Blowback marker sucking inward?

[BlindSeaman]

I'm really sorry if this doesn't belong here, but I've had something sort of strange happen with my spyder... (cringes and watches everyone stop reading) anyway, it actually has suction, and quite a lot of it. If I put two paintballs in the vert feed the one on top will not pop up at all, the same happens if I put three.

Here is a quick vid of the toilet paper test I did:
http://home.attbi.com/~blindseaman/suck.AVI

I could understand if didn't have any blowback, but does anyone know why it is actually able to suck in? Just to let you all know, my marker is completely stock mechanically except for the reg and I removed the venturi out of the bolt. Have any of you heard of anything like this before? Thanks.

[cphilip]

Odd... (moving to main by the way)

Hmmmmmm.... Lack of "Elves" perhaps?;)

[CHK6]

First the video does not show much. It looks like the tissue is already placed in the PF. For all I can see the bolt could be catching on tissue and pulling it in. But, lets not be skepticle and say the blow back is pulling the tissue in via a suctional force.

Now we all now the a simple rule of physics, the most likely path is the most taken path. Same holds true for fluid (gas is a fluid). If the both the hammer and striker are being forced back one might easily come to the conclusion that the volume the hammer and striker makes needs to be filled and equalized by atmospheric pressure. Atmospheric pressure averages to 14.9 PSI if I recall correctly. So with 14.9 PSI why doesn't the tissue get fully sicked in and what's the purpose of a PF anyways? Because on the Spyder design there are three open ports for the fluid to rush in and fill the volume to atmospheric pressure; the barrel opening, the PF, and the cocking slot. The volume that needs to filled is also realitively small. Also the volume that needs to be filled is not vacuum space, therefore the suction force is extremely small for equalization. Only noticeable by the lightness in weight of tissue paper.

Take off the PF and add a straight feed. Put in a few balls and fire. You'll actually see a force blowing the balls out of the feed neck and not sucking them in.

_OR_ it's what Cphilip said and it does lack elves.

[FeelTheRT]

ok, this is when the cocker gurus come in :). That is called suction timming on a Cocker, but i really had no idea you could get a Spyder to do that...

it's the exact oposite of blowback. The timming has to be extremly presise to get it right, I've yet to get it comleatly working on my Cocker but i'm working on it. The hammer has to be released as soon as the trigger is pulled then teh bolt has to be in it's cocked position after the paintball is fired. That meens there has to be a gap inbetween when teh gun is fired and when teh gun is cocked. Beacuse of that, the trigger pull has to be fairly long and easier to short stroke on a cocker.

but honestly, i had no idea a Spyder could do that, i alwas thought Spyders had blow back because most of em had powerfeed.

[BlindSeaman]

Take off the PF and add a straight feed. Put in a few balls and fire. You'll actually see a force blowing the balls out of the feed neck and not sucking them in.

Well it doesn't have a p/f because it is a vert feed spyder. Also, I already mentioned that I did it with three balls and two balls stacked in the vert with absolutely no blowback. As for me pushing it in already, I can honestly say I didn't although I don't know if you will beleive me. And the tissue indeed does move quite a lot, it almost looks instant just because it goes so fast and I beleive that camera records at 24fps.

[Sledgehammer]

CHK6, either you need glasses or I do, that tissue was no way tucked into the feed!

[liigod]

If that works and that isnt like an edited video or anything. DAMN DUDE! you are one lucky ----. Slap a booyah on there and that thing will RIP. (How many times do I got to edit this same word? Stop using metaphors for the F word! - cphilip) cheaper and as fast an an angel.

[CHK6]

the right side of the tissue looked tucked in, but now that I take a second look it looks to be resting on top of the feed port. I have no reason not to believe BlindSeaman; dare I say I blindly trust him?

I have seen the same thing with the Model98. Being that the hammer and bolt behave differently than the Spyder and Cocker.

I'm sorta remembering something here. If one fluid flows past a junction point it pulls the fluid from a subjuction. Ok, maybe that's it. As the air rushes down the barrel the momentum it carries pulls in air from the surrounding environment in one direction. Sorta like standing near a highway and watching your shirt being pulled in the direction as cars pass.

I'm really not sure as these are all guesses. Instead of using a tissue put your hand over the feed port. I curious to know if it's really suction (pull) or enviromental equalization (push). Either the tissue is being sucked in or it's being pushed in. Answering this should help narrow down the possibilities. Also if this is two ply tissue seperate the layers down to one layer. Now what we want to try is the "suction" we precieve enough to benefit in feeding balls into the chamber. Cut the single layer tissue into a small patch, as to hold the ball in position lightly in the feed port. Basically preventing the ball from falling into the breech, not preventing it to overcome the suction force. Then fire the marker and see if the ball is sucked into the breech.

Or turn the marker upside down and place the ball on the top of a table. Move the feed port over the ball like a vacuum cleaner. The feed port should be 90% over the ball and all you should see is the bottom of the ball. Fire the marker. If the ball lifts up then you know the force to move the ball is greater than the force of gravity and in my opinion is substantial force to brag about. So on a vertical feed if this experiment shows to lift the ball you can calculate the minimum force the suction exhibits. The maximum force you would need some equipment.

