Variable pressure _and_ volume?

[bjjb99]

Greetings,

Has anyone heard of a dump chamber paintgun design (like the mag, shocker, etc.) that allows one to vary both the pressure and the volume of the gas released?

I'm thinking one could optimize a paintgun's performance by varying both of these parameters, rather than just one or the other, particularly when one uses multiple barrels of differing lengths. Theoretically, one could go from a high pressure/low volume gun to a low pressure/high volume gun by adjusting two screws.

If the amount of gas released (number of molecules) is the same, does it really matter whether it was released at a pressure P and a volume V rather than at P/2 and 2V? How about 10P and V/10 (yes, this is extreme)? I think it may make a noticeable difference in the gun's performance (accuracy, in-barrel breaks, etc.).

Thoughts?

BJJB

[FooTemps]

I find this a bit impossible. How could the valve assembly be able to adjust its own air chamber size (volume) while still remaining consistent. A variable chamber would be to easily set "out of whack" and the consistency would go off the wall. It could lead to shooting hot or having very bad drop off.

This is because there would be no way to secure the adjustment of the chamber. The moving parts that adjust the chamber size would easily be at fault. If there was a piston to make the chamer smallers the pressure would be able to overpower the spring over time and there would be drop off. If the chamber itself were to expand with some weird method, there would be no sure way to secure it so it wouldn't expand or shrink after and before a shot.

[squidboy69]

UP

[manike]

I don't know of any dump chamber style guns that do this, but many knock open type valve guns do this automatically. They vary the volume of gas delivered depending on the pressure behind the valve. A higher pressure closes the valve quicker so you get less volume and vica versa.

People have talked about a chamber that could change in size to allow another tuning variable to dump chamber style guns, but no-ones come up with a practical version that I know of. It should be possible and might be very useful to aid tuning of such gun designs. There seems to be little point to having a moving piston in the chamber that would increase the volume and lower the pressure for each shot. All that would do it is take energy from your system. It's better to accurately regulate the air to start with.

Squidboy, posting 'up' in deep blue is not deemed an acceptable form of post here. In fact it's exactly what Deep Blue was originally conceived to stop. :)

manike

[bjjb99]

Foo Temps, I'm not considering a dynamically adjustable chamber volume, but rather one that the player could set, lock down, and then adjust his chamber pressure independently. Two adjustment screws (with tourney locks, if needed) instead of one. Folks like to tweak variables... autocockers are proof of that. ;)

Manike, perhaps taking the current 'mag dump chamber and rotating its orientation 90 degrees (around the 'Z' axis) so that the cylindrical chamber now faced left to right? Now the entry and exit holes for the dump chamber would be in the curved walls of the cylinder instead of the flat faces. Then remove either the left or the right face and replace it with a piston driven by a screw, with a spring inside the dump chamber to provide resistance when the gun is not pressurized. It would clearly look bizarre, with a screw sticking out the side of one's gun, but it might allow the adjustability I'm describing

I'd draw up a graphic, but I don't have the necessary software on hand. If I remember this evening, perhaps I'll scribble something up and post it.

BJJB

[squidboy69]

my apologies about the post, I was ina terrible rush, and wanted to stay abreast of this thread.

could you not leave the axis of the chamber intact, and have a threaded collar that was adjusted after the (in the case of a mag) power tube was removed? my scanner is down, so I can't post the pic I'm looking at, I'll try tommorow. but imagine an autococker IVG screw at behind the power tube, which you could screw in/out to adjust the volume in the chamber. sprung of course. this would lead to a longer valve chamber, to allow for the diameter of the spring from it's circumference, and would be 'locked' as it would be inaccesible with a bolt in the gun.

[Low Down]

I don't want to step on anyones toes here, but i just wanted to ask one question. Why? Isn't the beauty of the automag design the simplicity of it? In order to achieve the greatest consistancy you generally need to remove as many variables as possible right? Isn't it easier to tune a gun when the air chamber is a constant size? :confused:

Ok that was like four questions.

I admit that the physics of a variable volume air chamber are interesting, but would it be practical for those of us who aren't physics majors. :)

Sorry Sorry. talking about practicality on the deep blue forum, what was i thinking. :D

[squidboy69]

You're right, the more 'parts' you add to a gun the more finicky it becomes, the more things that can go wrong. converseley, the more adjustments, the closer to the 'edge' you can tune the gun.
I spoke to a fellow on the weekend who wasn't happy with his shocker, so he rewrote the chip to allow .5ms adjustments in all the variables, as opposed to the stock 1ms. you tell me if he cares about reliability in that 5000th of a second or not ;)
There is always a nasty practical side to every innovation... I rebuild my cocker almost monthly to keep it performing the way it does, but boy does it perform.
alas I'm getting off topic. I better shut up and go thread my valve chamber for an IVG :D .

