Is this sprinkler valve OK?

[sbell25]

Just so you know, schrader valves can also be filled with an air compressor if you have the right adapter, which are very common.

Also, I don't know what it's like in America with PVC primer and cement, however over here in Aussie we have two different types of cement: Type 'N' and Type 'P'. Type N is for non-pressure applications and is blue, and Type P is for pressure pipe and is green. Just read the label on the primer and cement cans, making sure that it says it is designed for PVC pressure pipe and you should be fine.

[Silence]

I think the port used for air compressors is called an "air coupler". But you're right - you should be able to get a piece that connects an air coupler to a Schrader valve.

[adiventure]

I think I managed to get that piece today now I'm just waiting on the valve, the shrader valve, and the primer. The PVC cement seems fine (there doesn't look to be any pressure/non pressure label), so I think I'm set on that front. There was one new question that came up this morning, it seems the 3"-2" converter I bought is actually 3" true, not three inch ID, could anybody offer an explanation? The other converters seem fine, and the 4"-3" series is going by ID. I inputted all the data into GGDT for firing at the maximum of 150 psi (the rating of the valve I bought, all my pvc is rated to 220+) (though I estimated with the projectile information) and was getting about 170fps, and 500 feet maximum range with a three inch balloon, and about 900 with a 2" balloon. Does that sound reasonable? That would be with a 60" barrel (3"ID), and a 54" pressure chamber (4"ID), I wanted a somewhat smaller chamber, but as this will mostly be stationary, and I have access to a compressor so I don't worry too much about pump time. Being quite new at this I don't really know how reasonable those ranges are, and how much I can scale it down, but for a yet unmodified valve that seems fairly good.

[sbell25]

There are 2 different types of reducers. The first is the reducing coupler which looks like a funnel, and has socket (pipe goes inside) fittings on both ends. The other is the reducing bush, which looks like a cylinder with a hole in the middle. It has a spigot (pipe sized) fitting on the outside, and a socket fitting on the inside.

So which type is your 3" to 2" reducer? Both types are equally common, just offering different ways of connecting to other parts.

EDIT: Forgot to answer the second part of your question. First off, I wouldn't recommend going up to 150psi with a PVC cannon. While your pipe may be rated to 220psi, PVC pipe is NOT designed to store compressed air. While I don't think this actually increases it's chance of failure, if it does fail it is very bad. PVC pipe is brittle and will shatter, so if something breaks and it's loaded with compressed air, you've pretty much got a 150psi shrapnel bomb. Going at a lower pressure like 100psi means that you're less likely to have something fail (badly glued joint, cold weather, or a hard impact can cause a failure).

Also, I'm not sure whether those ranges from GGDT are going to be accurate, to be honest they sound a little low for the size of your cannon. I can't say what your ranges should be, as I've never used a sprinkler valve before. Using GGDT, try a smaller barrel and chamber, and see if it makes much difference to your range. That thing is going to be hard to carry around!

Also, modify that valve as soon as you can! They open MUCH faster once they're modified, as the solenoid that comes with them isn't designed to open the valve very quickly.

[adiventure]

Thanks for the bit about the reducers, we got kinda stumped on that one, probably well take it back and try to get the other kind, it seems less work than getting an extra piece to connect it. We don't really intend to go up to 150, and I understand that it is fairly dangerous even with a good margin of error, but I do need to atleast have range estimates for the maximum. If we were to go that high it would be from relatively far away, hopefully behind a solid object.

The GGDT numbers were throwing me too, I tried changing everything but the valve, and projectile information (which I believe was reasonable), but couldn't get higher than 500 with a 3" barrel, 4" pc, and sprinkler valve. I intend to mod the valve anyway, so I assume those figures will shoot up. At this point I cant really change the chamber size, and getting the 2" barrel will take a whole lot of convincing, so I think I'm pretty decided on the Internal diameter. I am fine with decreasing length, but I was getting much lower numbers as a result of that, and I keep getting odd "the barrel is too long" errors, even with obsene changes (like having the pressur chamber be multi hundred feet).

[Silence]

The GGDT is very difficult to use. See all the various fields that you enter information into? I don't even know where to begin. Most likely one of the fields, say the friction between the projectile and the barrel, is too high. Maybe the pressure is so low the projectile can't even move an inch.

Anyway, try changing variables other than barrel and chamber size. I wouldn't worry too much about perfect modeling, though...

[adiventure]

Yeah, I think I have it worked out pretty much now, the values are all filled in, and all with seemingly reasonable numbers (though I don't quit understand the effect of the external diameter on the pressure chamber). It seems that with an unmodified valve the point of deminishing return starts at about a 5' barrel. I can change the numbers a bit, but anything longer gives only marginally more range (example being a 100" barrel and pressure chamber giving less than 70' more of estimated range). Hopefully this will get built by next weekend, and I can post some pictures/real data.

