SpudFiles

By all means dont get into the idea of using water for such low pressures...If you own a bike pump you will have the same thing for a fraction of the cost, time and worries. Further more the water pressures in pipe lines can varry greatly from place to place, it being 145psi in switzerland and about 50 in the US... A hand pump can really achieve all kinds of pressure, look up high pressure hand pumps, they can reach 3000psi so really they can be all you need.
A bulk tank is an ok idea but prices vary, for me the best deal was to use my scuba tanks fill em up for about 3$ to 3000-4000psi and then strap a regulator on, but that may be different in your area. Really the only time you would want a bulk tank is when working with helium or hydrogen inorder to break the sound barrier, but that is another matter. For your first cannon use a bike pump, anything else coupld result in you blowing your self up(especially with a PVC cannon).
Look around in the pneumatic showcase area of the forum, there are lotsof simple cannons there which you could look at for insperation.

I wasn't planning on truely using water, more just curiosity. At what point (PSI) do you risk causing catastrophic failure in the bike pump? (I am assuming this is after the pvc explodes but still, always good to ask)

you cant pump up to pressures that high m8, itll be so hard to pump, no way in hell you can, but i guess its around 400psi when things start failing... remember there are alot of things that will just let air out at a specifict pressure(the check valve, tubing, threads) I doubt you could manage to just burst the pump, besides with a bulk and the desire to do so...

Would I probably get better results out of an unmodified sprinkler valve or a ball valve for my first cannon?

i think even an unmodded sprinkler is faster than a ball valve. for you first a ball valve would be fine but you would quickly get bored of its performance. you could attach it to a spring to help it open quicker but still a sprinkler beats it. also if you could, dont glue the sprinkler in. just use teflon tape(available almost everywhere in plumbing section) and thread it. that way when you get bored of your first cannon you could just unscrew it and still have the valve.

Would stores thread the PVC pipe or are there either cheap tools or pre threaded pipe available?

Tools are not cheep but ask the guy who does your pipe lines or toilets, they can thread any pipe for you(ussually fro free)

john bunsenburner wrote:By all means dont get into the idea of using water for such low pressures...If you own a bike pump you will have the same thing for a fraction of the cost, time and worries. Further more the water pressures in pipe lines can varry greatly from place to place, it being 145psi in switzerland and about 50 in the US... A hand pump can really achieve all kinds of pressure, look up high pressure hand pumps, they can reach 3000psi so really they can be all you need.
A bulk tank is an ok idea but prices vary, for me the best deal was to use my scuba tanks fill em up for about 3$ to 3000-4000psi and then strap a regulator on, but that may be different in your area. Really the only time you would want a bulk tank is when working with helium or hydrogen inorder to break the sound barrier, but that is another matter. For your first cannon use a bike pump, anything else coupld result in you blowing your self up(especially with a PVC cannon).
Look around in the pneumatic showcase area of the forum, there are lotsof simple cannons there which you could look at for insperation.

hmmm...hydrogen....

what did I do wrong?

Why do you need to thread pipe? ... Just use the threaded fittings.

jared555 wrote:Would stores thread the PVC pipe or are there either cheap tools or pre threaded pipe available?

You buy threaded PVC fittings and glue them to the PVC...

Ya, i had something similar going through my mind...

Ha!

After reading all of the replies to this topic (after the post about using water pressure to fill your cannon) , I'm left thinking that some of you may not understand the concept, so here goes:

1.) Of course it ties you down to your backyard, or to anywhere that actually has a hose bib, but it is a cheap alternative to having NO compressor at all.

2.) The "compressor chamber" must be a larger volume than your launcher's chamber, to maximize whatever pressure that is available at the hose bib.

3.) Even though someone posted that the water pressure overseas may be close to 140+ psi, the pressure IS controllable, as it DOES take a while to fill the "compressor chamber"; Using the ball valve ( V1 ) as a flow control, you only have to barely crack it open, to fill the chamber slowly enough to prevent over-pressurizing. - Most launcher fabricators will incorporate a pressure gauge on their chamber anyway, so just shut the supply off when you've met the desired pressure.

4.) Filling a ball-valve actuated launcher is just fine, with a bike pump.
But filling a modded-sprinkler valve actuated launcher will sometimes not work, especially if you have a large chamber. The reason being, is that a sprinkler valve's diaphragm has a tiny equalization port in it... When filling a larger chamber, each pump from your "bike pump" adds only a fraction of a pound-per-square-inch of pressure. This fractional pressure will quickly bleed out of that hole, unless you can pump like your Beavis on Ritalin. - You could overcome this dilemma (of course) by adding a ball valve between the chamber outlet and your sprinkler valve (same diameter) ... and this is (of course) an unwanted addition, for most.

5.) The least expensive alternative (by far) is to use a disposable propane tank, to pressurize your launcher. Propane IS heavier than air, so you WILL lose a small amount of "performance". And let us not forget:
Propane IS flammable!!! ---

Image below lists the vapor pressure inside a propane container, at a particular temperature, containing some liquid but not more than 80% total capacity. This allows for a 20% vapor space. (courtesy: <a href="http://www.propanecarbs.com/propane.html">Alternate Fuels Technologies, Inc</a>

<img src="http://www.propanecarbs.com/propan4.jpg">

I've used those little 16.4 oz. disposable propane bottles to pressurize many different launchers. Using them in weather below 50*F, runs the risk of your fill valve freezing, so be careful if attempting to use this.

Any leaks in your launcher and a small spark, would be all it would take to render you F.U.B.A.R, so do so at your own risk!

To me though, using CO2, with the bottle filled to a whopping 800psi, is far more dangerous, and the darn bottle will always freeze up at temperatures below 40, anyway.

And propane wont freeze your pvc?
and that is one of the reasons i am against sprinklers...

...

No, you wont pressurize the room your in. No way. Still don't blank fire it 3 inches from your dear mother's china.. Keep in mind several things when using CO2. 1: it's inert, so you will need good ventilation (it's heavier than air, so windows won't help much...), 2: CO2 gets very cold, which turns PVC brittle. As for air compressors, I can't really reccomend anything. We have one with a gigantic tank that is easily powerful enough, but it requires a power source. Not a problem seen as I have an inverter in the car for my laptop, but it's still heavy.. A foot pump also works well.