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Piston valve help, **PICS NOW UP**

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Piston valve help, **PICS NOW UP**

Unread postAuthor: devilman » Thu Jan 24, 2008 3:28 am

Hey all, ive decided what bb rifle im going to make, the only problem is im unsure how to make a piston for it, as i want to use it near 300 psi.

The piston is going to be housed in a 3/4" Tee. I had a look at the how to but it didnt really tell me how to do it in somethign smaller. Is anyone able to give me a quick parts list and a little diagram of it? Cheers

Also is it possible to get more then one shot out of a gun useing a piston valve?

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Last edited by devilman on Fri Jan 25, 2008 6:23 am, edited 1 time in total.
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Unread postAuthor: mega_swordman » Thu Jan 24, 2008 2:36 pm

More making a piston, take a look at Brian the Brain's 100% seal piston. Also, that hose is too long and will effect the efficiency of your cannon.
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Unread postAuthor: MrCrowley » Thu Jan 24, 2008 2:57 pm

The hose isn't actually that bad, but you could cut down on the pilot volume in the fittings behind the tee.
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Unread postAuthor: LikimysCrotchus5 » Thu Jan 24, 2008 3:08 pm

Looks good.

just cut the pilot volume like MrC said and if youd like, you could buy a rifled barrel for Judge, (Judgement_arms) and it will increase performance depending on the ammo. (See im advertizing for you! :) )

If you want to vent with a blow gun you are going to need a small pilot volume.
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Unread postAuthor: devilman » Fri Jan 25, 2008 1:09 am

i brought everything for it today, and it changed alot from this little drawing :P The thing is the pilot voloume is now huge, because of how its made, ill get some pics up asap once the epoxy drys
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Unread postAuthor: LikimysCrotchus5 » Fri Jan 25, 2008 1:27 am

Make the piston bigger to cut down on the volume.
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Unread postAuthor: devilman » Fri Jan 25, 2008 6:26 am

Here are the pics of my rifle. I still dont fully understand how to make a piston inside of it, i used a small piece of pipe with rubber either end, but it didnt seal the barrel? i used an o ring on it also. What did i do incorrect?

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Unread postAuthor: Necrosis » Fri Jan 25, 2008 8:07 am

I think it will be safe to say that the pilot volume is a little to much (from what I can see it's bigger than the actual chamber, lol).

edit after some photoshop magic, this will be what you'd want to end up with.
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Unread postAuthor: POLAND_SPUD » Fri Jan 25, 2008 8:20 am

first of all i don't know much about piston valves - I've never build one.... but there are some things obviouse here:

1. your pilot volume is enourmous - you have to make it as small as possible... acctually you should put/thread/join that brass filling/piloting T directly to the piston T.....

2. a blowgun has very limited flow - use ballvalve or something else

3. keep your stock as it is - but don't use it as pilot volume or chamber... it should be just a thing build out of pipes and fittings - not holding any pressure inside....


anyway it is good to know that there are more people out there who build full metal spudguns

here a pic with my suggestions - sometimes it is better to show something using a picture
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Unread postAuthor: devilman » Fri Jan 25, 2008 5:08 pm

Yeah i gatherd the pilot volume was just a *Little* to big :P

Loke the photo shop work also:P

And yeah i was thinking last night if getting a plug so i can still use the stock, on the other hand i might just make it out of wood or something because this thing is damn heavy :P
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Unread postAuthor: DYI » Fri Jan 25, 2008 6:01 pm

You had better get rid of those pictures quickly. If JSR sees them, his brain will explode.

Everyone else has given you the right answer, just decrease the pilot volume by about 100x, and it should work better. I really have never seen a pilot volume anywhere near that size before.
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Unread postAuthor: devilman » Fri Jan 25, 2008 6:30 pm

LMAO. yeah well im am new when it comes to compressed air as a propellent. I can make stuff explode good tho :P

I re-did the gun taking into account the suggestions, only problem is i dont have a ball valve to use as a pilot valve.

Here are some new pics, is this more like how it should be?

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Unread postAuthor: POLAND_SPUD » Fri Jan 25, 2008 6:37 pm

you could cut that pipe between the filling/piloting T and the piston T to make it better... idealy that pipe should be as short as possible...
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Unread postAuthor: Novacastrian » Fri Jan 25, 2008 6:38 pm

Ahhh, much better indeed. That is what it should look like!
Must be a shat load lighter now too :D
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Unread postAuthor: devilman » Fri Jan 25, 2008 7:04 pm

Yeah i could cut the pipe but its all threaded fittings, and that was the smalles threded pipe i could get. If i cut it i couldent re-thread it.

and yeah, its a TON lighter now :P

All thats left is the piston. i have been looking over a few piston cannons/rifles and i think i know what i ahve to make, here is a drawing of it, is this how i need to make it

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