" what? You've mentioned three different things all being 0.5" in diameter, can you clarify which one?

Details about?

The cannon. So you want a 2" barrel and a 1/2" barrel. From the picture I can sort of tell your chamber is 3" in diameter? Why is it behind the piston valve? Why is the bottom port of the piston tee empty, it leads to nowhere? So you want a 1/2" tee, with a 1/2" piston in side it? I wouldn't recommend having a 2" barrel reduced down to 1/2" and threaded in the piston housing tee. Without a good barrel support, there would be too much stress on the joints.

Also, a 3" chamber is way overkill for a 1/2" valve. You should download and use GGDT to optimise your cannon. A 3' length of 1/2" pipe would be perfect for a 1/2" valve.

Yes, the sprinkler valve would work, but with what? Do you want a 1" sprinkler valve to pilot the 1/2" valve or do you want the 1" sprinkler valve as a separate valve? I don't get your intentions, you need to clarify. A 1" sprinkler valve might even give the same, if not better, performance than your own 1/2" piston valve.
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 4:48 pm

Ohh alright got a bit confused there for a second but I got it thank you :)
Ya I figured going from a 1inch valve into a 1/2 inch it'd increase the pressure equallying more power

Yes the diameter of the piston would be 1/2 inch as to Match the diameter of the barrel and valve port for the greatest seal correct?

Alright I'll take a look
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Unread postAuthor: MrCrowley » Fri Oct 15, 2010 4:54 pm

Ya I figured going from a 1inch valve into a 1/2 inch it'd increase the pressure equallying more power

How would a smaller diameter increase pressure? If you mean that pressure rated 1/2" PVC can take higher pressure than a sprinkler valve, you are right but if you have a sprinkler valve as a pilot, that limits your pressure anyway.

Yes the diameter of the piston would be 1/2 inch as to Match the diameter of the barrel and valve port for the greatest seal correct?

The seat/barrel port inside the tee will have to be smaller than 1/2" otherwise there is no pressure differential. There needs to be an area on the sealing face that is exposed to pressure, if the sealing face of the piston and the barrel are the same diameter then there is no pressure pushing the piston back and when you go to trigger your piston, it wont move.
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 5:08 pm

Well no I mean because a 1 inche valve is emptying alot of air thats going to go into a smaller barrel making more force


So a little wiggle room? And the sealing face is the bolt part wich I have a hole go al the way through and have a washer cover a whole made while makin the piston.
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Unread postAuthor: MrCrowley » Fri Oct 15, 2010 5:13 pm

Well no I mean because a 1 inche valve is emptying alot of air thats going to go into a smaller barrel making more force

Yeah, so the 1" sprinkler valve could be the same if not better than the 1/2" piston valve.

I'm not following you at all because you're not clarifying what you want to say, here's an example:
1inch valve into a 1/2 inch

A 1/2" what? You've listed three things as being 1/2": a barrel, piston and tee fitting. How am I supposed to know which one of those three things you meant when you said 1/2"? Hence the confusion.

And the sealing face is the bolt part wich I have a hole go al the way through and have a washer cover a whole made while makin the piston.

The sealing face is generally a rubber washer or gasket on the front of a piston that seals against the seat (barrel port). You can bolt it, glue it or epoxy it to the front of a piston, it doesn't matter so much as long as it's going to stay on.
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Piston bolt hole

Unread postAuthor: Technician1002 » Fri Oct 15, 2010 5:24 pm

There is no reason to make a hole all the way through a piston when it is made on a drill press. The prevents it from leaking through the bolt hole.
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Attachments
Pilot side.JPG
Pilot side has no hole to leak.
Piston Face without seal.JPG
Piston face has a place to screw on a rubber washer.
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 5:39 pm

Ohh alright I see now :D
And that gut with the o ring should be able to smoothly slide up down the release for air were it will be moving right? And the rubber washer acts like a bumper. Just wanna make sure before I get into building it.
Also I'm going to draw a 3/4 circle from template then cut with a bandsaw so it is round instead of rigid because the drill press moves fast. Length 1inch?

EDIT BY MRCROWLEY - Double Post.


MrCrowley wrote:I'm not following you at all because you're not clarifying what you want to say, here's an example:
1inch valve into a 1/2 inch

A 1/2" what? You've listed three things as being 1/2": a barrel, piston and tee fitting. How am I supposed to know which one of those three things you meant when you said 1/2"? Hence the confusion.


Oh :o sorry about that man I'll make sure I explain what I am doing in good clear details
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Unread postAuthor: jhalek90 » Fri Oct 15, 2010 8:07 pm

You sir, must not speak English as a primary language.

If i am wrong, please, work on your english....


It seems to me that you have a horrible understanding of the way piston valves work. i suggest looking at MrCrowley tutorials.... they should clear everything up for you.

Good luck to you.
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POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 8:11 pm

I sear actually speak English and only English and also I was born in America. I'm just a highschool student only using an iPad to type which is really really annoying! Also I have a decent understanding of pistons I just needed some help on it. It doesn't hurt to get extra help.
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Unread postAuthor: Technician1002 » Fri Oct 15, 2010 8:27 pm

OK.. The rubber on the face of the piston is to keep air from leaking into the barrel before it is fired. The bumper goes in the pilot so the piston doesn't crash out the back when it is fired. One is a pad, one is a seal against leaking. The o ring reduces the leaking from the chamber into the pilot area for a barrel sealer piston valve. I hope that helps.

If the piston is 1/2 inch in diameter and the barrel is 1/2 inch in diameter, the piston may blow out the barrel as it can fit inside. :roll:

The Wiki on Piston valves is a good resource too. The only piston where the piston and the barrel is the same size is the QDV valve which does not use pilot pressure to move the valve.
http://www.spudfiles.com/spud_wiki/index.php?title=Piston_valve
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Unread postAuthor: Benjg555 » Fri Oct 15, 2010 8:34 pm

Hmm alright, alright ya thanks man that helped :)

Haha I'll figure out something if not it's going to get interesting haha :D
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