Limited pressure drop design

[Silence]

Grrr...I'm not going to make it now. We're headed through there next weekend, and we can't change the date thanks to this. Another trip this weekend isn't feasible. Sorry.

This whole wars thing is a pain. After this year I'll be in college, which definitely frees me up to plan trips based on "inconsequential" things like water wars. But then there's no guarantee I'll be on the mid-Atlantic seaboard, let alone the East Coast, although I should be here in the summer. Hopefully we can make this thing happen sometime in the future, provided the older members stay in the community long enough.

Are you still going to the water war? Hopefully I wasn't the only reason you were considering it. Judging from the Facebook conversation on the calendar, it unfortunately doesn't look too serious.

Sorry for the thread hijack. Back to our regularly scheduled content.

[Ben]

Well, Drenchenator and I should make a trip down there to buy books anyway, so if that's a good excuse we'll do it. I actually have every book I need according to UMD's website, but I assume some more are going to be added later, likely so I can't buy them used as easily. I bought my thermodynamics book at the beginning of the summer in adequate condition for about $100 from what I remember... the used price was $120 and the new price was over $200... or something like that. I'm glad I got it for "cheap."

[cantab]

Two hundred dollars for a fricking textbook!!!! That's a goddamn ripoff. I've known books be expensive, but never anything like that even at current (ie weak dollar) exchange rates.

In any case, I own precisely zero textbooks :-D School and sixth form gave us books (we had to give them back though). University, in my first couple of years, I didn't really need them, my lecturers mostly gave good handouts, and if not the librariers are quite well stocked, though I guess popular titles could become tricky in the exam term. In the later years we go beyond textbooks and are expected to be reading scientific papers.

[Ben]

I try to get by on PDFs, borrowing books, and only buy books when I know I will use them. That wasn't necessary this time around however. Drenchenator already owned some of the books I needed, and some of the books I needed previously could be used in other classes. The Thermodynamics textbook was copyright 2008 and we all know they change minor details like the problems to be incompatible between versions. Usually the PDFs I can find are a few years old.

The textbook industry is a severe rip-off. The state of Maryland was trying to pass some textbook reform act and I don't remember what happened to it. I think they said they'd publish ISBN numbers now, which is somewhat helpful, but not very, because a lot of these books still aren't available anywhere but the bookstores on campus or near campus. That and if you can't find the ISBN number from the textbook title on most of these books you probably shouldn't be going to college...

[Ben]

Due to some other projects I was working on it looks like I'll miss getting this gun and the other prizes out on Monday as I said. I apologize. I don't work tomorrow and only some final PVC cementing and testing needs to be done so I'm going to try to finish most of the remainder tonight.

Some more pictures are on the way. I might edit them in so check back.

[Ben]

I'm attaching a picture of the finished product.

More information will come in a future edit or post.

[Silence]

So it's mostly symmetrical except for the pipe at the bottom, right?

Looks fairly compact for such a powerful water gun, though. I guess I'll wait to hear of the performance.

[Specter]

How many wraps of Teflon tape do you use on the threaded parts? It seems like theres a mountain of tape on each fitting.
I read somewhere that ~90% of people use Teflon tape incorrectly and use way too much for the job. You really only need 2 to 3 turns of tape for any threaded fitting.
The Teflon in the tape makes a very tight, waterproof, and air-proof seal. (but you know that already)

[Ben]

I use two wraps of the pink tape (which is thicker than the white tape). It looks more obnoxious than it is.

The water gun was just sent to C-A_99 so he'll probably get it in a few days.

[Specter]

oh, ok. I guess thats why it looks like there's alot.

[JLspacemarine]

That's one intimidating homemade water gun! Can't wait for stats. As SilentGuy said, it looks fairly compact in overall. To me it seems like it's about as long as a CPS 2000/2500 (about 33 inches).

Good build, as always.

[Drenchenator]

The gun wasn't as big as you'd think. I didn't help in the construction or testing at all (well, I helped slightly in the testing; I held the solar shower reservoir up while Ben pumped), but I can still say that the shots looked good. Range was over 50 feet from what I remember. The gun was tightly built and about the size of a CPS 3000, about 30 inches long if I were to guess. The only real downside I see to the gun is that it lacks an on-board reservoir, which you could just add if you wanted to though.

[Ben]

The range at about 40 PSI with a 0.200 inch nozzle meant for filling water balloons was about 48 feet with the rough stride method. I didn't take detailed ranges because I knew it wouldn't perform any differently from any other water gun, and it already looked to be performing great. I think with a 3/8 inch nozzle at 60 PSI or higher it could easily get 60 feet or more of range.

The consistency of performance was great. This is superior to the old CPS series in that regard. I'd consider it second only to regulated pressure.

The test gun itself was interesting. I don't know if I'd do the layout like I did again. The gun is fairly heavy (at the post office the box weighed 11 pounds!) due to the amount of PVC in it. Larger diameter pipes and less fittings would be better. If I did do this layout again I would be sure to use more threaded parts... I only made the PC threaded, and I'm glad I did because of what I'll say in the next paragraph.

The use of a single piston proved problematic. When the shot is complete the gun slowly leaked air out of the nozzle. The seal must be bad there somehow, likely due to the stoppers I put in. I cut off the end of the PC and sent it to C-A_99 with some extra parts to rebuild it. To do this I had to remove the PC partially by unscrewing it. I'm going to send C-A_99 an extra piston cup to have the double piston assembly used in Supercannon II which was no problematic at all.

The pump leaked a bit at higher pressures. My construction was probably faulty and the higher pressures of the gun make it leak more.

The gun was an interesting experiment with a promising new technology. I'm looking forward to what we could do with this technology in the future... it truly is a real replacement for old CPS.

Attached are some photos of the completed gun.

[Silence]

How tight was the seal compared to Supercannon II's? Note that 3" PVC is 3" in ID; all sizes above that are smaller than advertised, and all sizes below that are larger than advertised. I'm guessing the pipe you used here was much looser anyway.

It's cool that you got near-constant performance. Make sure you bold that sentence in the actual article.

[Ben]

The tightness was about half of what it was for Supercannon II, largely because only one seal was used. There was much less friction due to the reduced surface area from using one seal and using a smaller diameter seal. With two seals the tightness would be similar to Supercannon II.