[rhetor22]

I'm not sure if its just my computer being slow, but I could actualy hear the hammer go backwards, then the sear latch on. Did anyone else hear this??

I doubt this is it, but maybe just the bolt moving back caused suction.

What type of barrel/how long of a barrel do you have on there?
I noticed that you have a spyder that comes stock with a rear cocking bolt, yet yours is not coming out the end. What type of bolt did you put in there?

That is very interesting.

[rios_creos]

hey blindseaman.

i downloaded your video on PBREVIEW.com (remember "spydersdonhaveblowback" :)) and i was showing my friends a couple weeks ago. that is badazz.

and, how did you take the venturi out of the bolt. did it make the airflow greater, are there any negative side affects.

i want to know because it seems as though it would work almost as well as an aftermarket bolt and i have a rebel deluxe and they only have 3 bolts for it.

a venturi bolt
bob long cyclone
delrin bolt

and i don't want any of them.
but i want to go low pressure and i know you need a new valve and a higher flowing bolt and a reg.

so please reply.

THANKS A LOT

[BlindSeaman]

CHK6- I'll try some of those later If I get the chance. I don't remember if it was double or single ply because I actually made that vid in the middle of the summer. I just now decided to post it here after browsing a bit, and realized this message board is smarter than the average one.:D


What type of barrel/how long of a barrel do you have on there?

Its a DYE SS and 12" long. That is one thing I noticed, I need an almost perfect paint to barrel match for it to work. Otherwise I get a little blowback.


yet yours is not coming out the end. What type of bolt did you put in there?

Stock bolt, and that is the normal cocking rod. You just can't see it move because it goes in and out too fast.


how did you take the venturi out of the bolt. did it make the airflow greater, are there any negative side affects.

There are countless places which will tell you how to take it out, go to PBC and hit there spyder forum if you want, or pbreview. I'm not sure if it made a greater airflow because I took it out before I got my reg, and I have not noticed anything negative. Just stick with the stock bolt, the rest are all pretty much hype.

[nerobro]

Science can't suck ;-) What's happening is that as the ball leaves the breach it's building a vaccum behind it. when the bolt opens, the air in the room trys to rush in to fill that void, and will carry whatever is in it's way with it. Be it a paintball or whatever.

Crazy thing is.. a spyder is always timed perfectly like that ;-) the force is never THAT great, but as we can all see, it works ;-)

[cphilip]

Right! same thing kindda happens on a plane wing to create "lift".

And next time you see someone out at the field with a blow back marker tell em "they suck" and you can prove it! :D

[CHK6]

Neobro,

I hope you don't mind my humble questioning..... If there is a vaccum that builds up behind the ball, then theoritically if you had a really really long barrel with no porting and traced it's path we would see the ball eventually being pulled back by the vaccum it creates. I'm I correct? I believe I understand what your saying as you can easily see this with a syringe and water.

But how does one explain the same effect with CO2? CO2 has a great expansion rate, thus does not create a vacuum since it expands. Sometimes the expansion can be seen on cold days.

I think cphilip might have the "ticket" and we are comming to possibly the solution. Wing lift is bassed on the Bernoulli (sp?) principle. Where by creating a difference in atmospheric pressure over an object will cause a change in the object; i.e., usually lift. Lift is caused by higher pressure on top and lower pressure on bottom.

Here is a trick. Take a little spoon and go to the sink. Turn on the water to a good strength but not show much as the water is spurting everywhere. Hold the spoon lightly with two fingers at the end and slowly move the convex side of the spoon close the water stream. Notice how the spoon is eventually pulled towards the stream. This is pressure difference in fluid flow. (There is no difference between liquids and gases when it comes to fluidic laws. We actually breath fluid but not liquid. Eh?)

Maybe the answer is the burst shot of the gas is a higher pressure than the surrounding atmosphere and the ball is drawn in to the higher pressure. I.E. The gas is the water and the ball is the spoon.

If only teachers used paintball for science.

[nerobro]

a really funny thing is that the majority of the lift a plane wing makes is due to newtons law.. not benuli's princapal. And actually it's newtons law that's causing this effect. The air rushing down teh barrel has momentum. And when the flow of air from the valve stops the air flow does not INSTANTLY stop, it keeps moving, generating the vaccum behind it. :-)

[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! :D

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!:cool:

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]

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/airplane/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]

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.

[Lone Gunman]

It's kind of like what happens when I shoot my pnuematic spud gun. Once I pump the resivour(sp) tank with about 80 psi, put a tight fitting object down the barrel, and fire it actually sucks air back down the barrel.

Thus the momentom idea creating a vaccum.

[pumpamatic]

Honestly, does having this vacuum actually do that much? I mean yes, it is better than blowback gases, but if I had a cocker I would time it to have the shortest trigger pull possible with absolutely no blowback. I wouldn't waste all that time just to have a perfect vacuum with a marginal trigger pull. Just my thoughts. And is there anyway to find out if a powerfeed or standard Mag has suction?