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2" Coax Pilot Options? Updated

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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Unread postAuthor: Crna Legija » Wed Apr 06, 2011 10:22 pm

use a sprinkler valve and keep the solenoid in you will need batters wire and a switch. 3/4 will be fine.
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Unread postAuthor: Technician1002 » Wed Apr 06, 2011 11:56 pm

tony48 wrote:Ok attatched is my planned layout. I think it looks alright. It's kinda vague so any questions will be gladly answered. Still not sure about a pilot valve.

It will use ~18" of 2" pipe for the chamber, ~36" of 3/4" pipe for the barrel and a small piece of 1" pipe for the piston to ride in. This gives around a 1.8:1 chamber to barrel ratio.

The piston will be turned out of wood (unless a better option can be found) and I think I will decide to add a floating O-ring.


This looks good. The advantage of the smaller piston is it will remain closed until the pilot pressure is much lower so when it does open, it opens all the way.

Small pistons if made to precise dimensions won't need an o ring. My Mouse Musket used a 1 inch barrel, a 1.25 inch valve seat, and a 1.5 inch piston. It did not use o rings. The replacement valve construction is in a link in my sig. The piston should barely fit for minimal gap, but loose enough to move freely.
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Unread postAuthor: tony48 » Thu Apr 07, 2011 5:59 am

Technician1002: that looks exactly like what I'm planning to make. Would it be possible to run a hose down to one of my handles and use a modded blowgun there as the valve?
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 07, 2011 10:24 am

Choice of pilot depends largely on piston tightness. I was able to pilot this 2" piston with a schrader because of the floating o-ring.

I agree though that for a 3/4" barrel, a 2" piston is overkill, it doesn't need to be bigger than 1" - this will cut down on pilot valve requirements for a given performance due to just 25% of pilot volume vis a vis the 2" for a given piston travel, as well as reducing leaking past the piston for a given tolerance.
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Unread postAuthor: Technician1002 » Thu Apr 07, 2011 10:44 am

Whether the valve can be piloted by a moded blowgun on a hose depends on how much air leaks past. A 1/4 inch ball valve works great.
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Unread postAuthor: tony48 » Thu Apr 07, 2011 11:07 am

Technician1002 wrote:Whether the valve can be piloted by a moded blowgun on a hose depends on how much air leaks past. A 1/4 inch ball valve works great.


I know a 1/4" ball valve would be best but I want it to have a trigger without a sprinkler valve. I've decided to make the piston out of a 1/2" PVC endcap that will ride inside of a 1" piece of PVC. I want to find o rings that will fit but I've been having trouble so we'll see. Hopefully I can find out what the best size is.

I was looking through the cannon section and found a gun similar to the ergonomics I'm trying to create. Below is the link to the gun. It is piloted by a sprinkler valve though which I would like to avoid

http://www.spudfiles.com/forums/extreme ... t2146.html
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Unread postAuthor: tony48 » Thu Apr 07, 2011 3:22 pm

I just turned the piston out of the 1/2" PVC endcap. I used a piece of sheet PVC to make the other face. the only thing left to do on it is add the sealing face. I really took my time on the lathe so the piston is really smooth and fits perfectly in the 1" pipe with a very small amount of friction and a very good seal. See the pictures below of the piston and the bones of the cannon.

My concern now is that the pison is the exact diameter as the OD of the 3/4" barrel.
Will the air in the chamber still be able to open the piston since there is no piston face area around the barrel that is exposed?
Piston Front
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Piston Back
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Overall layout dryfitted together. just need the pilot valve and 2" PVC
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Unread postAuthor: Technician1002 » Thu Apr 07, 2011 4:32 pm

If you slightly taper the end of the barrel (gently sand the end smooth with sandpaper so the end is slightly rounded) This will make the diameter of the valve seat smaller than the OD of the piston by enough to make it work well.
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Unread postAuthor: Gun Freak » Thu Apr 07, 2011 4:34 pm

Will the air in the chamber still be able to open the piston since there is no piston face area around the barrel that is exposed?

No, because the pressure has nothing to push on. If you do what Tech said, it might. Looks very nice so far though. Remember, those bushings won't go directly in the pipe... it needs couplings :lol:
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Unread postAuthor: tony48 » Thu Apr 07, 2011 4:47 pm

Gun Freak wrote:
Will the air in the chamber still be able to open the piston since there is no piston face area around the barrel that is exposed?

No, because the pressure has nothing to push on. If you do what Tech said, it might. Looks very nice so far though. Remember, those bushings won't go directly in the pipe... it needs couplings :lol:


I sure hope this works or I'll have done all of this for nothing! I'll work on tapering the end of the barrel but I'm nervous about this working. Is there any way to calculate what area of the piston needs to be showing to get this to fire?

Update: tapered the barrel. The OD of the new tapered face is .89" and the piston face is 1.02" measured with calipers accurate to the thousandth. I hope this leaves enough barrel material for the piston to seal against. Here are some pictures of my work and how the piston/barrel line up.

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Unread postAuthor: Gun Freak » Thu Apr 07, 2011 7:09 pm

That looks nice, hopefully the seat will hold up. What pressures are you planning to use?
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Unread postAuthor: tony48 » Thu Apr 07, 2011 7:21 pm

Gun Freak wrote:That looks nice, hopefully the seat will hold up. What pressures are you planning to use?


No more than 80 max. Probably average around 60-65. I'll try to pilot it with a modded ball valve but may step up to a 1/4" ball valve if I need to. I'm hoping that this will give it enough area so the piston will open and the seat will hold up
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Unread postAuthor: Gun Freak » Thu Apr 07, 2011 7:48 pm

tony48 wrote:No more than 80 max. Probably average around 60-65. I'll try to pilot it with a modded ball valve but may step up to a 1/4" ball valve if I need to. I'm hoping that this will give it enough area so the piston will open and the seat will hold up

Sounds good pressure wise. As for the modded ball valve/ .25" ball valve, I don't know what you mean. You mean a spring loaded ball valve? I think a modded blowgun will have no trouble assuming your piston has a good seal.
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Unread postAuthor: tony48 » Thu Apr 07, 2011 7:54 pm

Yes sorry, I meant modded blowgun. I think I will run a hose to one of the grips and use a modded blowgun as a pilot valve. Only concern with this is that the hose will increase pilot volume
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Unread postAuthor: Gun Freak » Thu Apr 07, 2011 8:06 pm

tony48 wrote:Only concern with this is that the hose will increase pilot volume

That is a valid concern. You could always pick up a QEV and pilot that with the blowgun connected via hose, but I'm not sure a blowgun alone would be up for the job. It doesn't hurt to try though...
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