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tri-valve pneumatic

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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tri-valve pneumatic

Unread postAuthor: dinsdale » Sat Feb 16, 2008 11:50 am

I've been toying around with the idea of a new cannon.
I'm thinking about a W shaped compression chamber/base with 3 modded sprinkler valves angled into the barrel, these 3 valves will be connected to a manifold with another sprinkler valve for a blow off. the compression chamber will hold approximately 1000 cubic inches of air around 125 psi, with the three valves for quick delivery of air to the 8 foot barrel.
my concern is in the blowoff manifold, as i'm worried it might create a bit too much pilot volume even though its being blown off with a fourth modded valve. has anyone tried something like this?
any suggestions?
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Unread postAuthor: Velocity » Sat Feb 16, 2008 12:00 pm

I'm not exactly sure what you mean by blow-off valve... could you draw a diagram of what you intend to build?
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Unread postAuthor: bigbob12345 » Sat Feb 16, 2008 12:01 pm

It is a bad idea because double wyes are dwv and have a risk of exploding.
And why use threee sprinkler valves when you could just make a piston valve or use a burst disk.
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Unread postAuthor: elitesniper » Sat Feb 16, 2008 12:04 pm

i think using three valves is just a waste of money, you could just do as bigbob said and make a piston, or even better a burst disk valve.
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Unread postAuthor: STHORNE » Sat Feb 16, 2008 12:07 pm

125psi would be a little too much pressure on the sprinkler valves because i'm pretty sure they are intended for 80-90psi (if im not mistaken). otherwise the piston wouldn't hold a seal.

otherwise the whole concept sounds kinda cool :D mind posting some pics of what you intend to do, im still a little confused by what you mean about the "blow off valve"

thanks
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Unread postAuthor: frankrede » Sat Feb 16, 2008 3:17 pm

sthorne wrote:125psi would be a little too much pressure on the sprinkler valves because i'm pretty sure they are intended for 80-90psi (if im not mistaken). otherwise the piston wouldn't hold a seal.

otherwise the whole concept sounds kinda cool :D mind posting some pics of what you intend to do, im still a little confused by what you mean about the "blow off valve"

thanks
--sthorne
You clearly have no what you are talking about.
Most sprikler valves I have seen are rated between 125-150 psi
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Unread postAuthor: MrCrowley » Sat Feb 16, 2008 6:06 pm

@sthorne


Just because you couldn't get your sprinkler valve to pass 80psi for what ever reason, doesn't mean you have to falsely inform other people.
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Unread postAuthor: Mitchza89 » Sat Feb 16, 2008 6:07 pm

sthorne wrote:125psi would be a little too much pressure on the sprinkler valves because i'm pretty sure they are intended for 80-90psi (if im not mistaken). otherwise the piston wouldn't hold a seal.

otherwise the whole concept sounds kinda cool :D mind posting some pics of what you intend to do, im still a little confused by what you mean about the "blow off valve"

thanks
--sthorne


80 to 90?!?! :shock: Wow I must have gotten a good deal. Mine is rated to 180psi :D
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Unread postAuthor: pizlo » Sat Feb 16, 2008 6:54 pm

By blow-off, he means actuation. Like what a blowgun would normally do, god that obvious. :roll:
If your willing to pay for 3 valves it will sure be a beast, what barrel width are we talking, because theoretically it should perform like a 3 inch ssprinkler. I bet you could bet away with a 4 inch barrel.
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Unread postAuthor: EGOed » Sat Feb 16, 2008 8:00 pm

Lets not be hasty with sprinkler valve psi ratings.....These valves are not made out of some super plastic that can withstand tremendous amounts of compressed air pressure ....They should be subject to the same safety standards that you use for pressure rated PVC pipe......They may be rated safely for 150 psi when used for their intended purpose which is watering your lawn with water , not compressed gas I hope......Plastic valves are just like PVC pipe and should be treated the same ..... They are very unforgiving when subjected to impact and should not be used in cold weather.
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Unread postAuthor: Mitchza89 » Sat Feb 16, 2008 8:26 pm

The valve I have is worth 90 bucks. I got it for 30 (the price of a regular valve) It's rated to 180psi, even with air. I took it that high when I was a fire extinguisher bottle chamber. Flow wise, I reckon this valve has similar flow to a piston valve. It's diaphram is massive and the body itself is huuuge.
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Unread postAuthor: MrCrowley » Sat Feb 16, 2008 8:32 pm

EGOed wrote:Lets not be hasty with sprinkler valve psi ratings.....These valves are not made out of some super plastic that can withstand tremendous amounts of compressed air pressure ....They should be subject to the same safety standards that you use for pressure rated PVC pipe......They may be rated safely for 150 psi when used for their intended purpose which is watering your lawn with water , not compressed gas I hope......Plastic valves are just like PVC pipe and should be treated the same ..... They are very unforgiving when subjected to impact and should not be used in cold weather.


150psi of water is the same as 150psi of air. The difference is that when they fail, 150psi of air is going to give far more energy to the plastic shards, so they will travel at a higher velocity and possibly into your skin.

If it says it's rated to 145psi, it can take at least 145psi if it is in perfect condition. The diaphragm or blowgun (if it's modded) will leak before it blows up unless you fill it extremely quick, with CO2 or similar.
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Unread postAuthor: Mitchza89 » Sat Feb 16, 2008 8:34 pm

MrCrowley wrote: The diaphragm or blowgun (if it's modded) will leak before it blows up unless you fill it extremely quick, with CO2 or similar.


Lets pray that that lesson wasn't learnt by personal experience mate :P
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Unread postAuthor: DYI » Sat Feb 16, 2008 8:41 pm

Let's get something straight here: a valve rated to 150 psi with water WILL NOT EXPLODE at 150 psi with air, unless it is badly defective. The reason being that it is the same pressure, whether it be water, oil, air, or Coca Cola. The only difference is that if it did explode, there is a lot more energy in a gas filled chamber of a given size and pressure than one filled with a liquid.

One problem that you sometimes do run into is when you use things designed for hydraulic systems on pneumatic systems. I've so far encountered this problem twice:
#1. The hydraulic quick connects on the filling hose for my SCTBDC. Although they're rated for 3kpsi with hydraulic oil, they leak slightly at 500 psi with nitrogen.
#2. The blowgun I bought for my indefinitely postponed high pressure helium BB gun project. The blowgun is rated for 4kpsi with water, and leaked severely at only 2kpsi with nitrogen.

As far as the actual topic goes, it should work fine as long as you keep the pilot volume down, but it's really a waste of money. You could use a single burst disk valve the same size as the sprinklers, and get better flow than all of them combined, along with a faster opening time.
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Unread postAuthor: MrCrowley » Sat Feb 16, 2008 8:51 pm

DYI wrote:Let's get something straight here: a valve rated to 150 psi with water WILL NOT EXPLODE at 150 psi with air, unless it is badly defective. The reason being that it is the same pressure, whether it be water, oil, air, or Coca Cola. The only difference is that if it did explode, there is a lot more energy in a gas filled chamber of a given size and pressure than one filled with a liquid.


Sounds familiar, *cough* Look up *cough* :roll:

:)
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