Is this sprinkler valve OK?

[sbell25]

If you're using a ball valve, put in 'generic' for the valve type. I'm unsure of the opening time though. I always thought it was around 150 milliseconds, however the velocities that GGDT calculates seem to be too low when using that figure.

For sprinkler valves, I found this post on a spud gun forum:

Ok, GGDT inputs for 1" and 3/4" Orbit Watermaster valves

Valve Type: Barrel Seal
Flow Coef: Still trying to work on figuring these out, for now I would go with current estimates... around 6 for 1"
Seat Diam: .95" in a 3/4"...1.1" in a 1" (diameter measured at where the seat actually seals if anyone is wondering where that came from)
Piston Diam: 1.8"
Piston Mass: .8 oz
Vent diam: .05" with solenoid, .1" to .2" depending on the blowgun. .2" usually requires modification on most blowguns.
Pilot volume: 1 in³
Dead vol: up to the end of the threads. 1.5 in³ in 3/4", 2.2 in³ in 1"

NOTE: GGDT has changed since this information was posted. For the flow co-efficient, 30% seems to be a good number for sprinkler valves.

For the chamber and barrel size, there are so many factors that it'd be very hard for us to recommend the ideal setup. Just plug in some data into the GGDT, and tweak it until you get the result you want. You'll eventually find that sweet spot where you get good performance, without an unnecessarily large barrel and chamber.

Generally speaking though, there isn't much point in going for a chamber to barrel ratio of more than 1:1. After that, the benefit you get from the bigger chamber just isn't worth it. For example, if I doubled the chamber size on my launcher (which has a 1:1 ratio) I would only get a 17fps increase in muzzle velocity. And trust me, unless you've got an air compressor you'll want as efficient a launcher as possible, as pumping up huge pressure chambers gets old fast!

As for balloons popping, as I mentioned in another thread that helium balloons are very tough. I can shoot them out of my cannon at 80psi, using a plastic lid as the sabot with no troubles. And that's using a very powerful valve, so rest assured that a helium balloon should handle anything you can throw at it.

[Silence]

The ratio depends on your valve, as sbell25 has hinted. A ball valve opens slowly (about a quarter of a second, depending on how fast you pull), so having a long barrel means the projectile will be in the barrel longer, until the valve is completely open.

Some valves, like quick exhaust valves/piston valves, snap open immediately (in less than a hundredth of a second). With the valve wide open from the start, all the air will escape sooner and a shorter barrel is better.

Of course, things like sabot-barrel friction are also important, and I'm not sure what values you put in there.

[C-A_99]

If you're using a ball valve, I would go with a PVC valve with an attached torque arm if possible. The plastic valves are cheaper and with the torque arm (considering you can make your own, one that's longer and more effective) are at least as good as the metal valves.

Is a modded sprinkler valve really that likely to pop the balloons inside the barrel? Odd...

[adiventure]

It had been my intention to use a modded sprinkler valve, hence the original thread, but I have gotten a bit confused as to whether that would be most effective for range.

[sbell25]

A sprinkler valve is good, but is nowhere near the most powerful you can use. The most powerful 'plug and play' valve you can use is a piston valve. They're a homemade valve, however you can buy them from LaunchPotatoes.com. The piston valves on that page are the ones that look like PVC tees. If you're willing to spend the money, those valves easily outperform a sprinkler valve of equivalent size.

[adiventure]

Thanks for the link. I understand that a piston, or even more expensive valves will out perform a sprinkler valve, but what is the limit of performance at which a waterballoon (or balloon with water as someone suggested) wont break? And what would the recommended barrel and chamber lengths be? I am somewhat open budget wise, as I can get about 40 bucks from my mother, and 20-30 through my grandparents and contribute a fair bit myself, but spending 70 on a valve like that, with no assurance that it wont pop my balloon seems a bit much.

[Silence]

Don't bother buying piston valves - they're expensive and not a good investment for water balloon launchers. Depending on your balloons and sabots, a modified sprinkler valve itself could break a balloon.

Piston valves are meant to shoot solid projectiles fast and far. All current water balloon launchers already shoot water balloons further than you could hit somebody.

[sbell25]

As for balloons popping, as I mentioned in another thread that helium balloons are very tough. I can shoot them out of my cannon at 80psi, using a plastic lid as the sabot with no troubles. And that's using a very powerful valve, so rest assured that a helium balloon should handle anything you can throw at it.

