simple homemade cps gun help

[Commander Soakage]

I need an idea for a simple cps water gun, will someone please direct me to or post a write-up, thanks

[Ben]

This is as simple as it gets unless you use balloons for the pressure chamber: http://www.sscentral.org/homemade/leftovers.html

I plan on making a more detailed guide for a more "professional" version of that water gun design later this year.

For more ideas check this out: http://www.sscentral.org/homemade/supercps.html

[Commander Soakage]

thanks, ben; I looked at your super cps and figured I could probably manage to build it (provided my dad will let me). two questions though, how much do the materials cost and how long does it take to build it.

[Ben]

I have no idea how much it will cost for you because that depends on many factors. Where do you live? If you live in the US, you should be able to get every part. If you're not in the US, you will have to research where to buy LRT (which shouldn't be hard because there are distributors everywhere). Apparently the minimum lengths for LRT today make the order cost at least $40. That was not a problem when I built SuperCPS.

To give you a ball park figure, you shouldn't have to spend more than $150 at most even if you have to bulk order a lot of tubing and make some mistakes. Or at least I hope.

Killer_7 could be more specific about because he has built a CPS water gun more recently. If he doesn't post here because he's busy, feel free to send him a PM.

I couldn't see anyone spending more than 4 hours on most homemade water gun designs in the building stage. Cementing overnight takes much longer. It will take you one afternoon if uninterrupted and the next night to cure.

[Killer 7]

My newest CPH cost around 120-140 dollars US to make, but I messed up and ordered the wrong LRT at first. The actual order that I needed was only about $38. It consisted of three lines each two feet long, so LRT from Mcmaster is not too expensive. The cost will also depend on how thick of a chamber your want. For a really powerful thick one is con cost $45 or more, but as Ben said it all depends.

[Commander Soakage]

I've heard that pvc is really bad for the environment, I need alternatives. please tell me

EDIT by Silence: merged this post into the original thread.

My budget is about $50 I can afford to simplify it but it can't go over $60. also, I need to know if there is an alternative to PVC that will get the job done(PVC is REALLY bad for the environment).

[Silence]

There are lots of plastics (polypropylene, PVDF, CPVC) used for pipes - look through McMaster-Carr's website, but there's not much information on how safe all of them are. You could also use nearly any metal. Sadly, every convenient alternative is far more expensive than PVC.

To be honest, it's very difficult to source cheap alternatives because the anti-PVC movement is new and subsidies aren't on the political agenda. Many manufacturers are also appealing to the medical and flooring industries rather than plumbing, at least at the moment. For the next 5-10 years at least it will still be impractical to get small quantities of pressure-rated PVC alternatives.

If you don't want to spring for copper (which has been used by homemade builders in other countries), which is heavier and more expensive, you could try getting PVC scrap. There's a lot out there; I believe Ben wrote several years ago about scavenging from construction sites. Getting PVC from such "sources" would bypass unnecessary PVC production and trashing.

[Ben]

There's nothing else that is as cheap, convenient, and lightweight as PVC at the moment. Much of what the anti-PVC movement says is exaggeration, especially considering that PVC manufacture has improved in the past decade. PVC additives (not the PVC itself) are somewhat bad for the environment, but not "really" bad. They can give you cancer and more if ingested or if you are exposed to them for a a really long time, but there's no PVC epidemic so it's obviously only a marginal problem (at least from my perspective). I'm all for environmental issues, but I never really saw PVC as a serious threat. Yes, they do need to change it, but from what I know there's not too many better alternatives, especially considering cost.

Look into aluminum if you want something lightweight, but you lose convenience and the price increases dramatically.

Other plastics might work okay too, but they will be more expensive and I can't say if they're "better" or not than PVC.

You might want to read some pages like this one which outlines some different options: http://www.healthybuilding.net/pvc/pipes_report.html

They rated ABS pipe as only marginally better than PVC. Polyethylene pipe they said is an improvement. They had multiple problems with copper pipe and said that the manufacture of other metal pipes is a problem too. It seems to me that nothing is perfect.

They don't discuss polypropylene pipe on that page so I don't know how much "better" it is than PVC pipe, but people have made water guns with that plastic before: http://forums.sscentral.org/t4794/

Aside from wood, I don't know what's completely benign.

[Commander Soakage]

I think I found a decent alternative to pvc, it's called high density polyethylene (or hdpe)
but i need to know if it's reliable. also, I was wondering if ANYONE knew a different place to get it than mcmaster carr.

[Drenchenator]

McMaster-Carr says that 10 feet of 3/4" polyethylene pipe costs 21.19 USD. It's only rated for 160 psi though. Frankly, I don't find it worth the trouble at that price and only with that pressure rating. I can only recommend looking around for other places to buy pipe--and the only other place that I know that sells odd pipe types and sizes is Nolands, but I don't know if they sells this. Best of luck.

[Commander Soakage]

correction, the material I mentioned is actually called polypropylene

[Silence]

Polyethylene is a commonly-suggested alternative, but it's not the strongest of materials. Polypropylene is better in that regard.

Nolands only has stores on the East Coast, and they don't sell online (I think - you could call), so you may be out of luck.

[Drenchenator]

10' of 3/4" polypropylene costs 28.01 USD at McMaster-Carr; 10' of 1/2' is 24.05 USD. They are rated at 330 and 410 psi respectively. If you can't find a place locally that sells it, it may just not be worth buying. PVC is really the only kind of plastic pipe that's available and cheap everywhere in the US.

[Commander Soakage]

piping problem solved, now for another puzzler: what kind of stores would sell latex rubber tubing.

[Ben]

Home Depot and Lowes sell latex rubber tubing. However, they sell only one type and it's terrible for what we're doing.

From what I've seen, the latex rubber tubing we want can only be ordered. McMaster-Carr resells it. Other distributors will make custom orders for you, but many sizes have such huge minimums that ordering would be impossible for most people, and "low" minimums of 20 feet or whatever it is will still cost an arm and a leg. If you can't order from McMaster-Carr, you will have to do your own research because I don't know any other resellers that sell the tubes we are looking for. And I have looked. There are some that has some tubes, but not a very good selection and what they have costs more than McMaster-Carr.

Looking at your profile I can see that you're younger. If not using McMaster-Carr is about convincing your parents to let you order something, show them your plans and say that you want to build it. Tell them it's something you're really interested in and that it has educational value. I'm not an engineering major for no reason. A big part of that has to do with me building water guns when I was younger. It's a great introduction to the problems involved in engineering. Tell them that.

Edit: If you can't get LRT, you can still use balloons or bike tubes layered to get good power. It won't be as professional as LRT but it would work.