Search found 2862 matches

by DYI
Sun Aug 17, 2014 5:25 pm
Forum: Pneumatic Cannons
Topic: Question about piston valve
Replies: 3
Views: 645

Re: Question about piston valve

All that's really relevant here is whether or not the "DWV PVC" is cellular core or not. If it's solid, its behaviour under these loading conditions will be similar to that of a pressure rated section. If it is cellular core, it is very likely to stand up to the static pressure in the valve body, bu...
by DYI
Sat Aug 16, 2014 9:28 am
Forum: Hybrid Cannons
Topic: New to hybrids
Replies: 67
Views: 7568

Re: New to hybrids

The point of a piston hybrid is to trade off some performance for increased ease of use. Using a burst disk pilot on a piston hybrid combines the difficulty and decreased performance of a piston hybrid with the inconvenience of a burst disk hybrid.
by DYI
Wed Aug 13, 2014 10:33 pm
Forum: Hybrid Cannons
Topic: New to hybrids
Replies: 67
Views: 7568

Re: New to hybrids

It should work, although you'll obviously need to adapt one side to copper tube. Copper tube makes for fairly consistent, safe barrels anyway, so on a low pressure design like this there isn't much against using it. The pressure rating on parts like these usually has more to do with their shoddy tol...
by DYI
Wed Aug 13, 2014 10:25 pm
Forum: Off-Topic Hobbies
Topic: Need help from someone in the United States!
Replies: 12
Views: 1318

Re: Need help from someone in the United States!

Don't get too carried away with very high voltage stuff - in the long run, it's a more sustainable approach to have a short, controllable arc length. I've ignited 3:7 propylene/oxygen mixes consistently using a 0.003" long spark powered by a small electronic BBQ igniter. Using a higher voltage suppl...
by DYI
Sat Jul 26, 2014 3:11 pm
Forum: Hybrid Cannons
Topic: MHSSR-1 (From the beginning to the end)
Replies: 10
Views: 3696

Re: MHSSR-1 (From the beginning to the end)

Getting effects like that requires fairly high oxygen pressure, on the order of hundreds of psi at least. I was under the impression that the OP was looking at something which would only require a few tens of psi oxygen pressure. Obviously there are design and operational issues involved with high p...
by DYI
Thu Jul 24, 2014 10:36 pm
Forum: Hybrid Cannons
Topic: MHSSR-1 (From the beginning to the end)
Replies: 10
Views: 3696

Re: MHSSR-1 (From the beginning to the end)

I'm one of those people who have used propane/oxygen mixes in the past (and I still do, although more propylene nowadays). The one you really want to speak to on this is SpudBlaster15, as he has actually built a large bore piston hybrid (he invented them in their modern form) and used propane/oxygen...
by DYI
Thu Jul 17, 2014 6:45 pm
Forum: Hybrid Cannons
Topic: Fueling
Replies: 8
Views: 1181

Re: Fueling

There are two slightly different definitions of the X number in wide usage: 1. amount of fuel for 1X is equal to the amount which could be burned at the desired mix ratio if one started with a SEALED chamber full of air at 1atm and injected fuel until the desired mix ratio was reached. Under this de...
by DYI
Wed Jun 25, 2014 9:59 pm
Forum: BB, Airsoft, and Pellet Guns
Topic: Barrel problems
Replies: 22
Views: 2843

Re: Barrel problems

It would probably work. The melting temperature of isopropyl alcohol is -89C, about 10C below the sublimation temperature of carbon dioxide. This will be more viscous than acetone, possibly by a wide margin. I can't find any viscosity data for isopropyl alcohol down below -10C, but I would assume it...
by DYI
Tue Jun 24, 2014 10:34 pm
Forum: BB, Airsoft, and Pellet Guns
Topic: Barrel problems
Replies: 22
Views: 2843

Re: Barrel problems

I've had a wood "ramrod" get stuck in a barrel before too, to the point that I couldn't move it with a sledgehammer (in hindsight, that probably made it worse). Depending on how thick-walled and hard the barrel is, you have a few options. The least likely to damage the barrel is chilling it in liqui...
by DYI
Sun Jun 22, 2014 8:11 pm
Forum: General How-To & Discussion
Topic: "In the world of spuds today"
Replies: 2411
Views: 137113

Re: "In the world of spuds today"

ITWOSY, after a very long delay spent learning more than I ever wanted to know about equations of state, I finally have a working 1-D model of a gas gun. It isn't very feature-rich or easy to use right now, but it accurately replicates analytic results for shock tubes and piston-cylinder arrangement...
by DYI
Fri Dec 20, 2013 9:49 am
Forum: Pneumatic Cannons
Topic: 6mm piston valve air gun
Replies: 20
Views: 4651

Re: 6mm piston valve air gun

Mach 1 is certainly a functional rule of thumb - but that's more a coincidence than anything. Deviate from the standard design parameters a bit, and you'll climb up over it. I wouldn't say that my explanation was "horrendously over-complex" - perhaps giving the derivation would have been overkill in...
by DYI
Fri Dec 20, 2013 12:40 am
Forum: Pneumatic Cannons
Topic: 6mm piston valve air gun
Replies: 20
Views: 4651

Re: 6mm piston valve air gun

While it initially sounds appealing, Ragnarok's assumption about the maximum attainable speed in an "ideal" gun (one with a massive propellant gas, but assuming an ideal gas EoS, 1D behaviour, no viscous effects, preburned (or pneumatic) propellant, and whatever else I forgot) is incorrect: the maxi...
by DYI
Wed Dec 18, 2013 12:43 am
Forum: General How-To & Discussion
Topic: Equations of State for Gas Gun Applications
Replies: 3
Views: 1147

Re: Equations of State for Gas Gun Applications

The issue is with moving the set of data from a scan of a typewritten page into a format where it can be worked with. That will require a script employing text recognition, which would be a project in itself. I'll do it if it's the only option, but I was hoping to find an EoS which more readily matc...
by DYI
Tue Dec 17, 2013 1:00 am
Forum: General How-To & Discussion
Topic: Equations of State for Gas Gun Applications
Replies: 3
Views: 1147

Equations of State for Gas Gun Applications

As usual, I'm up to something, and I've hit a bit of a stumbling block; Most of the "real gas" equations of state currently in use have been developed with various chemical industries in mind and are thus more oriented toward modeling significantly non-spherical and interacting molecules and mixture...
by DYI
Mon Dec 09, 2013 1:22 am
Forum: Pneumatic Cannons
Topic: Timberwolf resurrection project
Replies: 28
Views: 5062

Re: Timberwolf resurrection project

I believe velocity is referring to the common problem with high pressure seals where a rapid decrease in pressure does not allow sufficient time for gas previously absorbed by the seal to flow out, causing the seal to literally explode from internal pressure. Generally not a problem at PVC pneumatic...