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How does my piston valve look?

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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How does my piston valve look?

Unread postAuthor: gwoloshyn » Thu Aug 23, 2007 2:15 pm

Hey, I this is my first attempt at a piston valve and would like some feedback as to how it looks and if it will work. It is a 1.5 inch T fitting, 1.5 inch plug, 1.5-1 inch bushing and i made a rubber disc out of a rubber pvc end cap (its not exactly flat, but it seems like it will seal up the barrel). Have a look.

I made this post because I Don't want to build a whole launcher and then figure out the valve doesnt work :( Does anyone spot any problems?


Also.. when I go to tap my fill valve into the valve, can i tap it into the side of it (seen in picture) rather than on the end plug because its only a 1.5" and the spring takes up a large portion of it. I don't thing a fill valve would fit in there.
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Unread postAuthor: rednecktatertosser » Thu Aug 23, 2007 2:32 pm

I see a major problem, your piston wont seal the chaber off from your pilot area, so when you go to shoot, instead of the piston actuating, you will just loose all your chabered air out the pilot valve. you need a longer piston, that will seal off the chaber, i reccomend molding one out of hot glue, that way you can tailor the piston to your needs. also it will make the piston airtight against the tee, therfore you would need a equalization hole.
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Last edited by rednecktatertosser on Thu Aug 23, 2007 2:39 pm, edited 1 time in total.
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Unread postAuthor: Pete Zaria » Thu Aug 23, 2007 2:36 pm

I agree with Redneck completely. And hot glue pistons do work pretty well, if a tad bit heavy.

You could also extend your barrel farther into the T, to reduce pilot volume. You'll still need a larger piston, but that will make things easier.

I'm pretty sure you can still get a pilot valve on the back cap, tapping it into the side of the T fitting IS A BAD IDEA. If not, you could eliminate the spring by using a design with a longer, larger piston, and a bumper. That would free up room in the back, and would probably actuate faster, too, but you'd also need to fill the piston from the pilot.

Just my $0.02

Peace,
Pete Zaria.
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Unread postAuthor: hi » Thu Aug 23, 2007 2:41 pm

yep, the piston accually needs to fit in the bushing. what you have isnt a piston, its just the seal face. its a problem, but you can make one out of epoxy or hot glue. other than that, it looks fine.
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Unread postAuthor: Matheusilla » Thu Aug 23, 2007 3:07 pm

I don't know if this design will work at all, but correct me if I'm wrong. I see the rubber connected to the piston via a spring, correct? If that is the case, wouldn't the spring just stretch when the piston is actuated? A heavier spring would solve this, that is if I understand the design correctly. I looked over the pictures a few times and that is what I see.
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Unread postAuthor: singularity » Thu Aug 23, 2007 3:32 pm

he doesn't need a larger piston all he need is to move the barrel back further
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Unread postAuthor: jackssmirkingrevenge » Thu Aug 23, 2007 5:06 pm

I think it's best to pause and understand how piston valves work before proceeding any further...
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Unread postAuthor: gwoloshyn » Thu Aug 23, 2007 10:03 pm

jackssmirkingrevenge wrote:I think it's best to pause and understand how piston valves work before proceeding any further...


I think its best to understand that what I did here was a rough, first time design and the point of this topic was to figure out what flaws it had. I wasnt planning on using this on a real launcher yet until I figure out how to build one properly. Of course I visited that page you just wasted your time linking that to me :/
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 10:10 pm

jackssmirkingrevenge wrote:I think it's best to pause and understand how piston valves work before proceeding any further...


I agree. The creator of this valve obviously doesn't have the slightest clue as to how a piston valve is supposed to work.
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 24, 2007 12:05 am

gwoloshyn wrote:Of course I visited that page you just wasted your time linking that to me :/


Of course you did, I wasn't trying to be unkind, but after seeing your design that was clearly never going to work as it was (as everyone else agrees) it was obvious that you hadn't understood exactly how a piston valve works.

A piston valve needs two separate gas reservoirs - a small pilot area behind the piston and a main chamber area in front of it - to work. Your current design only has one chamber, so when you try and actuate the piston all the air will simply rush out of your pilot valve.

Draw a diagram and try and imagine what I'm saying, if it still doesn't make sense to you let us know.
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Unread postAuthor: Novacastrian » Fri Aug 24, 2007 12:40 am

It took me a full 15 minutes sitting and looking at the most simple piston valve to understand how it worked, thanks to Jack :D
Like a bike i suspect, once you get your balance you just want to go faster!!
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Unread postAuthor: noob of noobs » Fri Aug 24, 2007 7:46 pm

Besides the piston, everything looks up to par :thumbright: One concern I have however, is the servicing of the valve. On the first 2 pictures, there aren't any screws, so I thought you might have decided to use cement to put the back plug on. That would be a mistake, because once you have a problem with the piston, you are very unlikely to ever fix it. Then on the third picture, I see screws. That is good, but you'll also probably need a gasket to completely seal the back plug. If you don't the back cap will leak a lot. Did you do this?
Anyway, other than that, it looks good. Good luck! :D
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Unread postAuthor: Novacastrian » Fri Aug 24, 2007 8:25 pm

Hey noob, your avator F'n cracks me up every time i see it, just had to tell you.
Sorry for off topic :)
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Unread postAuthor: noob of noobs » Fri Aug 24, 2007 10:08 pm

Novacastrian wrote:Hey noob, your avator F'n cracks me up every time i see it, just had to tell you.
Sorry for off topic :)


Heh, thanks! There are a lot of funny pictures on uncyclopedia.org http://uncyclopedia.org/wiki/Main_Page I had to shrink the picture on paint though to fit an avatar, so it's a bit pixaly. :roll: Any way, back to the topic...

I'm building a piston valve myself, and I'm using galvanized steel as a T with other steel parts. Getting the piston to fit into the end of the T when the valve's closed is tricky since the pipe threads are almost touching the bottom port. So is it a big problem if the piston isn't always housed in the back port? I know with gwoloshyn's valve it's a big difference, but if it's just hanging over a centimeter or so, is it okay?
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Unread postAuthor: frankrede » Fri Aug 24, 2007 10:29 pm

noob of noobs wrote:
Novacastrian wrote:Hey noob, your avator F'n cracks me up every time i see it, just had to tell you.
Sorry for off topic :)


Heh, thanks! There are a lot of funny pictures on uncyclopedia.org http://uncyclopedia.org/wiki/Main_Page I had to shrink the picture on paint though to fit an avatar, so it's a bit pixaly. :roll: Any way, back to the topic...

I'm building a piston valve myself, and I'm using galvanized steel as a T with other steel parts. Getting the piston to fit into the end of the T when the valve's closed is tricky since the pipe threads are almost touching the bottom port. So is it a big problem if the piston isn't always housed in the back port? I know with gwoloshyn's valve it's a big difference, but if it's just hanging over a centimeter or so, is it okay?

When you finish taht valve you wouldn't mind showing me how you did it?
Because I tried making a piston for a metal T and I was stumped.
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