Dry ice?

Threads about how water guns work and other miscellaneous water gun technology threads.
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H3L10S
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Dry ice?

Post by H3L10S » Fri Aug 11, 2006 9:35 am

I have just made a large (~2 gallon reserve) super soaker out of pvc. I bought a pressure guage for safety. But what I want to know, is, has anyone ever tried putting dry ice in their super soaker? I realize this is a really stupid and pottentially dangerous thing to do, but I will make sure the pressure does not rise above a safe level. Will this be effective, or will the water freeze, ruining my reservoir?

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SSCBen
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Post by SSCBen » Fri Aug 11, 2006 12:02 pm

Welcome to Super Soaker Central!

Would have been better to read the stickies: http://forums.sscentral.org/t3876/

From what I know, dry ice builds pressure far too quickly to be controlable as it turns directly into CO2 gas via sublimation. I am sure that there is a safe amount of dry ice that will build a safe amount of pressure. Anything more however would be dangerous and anything less would be disappointing.

Here they don't let you buy dry ice if you are not 18 years old yet. I'm fairly sure that's consistent everywhere. So dry ice is out of the question for most here.

Last time I checked, there was nothing wrong with air pressure. If you're willing to spend the money on a bunch of dry ice, you might as well just buy a good air compressor. ;)

"For safety" on my most powerful water gun, I have not only a pressure gauge, but a real check valve and an air coupler (better than the crappy schrader valves), and an emergency release valve to immediately release all pressure. The release valve has to exist because the water gun uses a piston, but it's a good idea anyway.

I realize that some people will read these threads and try to use dry ice, so if you do be extremely careful and install a Pop-Safety or Relief Valve available from McMaster-Carr.

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Silence
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Post by Silence » Fri Aug 11, 2006 4:17 pm

Yup, safety is always important. I would only use a metal tank and tubing, a pressure release valve, and a small amount of dry ice--a bit of research on the properties of carbon dioxide will probably tell you how much volume a specific amount of dry ice will expand to fill, and you can use Boyle's Law to find the pressure.

So I suppose it's possible with PVC if you find the right amount, but I still don't recommend it. And yes, you can do far more with an air compressor... ;)

H3L10S
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Post by H3L10S » Fri Aug 11, 2006 4:58 pm

Sorry about not reading the sticky. I guess I'm a little dumb. And that is certainly no way to introduce myself to an online community. SO I guess dry ice is out of the question. But I would like to know how to stop it from leaking at the screw cap and one of the elbows.
Here is the gun:
Image
Last edited by H3L10S on Fri Aug 11, 2006 5:13 pm, edited 1 time in total.

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Silence
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Post by Silence » Fri Aug 11, 2006 5:06 pm

Well, whatever you do, just remember to be careful. That'll get you far in life.

Could you get a picture of your homemade? At any rate, there are several things you can do to create a better seal for the PVC. You could try to pull apart the pieces and reglue it (although I doubt you could pry them apart), as Ben said at iScF you could use an acetylene torch to literally melt and weld the parts together, or you might have to restart on those parts completely.

In situations like these, preventative measure far exceed the limitations of repairs. So the least you can do is to use primer and cement and perhaps clamp the parts together even more thoroughly the next time you put a gun together. Anyway, good luck with this!

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Drenchenator
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Post by Drenchenator » Fri Aug 11, 2006 6:18 pm

This homemade looks pretty good so far. You can fix the leaks from the threaded cap easily by using thread seal tape. It should be available in the plumbing section of Lowes, Home Depot, or hardware stores. I am assuming that you unscrew the cap to fill the gun. Caps tend to be difficult to use, so you may want to replace the cap with a threaded ball valve (this photo shows a ball valve used in this manner).

You would probably have to do some fillet welding to fix the leaking elbow. Ben's plumbing book says that "fillet welding is the generally accepted practice of repairing leaks in thermoplastic piping systems", so it seems like your best bet. I think that you have to do pretty much what SilentGuy said, but you have to clean the pipe. I am going to try to scan in the pages from that book that tell exactly how to do this, it seems that many people want to know how to fix leaks like this.

EDIT: I scanned in the pages.

Page 144 - Solvent Welding
Page 145 - Threaded Joints, Fillet Welding
Page 146 - Fillet Welding
Page 147 - Fillet Welding, Underground Installation

I also combined all of the pages about fillet welding into one, very large image available here.
Last edited by Drenchenator on Fri Aug 11, 2006 7:02 pm, edited 1 time in total.
The Drenchenator, also known as Lt. Col. Drench.

