What is the VOLUME of air required to go 300 FPS?

[Koosh]

Yes I know the big spiel about about pressure and volume... Higher pressure equals lower volume, PV=nRT and such...

But doesnt it make sense that there should just be a fixed volume (At Standard Temperature and Pressure) of air that is needed to accelerate a ball 300 fps? Of course assuming barrel, paint and other things are as constant as they can be.

With that said, why are some guns more effecient then others? If all they are doing it putting out a certain VOLUME of air that is needed to go 300 fps, it would reason to believe that they are all the same. Well aside from the guns that require some air to run the internal componets, or the ones that waste gas needlessly (Like in the data thread, the matrix holding the bolt closed after the ball left the barrel... does that vent gas too?)

I know I'm missing a few giant points here, and it would be helpful for someone to tell me what they are

[RenagadeOfFunk]

here comes a 15 year olds answer...

1. volume doesn't matter.
2. Pressure matters. (you can have 1 million cubic feet of air at 2 psi and my 1 cubic foot of 3000 psi will shoot better/ quality over quantity )
3.What psi/pressuse is the volume at
4.Low pressure or High pressure gun.
5.Guns Air efficentcy.
6.What type of source (co2/nitro?)

all these factors play a role...

[Koosh]

eh...

I need to see why pressure would matter so much. In the data thread it even shows that the ball only sees about 50-100 psi worth of pressure, and then for only a fraction of a second.

I was thinking more about why the Viking is so darn effecient!

If you were put an empty plastic bag over the barrel of an Emag and a Viking, and dry fire, would the Vikings bag simply have less air in it? Is that what makes them so good? Is the mag "wasting" air somehow? If it does have less air then other guns, how can it still shoot at 300 fps? (I'm pretty familiar with the mags design and if its wasting air, I don't know where it would be)

Just random questions from an inquisitive mind

[SSMercury]

Mmmm...doesn't unported barrel length factor in a good bit as well? I.e., how long does the air get to stay behind the ball, accelerating it. The longer it's pushing, the more force applied.

[QUINCYMASSGUY]

hmmm

Hmmmm.... ok here is what I think so far, and I guess alot of technical knowledge is required to fill in the details.

A paintball takes I believe 3ms to go from the breech to out of the barrel where the air no longer accelerates it. Hear that cocker guys? It is NOT more accurate because cockers send the ball out of the barrel at the same velocity. Anyways, the reason I think 20-30psi would never work is because of the amount of time it would take to push the ball down the barrel. If it even made it since barrel friction exists. But on the same side 500-600psi in a small volume would be pointless too. So there is a range which is optimal to fire paintballs at the speeds they currently go at. I bet it's 100psi-850psi or so (CO2). But a larger volume would be needed for the 100psi and a smaller volume for the 850psi.

So the question is actuallly: What are the different psi to volume ratios that can be used to shoot a paintball? But now you have to factor in barrel friction, paint-to-barrel match, porting, etc, etc...... and this is where I leave it to the next guy to explain how you know what PSI/volumes work in what kinds of setups and which are the most efficient and why. I bet a bell curve exists with HP guns on one edge, LP guns on the other, and Vikings near the optimal place.

PS-Koosh, great quote under your name. Am I saying Meow? Great movie.

[SSMercury]

Furthermore, a cubic centimeter (hereafter shortened to cc. I use them because they're standard for scientific measurement and calculations) at 800 psi is the same amount of air that exists at 8 ccs of 100 psi.

See here for a glimpse of this question. I KNOW this has come up here before.

Heh, I think that's part of the problem of having read the entire forum at least once. I get confused where I've read about something. Not to sound snide, but do a search, you should find something. "pressure", "barrel", "length", "needed" together should home in on what you're after.

There appear to be some on Deep Blue, such as this one

I think I should shut up know and post.

[athomas]

The one thing that makes one gun more efficient than another is air flow. Guns may vary in psi behind the ball as the ball starts to move down the barrel depending on the ability of the gun to supply air. A gun that uses a higher pressure volume of air has a better chance of maintaining efficiency than a low pressure gun using the same delivery method.

The high pressure gun has a higher pressure differential and therefore the air gets more push to flow out the bolt. The pressure differential overcomes some of the flow restrictions that may exist.

A low pressure gun is efficient if the flow path is nonrestrictive.

Ideally, all the pressure of the valve chamber should be available behind the ball until such time that it is not required. At this time, the flow would stop and the pressure would taper off as the ball moved down the barrel and the barrel volume behind the ball increased. If this could be achieved, then the ideal volume of air could be figured out. It would probably be virtually the same for all psi-volume combinations.

The actual amount of air used in an ideal situation is a combination of pressure(psi) and volume(cubic inches). The resulting energy used would be inch-pounds of work done. One cubic inch of air at 400psi would have the same ability to do work as 4 cubic inches of air at 100psi. Both can do 400inch pounds of work.

