Elasticity of Latex Rubber Tubing

Build a homemade water gun or water balloon launcher and tell us about it.
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falconfighter
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Post by falconfighter » Wed Jun 29, 2005 12:01 am

I was browsing at McMaster-Carr, and saw that they had latex rubber tubing for sale. I was thinking of a gun with 2 PCs of 4". I see that they all have a max pressure rating, but considering that they will be in a PVC tube restraining them from oversizing, how much pressure can you put in them? What size should I go with in order to get a 4" inflated pressure chamber?

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SSCBen
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Post by SSCBen » Wed Jun 29, 2005 12:11 am

Welcome to Super Soaker Central! Your account is upgraded.

They won't "oversize" like you are thinking. I've run these tubes with nothing over them at all. The only time you would worry about them bursting is when you overpressurize them to the point where they get too long, not too wide. Simply put, you should only use a housing to (1) protect the chamber from damage or (2) restrict the size of the chamber if it is getting too wide (which shouldn't happen).

The pressure as far as we are concerned is how much power the rubber will provide (I believe, but am not sure, that is how much pressure is required for the rubber to expand). With that said, simply buy the same 35 PSI tube I have before and don't spend a second thought on it.

Lastly, you should not use multiple CPS chambers. I have not have good experiences with multiple CPS chambers - the weaker one will expand and the other one will not. It is usually impossible to determine which tube is weaker other than by feeling them around for differences in thickness. Just make a single longer chamber to avoid that problem and keep the system simple. ;)

falconfighter
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Joined: Tue Jun 28, 2005 11:46 pm

Post by falconfighter » Wed Jun 29, 2005 12:37 am

Did you ever finish your SC backpack homemade?
How hard is it to pump 35 psi with a decent pump?
Would a higher psi rating (~50-ish) be too hard or not?
Which diameter tubing should I use?
Is there a consensus on the usefulness of pressurizing the CPS bladder, then pressurizing the PC that contains it?

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SSCBen
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Post by SSCBen » Wed Jun 29, 2005 12:51 am

Did you ever finish your SC backpack homemade?


Yes, of course. I made one, disassembled it later and then rebuilt it. Afterwards, I disassembled it once more to use the pressure chamber in my Vaporizer modification.
How hard is it to pump 35 psi with a decent pump?
Would a higher psi rating (~50-ish) be too hard or not?


A normal 1/2" PVC pump won't have any trouble with either pressure. I stacked tubes over each other to make a very high pressure tube and it wasn't very hard to pump at all.
Which diameter tubing should I use?


Use the only 35 PSI tube McMaster stocks: 3/8" ID, 3/4" OD, 3/16" Wall (#5234K53). Then stack the 1" ID, 1 1/2" OD, 1/4" Wall (#5234K62) over that.
Is there a consensus on the usefulness of pressurizing the CPS bladder, then pressurizing the PC that contains it?


Everyone thinks of this idea and I will offer my opinion on it: it is a bad idea. The tubing was not meant to take outside pressure - I wouldn't even squeeze it, but I will stack other tubes over it because that squeezes evenly (and I've seen chambers blow from rubber stacked over them).

Air pressure will squeeze evenly, but it's just a bad idea simply because it makes CPS no longer CPS. If you wanted to do something like that, simply make a Constant air pressure setup to simplify everything.

Not only that, you will have to construct this setup. Latex rubber tubing thins and I recommend replacement when power is visibly lost. Not only that, but when putting stress on the rubber the chamber may pop. You would have to design it to have the pressure chamber be opened for replacement in short.

You could, in theory, use a constant air pressure system on top of a latex rubber tube, but that would make things far too complicated. It would be far easier to turn up the pressure and get the same or better results.

You'd also have to pressurize the other chamber for the added pressure. Imagine pumping twice or twice as hard with each pump!

It simply would be easier and better to use the rubber by itself or make a different type of CPS system.

falconfighter
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Post by falconfighter » Wed Jun 29, 2005 1:36 am

How does the CPS tube compare to a, say 100 psi homemade, besides being able to be fired on it's side?

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SSCBen
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Post by SSCBen » Wed Jun 29, 2005 2:07 am

It would be hard at best to compare CPS pressure to air pressure, so please, do not take what I say as an exact answer.

In my experience, a chamber about 7/16" thick gets about 60+ feet of range with a straight flow from the PC to the nozzle. I'm not sure about how 100 PSI exactly of air pressure will perform against it, but that's trivial because the thicker you make it, the more powerful it is. ;)

falconfighter
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Joined: Tue Jun 28, 2005 11:46 pm

Post by falconfighter » Wed Jun 29, 2005 11:43 am

What's your recommendation for more layers? Increase by 1/2" ID over the old OD every time, with the thickest possible walls?

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SSCBen
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Post by SSCBen » Wed Jun 29, 2005 2:33 pm

Use the only 35 PSI tube McMaster stocks: 3/8" ID, 3/4" OD, 3/16" Wall (#5234K53). Then stack the 1" ID, 1 1/2" OD, 1/4" Wall (#5234K62) over that.
McMaster only stocks tubing small enough for two layers, and I already had said which tubes to use. ;)

Believe me too, you won't be able to stack tubes that are the same size or smaller ID than the tube you are stacking over's ID. Even though when the tubes are pulled they thin a bit, that doesn't help much.

You will need a tube that is larger in ID than the other tube's OD, and that's what this combination of tubes has.

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