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SSCBen
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Post by SSCBen » Fri Aug 11, 2006 9:34 pm

It does appear that you have used thread seal (teflon) tape, and that's good. You also did use tubing clamps. Normally those are most people's problems. Some people prefer a chemical sealant which they claim works better, but teflon tape never has failed me. You might want to try that if my suggestions below don't help. If the tubing clamps don't work either, go to a car store and buy the expensive permanent tubing clamps that require a special tool to install. That's what I need for one of my water guns because the force is too much for the tubing clamps.

The problem with the leaking most likely is due to the fact that you used a thread tap to make the threads for the barbed fitting. A lot of people think that kind of stuff works well, but it doesn't. Other than what others have recommended, I'd just remove that tee and replace it with a cross and the right reducers to use a real female coupler to attach the tubing barb. Shouldn't be too much trouble.

A lot of people think the only way to attach schrader valves and the like is to tap a hole into the PVC. Don't ever do that. I would never trust that. It's always better to use the right couplers and adaptors if you can. Most schrader valves can be threaded into a coupler that will thread into 1/2" threads. Works great. I can switch between schrader valves and air tool couplers easily with no leaks with that system.

Don't worry about making a good impression either. You already have. :)

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Silence
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Post by Silence » Sat Aug 12, 2006 1:30 am

Thanks for getting the picture. I like the design--it's fairly unique, perhaps because few designs allow for pressure inside the hose.

Another effective but unreliable (a slight oxymoron, but I don't really know how to describe it) solution is to try epoxy. It'll be hard to get the epoxy into the crack as opposed to on top of it; it it's on top then the seal will be weak, but if it's inside then it will be strong. It's something to try, but don't count on it. JBWeld and other good types are extremely strong once dried, but nothing stops the entire epoxy section from coming off of the PVC.

Of course, it would be quite a challenge to get the epoxy inside without a huge mess. Perhaps some strong glue that comes in a tube as opposed to two containers would work better, but that would also be hard. If you have the correct tools, then I would just go with fillet welding.

Hopefully, you'll be able to get this problem resolved--and at any rate you'll have learned a lot in the process. One other thing you might want to do--and that is still possible with this design--is to put the backpack part (I think there's a backpack in the design) into a real backpack. From the looks of it, it seems the duct tape straps and the piping wouldn't be very comfortable. However, if you do end up sticking that entire part into a backpack, make sure the tube connection is at the bottom of the backpack so the water comes out instead of air. Hopefully, the hose won't be too short...

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Post by H3L10S » Sun Aug 20, 2006 2:58 am

Well, over my vacation of waterskiing, I added a 4"x24" abs pressure chamber, and fixed all the leaks, so now it is functional! I am pleased. :) It shoots a really non-contiguous stream out to about 30 feet at a 20 degree angle. Any advice on better nozzles?

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Silence
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Post by Silence » Sun Aug 20, 2006 1:39 pm

All I can say is to keep on experimenting with the nozzles until you find the right one. Ben had suggested using a quadratic (you don't even need to use a graphing calculator to find the equation) to find the peak range, but I don't trust that--I'm pretty sure calculus has much better equations to use.

What you'll want to do, though, is to have an extension that uses a hose or a fixed angled joint or something to put the nozzle at a different angle from the PC (I think the new gun is supposed to be different from the picture, but I'm not sure); otherwise, the area of the water surface will change. A piston would be the best solution, but it's probably too late.

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SSCBen
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Post by SSCBen » Sun Aug 20, 2006 2:22 pm

Sure, there are better equations to use. A bell curve for example. In fact, the curve does follow very closely a bell curve. The problem is, most people's calculators don't have the ability to make a bell curve regression. A quadratic equation is a good approximation, which is all the calculated ideal orifice diameter is, an approximation.

The only true way to know for sure is to test every drill bit you have. ;)

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Silence
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Post by Silence » Sun Aug 20, 2006 2:56 pm

Well, I suppose the difference can't be too bad. But does this mean that the orifice sizes you use to approximate should be closer to what you'd guess is ideal? It seems like a bell curve and a quadratic would mainly be different at the extreme domain values.

Wow, this is fairly off topic..but it could be worse.

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