DWV parts

bob-a-lu · Mon Oct 08, 2007 4:18 pm

is it safe to use on a combustion cannon?

th3p0p0 · Mon Oct 08, 2007 4:19 pm

yes a "spray and pray" one. i have three of them and they still work and iv had them foe like 3 years so yah

.

DYI · Mon Oct 08, 2007 4:20 pm

What are you combusting? Propane, hydrogen, HMX?

Ask a stupid question...

noob of noobs · Mon Oct 08, 2007 4:47 pm

I'm pretty sure it won't blow up on you if you use a simple aerosol combustion, but I'm not sure about stronger fuels. I wouldn't use it if I were you, the small difference in price is well worth it.

Dornep · Mon Oct 08, 2007 4:59 pm

Then again there are a lot of spray and pray combustions on youtube that have failed.

Do a quick youtube search on potato gun explosion and you will see several. Most of them are either using cleanout caps and bell reducers which fly off, or Wyes and Tees that shatter. Like the Noob of Noobs said, the piece of mind is well worth the small price you will pay for NSF-pw parts.

iPaintball · Mon Oct 08, 2007 5:30 pm

DWV parts are usually OKAY to use with low powered combustions, but if you are using metered propane, a chamber fan, and an efficient ignition system, you should try and use pressure rated parts just to be on the safe side. A properly solvent welded DWV cannon of mine even survived a blast of acetlyne gas. Now THAT was loud.

DYI · Mon Oct 08, 2007 5:45 pm

On a serious note, using DWV PVC is fine for a spray'n'pray, and solid wall DWV ABS is good for any combustion short of a hybrid, even oxygen enriched mixtures (as long as you don't hold it).

bob-a-lu · Mon Oct 08, 2007 5:51 pm

its just the fittings that are dwv the rest is pvc. and im using oust for fuel

DYI · Mon Oct 08, 2007 5:55 pm

Uh oh, my bad. I assumed that you meant Drain Waste Vent PVC, i.e. non pressure rated solid wall PVC, but it seems as though you are actually using a material called "DWV". In that case, I have no idea.
[/sarcasm]

Do you mean DWV PVC, DWV ABS, DWV copper? Some clarification would be nice.

Flamex · Tue Oct 09, 2007 11:32 am

I'm a noob who's bought some parts for a combustion gun I'm going to build, and they are DWV ABS. They seem to be solid wall, but it's not indicated on the piping, it only says it's DWV. Are there any printed labels that indicated whether the ABS is cellular core or not? I'd like to know so that I can return the parts if they are not solid wall.

Fnord · Tue Oct 09, 2007 11:55 am

If it's noticeably lighter than pvc, it's probably cell core. If it's just a little bit lighter, it's probably solid walled.

Cell core dwv-abs is typically ok for a cumbustion, just avoid drilling through it if you can.
If you can get solid wall stuff, go for it. It isn't as easy to find where I live, so I don't usually bother.

jimmy101 · Tue Oct 09, 2007 12:07 pm

Usually cell core pipe will say so on the pipe.

If it doesn't, then look at the end of the pipe. Does is look like a solid piece of material with no difference between the surface layer and the core? With cell core pipe it will look like there is a shell of one material covering a core of another. With solid PVC there is no apparent cover/core boundary.

williamfeldmann · Tue Oct 09, 2007 12:10 pm

If the side of the pipe does not say solid core, I am pretty sure that it is not solid core. Even DWV parts should say if they are solid. The stuff around me says on the side of the pipe and fittings if they are solid or cell core PVC or ABS.

ABS cell core will probably work for your gun and fuel, but the price difference isn't worth worrying about, just return the parts for solid wall.

Drilling holes is not recommended even though almost all simple combustions have holes drilled for ignition and whatnot. Less holes = more stable and safe gun.

Flamex · Tue Oct 09, 2007 12:13 pm

I've got a 3' length of 1.5" pipe and it feels pretty hefty, i'd say the pipe thickness is about 4mm and the pipe itself weighs in at about 2.5lbs. And I just checked the cut of the pipe and there is no difference between the outer material and inner material.

Pete Zaria · Tue Oct 09, 2007 2:50 pm

I've built two metered propane combustion guns, both using DWV cellular core ABS pipe, 4" chambers and 1.5" - 2" barrels, chamber fan, spark strip, ball valve venting, etc... Never had a problem with the pipe. However, here are some tips:

Avoid using cleanout caps - these are by far the most likely part to fail.

Rough up the pipe and fittings a bit with some rough sandpaper before gluing, apply glue liberally, TWIST the fitting at least 1/4 turn as you insert it, make sure it goes all the way to the bottom of the socket, and let it cure for a full 24 hours before testing.

As someone already pointed out, avoid drilling any more holes in the chamber than absolutely necessary, and where you must drill a hole, do so where a pipe and fitting overlap (through two layers of material) and never drill a hole in a sidewall of the pipe, this will weaken it and give it a place to fail.

I've personally pressure tested ABS cell core DWV pipe to 125psi (as high as my compressor goes) overnight with no failure, this does NOT mean it's safe to use for pressure, however, I'm very confident that if the cannon is built properly and the ammo is not "stuck", there's no reason ABS DWV should ever fail in a combustion gun.

Take your time, do a good job gluing, don't put holes in your chamber, and be careful. The pipe shouldn't ever fail. But don't blame me if it does.

Just my two cents.

Peace,
Pete Zaria.