Blowback marker sucking inward?

[cphilip]

True. Air acts more like a fluid in that way than most would think. It Flows.

[nerobro]

Actually.. air behaves as a gas.... Just gasses have mass and momentum. Gasses share a lot of properies with fluids... other than that fact gasses are compressable.

Given he's shooting a 12" barrel I doubt there's a real vaccum being developed behind the ball from the plunger effect. My money is on it being the gasses momentum... though both are plausable causes.

As for co2 expanding more.. Co2 is more dense than n2, and carrys mroe energy, it is DONE expanding by the time it gets to the barrel, and will actually increse the effect of what we are seeing. More mass = more energy = more momentum ;-)

[nerobro]

the effect you are seeing with the spoon is actually the tendancy of liquids and gasses to attach themselves to surfaces. when the spoon touches the water, it's getting slung aroudn the side of the spoon. action = reaction... and the spoon get's pushed further into the stream of water. (yes this is with the rounded side facing the water) it's the same reason 911's generate lift. and the same reason that the corvette has a sharp rear end.. to speerate airflow from the body of the car. But.. this has nothing to do with the subject on hand.

[cphilip]

Obviously you have never lived in the South. Our air is mostly water most of the year!

No just kidding! Kinda. But yes thats what I ment about the behaviour was in some respects "like" a fluid.

[steveg]

You fellas have been circling around the answer for a
while now. it's just good olde venturi effect.
Its what makes a hand pump bug sprayer, or spay gun work.

[nerobro]

I think i have my term fluid mixed with liquid ;-) Fluid = gas or liquid... And the laws and behaviours are about the same on both.

[nerobro]

It is not the bernuli effect. The bolt is closed for the duration of the airflow coming from the valve. in fact, the bolt CAN NOT be open while air is coming from the valve. if it were the bernuli effect, mags would create a vaccum in their breach as well.

Thre is actually a term for hte resonant vaccum we're seeing....... I gotta talk to my SAE friend.

Originally posted by steveg
You fellas have been circling around the answer for a
while now. it's just good olde venturi effect.
Its what makes a hand pump bug sprayer, or spay gun work.

[steveg]

if it were the bernuli effect, mags would create a vaccum in their breach as well.

not necessarly so, I would imagine that the mag is still
discharging above atmospheric pressure while the bolt is
retracting, this is the blowback, along with the fact that
the bolt is not sealed. after that pressure is disipated
there very well could be a moment of low pressure,
but the ball in the breach has already been blown shy high

[cphilip]

This is actually getting right good isn't it? Who wooda thunk it!

Also I think this is the first post that had the word "suck" in it that turned out ok! An AO first!!!!

[nerobro]

I suppose you could be right. We also get to play with teh fact that the valve in a spyder is open, or closed. Instead of being a container that's being allowed to drain.

the new superbolts are getting closer to having no pressure in the breach when the gun completes fireing, because of a tigher bolt/barrel fit there's less blowby. it appears that blowby is the major cause of positive breach pressure in the mag. And as you mentioned, we still have the AIR chamber draining as the bolt returns... so there's never a time where a valve is closed and NO air is coming out......

[CHK6]

Who's right?

Bernoulli vs. Newton? Who is right? I wasn't exactly trying to compare the two as much as direct you in the general direction and give you a general sense of where I was going. But if really want to say Newton it is then you can stick with your guns. However here is what the folks at NASA have to say. http://wright.grc.nasa.gov/WWW/K-12/...e/bernnew.html

As for a vacuum.... I'll assume you mean "a space in which the pressure is significantly lower than atmospheric pressure." If this is true to hold the same meaning of the word in context you use it in we are on the same wave length. If your theory is that the bolt creates a vacuum once would ask why don't we see CO2 vapor on a cold day sucked back in through the barrel tip and only through the feed port. So if we start from the begining the marker chamber is at local pressure, then the gun is fired and the pressure in the chamber greater than atmospheric pressure, then the chamber re-equalizes with atmospheric pressure, and finally the bolt moves back two ot three inches so fast to create a vacuum.

Oh gotto go, I'll pick up where I left off...I'm not done.

[CHK6]

Where I left off

To the point. Though I can truely see what you are saying and if it turns out I'm incorrect then I'm all the wiser and we had an excellent debate. However I'm trying to prevent my mind's eye from fooling me into a false preception. Physics does that a lot. The brain takes what we know and makes sense of what we see and makes a bridge between the two. Then our opinion turns into theory and then some how into fact. That's what I don't want.

So lets think of some simple ways to figure out if its a vacuum or fluiditic flow.

I was thinking that the single-ply tissue might be more closely examined. As the tissue is sucked into the breech its tip might be facing in the direction of the pull. If its direction is towards and down the barrel then we can lean towards fluid flow. If its direction is towards to the bolt then we can lean towards the bolt creating a suction.

A test with a ribbon could also help. Coat the inside of feed port with vaseline or a wet wax (like chapstick). Then place a ribbon in the center of the feed port, making sure it doesn't touch the walls of the feed port and will not be caught by the bolt when firing. What I hope to see is the ribbon will go in the direction of the pull and stick the the wall of the feed port. That way if the pull is really to fast for the eye the ribbon will stick to the wall as evidence in the direction of the pull as air rushes in.

I think we can trust BlindSeaman on testing this for us. He doesn't have to video record it. Are you up to it BlindSeaman?

[nerobro]

I think I have our answer. During testing of airflow from an automag after a ball is fired.. it was found that no air exited the barrel after the ball left. indicating a lack of air movment in the barrel......... So maybe it IS the plunger effect.

when i say vaccum, I just mean a lower pressure aera. Not a total vaccum.

The funny thing is, if either of us are right, the ribbon would go down and forward into the barrel. either carried into the stream of air as per bernuli, or with the rush of air as per newton... or with the rush of air as per the plunger effect (no better name for that now....)

Hmmmmm.......(digs out his dragun black) I wonder if this will vaccum feed? It probally will... the real quesion is how to determine how the vaccum is being formed....

what comes to mind is a pair of sensors. one embedded in the valve, the other in the barrel. If it's bernuli we'd be talking even pressure at the breach and in the feed port. If the pressure is positive at the valve when the feed port goes negative, then we're talking bernuli. If it's newton, it'll be negative both places. *wishes he could get time on AGD's gun dyno*

[314159]

with my autococker, timed to have the ball suck at it's peak. with a wad of tissue in the feed tube. when the gun is fired. the wad of tissue will be sucked into the breach and a little out into the back of the barrel. (no paintball was fired in the preciding shot)

i think that objects in motion tend to stay in motion sums it up best.

because of the forward velocity of the air, it will want to continue moving forward. if the bolt is opened when most of the air has left the barrel (the pressure in the barrel would have to be less than the inertia of the air moving forward). suction will be the result

[BlindSeaman]

I know this is an old thread, but I decided to do a little update. I recently picked up a CP 12" barrel with a bore size of .685 so now I have the DYE and the CP barrel. I got some blaze which fit the CP perectly and tested for suction. With a very good paint match i had the same suction as indicated in the video. Next I tried it with the larger bore DYE barrel, this caused pretty bad blowback. So to all v/feed spyder owners out(lol, i'm sure theres a bunch here) there a good paint to barrel match is more important than just efficiency and consistency. I also got a free Tarantula delrin bolt. I have been hesitant to try aftermarket bolts for fear of ruining my suction and seeing no need to upgrade. Well I tried it out and suction seems to still be maintained, this bolt does seem to be a little looser than my original though. Mostly I just wanted to post this to bring up that a bad paint to barrel match=blowback.