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Help making a line launcher

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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Unread postAuthor: dewey-1 » Fri Aug 30, 2013 7:42 am

A flow regulator will control the "fill" rate and be much cheaper and smaller than what dart guy is proposing.

http://www.harborfreight.com/125-psi-ai ... 68219.html

You can see one in the 3D model attached.
The overall length of this model is 36 inches.

Edit to update drawings
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Unread postAuthor: ascientist » Fri Aug 30, 2013 11:01 am

Gun Freak
Agreed. I already have a 1.5 " diaphragm valve on the way.

dewey-1
I just plan on using a schrader valve to fill the chamber, so I don't think I will need the extra valve or a regulator to fill it. That's a great model. Any idea where to get the air tank you have shown and adapters. An all metal unit would be ideal. I'm waiting for the diaphragm valve to arrive than will be driving to various pluming stores looking for pipe and adapters. Schedule 40 2.5" PVC to fit a tennis ball will be hard to find and I would prefer light gauge metal. I may end up buying online, but am leery of making purchase without being able to pretest fit.
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Unread postAuthor: dewey-1 » Fri Aug 30, 2013 11:17 am

ascientist wrote:dewey-1
I just plan on using a schrader valve to fill the chamber, so I don't think I will need the extra valve or a regulator to fill it.


The real benifit is the small guage that is on the flow regulator.
Harbor Freight sells them cheap. You can still use a threaded Schrader valve.
You will need the gauge so you can adjust the pressures for different ranges of distances. Example: 50psi may be 400 feet, 30 psi may be 200 feet.

Also with a guage you will know if it is "armed" or not.

Check your e-mail.
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Unread postAuthor: Technician1002 » Fri Aug 30, 2013 11:23 am

Smaller launchers like that are OK for antenna launching and shorter distance line toss. They are good for a couple hundred feet. Don't expect the 1.5 inch valve variety to toss a water bottle 500+ feet.
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Unread postAuthor: ascientist » Fri Aug 30, 2013 12:52 pm

dewey-1
Now I understand. I'll pick up a flow regulator the next time I'm at Harbor Freight.

Technician1002
A solid 200' range is what I need. Being able to go beyond that would be nice, but probably not ever needed for our application. Dust collector valves or QEVs larger than 1.5" seemed expensive. Couldn't I extend the range just by lengthening the barrel with a larger air chamber? I'm still not sure what those monuments should be.
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Unread postAuthor: dewey-1 » Fri Aug 30, 2013 1:58 pm

Get SCH 40 2 inch barrel (36 to 48 inches), 2 to 1-1/2 threaded bushing, a 2 inch coupling and some of these for a fun time.
Check at your local dollar stores for best prices!
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Unread postAuthor: Technician1002 » Fri Aug 30, 2013 3:42 pm

If you use GGDT you can get an idea of the rough performance as it doesn't compensate for towing a line.

A longer barrel or larger chamber does not always = longer range as the barrel projectile combination is partially limited by the max flow rate of your valve. If the barrel is too long even with a huge chamber, the projectile will get a great push to get up to speed, then exceed the flow rate available through the valve and begin to slow back down to the flow rate the valve can provide into the barrel.

Using this limitation, you can optimize the chamber size and barrel length to maximize the performance of the launch while at the same time reducing the excess air lost in too large of a chamber. Larger barrel and chamber only benefit from a larger valve to provide the flow needed. A 1.5 inch diaphragm (dust collector or sprinkler) valve does have a finite limit on the max flow into the barrel.

A 2.5 inch Sched 40 will fit a stuff fit tennis ball and the Nerf footballs listed above, but won't fit pop cans or water bottles.

If you need very few or only one shot on site, a tire inflater tank works well. Keep it filled to 125PSI to be ready to go.
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Unread postAuthor: ascientist » Fri Aug 30, 2013 4:59 pm

Technician1002
Thank you I understand. I did not know about the Gas Gun Design Tool (GGDT). I'm hoping to make the barrel interchangeable, then I can experiment with several different projectiles for the throw line: weighted tennis ball, water bottle, pop can, throw bag, HighBall throw weight, etc).

I'm not sure what to expect form the from the 1.5" diaphram valve I ordered, but at least the GGDT should give me a rough idea of what dimensions I'm looking at. If you were me what valve would you go with? Again thank you. This has been a very enlightening and helpful forum.
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Unread postAuthor: Technician1002 » Fri Aug 30, 2013 6:34 pm

Off the shelf, Dust collector valves perform very well based on reports of those who use them. They are designed for high gas flow. A sprinkler valve on the other hand is designed for water flow. The design does not allow for gas expansion as liquid flows through the valve and the volume does not change.

Gas flow on the other hand expands when the pressure drops through the valve, and dust collector valves geometry is optimized for this gas flow instead of liquid. They are also designed to snap open, unlike a sprinkler valve which operates slower to prevent water hammer in the pipes.

Best of course is a large diameter home made piston valve. The disadvantage with them is they can be difficult to master the construction so they are reliable. The forums here are full of piston valves that don't work right.
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