Now putting the above analysis to work, the mag valve has a restriction at the bolt. The bolt spring is pushing back against the bolt causing the bolt stem to act like a regulator. This restricts the air flow out of the bolt. The high pressure behind the bolt overcomes this restriction initially through forward momentum of the bolt and high pressure in the chamber. As the chamber pressure drops from its initial valve as the ball moves away from the bolt, the pressure differential reduces and the flow becomes more restricted to the point that it eventually stops and the bolt is forced back by the spring. Initially the pressure behind the ball is high due to the pressure differential. This is where the power is developed. After the initial release, as the air pressrue tapers off, further air released never realy catches up to the ball to exert any force on it. It is wasted air and contributes to the inefficiency of the mag. The larger the bolt spring , the greater the inefficiency. That's why the level 10 is more inefficient than the level 7.

The viking has a more wide open delivery method to get the air to the ball. Therefore, it can operate at a lower chamber pressure and still get the same required pressure to the ball. By pulling the bolt back once it has delivered its required amount of air, it is effectively shutting off the air supply rather than letting it just reduce to the point of stopping.

[the electrician]

you're forgetting something about the air. it's density.

8 cc of air at 100 psi, is not the same as 1 cc at 800 psi
to simplify, change the cc to inches, since that what were dealing with for the pressure measurement.

8 cubic inches of volume at 100 psi is not equal to 1 cubic inch at 800 psi.
if you do the calculations, you'll see that 1 inch of air at 800 psi is 56.85 cu.in. of air when depressurized to atmospheric pressure.
8 cu. in. at 100 psi is 62.69 cu. in. at atmospheric.

but I can't say that higher pressure is more efficient because of this, it's more than that of course. athomas has done an ecellent explanation.

perhaps the lvl10 bolt can be modified to be a bit more efficient?

theflamingkoosh - I have calculated out that my cocker uses approx. 12 cu. in. of air at atmospheric, per shot at 200 psi of input, with it's particular set-up, at 60 degrees. that's not great, but it's pretty good.

[nippinout]

It's all about potential.

The Matrix had poor efficiency because it would leave it's dump chamber open until it went to ambient pressure. On the newer ones with the fancy screens and boards you can change the forward and reverse pulse times. You want to close the dump chamber before its pressure drops to ambient. This way, when the dump chamber is recharged there is still potential energy retained.

The same goes for the mag. When you dry fire you get less shots than when shooting with paint. The paint is a restrictor and keeps the dump chamber's pressure from falling as low as firing without paint.

To obtain high efficiency, you have to keep post-valve expansion to a minimum and limit dwell time so you don't have gas still expanding when the paint hits porting or exits the barrel.

[Cristobal]

I submit that the fundamental quantity you want to know is neither pressure nor volume... but ENERGY.

Essentially you want to transfer some potential energy in a stored gas into kinetic (motion) energy in the paintball. The potential energy is equal to volume of the gas you release times the pressure you release it at. Thus, if you find the energy you need, and you know the pressure your gun operates at, you can determine the volume of gas that must be released at that pressure to accelerate the paintball. It gets a bit more complicated than this, because you have a limited barrel length in which to accelerate, but that's the basic idea.

There's lots of good reading in Deap blue about this.
First a thread which asks almost the exact same question:

http://www.automags.org/forums/showthread.php?s=&threadid=46744

Here's a good thread about the relationship between energy, pressure and volume:

http://www.automags.org/forums/showthread.php?s=&threadid=74941

My post in this one also links to a bunch of other threads related to the subject

[Wat]

Instead of worrying about pressure and volumetric flow, if you can get mass flow, you'd have all your answers.

As for efficiency, i believe it may be in how much energy is wasted recharging the system (not cycling). Let me ramble with a barely related example.

With a two liter soda bottle, the soda gets flat and never lasts long, especially when you're like half way done with it. The reason is quite simple, CO2 gas wants to bubble out of the soda until the bottle pressure is high enough to reach equilibrium when no more co2 gas leaves the soda. When the bottle is mostly full, the amount of empty space it has to pressurize is small, so less co2 is lost. When the bottle is half full, the amount of empty space is larger so more co2 has to be lost to pressurize it. If you want to extend the life of your 2 liter soda, squeeze the empty air out of it as you consume soda, it can last for days if you do that.

So back to paintball guns, lets oversimplify and use a dump chamber example. One that needs to run at say, 300psi to shoot 300fps. But in reality, we don't use all 300psi to launch the ball. Lets say, by the time the gas has expanded down to 100psi, the ball's already well down the barrel and the remaining 100psi isn't accelerating the ball anymore. But lets say the valve doesn't close fast enough and the dump chamber gets vented to atmosphere and drops to 0psi (relative, not absolute). Now, when we recharge the system, we have to refill the dump chamber to 300psi. Each shot, we're using the top 200psi to launch the ball and the bottom 100psi gets wasted. A more efficient gun would say have a residual dump chamber pressure of say 50psi instead of 0. I think there's a balance required, larger passages improve flow but also create a larger void that has to be repressurized after each shot.

