SpudFiles

I need to know that to put the data in GGDT so I can find the most efficient pressure to use, now I have to build it first to shot
That would be too late...

Can a direct acting 2way solenoid valve be pneumatically modified? I know modifications are usually done with indirect acting valves like sprinkler valves, but can it be done with these?

Lockednloaded wrote:Can a direct acting 2way solenoid valve be pneumatically modified? I know modifications are usually done with indirect acting valves like sprinkler valves, but can it be done with these?

Might this thread be relevant? http://www.spudfiles.com/forums/1-1-2-s ... 23277.html

Does anyone know where to get a solenoid activated 3 way valve to use to fill and pilot a QEV?

Edit: Im seeing a lot of these on ebay, would they work?

Also, I see a lot of people suggesting 1/8" or 1/4" QEVs for BBs, because the standard 1/2" or 3/4" are overkill. Are the smaller ones actually better, or just all that is needed? Which should I use if I want to be able to fire everything from 6mm to 1/2"?[/url]

1/4" and 1/8" are best for bbs because if you have a large valve the air would be wasted as the bb would have left the barrel already. High pressure low volume is best for small projectiles, i have had good results with 1/4" qevs with a .45 barrel at 400psi

I found two pcp pumps that I can afford, both are the Hill mk3 pump, one of them has a moisture filter the other one doesn't. The one with moisture filter is actually cheaper than the other one, but the site where I found it doesn't have much information about the shipping (it says free for things that are more than 10 pounds also less than 2kg), but I doubt it's only for inside UK (www. Best-fittings.com.uk).
The other is from a Portuguese site, so I prefer this one, less shipping time and safer.
So, is the moisture filter really crucial? Can it be replaced by a normal filter for shop compressors?

Thanks a lot
I don't mind open up my gun and clean it every month, I would be glad to do so actually so I'm gonna buy the one without moisture filter, just a standard air filter to keep away dust

Hi spudfiles
I have a problem, i am in the process of building a slide valve pneumatic cannon but i can't figure out how big my firing chamber has to be. My barrel is going to be 6mm or 1/4" ID at 32" or 81 cm and minimal firing pressure about 150psi

sorry for asking but i have been looking around and cant find anything that helps and i dont have access to GGDT

I have worked of just a volume calculation so far but i would like to get it as small as possible for more shots, Can someone please help?

TheNewKid22 wrote:I have a problem, i am in the process of building a slide valve pneumatic cannon but i can't figure out how big my firing chamber has to be. My barrel is going to be 6mm or 1/4" ID at 32" or 81 cm and minimal firing pressure about 150psi

Depends on what sort of performance you're after.

Assuming a 1 gram projectile at 150 psi, 0.5 cubic inches gives you 335 feet per second and 4 ft/lbs. Good enough for plinking & more than enough for airsoft. 10 cubic inches gives you 573 feet per second and 11 ft/lbs, about the same as an adult air rifle. Beyond that, any performance increases from more chamber volume will be marginal.

Thanks for the reply, i'll try keep this short

I am planning on using this gun at higher pressures but i think 150psi will be the lowest working pressure, I like the thought of the high power but i would like to have about 4-5 shots. my secondary chamber is a gas canister that has a diameter of 7cm and a length of 24cm and i've stuck with this because it is the perfect size for fittings and valves and also has a threaded port for the tire valve.

Thank you again for the help, it's greatly appreciated

That's under a litre. I imagine you're not going to put a regulator between the tank and the slide valve.

What pressure are you planning on filling it to, and what's the power you expect?

Let's say you start with 600 psi, and start with a 10mL chamber. That will give you quite impressive power. Let's say total chamber and slide valve area is 15mL.

Assuming an ideal gas, after each shot pressure goes down to 98.4% of the previous pressure (because the pressure previously filling 923 cm³ now has to fill [923+15]cm³, so to get the pressure for the next shot it's [923/938 x current pressure]). Therefore in the example above:

Shot 1) 600 psi

Shot 2) 590 psi

Shot 3) 580 psi

Shot 4) 571 psi

Shot 5) 562 psi

Shot 6) 553 psi

Shot 7) 544 psi

Shot 8) 536 psi

Shot 9) 527 psi

Shot 10) 519 psi

That's ten shots at very good power, and not a huge pressure drop.

Pessimistic GGDT gives 709 fps/17 ft/lbs for the first shot with a 1 gram (equivalent to a medium weight 0.22" airgun pellet) and 681 fps/16 ft/lbs for the tenth shot, not a big drop in velocity which will allow for reasonable accuracy.

I know some members here are from europe, so anybody know where I can get a long .22 and .177 pellet gun barrel? I live in Portugal so anybody knows a site that sells them and do the shipping? I can only find breaking barrel springer for Camos, most of them are less than 50 cm, I´m looking for longer than 60 cm.

Hey wyz if you call up Crosman they may be able to sell you a 24" barrel in either caliber.

they only sell to canada and us... I'm try to find a European site, cheaper shipping probably.