Is this sprinkler valve OK?

[adiventure]

Would this be an ok valve? If so, how would I go about modding it (I have read that I would need something with more flow than a blowgun)? If not, what recommendations would you have for valves in a similar price range.
http://cgi.ebay.com/Hardie-217B-2-Comme ... dZViewItem

[Drenchenator]

Though the valve looks like it perform well, but I would not recommend buying it for two reasons: the price and the guide rod. 67 USD is far too much for a valve that you would have to do extra work on. 2" NPT is overkill: You won't see a vast improvement in performance in a launcher--which is what I'm assuming you will use this for; if it's a soaker, use a ball valve.

Plus, the guide rod in this valve will make it much more difficult to modify. Modifying a sprinkler valve without a guide rod is fairly straightforward, but the guide rod complicates things greatly.

If you have that much money to spend, spend it on a valve without a guide rod; you'll have plenty of choices that will be easier to modify and possible more powerful.

[Silence]

What do you want to use the valve for?

A) a water gun - skip the sprinkler valve and get a ball valve instead. Sprinkler valves use a diaphragm inside, which only opens a bit to let fluid through. A ball valve opens all the way for more flow.

B) a water balloon launcher - flow isn't too important. Even in this case, just get a smaller (1/2" to 1") valve and modify it if you really want better performance, as Drenchenator suggested. And also, water balloon launchers don't need tremendous range, and too much airflow in a valve could burst the balloons.

[adiventure]

I was actually doing a waterballoon launcher for a school project (get a three inch balloon as far and as accurately as possible using air pressure). I thought the three inch was fairly convenient as I could use this: http://www.sscentral.org/homemade/shells.html sabot too.

[sbell25]

You'll probably have trouble shooting water balloons with this valve. As I found out with my 2" piston valve, because it opens so quickly and with such high flow, the huge acceleration pops the balloons even at low pressures. Using a smaller sprinkler valve or even a ball valve, you can achieve a higher muzzle velocity (although it's less efficient) because the balloons don't pop so easily, due to the more gentle acceleration.

Besides, for $67USD, you might as well buy a piston valve which would outperform it anyway and wouldn't require any modifying. Of course if you did that, you'd run into the problem I mentioned above.

[adiventure]

Will a sabot noticeably lower the chance of popping en launch, or is it just the sheer air pressure and drag that do it in?

[Drenchenator]

I believe it's the acceleration that pops the balloon; regardless of how it's accelerated, the magnitude of acceleration dictates whether it pops. That doesn't mean that you can't get a balloon to a high velocity--it just means that you can't do it too quickly. Too good of a valve as demonstrated by sbell25 accelerates the balloon too much, popping it. The sabot doesn't slow down its acceleration, so it can't stop it from getting popped in this sense.

[adiventure]

I believe it's the acceleration that pops the balloon; regardless of how it's accelerated, the magnitude of acceleration dictates whether it pops. That doesn't mean that you can't get a balloon to a high velocity--it just means that you can't do it too quickly. Too good of a valve as demonstrated by sbell25 accelerates the balloon too much, popping it. The sabot doesn't slow down its acceleration, so it can't stop it from getting popped in this sense.

That makes sense, then what would you recommend for a valve for a launcher aiming for range?

[Drenchenator]

A basic 3/4" or 1" NPT sprinkler valve. It should open fast enough to accelerate it well enough, and tied in with a long barrel, it could get a very high velocity when it leaves the barrel. This should get the best range.

[Silence]

With great amounts of acceleration comes enough force to stretch and contort the rubber. The balloon pops if the rubber is stretched too much at any point or, more likely, if the balloon flattens around a sharp part of the sabot.

With a well-designed sabot, the balloon will likely keep its shape, without encountering burrs and edges that could puncture it. A concave face should support the balloon's skin.

[sbell25]

You could always cheat, and use regular sized helium balloons like I do. They can take a lot of acceleration without popping, so you could use whatever valve you wanted.

If you have to use water balloons, I would actually recommend a metal ball valve. WaterWolf mentioned in another topic that his 1" sprinkler valve also has trouble with popping the balloons. Metal ball valves are the tried and true method, they still get good ranges and are more gentle on the water balloons.

To reinforce this, my 1" ball valve cannon actually out-ranged my 2" piston valve (very powerful) cannon when shooting water balloons. The only reason for this is that water balloons never survive the trip out of the more powerful gun. It's the acceleration, not the velocity, that kills the balloons.

[adiventure]

I guess in leu of the information you guys have presented I'll change the question a bit. What do you think would be the best design (hopefully using a sprinkler valve, however assuming reasonable price and complexity everything is possible) for launching a 3 inch waterballoon (or balloon filled with water) a great distance acurately? Thank you all for your continuing help.

[Silence]

Anything with a pressure chamber and a 3" barrel should work. The chamber to barrel volume ratio should be anywhere from 1:1 to 1:2. A larger chamber would provide more power, but for water balloon launchers, using a small chambers means less pumping. A long barrel should make use of as much of the compressed air as possible.

The Gas Gun Design Tool allows for precise calculations, but you need to know lots of information about the barrel material, pressures, the projectile, and the valves.

[SSCBen]

Perhaps it would be beneficial to determine the velocity at which balloons in certain sabots pop at. Then we could make water balloon launchers perform at peak performance (literally). Someone with a WBL and the GGDT SilentGuy mentioned could do some tests.

[adiventure]

Hm, that program is quite interesting. The only thing that confuses me is what form of valve to put down, and why it has told me that I should have a 5-1 barrel-chamber ratio. Furthermore I was considering a 5' barrel, and 4' (of 4" ID) chamber. Does that sound good or am I destined for disaster? The pump time is of no concern, it is mostly for a school project, then just for fun fooling around with friends.