Quote from one of my previous posts. Helium balloons filled with water are very tough. I am using the most powerful of those piston valves in my cannon, and the balloons don't pop even at 80psi. Here's the original topic discussing the water balloon acceleration problem. If you read through it, you'll even find a couple of videos I made, shooting helium balloons at 80psi. Remember, you cannot buy a more powerful valve than what I'm using, so helium balloons will be fine.

Now I'm not saying that you should buy an expensive valve, I'm just saying that getting a powerful one will still work as long as you're shooting helium balloons. You can use whatever you want to, really. Considering the cost of a piston valve, I would recommend using a ball or sprinkler valve for your first cannon. They're still quite powerful and a lot of fun. Then, if you decide you want to build another one with a lot more power, go for a piston valve.

[adiventure]

That video was amazing, thanks for linking me to the thread, it was quite informative. I had a couple new questions though, one, is do you know how much acceleration a a normal sized balloon can handle? Ie, could it take being launched by a similar design at say, 100-150 psi? Which leads to my second question, of whether a modded sprinkler valve at 100-150 psi would be more effective than piston at 80 or so. Lastly, probably quite the stupid question, assuming whatever valve one uses is threaded, do you have to glue/epoxy it to the PVC, or can it just be screwed for easy removal and switchout?

[sbell25]

On my gun, 80psi seems to be the limit of a helium balloon. After that, they start popping or the sabot gets blown to pieces.

According to GGDT, a 1" sprinkler valve at 150psi is around the same performance as a 1" piston valve at 100psi. However, most sprinkler/piston valves aren't rated to 150psi, so I wouldn't recommend going that high.

And yes, sprinkler and piston valves are threaded, so you can just screw them on and off. No glue required. You'll need to use teflon tape on the threads, and re-apply it each time you screw the valve on. So the valves are removable, however it's a little more involved than say, unscrewing a Coke bottle lid.

I would still recommend going with a 1" sprinkler valve, as this is the cheapest option yet is still quite effective. Also, I'd recommend going with a 2" barrel. This means you'll have smaller (lighter) balloons which should fly faster and further than 3" ones. If you do use a 2" barrel, you should be able to use regular water balloons with the 1" sprinkler valve. Plus, your chamber can be smaller so it's easier to carry and pump.

[adiventure]

Yeah, I would definitely go with the 2" if I could, but as it is I am limited by the design of the assignment itself. I may opt to get some 2" pvc and use that as an alternative barrel, but it needs to have the capability of launching 3" balloons. If they are threaded Ill definitely get the sprinkler valve as apposed to the piston, and in the future maybe try my luck with a piston valve (maybe in a whole new 2" system). Thank you for all your help sbell.

[sbell25]

If you were planning on 'upgrading' your sprinkler valve gun with a piston valve later on, you'll have to rebuild a large part of the gun, as piston valves and sprinkler valves attach differently. Sprinkler valves have their inlet and outlet ports in-line (just like a ball valve). Piston valve have their inlet and outlet ports at 90 degree angles to each other, so the outlet is facing across, but the inlet is facing downwards.

You will still be able to re-use your barrel, but you'd need to build a new chamber. Just something to watch out for.

[adiventure]

Well, I went out and bought most of the components (missing the valve, the pieces to mod the valve, and whatever valve I use to insert air), and had a couple more questions. 1 What do I need too hook the bike pump to the pressure chamber, and can the same piece be used with a compressor? 2 Where would I get such a piece, as home depot seems clueless. 3 Do I need any special kind of primer and pvc cement? Also thanks for the information about the piston valve, I was not aware that the inlet was at a different point. Hopefully Ill be done and ready to test by next week.

[SSCBen]

You need a schrader valve to hook a bike pump to the pressure chamber. They might (actually, should) sell them at Lowes or Home Depot in the air compressor section. McMaster-Carr part number 8063K38 works too. You'll also need a 1/4 inch female NPT to 1/2 inch male NPT bushing that you should be able to find in the plumbing section. You can then screw all those together with teflon tape to attach to a PVC threaded coupler.

What do you mean by special primer and PVC cement? There aren't too many varieties of primer and cement other than the types marked "heavy duty."

[Silence]

Generally you screw the valve into PVC fittings. Those fittings are solvent-welded to the pipe using standard PVC primer and cement.

I'm not sure if that's what you were confused about...