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Inline 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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Inline Piston Valve

Unread postAuthor: PinHead » Thu Sep 11, 2008 6:21 pm

I've been trying to think of a valve to use for an RPG or bazooka-style weapon for scenario paintball. A regular sprinkler valve would work fine of course, but I really wanted to make a piston instead; I also wanted something that would fit inside a single tube, which would probably break open on a hinge for breech loading. So I came up with this.

Image

Basically, it's just a small piston within the larger bore of the launcher's main body, with a flat sealing face between the barrel and chamber. Since the piston is so much smaller in relation to the bore, the pilot volume should be smaller then normal, which is good of course. I don't think the flow would be as good as a normal barrel- or chamber-sealing piston, for obvious reasons, but the pilot actuation should be faster. The size of the piston would be half of that of the bore; in my example, a 1 inch piston in a 2-inch nerf launcher.

The only PITA would be assembling everything in the right order to get it all together, and the pilot/fill having to go thru the chamber might be a pain, but it could be done. Also, you'd need to have the sealing face be removable so the piston could come out the front in order to be serviced.

I don't doubt that someone has already made/designed something similar, but I came up with this myself a couple days ago, so let me know if it's been done.
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Unread postAuthor: potatoflinger » Thu Sep 11, 2008 7:10 pm

This won't work, you have to have pressure pushing the piston back, and in your design you have the front of the piston sealed off. I think your best bet would be a coaxial, as it is pretty similar to your design. The only bad part about a coaxial is that the barrel has to be smaller than your chamber.
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Unread postAuthor: MrCrowley » Thu Sep 11, 2008 10:31 pm

I pretty much had the same idea, except mine will work. :wink:

I can't be bothered finding the topic but here's a diagram:

Edit: That's an old drawing, can't find the new one. The advantage of the new one is that it's assembled inside a coupler and uses two halves of a bushing on the bottom to support the piston housing. Allowing more flow then this diagram.
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Unread postAuthor: Gippeto » Thu Sep 11, 2008 11:35 pm

Two words;

Toolies piston.

Judgement Arms made one not too long ago. It's simple and it's in-line.

http://my.freeway.net/~toolies/
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Unread postAuthor: clide » Fri Sep 12, 2008 12:00 am

As Gippeto mentioned a toolies style piston would be the easiest way to accomplish the same goal.

As for prior examples of such a setup. Man-o-brass designed one in a chamber sealing configuration, but it would just need a change of equalization hole to be barrel sealing. http://www.geocities.com/man_o_brass/in ... valve.html

There is a commercial air cannon for unclogging silos that uses a similar setup as well. http://www.vibco.com/pdfs/air_cannon.pdf

Navigator7 had plans to build a steam cannon with such a valve, but I don't think he ended up getting anything built.
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Unread postAuthor: ALIHISGREAT » Fri Sep 12, 2008 1:25 am

i would just make a coax, then make it breach loading by using a lever couplings on the back so you pop the pilot setup off, pull the piston out, put your ammo in, put the piston back in then put the pilot setup back on and charge the cannon.... it also allows a longer barrel!
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Unread postAuthor: PinHead » Fri Sep 12, 2008 8:26 pm

I see what you mean now about not having pressure on the face of the piston; I had considered that but didn't know how much it mattered. I thought about simply sanding the sealing surface into more of a shallow cone shape, rather than one that was completely flat; this would allow some force on the piston surface. Otherwise a pull spring would do the job too.

The concept that man-o-war used occurred to me too, with the piston being on the barrel side and getting pushed straight back upon actuation (picture my drawing backwards), but I decided not to go that route since it would have required an extra o-ring. I would think that it would actuate extremely fast though.

I had been leaning towards a coax for a while, but they're always fatter by nature, and they don't lend themselves to fast breech loaders as well, especially with an odd-shaped projectile like a nerf. I've only thought of one design that would work, but I would have to basically fabricate a bunch of pieces by hand and weld them all together (I'm a full-time welder by trade)... cool, just not what I want to do with this one. Thanks for all the constructive advice so far guys.
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Unread postAuthor: ALIHISGREAT » Sat Sep 13, 2008 1:43 am

yes but the method i explained for breach loading a coax sould take long at all?
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Unread postAuthor: LikimysCrotchus5 » Sat Sep 13, 2008 12:29 pm

Coax's are ok i just dont like the fact that it reduces alot of your volume that can be contributing to power.

In my perspective, just go with the toolies, biged just 2 beautiful cannons using this piston. He made a mortar and a "bazooka" you should check them out pinhead.
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Unread postAuthor: PinHead » Sat Sep 13, 2008 12:59 pm

I saw Biged's MA1A bazooka just the other day. I agree, it's a very nice piece of work. I had no idea that he used a toolies, I just saw that he piloted it with a QEV. I'll have to keep that in mind.

Ali, I don't mind a coax, but I really don't want to have to remove the piston to get a nerf in there; there's nothing wrong with it, I just decided that a coax was unnecessary and that an inline was easier. The break barrel that I have in mind will be very similar to this thing.
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Unread postAuthor: biged » Sun Sep 14, 2008 7:33 am

Pipes, washers and a welder.

This is a pic of 3" piston that's in the 4.2 mortar. It's the same design that is in the bazooka, except that the bazooka is a 2".

Image


Image
Here's a set of "nerf" internals that will fit inside a demill AT4. They were designed for a m72 law but they were too large. I am reworking the design for the law so that the barrel can also collapse and extend.

///ed///
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Unread postAuthor: ALIHISGREAT » Sun Sep 14, 2008 7:44 am

nice piston design... but i still prefer coaxials :wink: (mainly because a muzzle loader is less threatening)
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Unread postAuthor: VH_man » Sun Sep 14, 2008 8:35 am

@ Biged:

I think I might have to steal that design for the Burstshell launcher I am Constructing. Might be alot more... Pretty.... then a QEV.
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