need autococker owner's opinions on this!

[FallNAngel]

This isn't saying that it will need to operate at some horrendously large OP, it's saying that the energy stored in the larger air chamber would have to be roughly quadrupled to maintain the same energy.

Don't you mean the energy stored in the smaller air chamber would have to be roughly quadrupled? Going off the numbers you gave, the energy in the smaller chamber (the mini) was about 1/4 of the full bodied cocker. Or am I misunderstanding something (which is entirely possible)

What's a midget cocker now???

A picture is worth a thousand words:

http://www.pbreview.com/forums/showthread.php?s=&threadid=199127

I did qualify that a "well tuned AC could see 2000 shots per 68/45 fill". Most people take claims like this with a grain of salt from individuals, however from a company, they better be able to back-up their claims if someone challenges them.

True, but we can't assume that the mini cocker and full bodied cocker are both tuned well; which is my point. Just because one gets better efficiency means nothing if you're not comparing them on even ground.

Counter point - Consider the volumizing chambers on Angels, if those chambers are not pressent the Angel requires a higher input pressure from the HPR (like we see in Mini Cockers) in order to achive a given ROF without volocity drop off. No matter how quickly recharging a reg is there will be a fine point where the input pressure must be increased (either to the gun through the HPR or the input pressure from the air course) or the marker will starve.

But most people add those volumizers so they can lower their operating pressure, which allows them to lower their LPR pressure, thus lowering kick. They aren't doing it to prevent starving the reg and getting shootdown. I have to agree with gtrsi on this, if your reg isn't up to snuff, you'll get shootdown.

[JimmyBeam]

see, all this talk about cockers is really making me think i want one. my mag is great but its the same thing over and over.......air it up and it works fine, no adjusting or anything. i like working on my mag, but the only thing i ever have to do is clean it. i dont know, we'll see.....maybe ill start off with a no frills low end cocker and learn the ins and outs, then work my way up.

[VFX_Fenix]

The Ideal gas law assumes that your are somewhat close to atomspheric pressure and not much more. It is a poor model for how gasses behave at our higher operating pressures.

Ideal Gas law doesn't account for gasses doing things like condensing, it does, however, do a decent job of predicting relative pressures in pure gas states.

Angels with volumizers have never ever seen a performance increase, pre-speed. It was more stupid bling bling that people bought into. Secondly shoot down is most of the time caused by piss poor reg performance. I dont care how big your volumizer is if your reg sucks you are going to get shoot down, peroid. I'll even go a step further and call BS on guys who actually say that the volumizers on vikings do anything.

I meant Angel Speed and I'm sorry I didn't qualify that.

back on topic
Mini's: If you want a real answer I would ask BradAGD or Doc Nickel. They are one of the few guys on this board that have had a wealth of experience in working with millions of different types of cockers. I am amazed when I talk to Brad about cocker stuff and the litany of info that he knows.

I would totally agree - Talk to them, they would definately have a more practical view of the issue on efficiency, though they may not know why necesarily.

Don't you mean the energy stored in the smaller air chamber would have to be roughly quadrupled? Going off the numbers you gave, the energy in the smaller chamber (the mini) was about 1/4 of the full bodied cocker. Or am I misunderstanding something (which is entirely possible)

No, you understood, my lack of proof reading is getting the better of me here and thanks for the pic of the midget cocker.

True, but we can't assume that the mini cocker and full bodied cocker are both tuned well; which is my point. Just because one gets better efficiency means nothing if you're not comparing them on even ground.

Sure... you could, it would actually be better if you did, I'm just going from two claims again, however relivant they may be is beside the point, because you know that one cocker will always be better tuned than another based on the person doing the tuning. No two Cocker owners set-up their rigs exactly the same way, even if they have the same pneums/guts/what have you.

But most people add those volumizers so they can lower their operating pressure, which allows them to lower their LPR pressure, thus lowering kick. They aren't doing it to prevent starving the reg and getting shootdown. I have to agree with gtrsi on this, if your reg isn't up to snuff, you'll get shootdown.

Ever wonder why you can shoot at a lower operating pressure by expanding the volume of air before the valve? If you both consider this argument which neither of you have adressed or even apparently acknowledge.

