SpudFiles

Hey, guys!

It's been a REALLY long time since I've been on here.... Life has a habit of keeping you busy, eh?

Anyway, I've got a question for the more destructively creative among you. (yes, that WILL make sense, here in a minute)

So, I'm working on a hammer valve operated air-gun, hoping to get it to work for airsoft as a shotgun. It's copper, so it will handle pressure better and more safely. There's a chance I'll try to convert it to propane power sometime, but that's not really important yet. I've got the proof of concept working okay, except for one little problem...

I'm charging it via a Schrader valve for now. The copper end cap didn't really seem sturdy enough to hold the Shrader valve threads, so I soldered the valve to the pipe. Unfortunately, that melted the Shrader's o-rings and I've got a steady leak.

Help?! Is there anything you guys can think of? Should I find some way to thicken the end cap to hold the threads without solder, or am I going to have to figure out a different charging valve?

Removing the core from the schrader before soldering would have seemed fairly obvious. Now that the core is fubar'ed, go to the auto parts or bicycle parts store and purchase a replacement core and the tool to change it.



Many different tools to remove the valve core, and whatever store you go to will likely have at least a couple options. This is about as simple as it gets...

That was my initial thought, Gippeto, but I was under the impression that the valve body itself has an o-ring in it. I guess I was wrong?

mako wrote: I guess I was wrong?

No o-ring in the body of a schrader valve...all seals are part of the core.

So...yes.

Hahahaha. I guess I can live with being wrong, if it means less work in the long run.

So, what about the propane angle of this thing? I know a lot of airsoft guns run on it and I own one myself, but I don't know what kind of pressure it's stored under. You think it's safe to use standard copper piping with the stuff?

Edit: I got the hammer valve sealing properly and fixed the Schrader valve leak!
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Propane is a useable pressure source...not high pressure though.

Roughly 10bar (145psi) at room temperature. Might be a good idea to purge the reservoir a couple times to eliminate any possibility of a combustible mixture.

Great resource when working with copper...

http://www.copper.org/publications/pub_ ... ndbook.pdf

Not sure what you're using for copper in your build, but 3/4" type M has a rated internal working pressure of 701 psi. (pg.26 in the handbook)

Not leaking is good.

Ah, thanks! That's exactly what I needed to know.

With airsoft, 145psi is PLENTY. Anything more and you get way too much power to be safe.

Purge the reservoir? I assume you mean purge it of air, so the air and propane don't mix?

Thanks for the link. That's just the sort of thing Ive been trying to find all day. It's hard to find that kind of research unless you know EXACTLY how to search. :/

I'm happy, yeah! I'm going for a break barrel shotgun, so not leaking is great!

mako wrote:Purge the reservoir? I assume you mean purge it of air, so the air and propane don't mix?

I do indeed mean to purge it of air. They do this with new propane bottles, it seems a reasonable precaution and readily accomplished. Can't think of where erring on the safe side hurt anyone.

Makes sense. I guess the pressurized oxygen and propane WOULD be pretty flammable, now that I think about it...

Question on that, btw. I've never heard of anyone's airsoft propane catching fire, but what would you say the odds are of that happening? Assuming the amount of propane released with each shot is just enough to fire a sabot (plus BBs) down a 3/8" or 1/2" barrel approximately 16 inches long? This thing won't be in the vicinity of flame, but I guess there's always a chance of a random spark or static electricity zap...

Very slim chance...ratio of air and propane needs to be in a narrow window to be combustible.

Possible...not very likely. Even less likely if purged.

Okay, that's a weight of my mind, then. A small weight, but it's gone now.

(It's always that 'slim chance' that gets you, tho, isn't it )

An interesting problem I've been having with this valve, by the way. The opening on the reducing joint was bigger than I wanted it to be, so I soldered a washer into it. Worked great, until time came to solder the reducer to the pipe... when I did that, the solder on the washer melted. I DID get this fixed, but it got me wondering... there are solders with different melting points, right?
So, could I have used a high melting point solder to hold the washer and a lower melting point solder to join the pipes? The idea being that the lower temperature wouldn't melt the washer free.

There are indeed solders which melt at higher and lower temps. The issue with using the higher temp solders (brazing solders, silver solders) is that the temps required will anneal the copper...lowering the working pressure.

Best to avoid this scenario if at all possible...careful planning is key.

I hadn't thought of that. I didn't know copper HAS a temper.

Yeah, I'm starting to see that. The planning angle can really save some swearing and money, eh?

Question on hammer valves, btw. Do you know of any links to threads using hammer valves in conjunction with a reciprocating bolt to create full auto? I'm working on a design using it, but I'm not sure about it. I've seen several threads about it on here before, but I can't seem to find them.

If you refer to the handbook I linked to, you'll see there are different working pressures for annealed and drawn copper....straight copper tube is drawn, the copper tube that comes in a roll is annealed. Brazing temps anneal the drawn copper.

I admit "daka-daka" has it's charm, but it's never really been my thing. Using the air blast to cycle the bolt will be very wasteful of air. (blow forward bolt)

Believe this uses a poppet (hammer) valve, but a spring to cycle bolt closed/load ammo/trigger valve...more efficient design than blow forward bolt. IIRC, the air blast is responsible for firing projectile and re-cocking the bolt/striker.

https://www.google.ca/webhp?sourceid=ch ... achine+gun

Something else you might find of interest if you're thinking airsoft...

http://www.swanstrom.net/petes/shoot/autobb.htm

Also check the bb/pellet gun section for posts/topics by Antonio...smart fellow who was building some airsoft stuff.

Interesting. Y'really do learn something new every day, don't you?

Hahaha. Yeah, it's more wasteful, but when you're playing an action sport like airsoft or paintball... ROF becomes VERY important, eh? I just assumed the blown-bolt would be the most easily built. I know JSR likes the pop-off types, but from what I've seen, he's had trouble getting them to work properly. I

Thanks for the links!