Just a theory that popped in my mind while drinking soda. I think the key to efficiency is how much gas is needed to recharge the system vs how much is needed to fire a ball at 300fps.

[the electrician]

that's good stuff wat.
I like the example.

so in a mag, a slightly stiffer bolt spring would move forward slower, but then push back faster. perhaps leaving more pressure in the chamber?

maybe that's to many variables to say. it might not let the bolt go quite as far forward.

sorry, got off track.

great stuff wat.

[Wat]

I think a stiffer bolt spring could result in higher residual valve pressure, but if the 'dwell' is too short you may decrease velocity and require a higher pressure. Again, its a balance of pressure and dwell time. The goal would be to close the valve as soon as sufficient gas has been released to accelerate the ball to 300fps.

Another way to look at it is that any expansion of gas that is not used to propel the ball is inefficient. When the regulator recharges the system, it opens up briefly and upstream pressure is released until the downstream hits the set pressure and the regulator closes. With a full tank and a gun running at 300psi, the gun is using 4500psi pressure, to charge a 300psi system. Anyone who has used banked scuba tanks for fills knows this is inefficient.

If the technology existed to accurately control valve dwell time, you'd get the most efficiency by having no regulator. Put a valve right behind the ball and as little space between the valve and your HPA tank. On your first shot on a full fill, the dwell would be miniscule. As the tank pressure drops, you would increase dwell time to maintain velocity. Basically, you want to capture the full energy of your pressure curve instead of regulating down to a lower pressure. Obviously, this is impractical as it would require a precise and adjustable valve as well as a full understanding of the relationship between pressure, dwell time and velocity.

We frequently refer to how many shots per fill a gun gets, but i'm curious if there is different efficiency at different tank pressures. IE, two guns may get 1000 shots per fill. But do both guns get the same number of shots from 4000psi to 3000psi vs from 3000psi to 2000psi tank pressures? I don't know the answer, but i think it could provide insight into the efficiency question.

[the electrician]

I've been working on using a cocker to make a controlled valve dwell. basically a valve in the middle of a double acting cylinder. pressurize one side, and it opens the valve. the other side closes it. this is controlled by a solenoid valve. I've found that I could energize the solenoid valve for only 5 msec, and it was enough to fire the ball at 300 fps. any less time and it had low velocity. any more time didn't gain anything. I also noticed that this particular stock valve liked to be opened about 3/16". openinng it a 1/4" didn't really help and any less than the 3/16" gave low velocity. changing the time to be longer and trying to get the shorter valve opening to work didn't help either. it wanted 3/16" at 5 msec. this is all at 200 psi. that is the lowest pressure I could get to still shoot the ball at 300 fps no matter what I did with the valve.

I need to go back and do the tests at higher input pressures. thing is, I don't know how low I can go with the solenoid valve energize time. but I would like to see what the differences are. I know it's really specific to this particular gun and air system, but I have learned quite a bit about the function of the valve.

this has made me think about aftermarket valve design, and how much improvement could they really make. most aftermaket valves have a larger opening, and use really weak springs to make them work at lower pressures, but is the flow really any better? that orfice was already the same size as the rest of the system. and changing it's shape might help, a little, but I doubt it.
I've thought about increasing the size of the port between the valve and the breech. it's 1/4" now, but that would cause gas expansion, and possibly a loss in velocity.
wouldn't be much fun trying to reverse that decision if it didn't work.

I approximate the amount of air used per shot by taking the actaual amount of air in the tank, then fire a ceratin quantity of paint, and figure how much air was used. this is really the only way I have to compare two different guns, or the same gun operating on two different pressures. there are a few more shots in the last 1000 psi then in the first.but I haven't tried a higher pressure comparison yet.

so some regs are designed to operate well at low pressures. what are the differences compared to older regs that opeated at higher presures?

by the way, thanks for the interesting discussion wat.

[Wat]

I think people forget that gas regulators predate paintball by probably close to a century, so i always find it odd when people talk about super duper new regulators. The design is basically the same where you use mechanical springs and down stream pressure to balance upstream pressure. I think the only difference between LP and HP regs is probably just dimensions of the parts. Not sure though.

As for valves, i was thinking, why not use a cam driven poppet valve like automotive engines? At least for testing purposes, it may give you faster response times and greater control of timing than pneumatic or spring hammer driven ones. Of course, actually constructing one and getting accurate servo motors is a non trivial excercise. All you would need is a basic breech, barrel and cam driven valve and you could plot a dwell vs pressure chart which should be quite insightful.

I do think you're right on after market valves. People seem to be putting too much emphasis on flow rate and not enough on dwell. If your valve is open for two long, a higher flowing valve would waste even more gas.

Where in kansas are you? I grew up in Dodge City.