Yes, however, there's a little more at work than just straight pressures and volumes. The volume of gas that's released by the valve causes a temprature shift in the pre-valve chamber (like with CO2 but not as pronounced). This changes the amount of energy that resides behind the not only by volume and pressure but temp as well. Durring the firing cycle there will be a small portion of gas that will condense as a result of this momentary loss of v/p/t. By minimizing the volume and pressure change in the chaber during firing events the decrease in temp and condensation of the gas will be lessend which helps to maintain consistant consumption of the valve during firing events. (EDIT - Can we see that if this trend continues long enough higher volumes of air with less energy per volume due to temp. will lead to the equivalent of sucking mostly low energy liquid through the valve as opposed to high energy gas which results in decreased efficiency because you're pulling more volume through the valve.)

By gaining volume in exchange for pressure, no matter how fast your reg is, the proppellant gas will continue to cool and condense until the string ends when everything can come back to what ever ambient is. Durring the string however the cooler gas carries less energy so a higher volume of said gas is required to maintain pressure, this is where the efficiency is lost chiefly when making charge areas smaller.

or PV/T = PV/T. Usually we assume that Temp is constant so we toss it out, however in this model Temp. decreases with ever shot which means that if Pressure remains constant from the reg (say 300psi) and we cannot affect Temp (which is continually dropping) then Volume must increase in order to maintain the same ammount of energy. So assuming that pressure is constant because of the reg (which will have an infinitely fast recharge for the sake of my argument) we see that P is canceled on both sides of the equation and we're left with V1/T1 = V2/T2.

Here's the scenario now that we're all on the same page (and hopefully will get that point across that I'm trying to make). Consider that V1 is equal to the volume of air that is contained within the chamber at the initial firing event at T1 (which we'll say is 297*K) and assume that 1*K is lost per firing event over the course of a 41 shot string.

If V1 = 0.196 and T1 = 297K and T2 = 256K then V2 = 0.168942761. This means that ~0.0271 ci of air has been lost. The valve still remains open the same ammount of time and so more air is consumed by the valve as the propellant gas temp. decreases per firing event. This might not seem like much, but that's almost a 14% loss in volume over the course of 41 shots. By calculating the total volume lost over the string that's roughly 290%.

Larger air chambers act as a buffer for this by allowing lower pressure opperation of the gun. This means that the change in PV which directly influences T will be smaller. If we consider a larger V1 or .785 and again, assume that P is constant becase of the ideal reg and that Change in T due to a firing event is .95*K we see that V2 = 0.682051347. Here ~0.1029 ci of air has been lost. Now I know you're thinking HA!!! He's BONKERS!!! but wait, the % volume lost is only 13% at the last shot of the 41 shot string vs. 14%. Again, by calculating the total percentage of volume lost over the course of the string, we see that 275% of volume is lost.

So you see that by simply preventing the chamber temp from shifting a little we can see an improvement in efficiency. Even if it's 0.05*K. This is why Mini conversions loose efficiency vs. their full sized brothers. Our debate has actually helped me to think through what's going on and I appreciate your points which inevitably point me in the direction of truth in explination.

[VFX_Fenix]

As for my proof of idea, which I neglected YET again. Consider venting High Pressure Gas from a nozzle, notice that in some cases the gas will form a mist jet and in a few ice crystals will form around the nozzle reflecting the loss in temprature due to expansion.

[hawpunch]

hey thanks to all of you, especially vfx_fenix and FallNAngel for your responses. your arguments made sense, and opinion seems to be divided on whether going to a mini body will traumatically effect efficiency and rate of fire. i'm using an air america messiah regulator and running 800 psi in and 320 psi out and it seems to be doing okay. anyone else have opinions?

jae park

[VFX_Fenix]

I suppose I should also qualify that my argument really only works in terms of shooting long strings of paint. If only shooting a few balls ever second or so, or shot fast bursts, everything being equal, there shouldn't be an appreciable loss in efficiency.

