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2" piston valve or dual sprinkler valve?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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2" piston valve or dual sprinkler valve?

Unread postAuthor: Nick481 » Mon Jan 28, 2013 3:40 pm

Hey spudfiles,
I have recently built a 1 inch jar top sprinkler valve golf ball cannon. The sprinkler valve is piloted by a blowgun via a vinyl air hose for trigger placement. The chamber is 36 inches of 2 inch PVC. The barrel is 4 feet of sdr 21 1.5 inch. It has what I think is a very good hop up and I get distances of about 1300 or more feet on 110 psi. I am planning on making a cannon with a 45 inch tank and with my remaining 6 foot section of thinwall 1.5 for the barrel. I know a sprinkler valve doesn't have enough airflow to be very efficient with a tank that size or bigger. I cant decide wether to make a 2" piston valve going by this http://m.youtube.com/watch?v=d40gG2hshig design (piloted by a 1 inch sprinkler valve with blowgun) or use a dual 1 inch sprinkler valve design with the blowguns hooked up together so both sprinkler valves are triggered simultaneously. I'm looking to get a lot more velocity and distance but don't want to take it over 120 psi. Any help is really appreciated.
Nick
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 28, 2013 3:55 pm

A 2" piston would have less flow than two 1" sprinkler valves, but less dead space. A 3" piston valve would beat both hands down.

Hop-up would actually reduce your range, because it's robbing the ball of forward velocity in order to spin it.
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Unread postAuthor: Nick481 » Mon Jan 28, 2013 4:21 pm

I could do a 3 inch piston valve, but do you know if I could follow the same basic piston design with materials for lowes? I.e. I don't know if they sell 3 inch o rings. Im wondering how much more flow and how much faster will even the 2 inch piston be than my current valve? And I believe the Magnus helps with distance because yes it may reduce velocity, but a no spin golf ball traveling at those speeds has a very inefficient flight because it hooks and corkscrews. But I'm not completely sure on that one yet, because it works well on my trebuchets that launch over a quarter mile but they also don't reduce velocity with back spin.
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Unread postAuthor: MrCrowley » Mon Jan 28, 2013 4:47 pm

It has what I think is a very good hop up and I get distances of about 1300 or more feet on 110 psi
I guess that could be possible with the right wind but I more commonly experienced distances of only about 800' using a 1" sprinkler valve with a 4" x 12" chamber and 4' barrel.

1300' is about what I got from a 1.5" porting (2" diameter) piston valve at 110PSI so I'm not sure if a 1.5" piston valve or two 1" sprinkler valves will even increase performance that much if you already get 1300' as it starts getting harder to chuck a GB much further than that at low pressures (in my experience).

but do you know if I could follow the same basic piston design with materials for lowes
They probably wont have 3" pressure rated PVC fittings so you'll have to buy from a plumbing merchant or online at McMaster-Carr or similar.

Im wondering how much more flow and how much faster will even the 2 inch piston be than my current valve?
Assuming you mean a 1.5" porting piston valve (can't remember if techwizzy's is actually 1.5" porting), it will have quite a bit more flow (like 3x more, I think) but is probably quite a bit slower because it's a lot heavier. Still, performance will be a lot better with the 1.5" porting piston valve.

Although JSR is right that two 1" sprinkler valves would have more flow than a 1.5" porting piston valve, I'm inclined to believe that the piston valve would actually offer better performance. I've got no hard facts to back that up, I just have a feeling that is the case even though the flow is less. That intuition may be due to me being biased as a 1" sprinkler valve is relatively quiet at 100PSI compared to a 1.5" porting piston valve at 100PSI and that's not a fair comparison.
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Unread postAuthor: Nick481 » Mon Jan 28, 2013 5:11 pm

I frequently take it out on the golf course next to my house and from the 303 yard tee one of the balls landed on the green on 65 psi so that's the only real confirmed distance I have (with no wind). So 1300 feet is just a rough estimation so it might be a little less. But I kinda decided I want to make I simpler piston design that is also lighter and I really like this one http://i715.photobucket.com/albums/ww15 ... 1275024415 And I'm guessing the air filled from the pilot just leaks around the 1 1/4 inch coupler? Not exactly sure where the lag screw is screwing into either. Maybe something hidden inside the coupler that I'm missing? And for the sealing face would a hard foam or a rubber washer work better (obviously sandwiched between two metal washers)? Thanks for all the help jack and mrcrowley I really appreciate it.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 28, 2013 5:18 pm

Nick481 wrote:And I believe the Magnus helps with distance because yes it may reduce velocity, but a no spin golf ball traveling at those speeds has a very inefficient flight because it hooks and corkscrews. But I'm not completely sure on that one yet, because it works well on my trebuchets that launch over a quarter mile but they also don't reduce velocity with back spin.


It would even out the trajectory, granted, but in terms of actual range you would get less distance firing at a given angle.

If you're serious about squeezing the best possible performance from a given psi and are limited to standard fittings, I would say go burst disk.

It will be cheaper to build and beat any other form of valve hands down.

