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1" pipe "bottle neck"?

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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1" pipe "bottle neck"?

Unread postAuthor: Lentamentalisk » Mon Oct 22, 2007 8:05 pm

I'm using a 1" sprinkler valve with a 2" chamber and 1.5" barrel. I am making it in the "over/under" style, with the valve on the bottom, then 2 90degree corners, and a bushing up to a 1.5" pipe. Will that much 1" pipe make too much of a bottle neck, especially with 90degree bends, and so I should bushing up to 1.5" before the bend, or do you think it will work?

sorry if this is hard to picture, I will try to post some quick paint sketch soon.
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Unread postAuthor: psycix » Mon Oct 22, 2007 8:11 pm

I think the 1" 90 degree turns wont restrict airflow alot, but i would suggest to use 1,5" turns so that the bushing is also at the bottom side
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Unread postAuthor: rednecktatertosser » Mon Oct 22, 2007 8:17 pm

you should try and use a 180 degree sprinkler valve, i think that would be a better choice, then you wouldnt have to worry about the bottle neck as much, seeing as you would just have the reducers straight into the valve.
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Unread postAuthor: DYI » Mon Oct 22, 2007 8:19 pm

The 1" sprinkler will restrict flow far more than the 1" pipe, so there's no need to spend the money for a bigger 180 degree bend.
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Unread postAuthor: Lentamentalisk » Mon Oct 22, 2007 8:35 pm

here is a little diagram.
what is the general consensus on whether I should use 1" or 1.5" for the bends?
Image

gaaaah! image link didnt work, just a sec
Image

lol finally up there...
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Unread postAuthor: ShowNoMercy » Mon Oct 22, 2007 8:45 pm

And what is wrong with that? If your really concerned with a bottleneck more the valve on top of the gun, but I don't think you will notice a difference.
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Unread postAuthor: Lentamentalisk » Mon Oct 22, 2007 8:52 pm

I put it on the bottom to conserve space. Since the 2" pipe has ~2x the volume per inch of 1.5" (please noobs dont correct me on the math lrn2 Πr2,) so it seemed more efficient to put it on the bottom where I already have lots of extra space. Anyways it seems to me that you guys don't think it will make much difference, so I'll leave it as is for useablity's sake.
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Unread postAuthor: ShowNoMercy » Mon Oct 22, 2007 8:55 pm

Thats the way I always make mine, I use the solenoid as a handle. But I don't mod my valves so I guess it depends on your application.
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Unread postAuthor: Lentamentalisk » Mon Oct 22, 2007 9:06 pm

Thanks for all of your advice guys!
and make this post long enough...
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Unread postAuthor: EGOed » Tue Oct 23, 2007 5:41 am

If you move the valve up top you can get it closer to the barrel and lessen the dead space (un-pressurized pipe) after the outlet of the valve.....If you are concerned with flow restriction with 1" pipe , you are already restricted to 1" porting by your sprinkler valve so upsizing your pipeing diameter will not increase your flow rate......Try to keep your valve exhaust outlet as close to the barrel, and projectile as possible for best performance.
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Unread postAuthor: williamfeldmann » Tue Oct 23, 2007 7:45 am

Yes, you would have more dead space with the current design, but not all dead space is a bad thing when dealing with a barrel that is significantly bigger than the valve. No dead space is actually detrimental to the performance, too much dead space is also going to decrease the performance of the gun (given a fixed chamber & barrel).

In this case the air will have enough time to collect and hit the spud (assuming that is what you are firing) with more pressure behind it.

I would leave your design alone. It is a tested and true setup. Just make sure you keep the gun compact heightwise to reduce the strain on those 90* elbows.
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Unread postAuthor: Lentamentalisk » Tue Oct 23, 2007 8:54 am

I was thinking a 3' long barrel, I will be shooting little cat tennisballs that fit perfectly into a 1.5" tube, and one of the whole reasons for not using 1.5" bends is to make it more compact, and I will make supports for farther down the barrel.
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