[GT]

So you see that by simply preventing the chamber temp from shifting a little we can see an improvement in efficiency. Even if it's 0.05*K. This is why Mini conversions loose efficiency vs. their full sized brothers. Our debate has actually helped me to think through what's going on and I appreciate your points which inevitably point me in the direction of truth in explination.

As for my proof of idea, which I neglected YET again. Consider venting High Pressure Gas from a nozzle, notice that in some cases the gas will form a mist jet and in a few ice crystals will form around the nozzle reflecting the loss in temprature due to expansion.

I'm not following your logic. Why would any gas, unless uder phase change, produce crystals when released to ambient? The whole problem with RT valves is that they heat up and increase the pressure in thier valve chamber causing "hot" shots. Basic law of thermodynamics is that you essentail lose some energy when releasing or filling a tank from the friction casued by the gas.

Any pressure change because of the decrease in temp is due to phase change, i.e. co2, which is not present in compressed "air"

Larger air chambers act as a buffer for this by allowing lower pressure opperation of the gun.

This is true, if your reg isnt up to the task.

Here's the scenario now that we're all on the same page (and hopefully will get that point across that I'm trying to make). Consider that V1 is equal to the volume of air that is contained within the chamber at the initial firing event at T1 (which we'll say is 297*K) and assume that 1*K is lost per firing event over the course of a 41 shot string.

If V1 = 0.196 and T1 = 297K and T2 = 256K then V2 = 0.168942761. This means that ~0.0271 ci of air has been lost. The valve still remains open the same ammount of time and so more air is consumed by the valve as the propellant gas temp. decreases per firing event. This might not seem like much, but that's almost a 14% loss in volume over the course of 41 shots. By calculating the total volume lost over the string that's roughly 290%.

Keep in mind that the it takes less volume to fill the mini as apposed to the full sized cocker. higher Volume does not equal better effiency.... nor does a lower operating pressure. Infact i would go as far to say that if you could reduce the heating issue of a high pressure system that a HP low volume gun would be immensly more effiecent.

[VFX_Fenix]

I'm not following your logic. Why would any gas, unless uder phase change, produce crystals when released to ambient? The whole problem with RT valves is that they heat up and increase the pressure in thier valve chamber causing "hot" shots. Basic law of thermodynamics is that you essentail lose some energy when releasing or filling a tank from the friction casued by the gas.

Because you're taking the gas in the bottle your filling to a higher pressure, not venting into an open space. As for the RT That is a slightly different situation and most closely related to the SCUBA to bottle analogy because you're taking air which is at 14psi in the valve and almost instantly ramping it up to operating pressure(~300-400psi) again. This doesn't happen in Autocockers, there will always be some significan ammount of pressure remaining in the pre-valve chamber. This is why an AC can operate at lower input pressures from a gas source than an Automag. Because even though they both use some measure of air to shoot and possibly even have the same operating pressure (Yes, the Mag is an LP gun kids) the Mag completely vents ALL of the regulated air where as the Autococker only vents a portion of the regulated air. Mags and Cockers use air in completely different ways.

Any pressure change because of the decrease in temp is due to phase change, i.e. co2, which is not present in compressed "air"

Not true, the air vented from a full scuba into atmosphere if you place your hand over it is cooler that ambient, and can cause a vapor jet if conditions are appropriate for such an event to occur. Ever notice the "smoke" coming out of the barrel of your Mag while shooting? That's condensation from venting ~300-400psi gas into atmosphere. If we look at a phase diagram we notice that as temp. decreases at a given pressure density increases (which indicates condensation) until a phase change is reached, at which point a flat spot is found then density continues to increase until the next phase change and so on to absolute zero.

This is true, if your reg isnt up to the task.

this is taken out of context, the full text is as follows.

Larger air chambers act as a buffer for this by allowing lower pressure opperation of the gun. This means that the change in PV which directly influences T will be smaller.

You'll also note that I included in my scenario an ideal regulator that had an infinitely fast recharge rate so pressure drop off wouldn't be an issue (hence why I neglect to inclue P in my equations).

Keep in mind that the it takes less volume to fill the mini as apposed to the full sized cocker. higher Volume does not equal better effiency.... nor does a lower operating pressure. Infact i would go as far to say that if you could reduce the heating issue of a high pressure system that a HP low volume gun would be immensly more effiecent.

