First Successful 2" Piston Valve Gun (Gun Name Pending)

[ntiemeier]

I Created this cannon based off of MrCrowley's SGA Golf Ball Gun but made some of my own tweaks, mods, and style behind it. So PROPS to MrCrowley for the baseline design idea.

Chamber: 2" sch 40 PVC - 36" in length not including the bends

Barrels:
1) 2" spud barrel 22"
2) 3/4" barrel 30" with silencer
3) 1/2" barrel 32" with silencer
4) (not finished) 1/4" copper tubing housed in 1/2" pvc barrel for air-soft. I'm letting the epoxy set and still thinking out the air flow.

Piston: Bondo cast in 2" end cap, bolted on neoprene sealing face. Lubed and JB Welded the nut end.

Piston housing: 2" tee. Serviceable piston via 4 bolts for sealing and a 2" end cap. Air tight seal with the implementation of an O ring.

Fill Setup: Optional! Schrader valve or 1/2" ball valve with a Quick-Connect

Pilot Valve: 3/4" Sprinkler valve with blower mod

The piston seals very well but still hear a little bit of hissing coming through the barrel. It is slow but still annoying. I may need to tweak the piston face just a bit. Other than that the gun fires very fast and effectively with awesome recoil.

I still need to come up with ammo ideas for the 3/4" and 1/2" barrels for good damage pics.

What do you all think?

[Demon]

Thats a very nice build :thumbright:

But two things :

1- the barrel seal is pretty small for the barrel size, it looks ready to break with the weight of the barrel ...

2- the sealing problem might be on the barrel seal, try to sand it to a very fine grit if you still can ( i've seen a little bit of glue at picture number 5 and 7 on the barrel port)

Other then that good job

[ntiemeier]

Thats a very nice build :thumbright:

But two things :

1- the barrel seal is pretty small for the barrel size, it looks ready to break with the weight of the barrel ...

2- the sealing problem might be on the barrel seal, try to sand it to a very fine grit if you still can ( i've seen a little bit of glue at picture number 5 and 7 on the barrel port)

Other then that good job

Agreed, Even though it feels sturdy, a support for the 2" barrel may be in order. The other barrels are no problem (not near as heavy).

As far as the barrel port, I'll take a look and do some investigating. I think what you are seeing in pic 5 is primer, not glue, which I don't think should affect the seal. Pic 7 is just the end cap and not a seal for the piston, the bumper just sits on it. I do agree that the small leak has to be coming from the barrel port/piston seal area though.

[Gippeto]

I would stop using that immediately!

With the o-ring groove being that deep, there isn't much material left to handle the force of the piston hitting the endcap let alone handle the loads induced by pressure.

It could...and likely will...fly off...with some "oomph" behind it.

What's behind it when it does?? Your face perhaps??

Re-do that with the o-ring groove cut into a plug...leaving the pipe wall intact to handle forces, and use the same 4 bolts (I'd use 6 1/4x20 screws) to fasten it. Place the screw holes at least 1.5x their diameter from the edge.

[Demon]

What is the recoil with that beast?

[ntiemeier]

I would stop using that immediately!

With the o-ring groove being that deep, there isn't much material left to handle the force of the piston hitting the endcap let alone handle the loads induced by pressure.

It could...and likely will...fly off...with some "oomph" behind it.

What's behind it when it does?? Your face perhaps??

Re-do that with the o-ring groove cut into a plug...leaving the pipe wall intact to handle forces, and use the same 4 bolts (I'd use 6 1/4x20 screws) to fasten it. Place the screw holes at least 1.5x their diameter from the edge.

OK, First, the o-ring is etched into the PVC leader to provide a good seal, however, the even thicker endcap is over it to support the leader providing an even thicker reinforcement to it. That is not only extremely snug on the leader but also bolted on. I can't see how anything would go flying off.

How would this setup be any different than a serviceable piston setup without the oring? In that case you have an even less-tight seal held on by bolts...logically, that doesn't make sense.

I do agree with reinforcing it with more bolts because...Why not, it's just that much safer.

Please correct me if I'm wrong...

[ntiemeier]

OK, OK...After reviewing it again, I see where you are going with this.

I can insert 6 new bolts in front of the oring (toward the barrel).

OR

I can glue a 2" coupling over the leader, fit another 2" extension and redo the o-ring either in the endcap or at the very end of the new leader... but I may have to see about the length of piston travel with the extended leader. Although, that may not be all that bad though to have some more force to seal the barrel port...hmm, but would the extension be smooth enough for the piston to travel in?

Good observation!! Thanks! :cheers:

[Demon]

How have you made the o-ring groove?

[ntiemeier]

How have you made the o-ring groove?

I made the o-ring groove by using the edge of a drill bit the same diameter as the o-ring. If you do this, it helps to start it with a hacksaw first so the bit has a groove to start in. Just keep at it until your oring just barely sticks out.

HOWEVER, Gippeto made a valid point that the oring should have been on the cap rather than the leader.
In my opinion, it could also be on the leader but at the end of the leader AFTER the bolts more toward the endcap. This way the bolts hold to the strong pvc and the weakened PVC is not supporting all of the pressure. This I will redo

[Demon]

You should consider buying an El'cheapo red dot scope

http://www.canadiantire.ca/AST/browse/5 ... 252B30.jsp

It adds great to a spudgun as you can really see around the target and the potato flight path because its an holographic sight

[ntiemeier]

You should consider buying an El'cheapo red dot scope

http://www.canadiantire.ca/AST/browse/5 ... 252B30.jsp

It adds great to a spudgun as you can really see around the target and the potato flight path because its an holographic sight

That's pretty sweet, I'll have to check that out!

[Demon]

After i have finished my 6 mm carbine, i think i will want to make a big piston cannon like yours, just for the fun of recoil and really punching the target down ( a potato at 350 fps gives 200 ftbls )

I have one of these red dot. They are not very accurate but certainly more then the spudgun ...

If you still have some spare money, you could also get a rifled 1.5" pvc barrel from spudtech, they give some pretty interesting increases in accuracy.

http://www.burntlatke.com/rifle150.html

[Gippeto]

Sorry, by "plug" this is what I meant...



Terminology...

Put the o-ring groove on the "front/pressure side" and the bolts where you have them.

Good strength, removable...and it seals.

[ntiemeier]

Sorry, by "plug" this is what I meant...



Terminology...

Put the o-ring groove on the "front/pressure side" and the bolts where you have them.

Good strength, removable...and it seals.

I see what you mean but finding a plug to go inside a 2" pipe will be hard as I can't ever remember seeing one (doesn't mean they don't exist)

What do you think about putting a 2" coupling over the o-ring groove and current holes, priming and glueing, THEN put the plug in the coupling with the o-ring as you described. I'd think it would all be flush on the inside for the piston too...I like that

[MrCrowley]

It's a shame about the o-ring problem, I found on the V.A.L it was much easier to just use threaded adapters sometimes it's just hard to find the right ones. Other than that, and the very small porting, it looks pretty good.

edit: Your piston must be pretty damn heavy, are you even using a bumper? I would also glue your sealing face on, just around the edges to stop any air leaking through it.