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how to make a piston valve

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 to make a piston valve

Unread postAuthor: SpudFarm » Tue Apr 08, 2008 1:29 pm

this topic saves me loads of work

on a piston you want a good seal between the piston and the housing so it can pilot/trigger. if it is too loose fitting it may not do anything att all.

a piston can be built up on many ways i can explain some of them.

one is for people that wants to get the job done properly the first time.
like the pic, there is: a sealing face, something behind it to support the thin rubber face, something to seal in the housing so it can pilot, o-rings are best, a guide rod to prevent it to flip, a bumper to soften the impact of the piston as it smacks into the housing and the pilot valve.

for newbies:
cut a wood dowel that is so long it cant flip in the housing so you don't need a guide rod, a sealing face and a pilot valve.


you do like this (simple design):
secure the neoprene (or other rubber sealings) to the front of the piston. the best way to do this is with a screw. make sure you get the stuff air tight.

then you get someway to attach a pilot valve on the back of the piston housing. you have to make a "pass through" barrel to get a seat that is what the piston seals against. the way to do this is to grind down the "stopper" that prevents a pipe to go all the way through your fitting. the seat should be so far back that when the piston is in there there is no gap where the chamber is leading in to the housing and the closed piston position.


the "advanced":
you need a sealing face, a pretty long screw, a fitting to attach a pilot valve, some steel washers, a nut and some air. (mabe o-rings and rubber hose)

you do like this: first you put a steel washer onto your screw that is a tiny bit smaller than your seat.
then you put your sealing face on.
after that you put on a steel washer in the back of your sealing face that is the same size as the housing.
on the back of the big washer you put a smaller one. if the hole in the big washer is to big for your nut.
then you screw the nut on until you can notice your sealing face start to bend a bit. the last touch is to close your pilot valve and screw it on the way you want it into to your fitting that connects the pilot valve to the housing and drop the bolt in to make sure that it not touches anything in there. if it does cut small pieces of it until it doesn't.

bumper for advanced pistons:
you can find a small washer that fits on you guiderod (the unused part of the screw) and put it on.
then you find a rubber hose that fits your guidingrod and drop it on, when you have done that you drop one more washer on the other side of the hose and put a tight o-ring or something on the back of your last washer to stop it from gliding of you guiderod and there you go!

and don't forget the rule that d/4 = piston travel. d/4 is diameter of barrel/4 so for a 1" barrel you need 1/4" of piston travel and on a 2" barrel you need 1/2" and so on. if you use longer travel than that you waste power on bigger pilot volume.
pilot volume is the volume of gass your pilot valve has to empty to get your piston moving.

the final touch is to put a light coat of oil/grease on your piston and you can put it in your housing. from there on it is your choice how to handle your new piston gun.





if you think i am missing something here you can notice me.

still not 100% done i am going to put the coaxial and chamber sealer on aswell :)

animation (photobucket removed the last two frames), my first so don't complain :D

another animation how to assemble the easy piston
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Attachments
pistonopen.jpg
this is the valve open. i have added a bumper there.
piston.jpg
this is closed.
simple piston.jpg
this is the simplest version of the valve.
easy piston2.jpg
small and better pic of the easy piston.
may want to look for any detail and note words so you know what i write above
easy piston2.jpg (26.65 KiB) Viewed 1319 times
piston diagram2.jpg
advanced piston number two.
not much to say other than note words and details
piston diagram2.jpg (21.49 KiB) Viewed 1319 times
Last edited by SpudFarm on Wed Apr 09, 2008 3:49 pm, edited 4 times in total.
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Unread postAuthor: MrCrowley » Tue Apr 08, 2008 11:40 pm

It's a bit confusing. Let me explain...

Try get some more pictures in, and number each step to an allocated picture. If I was new, I wouldn't know what half the terms you use, are. It's just a bunch of words that you need to get your head around. Bit hard to visualize if they don't have the materials on hand too.

There's really no design for an 'advanced' piston. It would just include things like o-rings, check valve, light weight, minimal pilot volume etc.

It's also difficult to make a piston when you can't find anything that fits. You're saying how to assemble a piston, not how to make one for a certain diameter.

You're also leeching off another topic, nothing bad about this, but it's a bit unprofessional and confusing.


To be honest, let's cut what I have just gone over and fix your topic to make it a potential sticky.

Okay this is my suggestion.

We don't have a topic that covers piston troubleshooting, like a troubleshooting guide or a guide with helpful tips when constructing pistons or some good ideas and tips. Like using o-rings, or talking about the d=1/4 rule, which only applies to co-axials.

I'd recommend skipping the whole 'how to make a piston' thing, we have two topics which covers this alright.

So you could try and make a troubleshoot/help guide/useful tips and suggestions for upgrades in an all in one topic...

Or you could try and make a copper based piston guide, you're pretty good with them I understand, and they can differ quite a bit from the common PVC piston. A guide on how to make piston valves for copper cannons doesn't sound too bad.

What do you think?