It can be as simple as this:

Image

All you need is a chamber tube, barrel tube and union between them - then basically find a material for the disk that bursts at say 120 psi (this can be tuned by adding layers of thinner material instead of a single disk, then fill the chamber from say a 150 psi shop compressor until *bang*, Robert's your mother's brother ;)

Again if performance is your goal, this is the way to go.

I've got no hard facts to back that up, I just have a feeling that is the case even though the flow is less.


:shock:

MrC, this is NO way to be a scientist!!!
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Unread postAuthor: MrCrowley » Mon Jan 28, 2013 5:24 pm

jackssmirkingrevenge wrote: :shock:

MrC, this is NO way to be a scientist!!!

#overlyhonest<s>methods</s>scientist :D

edit: wrote something else but realised I had a brain fade :lol:

edit 2: Actually, doesn't a 1.5" porting valve have more flow than two 1" sprinkler valves? 1" sprinklers have about 0.95"^2 of area each, for a total just under 2"^2 together, whereas a 1.5" porting valve has about 2.2"^2. Or am I having another brain fade? :P
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Unread postAuthor: Nick481 » Mon Jan 28, 2013 5:37 pm

I think I might have found a compromise for myself. I looked at hubb's tutorial and I think I'm going to make a simple piston with 1 1/4 coupling and on the barrel end a plug with a piece of felt and then a neoprene washer and then a metal washer on top of that. I'm going to skip a check valve and just rely on air to leak around the coupling. If it is too inefficient I can modify It to match hubb's. I was wondering what you guys would recommend for a bumper in the configuration I will use. I've seen cut up tennis balls are common. Gotta sell my current cannon to my friend first and then ill make a b-line to lowes and make the new cannon.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 28, 2013 5:43 pm

MrCrowley wrote:Actually, doesn't a 1.5" porting valve have more flow than two 1" sprinkler valves? 1" sprinklers have about 0.95"^2 of area each, for a total just under 2"^2 together, whereas a 1.5" porting valve has about 2.2"^2. Or am I having another brain fade? :P


Going by cross sectional area alone, 2 x 1" is 1.57 square inches, while 1 x 1.5" is 1.77 square inches.

What limits a 2" piston valve is the fact that air has to flow between the barrel and the chamber to reach the muzzle, and this (assuming a 1.7" OD barrel and 2"ID chamber) gives you and area of just 0.87 square inches, which is pretty dismal.
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Unread postAuthor: mattyzip77 » Mon Jan 28, 2013 8:29 pm

Use a 1 1/2 inch dust collector valve. I get over 600 yards with mine and its close to what you want to build...look at link below..there are ggdt results in the thread somewhere if interested...


http://www.spudfiles.com/forums/mattys- ... 23317.html

I actually have 3 of these valves 4 sale...pm me if interested..
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Unread postAuthor: MrCrowley » Mon Jan 28, 2013 9:52 pm

What limits a 2" piston valve is the fact that air has to flow between the barrel and the chamber to reach the muzzle, and this (assuming a 1.7" OD barrel and 2"ID chamber) gives you and area of just 0.87 square inches, which is pretty dismal
I still think the flow restrictions in two 1" sprinkler valves would be worse.

In one of my valves, I measured the diameter of the chamber inlet and it was only 22mm (the seat is 26mm). This distance between the wall of the seat and the 'outlet' was a mere 5mm. Also, as shown in the diagram below, the bottom of the valve is not flat (as depicted by the red line); there isn't much room at all for the air to spill over the top and out the porting. The sweeping bottom may even be more severe than depicted, the red line is just a rough guess. Granted, the air doesn't really need the volume at the back of the valve as it is trying to get out the front.

air has to flow between the barrel and the chamber to reach the muzzle
Is this for a coaxial valve? If so, a tee valve wouldn't have the same limitations if the seat is in the middle of the tee. In fact, wouldn't a tee valve almost be analogous to the sprinkler valve in the sense that the 5mm gap between the seat and outlet is equivalent to the gap between the bottom port of a tee and the seat, which, if the seat is placed in the middle, would be 25mm in a 50mm tee. That's a lot better than two valves with gaps of 5mm.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 29, 2013 1:41 am

Yeah, I was thinking in terms of coaxial.

One look at all the acrobatics the air has to go through to pass through a sprinkler valve should be enough to convince anyone to go burst disk.

OP, cowscankill's little writeup here on a triggered burst disk is worth looking at: http://www.spudfiles.com/forums/trigger ... 24868.html
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Unread postAuthor: Nick481 » Tue Jan 29, 2013 11:13 am

Yeah I just really don't want to go the route of a burst disc, even though the performance is great, I don't want to have to make the discs. I think I would really enjoy making a piston valve, and a simple one at first. Do you guys think the piston I described on my post from yesterday would work? Especially they way it's going to equalize.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 29, 2013 2:01 pm

Nick481 wrote:Do you guys think the piston I described on my post from yesterday would work? Especially they way it's going to equalize.


Well, the tutorial which techwizzy ( aka Gun Freak, hybridphobic extraordinaire :D) made certainly shows a design which works, so why not ;)
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Unread postAuthor: Nick481 » Tue Jan 29, 2013 2:08 pm

My bad, I dint't make that post clear enough. I meant the piston made simply from a 1 1/4 coupling and an end plug with a neoprene washer bolted below a metal washer.
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