True, however, every marker has roughly 2 points at which it is most efficient. A low pressure point and a high pressure point. Also consider that barrel selection will effect efficiency as well. According to TK an ideal barrel is between 10 and 12 inches long with a muzzle break (much like Crown Tip barrels that AGD produces and LAPCO's Autospirit/Bigshot). It is a known fact that a certain volume of air is reuired to accelerate a ball to a desired FPS given an acceleration zone of length X and pressure of Y. This is why HP guns can get away with really short barrels and why lower pressure guns require longer barrels to remain efficient.

[GT]

Not true, the air vented from a full scuba into atmosphere if you place your hand over it is cooler that ambient, and can cause a vapor jet if conditions are appropriate for such an event to occur. Ever notice the "smoke" coming out of the barrel of your Mag while shooting? That's condensation from venting ~300-400psi gas into atmosphere.

Sure, If the tank is cooler that the surronding air, but when it vents long enough it will heat up.

True, however, every marker has roughly 2 points at which it is most efficient. A low pressure point and a high pressure point.

Correct,
So why would the same gun with less volume mean that it is signifganly less effiecient? All you are doing with a mini is decreasing the volume, so increase the working pressure and I doubt you will see a statistical difference in effiency.

[VFX_Fenix]

Sure, If the tank is cooler that the surronding air, but when it vents long enough it will heat up.

Okay... P1/T1=P2/T2
Now P1 - 207bar (Pressure of the air inside the tank ~3000psi), T1 - 297K (temp of air inside the tank roughly 75*F and assume that abient is also 75*F) : P2 - 1bar (pressure of gas in atmosphere ~14.7psi) T2 = (T2=(P2T1)/P1) = 1.43*K
1.37*K is close to absolute zero, this number is hugely incorrect but that's because in reality the gas would have undergone a phase change to liquid (which requires a fair ammount of energy). EDIT - Using a correct gas law the venting gas is actually only 2*K cooler than initial as opposed to the rather large 290+K cooler.

Correct,
So why would the same gun with less volume mean that it is signifganly less effiecient? All you are doing with a mini is decreasing the volume, so increase the working pressure and I doubt you will see a statistical difference in effiency.

Not correct when considering that a major alteration to the gas system has been made. Any change must have some effect, for good or ill. I did qualify that the change would not effect efficiency at low ROF, however, at High ROF the effect would be magnified and become more pronounced.

[GT]

Okay... P1/T1=P2/T2

1.37*K is close to absolute zero, this number is hugely incorrect but that's because in reality the gas would have undergone a phase change to liquid (which requires a fair ammount of energy).

like i said, cant use ideal gas law at this pressure.

EDIT - Using a correct gas law the venting gas is actually only 2*K cooler than initial as opposed to the rather large 290+K cooler.

so you are telling me a 3*F change in temp is going to create condensation and decrese effiency on long strings? We still have not addressed the friction issue.

You almost have me motivated enough to pick up my freshman chem and phys. book..... almost

[VFX_Fenix]

So those numbers didn't look at all right to me, so I went and talked to some people and I was using incorrect values in my equation (I feel stupid now). So, without further delay, here's the actual temp. shift.
T1 = 297K
T2 = 282K
ΔT = 15K (~27*F)

I will be exonerated!

That was seriously bugging me.... Anyway. it's crash time, night!

[lew]

Low friction RAM (i.e. SMC or BelSales) combined with a good lpr and 3 way (BelSales/Freeflow/Plamer) will also help with your efficiency, though I don't know how much.

That kind of setup (LP ram and 3-way) won't do a whole lot for efficiency (adds maybe 10-20 shots), but where it comes in useful is a light trigger pull and possibly the ability to pinch paint instead of chopping. There would be less resistance in the 3-way, which would lead to a lighter trigger pull.

I feel so honored to have my claims being used. :)

[Fred]

Doc recommended AGAINST cutting down his Fastback bodies to min-length when I asked about it... it was on the Tinker's guild, IIRC it was the recharge issue.

---Fred

[Python14]

This has to be the most educated discussion on AO for a while.