[bjjb99]

Low Down, I agree that simplicity of design, operation, and maintenance is one of my favorite aspects of the 'mag. I'm exploring the possibilitiy of independently variable pressure and volume as more of a "thought experiment" rather than something that would eventually be put into paintball-slinging form.

One of the reasons I'm interested in being able to vary both pressure and volume independently is to optimize gas usage for different barrels, particularly non-ported varieties. Imagine being able to shoot around 300 fps with a near-zero pressure differential experienced by the ball as it exits the barrel, and doing it with a 12 inch non-ported barrel. It would be quiet, and likely very gas efficient. Accuracy, as always, would be dictated by paint/barrel match, but without any potential for gas deflection at the barrel exit.

BJJB

[AGD]

Ahem,,,,AGD proto'd a variable size air chamber in 1992. It changed chamber size in response to pressure and would dump the whole thing like the Mag valve does now. The proto valve sits on my desk here and is VERY large. When people ask me what it is I tell them "level 8, want to try it?" They all turn me down because it weighs like 3 pounds just for the valve.

Yes it's possible, no it doesn't make sense.

AGD

[bjjb99]

Tom wrote:
>AGD proto'd a variable size air chamber
>in 1992. It changed chamber size in
>response to pressure and would dump the
>whole thing like the Mag valve does now.

I'm not sure if this post was in response to something I or somebody else wrote... it's hard to tell who's replying to whom at times.

I'm sorry if I wasn't clear before, but I am not worrying about a dynamically variable chamber, which sounds like what you've described. Rather, I'm thinking along the lines of a chamber whose volume is set by the user, in a manner similar to how one would set a marker's operating pressure. I can easily see where the dynamically variable chamber design would be bulky and heavy, but I can't see where a manually set chamber volume would add much bulk or weight (a screw, a piston, a spring, an o-ring, and perhaps some reinforcement of the chamber walls and screw threads to take the resultant forces).

And, again, I'm not suggesting this as a modification to the 'mag. I'm interested in what theoretical effects such a design would have on a gun's efficiency, accuracy, noise level, and perhaps consistancy. Anyone got a decent dump chamber paintgun model that I could plug parameters into to see their effects? Am I going to have to figure a simple one up in Excel?

Out of curiosity, do you have any pictures of "Level 8" that you could post somewhere?

BJJB

[Doc Nickel]

In response to the original post, yes, there is such a gun that uses a dump-chamber and can vary the chamber volume.

It was called the Equalizer, and it was an open-bolt blowforward much like the 'Mag, except the bolt didn't seal the chamber.

The chamber had a sort of 'reverse power tube' that was sealed on the back end by a combination on-off valve/cupseal/poppet arrangement that was actually quite clever.

It really wasn't the design of the gun that was poor, it was the execution- it seemed as though Sheridan went out of their way to make the gun as upgrade-unfriendly as possible.

Anyway, back to the point, the Equalizer came with a "sleeve", an aluminum tube about an inch and a quarter long, that slid down into the dump chamber once you'd opened the body up.

It cut the chamber volume down by, I'd say nearly half.

According to the manual, without it, the gun ran at roughly 350 psi- with it it was closer to 500 psi.

So with one gun, you could have a high-volume/low-pressure (relatively) and a high-pressure/low-volume shot. I tried both ways, and even made a custom tube that was roughly halfway between the volumes with and without the stock tube, and I never noticed the slightest difference. Not in noise, accuracy, range, rate-of-fire (which was pretty poor due to the gun's long and convoluted regulator passages) or what have you.

I did, however, notice that the higher pressure gave a few more shots per tank, but at the time I didn't do any empirical testing, and weather, specifically cold, did have a factor.

Smart Parts also sells a very similar "sleeve" for the Shocker- you remove the rear fill-poppet assembly from the gun, and slide in this tube, which reduces the chamber volume by a certain percentage. It's meant for those who use the Shocker indoors, where the velocities are limited to 220 to 250. This allows you to keep the pressure the same as "outdoor" speeds, but shoot at the slower indoor velocities. so there's less fiddling with the Max Flow, and less inconsitency while hovering at the low fringes of the Max reg's capability.

If you had an older 'Mag with the removable power tube, you could make some arrangement quite similar and experiment with your own "Smart" and "Hyper" 'Mags. And then KAPP and CP would come out with a set of milled and flame-anodized graduated sleeves, and... :D

Doc.

[314159]

if you want to vary the volume and pressure, i think that this would be done the easiest by regulating the incoming air, and with a hammer and a valve both with adjustible springs

just adjust the hammer spring to pop the valve open under the imput pressure.

the valve spring would controll how fast the valve closes and thus the volume of air.

and adjust the incomming pressure via a regulator.