[sbell25]

It is confusing, but 'Inner Diam' and 'Outer Diam' doesn't actually refer to the ID and OD of your pipe. That little function is put in there if you're designing a co-axial cannon, so you don't need to worry about it. For a normal launcher like yours, just put the Inner Diam as 0, and the Outer Diam as whatever your chamber size is. Your results might have been skewed because of this.

Once you've done that, try comparing the range/velocity of your current design with one that is half the length (both barrel and chamber).

EDIT: Just plugged your cannon into GGDT, and I got 234fps velocity and 694 feet range at 150psi, with a 250gm projectile. Halving the size of your chamber, you only lose 17 feet of range. Halving the size of the barrel as well, you lose another 90 feet. Halving the chamber size again, you only lose another 16 feet. The reason that you're losing so little with a smaller chamber, is because you've gone over the 1:1 chamber to barrel ratio. While having a larger chamber is still going to be more powerful, the benefit is very small.

[adiventure]

Ah, that explains a lot. I'm using somewhat different valve data than you are (what I found on the GGDT website [mostly just a higher flow coefficient]), but otherwise I'm pretty clear on everything but the exact friction of the sabot. I'm not quite sure what it was that was getting you 694 feet range, as I was getting much lower range (200 feet or so) with what I thought were less conservative numbers (I can only get up to about 570, and that if I disregard friction). From what it looks like now, if I go with a 31" PC, and a 50" barrel, I can get about 500' (501) of range. I know that decreasing the barrel will give me only minimal range loss, but I would prefer to keep the range at 500, since it seems like a nice round number.

[adiventure]

I went out and bought everything besides the schrader valve, and the 1/4" tube today. The valve I finaly sourced from ace hardware, and the tube I am having one hell of a time finding anywhere. Home depot had 3/8ths tubes, but they were 50' long and designed for compressors. Any advice on where to find such a tube? Or another name which it might be called? I figure as soon as I get the valve I'll be ready for my first test run (I'll try a tennis ball, just to avoid some of the complications of waterballoons). Hopefully I'll be able to get the the tube soon too so I can mod the sprinkler valve.

[Silence]

Try searching for 3/8" pressure-rated hose, either plastic or fabric.

But what exactly is the tube for? It sounds like it's either for the pump connection or for modifying a sprinkler valve. Fabric- and rubber-covered tubes come with foot bike pumps and automatic compressors, but that's about it.

[adiventure]

Sorry I didn't specify, its for modding the sprinkler valve. I also just found a hose that works. Does the length of said tube matter much? Currently its wicked long, which would be nice for remote triggering, would cutting it shorter have any noticeable effect?

[sbell25]

Depending on your setup, cutting the trigger hose shorter may improve performance. This is a case where the GGDT comes in very handy. Calculate the internal area of your hose, and put that in as the 'Pilot Vol' in GGDT. Then compare that with a much shorter length/smaller area. Up to a certain length, it'll make no real difference but if it gets too long then performance can drop off quite a lot. Having a really long hose would be like using the original solenoid (or perhaps even worse).

You should be able to tell if your hose is too long anyway, as the gun won't sound 'sharp' when it fires. You can always cut it shorter if you have problems.

Also, the longer your hose the more lag there is between pulling the trigger and the gun firing.

[Silence]

Yep, a long hose isn't good for performance. The solenoid part of the stock valve is an electrically-actuated small valve; it release air in such a way that the rest of the valve opens. But the hole it releases air through is rather small. By modifying the valve to use a new pilot valve, you can use a very large opening instead, letting that "pilot air" out quicker and opening the entire valve faster.

A long hose is going to make the pressure drop slower and the valve won't perform as well. If you want remote triggering, I would go with the regular solenoid and use a long wire to a switch far away.

[adiventure]

K, I have the hose set up, and just waiting for someone with powertools to show up. Also I went out and got a shrader valve (finally found one at an ace hardware store), and that is waiting on the drill too. I tried to get as short as I could with the hose, but I worry it might still be on the long end (I cut it as short as I could and still readily reach the trigger, but it is coiled and doesn't uncoil well, so its longer than I would like). When modding the valve, is there anything else that can be done to increase performance? I had read something about putting glue on the leak valve, but had only seen that from one source. Also it seems air comes out of where the solenoid is, is that natural? I'll get access to the drill tomorrow or the day after, so it should be a relatively simple matter to install the schrader valve, and pressure gauge, and mod the sprinkler valve. I have yet to have any luck however on finding a piece to attach a shrader valve to a air coupler, but that is likely due to the ineptitude of the plumbing and hardware staff at my local home depot (and my own too).