Edit: And yeah, props for putting the effort in.
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Last edited by MrCrowley on Wed Apr 09, 2008 1:26 am, edited 1 time in total.
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Unread postAuthor: kablooie » Wed Apr 09, 2008 1:06 am

Also, for the piston troubleshooting guide, if you end up doing that, I recommend having a section focusing on small diameter pistons and sealing faces (they can be a major pain). Your diagrams look good, if a little bit cluttered. Basically, I second Mr. Crowley, but props for taking the time to write this all out and making those diagrams.
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Unread postAuthor: SpudFarm » Wed Apr 09, 2008 8:48 am

i am on paint now (or a animation) and is going to make a drawing how the parts sit.

thanks BTW
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Unread postAuthor: SpudFarm » Wed Apr 09, 2008 3:45 pm

ohhh no i have wasted to much time on this :'(
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Unread postAuthor: beans » Sat Apr 12, 2008 12:47 pm

I appreciate the attempt, but it is confusing, especially when you put that "beginner" "advanced" and the other one kind right after each other...I would suggest you do an instruction for one type of piston, with a numbered step by step process that has pictures to go along with each step...also, a materials list to begin with would be nice...and no "if you want this you should do this, but you don't have to"
also, how to add the piston valve to the cannon is key too.


but I really want to make a piston valve, so if you can help out, I appreciate it.
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Unread postAuthor: jrrdw » Sat Apr 12, 2008 1:10 pm

beans wrote:I appreciate the attempt, but it is confusing, especially when you put that "beginner" "advanced" and the other one kind right after each other...I would suggest you do an instruction for one type of piston, with a numbered step by step process that has pictures to go along with each step...also, a materials list to begin with would be nice...and no "if you want this you should do this, but you don't have to"
also, how to add the piston valve to the cannon is key too.


but I really want to make a piston valve, so if you can help out, I appreciate it.


I'd like to help you but your post isn't to the point of what you are having trouble under standing. What don't you under stand exactly? The piston valve is built into the cannon, a part of it.
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Unread postAuthor: beans » Sat Apr 12, 2008 1:15 pm

I know how the piston valve works, the concept behind it...that's about it. How to incorporate it into my copper cannon, I have no idea...how to build it, I have no idea...essentially, I have a simple ball valve copper cannon, and I want to make it better
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Unread postAuthor: jrrdw » Sat Apr 12, 2008 1:32 pm

Are you making a 'coaxe' type where the chamber houses the barrel, or a tee type where the storage chamber is connected to a tee houseing the piston valve?

The link above explains the valve build pretty good. Have you tryed searching through the Wiki for your answers? You will also want to search through 'copper cannons' search results. There is quit a few threads on copper cannons with good pictures/diagrams on how they are built.
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Unread postAuthor: SpudFarm » Sat Apr 12, 2008 2:43 pm

ok here is my piston..
hope it helps.
the reson i does not do much more on this thread is that it almost died out.
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IMG_0373.JPG
the piston and the "pilot" assembly. you make a connection at the end of your TEE or chamber to put this part. depends on how you build your cannon.
IMG_0370.JPG
this is how the piston is when open.
IMG_0374.JPG
piston from the side.
IMG_0375.JPG
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Unread postAuthor: watto » Mon Apr 14, 2008 9:25 pm

MrCrowley wrote:Like using o-rings, or talking about the d=1/4 rule, which only applies to co-axials.


Is the d=1/4 rule about how the piston should move back 1/4 of the barrels inner diameter? Whats the rule with a non co-axle like a piston in a tee?
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Unread postAuthor: MrCrowley » Mon Apr 14, 2008 10:27 pm

watto wrote:
MrCrowley wrote:Like using o-rings, or talking about the d=1/4 rule, which only applies to co-axials.


Is the d=1/4 rule about how the piston should move back 1/4 of the barrels inner diameter? Whats the rule with a non co-axle like a piston in a tee?

Yes. Not sure, I think someone worked it out. Just follow the d=1/4 rule but give it a little extra to be on the safe side.
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Unread postAuthor: bigbob12345 » Mon Apr 14, 2008 10:50 pm

I fail to see why the D/4 rule only applies for coax's. Is a barrel sealer different in any way other than the fact its in a tee.
It shouldnt make any difference because if the piston moves a certain length back in a coax and a piston moves the same length back in a tee valve and the porting was the same wouldnt the flow be too.

Sorry for the horribley worded post
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Unread postAuthor: MrCrowley » Mon Apr 14, 2008 11:03 pm

Maybe because in a barrel sealer the air comes from beneath the piston, so the piston could restrict the flow if the travel is small. Whereas in Co-Ax, the air comes from the front, keeping the piston back as far as possible, so there shouldn't be any flow issues.

That's why you may have to compensate in a barrel sealer.

Edit: Oh and this is a guess, not a statement :)
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Last edited by MrCrowley on Tue Apr 15, 2008 3:14 pm, edited 1 time in total.
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Unread postAuthor: watto » Tue Apr 15, 2008 8:58 am

well put, that makes sense
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