-disadvantages
consumes more air when dryfiring (less air resistance).
air effiencency changes with paint.
have to take in more factors into air volume calculations.

[mofod]

Hi,

I finally broke down and entered the world of Mag ownership. I've been playing paintball and messing with markers for a few years now and thought I might comment (although, I might be off topic/out to lunch)

I see that Tom mentioned a variable size air chamber and had moderate success, except for the size.

I wonder what an accumulator system might do? We use them in large application hydraulics to moderate pressure differentials. As the pressure drops due to demand (in this case, rapid fire), the chamber constricts, increasing pressure back to optimal operation pressure.

Pardon the simple schematic, I'm at work right now, so I don't have time to whip something off on CAD, but I might do so tonight. Anyways the basic system is a closed cylinder with a floating disc that seals the 2 sides from each other. I have attached a diagram with the basic information.

I'm curious as to whether an air chamber might be modified to operate in a similar fashion. You could pull air from the supply side of the marker prior to internal marker regulation and use it as a constant for the accumulator air chamber. You would need a seperate inline regulator to control this pressure and limit it to a safe level.

As a high ROF created a starvation of air volume and pressure within the marker, the accumulator would artificially boost the pressure by recompressing the air.
An advanced electronically controlled system could increase the control pressure to the accumulator to in fact maintain a constant FPS at the barrel despite the fact the gun is starving for air. (Man, that would be a trip to design).

Coordinating such a system in pure mechanical marker would be a big task. It would not take much error to get a wildly erratic marker, which from a practical point, makes this an unusable system.

I suspect that such a system would quickly get to big to practically applied to a marker, but its an interesting thought.

Sorry, might be somewhat off topic but I've enjoyed reading these boards and thought I might kick off my first post with something of note.

I'll post more later in regards to this.

mofod.

[Minimag4me]

I want to see a higher pressure mag maybe like 600-800psi, is it possible or break too much? Faster recharge rate? New power tube tip desigh to go with?

When I read this I thought of the way tippmann model 98's adjust velocity, which is a screw that goes into the powertube to restrict air or let it flow freely. With a mag you could have a similar idea, just a fat screw in the air chamber could greatly make the air chamber smaller(higher pressure, lower volume) and more restrictive(depends on the position of the screw in chamber). You couldnt really lower the pressure though. I dont think it would be too incredibly hard to do.

I hope that made sence.

[soilent green]

Its funny I was just thinking of this today and now I see this post and while reading this I was thinking of my old m98 and its velocity adjuster to But what I am also woundering is about air efficency I was thinking about the size of the mag chamber and if runing at high pressures and smaller chambers could help it and then I started thinking of "low pressure cockers" and why they were supposedly so air efficient so guys what do you think about this

[athomas]

There's a couple of methodologies available to limit pressure behind the ball.

1. Decrease the available chamber pressure. This has a direct effect on the pressure behind the ball. We now require a greater chamber volume to produce acceleration over a longer period of time.

2. Decrease the cross sectional area of the bolt/valve opening. The properties of thrust and the compressability of air/gases say that the exit pressure at the exit end of a tube is related to the size and material/smoothness of the tube. That is, if you decrease the size of the tube, you will decrease the available pressure at the exit to the tube. The end result is that the higher chamber pressure will exit at a lower pressure and be available for a longer duration the same as a larger lower pressure chamber.

Again we have to determine the most advantageous combination of chamber pressure , chamber size, and valve tube size to obtain optimum performance.

If we have too high a pressure we have to limit the valve tube size and this increases the friction which is a result of higher air velocity. An increase in friction is a loss in efficiency.

If we have to low a pressure we have less of a pressure differential. We need a pressure differential to have any acceleration. The end result is that more air is required to accelerate the ball over a longer period of time. Think of how long you would have to blow on a barrel to accelerate a ball to 300 ft/sec. It wouldn't happen. The air you expelled would be wasted, therefore making your blowgun very inefficient. The closer a paintball gun gets to regular air pressure the less efficient it gets.

In conclusion here. Since both ideas get inefficient at the extremes, we can conclude that somewhere in the middle we will have perfection.

[AGD]

Athomas,

Decreasing chamber volume lowers the pressure against the ball only if everything else stays the same. It is a simple matter to restrict the flow more or less to get a wide range of pressure behind the ball regardless of your chamber pressure.

All you really need to determine is what acceleration profile you want on the ball, the rest falls into place after that.

AGD

[athomas]

Yes, exactly. That is what I was saying, although it may have gotten mixed up in the rest of the message.

I was just stating that there are various ways to achieve the lower pressure phenomenon that everyone is trying to achieve. Each has a consequence.