When something in a pneumatic system fails the air pressure can continue pushing the object creating a projectile or bomb like scenario. When a hydraulic component fails it usually doesn't get that continued push.
Home made throw ball cannon!
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BS Tree Service
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In the situation of a failure of a pipe that makes sense. But as far as pressure ratings, why would it be different for air than water? Are there two different psi's for water and air when it comes to pipes?
BS Tree Service
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I understand that water has really no stored energy and that air can create a lot of energy causing pieces to fly everywhere in the event of exceeding psi rating but when it comes to psi ratings isn't it all the same?
mattfr12
The Bulldog
We use to make patato guns out of that stuff. It's pretty strong pipe. Used aqua net hairspray to shoot it
I am a tree guy, not so much a materials engineer. I looked into it in more detail 6-7 years ago when I made the pneumatic launcher, and it made sense then...enough that I intentionally decided to stay well below working PSI and included a pressure relief valve that blows just in case I decide to be dumb and see if I could max out the launch height by pushing up the pressure.
I am not saying I have never pressurized PVC with air (or that I will not do it again). It made me real nervous pressurizing it when it was 15 degrees out...things tend to start getting brittle - I wouldn't do that again.
I AM saying that I would not recommend somebody else do it or let an employee on the job use it (stuff happens, and I don't want that responsibility/liability).
I have also never claimed "I did my research on the material's and I am sure not to exceed manufacturer psi ratings" when it is simply not rated by the manufacturer for pressurized air.
If you want to read more on pneumatic launchers, Google "antenna launcher". Amateur radio guys use then to string wires for HAM radios. A tennis ball fits perfectly snug into 2.5" PVC. A sprinkler valve release air more quickly than a ball valve (but, I am pretty sure that is not rated for air either)
The conclusion I came to:
Air cannon = fun.
Big Shot = practical (and kina fun too).
I am not saying I have never pressurized PVC with air (or that I will not do it again). It made me real nervous pressurizing it when it was 15 degrees out...things tend to start getting brittle - I wouldn't do that again.
I AM saying that I would not recommend somebody else do it or let an employee on the job use it (stuff happens, and I don't want that responsibility/liability).
I have also never claimed "I did my research on the material's and I am sure not to exceed manufacturer psi ratings" when it is simply not rated by the manufacturer for pressurized air.
If you want to read more on pneumatic launchers, Google "antenna launcher". Amateur radio guys use then to string wires for HAM radios. A tennis ball fits perfectly snug into 2.5" PVC. A sprinkler valve release air more quickly than a ball valve (but, I am pretty sure that is not rated for air either)
The conclusion I came to:
Air cannon = fun.
Big Shot = practical (and kina fun too).
jomoco
Tree Freak
My pneumatic throwbag gun's over 20 years old now, made from aluminum piping, and has considerable recoil when fired at 160 psi, much like a 12 gauge shotgun.
And though the barrel's only a foot long, the recoil's such that when aiming at the crotch I want, I must actually drop my aim a foot or two below that crotch to compensate for the recoil of the gun's lift when fired.
It's that recoil that's going to really torque the hell out of BS Tree's pvc gun right where the launch barrel connects to his valve IMO. The longer the launch barrel? The harder the recoil's going to be, the more force applied to barrel and valve connection each time it's fired.
That's the weak point in BS Tree's design, that needs to be reinforced with an outer sleeve that keeps the pressure tank firmly aligned with the launch barrel during recoil when it's fired, IMO.
Without that reinforcement between the two chambers? That gun's an accident waiting to happen!
jomoco
And though the barrel's only a foot long, the recoil's such that when aiming at the crotch I want, I must actually drop my aim a foot or two below that crotch to compensate for the recoil of the gun's lift when fired.
It's that recoil that's going to really torque the hell out of BS Tree's pvc gun right where the launch barrel connects to his valve IMO. The longer the launch barrel? The harder the recoil's going to be, the more force applied to barrel and valve connection each time it's fired.
That's the weak point in BS Tree's design, that needs to be reinforced with an outer sleeve that keeps the pressure tank firmly aligned with the launch barrel during recoil when it's fired, IMO.
Without that reinforcement between the two chambers? That gun's an accident waiting to happen!
jomoco
160 psi 
How heavy of a weight do you shoot, and how high does it go? I get 90' from a 16 ounce tennis ball at about 50-60 psi.
How heavy of a weight do you shoot, and how high does it go? I get 90' from a 16 ounce tennis ball at about 50-60 psi.
BS Tree Service
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jomoco
Tree Freak
160 psi
How heavy of a weight do you shoot, and how high does it go? I get 90' from a 16 ounce tennis ball at about 50-60 psi.
A little over 16 oz, since there's an additional cordura nylon jacket sewn over the bag to protect it.
I get in excess of 120 feet at 160 psi.
Gun's pressure tested at 300 psi by the shop that built it for me, so I feel pretty safe under 200 psi.
I charge it with my CO2 bottle. Which has a braided steel line to handle that kinda pressure.
However the gun's been in the bottom of one of my truck's boxes for years now since I purchased a Big Shot.
Not the kinda gun that goes unnoticed on the job, and I've had cops give me the evil eye the few times I've used it in Balboa Park and other downtown high pedestrian areas as well.
jomoco
Aldegar
www.gigharborbigfoot.com
Moral of the story is that tree guys love bad ass toys, what we need though is a bat man ascender.
One pound per square inch is one pound per square inch doesn't matter if it's water, air or concrete. Now if the PVC fails with too much water presure you get a crack the water spills out and the presure immediately drops since water isn't compressable. Air is compressable so when the PVC fails you get a much bigger crack or cracks and then projectiles. The projectiles are the bad part. For safety sake wrap your pvc pressure tank with about 4 layers of duct tape. The tape will hold on to or atleast slow the shrapnel down.
The ratio betwen the volume of your barrel and air chamber should be around 1.5 to 1. Jomoco if you trippled the length of your barrel you could put throw bags in orbit. The longer barrel will allow for greater velocity with much lower pressure.
I keep a portable air tank on the truck to fill mine. I find it to be faster than a bigshot and with fewer misfires. Bike pumps don't last. 40 psi gets me around around the 70 foot mark, 160 psi put 180 feet of zing it and my throw cube in the air. The recoil was not even close to shotgun range.
We call ours the Crotch Rocket.
The ratio betwen the volume of your barrel and air chamber should be around 1.5 to 1. Jomoco if you trippled the length of your barrel you could put throw bags in orbit. The longer barrel will allow for greater velocity with much lower pressure.
I keep a portable air tank on the truck to fill mine. I find it to be faster than a bigshot and with fewer misfires. Bike pumps don't last. 40 psi gets me around around the 70 foot mark, 160 psi put 180 feet of zing it and my throw cube in the air. The recoil was not even close to shotgun range.
We call ours the Crotch Rocket.
BS Tree Service
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If you're using duct tape as a safety device, you might want to go back to the drawing board. Also, don't forget your safety glasses. Slows the flying pieces down.
jomoco
Tree Freak
Funny you'd say that DMD, since I did build one with a three foot launch barrel for the owner of The Care of Trees in Chicago, which got me an honorable mention in the last pages of Blair's Arborist Equipment, as capable of putting a throw bag into low orbit, or so I'm told by quite a few folks.
jomoco
I hope you charged John H.
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