X-valve Shootdown?

[TheJester]

pbguy and i were talking, and we sorta came up w/ a hypothisis....will the new x-valve have less of a velocity drop off issue than the original retro valve? Reason we thought it might is because the shoot down is caused by the cooling of the gas that is heated while entering the chamber. But the originaly retro valve had a stainless steel chamber, the x-valve has an alminum one, which serves as a better heat sink. So would the fact that the alminum can dissapate heat better than steel? In turn, causing less shoot down because the temperature of the gas is a little more constent?

[poopthatkilledelvis]

i think the difference is very minimal

[athomas]

The air itself changes temp too quickly for the outside metal of the chamber to react in a timely fashion to dissipate the heat (even aluminum). The slight changes in pressure as the compressed air returns to normal temperature cannot be compensated for by the regulator.

[TheJester]

Originally posted by athomas
The air itself changes temp too quickly for the outside metal of the chamber to react in a timely fashion to dissipate the heat (even aluminum). The slight changes in pressure as the compressed air returns to normal temperature cannot be compensated for by the regulator.

well in that case, wouldn't you have to not worry about the shoot down because you're shooting fast anyway? what i'm tlaking about is say after a long string of rapid fire (air is warmer), as it gets warm enough to warm the metal around it (in this case aluminum) the aluminum is alot more willing to dissipate the heat alot more, and alot faster than stainless, back on track though....as the air starts to heat the metal, it dissipates faster than in the stainless valve, therefore not becoming as hot, and being at a lower maximum temperature. A lower maximum temp would mean less of a temp range, hence not as dramatic drop off

[poopthatkilledelvis]

jester, you're thinking about this way too much.

[athomas]

The retro valve heats up on long strings of shots because of the heat from the air that's transfered to the metal. Its the hot air that causes the increase in velocity from "normal". A single shot or the first shot in a string will be of less velocity than the rest of the shots in the string because the air is at a normal temperature and at a pressure related to that temp. Any shot immediately following a previous shot will be at a higher velocity.

Jester, I think I see where you are coming from on this. By allowing the aluminum to dissiate more heat, you are attempting to show that you could provide more stability to the air temp. Afterall, its the air temp, not the valve temp that causes the problem. The valve temp is only a result of the air temp problem. Since its the front part of the valve assembly that causes the problem, you would have to get that part of the valve outside the body of the gun so it could adequately dissipate the heat, or it is of no concern what material is used.

I'm still not sure that the aluminum, even properly heat sinked, could provide enough heat absorbtion and dissipation fast enough to cool the air before the regulator fully completed its task.

[TheJester]

i haven't gotten an answer that seems like any 1 knows what i'm talking about, it's not exactly easy to word, so far though, athomas, you have been the most helpful.


Originally posted by athomas
I'm still not sure that the aluminum, even properly heat sinked, could provide enough heat absorbtion and dissipation fast enough to cool the air before the regulator fully completed its task.

i can say that it won't cool the air, cause i have felt my vavle heat up a little after a string. but because the material will dissipate heat better, the cahmber temperature wouldn't be as high, for example, say in the retro the chamber temp could reach a temp up to 140 degrees (i'm just pulling that temp out of the air) but because the aluminum is better w/ heat, say the maium temperature of the chamber in an x-valve is only 120 dgrees, wouldn't that in turn cause less shoot down, because there is less of a dramatic change in temp?

P.S. is this making sense to any 1 but me?

[athomas]

You are making sense and its an excellent observation.

The heat is generated within the valve chamber and I'm guessing that the actual air temperature inside the valve chamber reaches an extremely high value, much higher that 140 degrees F. The higher the temperature differential, the greater the effect of heat dissipation you will see by using a better heat conductor (ie; aluminm over SS).

The front of the valve sits in the body of the gun and is separated by an air gap. This would limit heat dissipation by the actual chamber directly to the outside air. The valve would have to dissipate the heat by transfering it to the back of the the valve and dissipating it to the air.

I wonder what the rate of heat transfer is for the aluminum valve vs the stainless valve. The differnce in operating temp of the gun could be observed by placing a temperature sensor on the valve and then rapidly firing the gun. try this with both valves and observe the differences in exterior valve temperature. It won't be an exact science but I'll bet it'll give an indication as to whether there is an operation temp difference.

If by chance the aluminum valve shows a lower temperature, then that means it will probably be more consistent in its output velocity.

Basically, the retro valve is extremely consistent while firing. Any single charge of air comes in hot and will cool if left for any amount of time. This cooling will result in a decrease in velocity when compared to all shots fired in rapid succession or any shot fired using the trigger release and shoot method the same as the chrono procedure for the retro valve. So, its not shoot-down that causes the problem, its shoot-up that's the problem.

By dissipating heat during the charge phase of the valve, we are attempting to bring the high temp closer to the normal resting temp. Less temp chamge means less velocity change.

[TheJester]

that's a good idea, and thanks for bringing up the point of the fact that it's in a stainless tube, i completely over looked that i'll have to get around to trying that temp. experiement some time, the only problems would be keeping the rate of fire the same, and finding some 1 around here w/ an original retro valve, i only know of 1 other mag in the area, and that's an e-mag, i guess that would work, but then it would be ever harder to keep the ROF's the same

[athomas]

If you have access to an emag, the experiment is easy. Electronically shoot the gun using a controlled pulse to control rate of fire and just monitor the temperature. Use the same rate of fire for both the Xvalve and the regular valve. Unless you have access to precision instruments and computer measuring devices the data won't be solid but it will still show general tendencies. You should be able to determine if there is a difference in heat dissipation between the two valves.

[nippinout]

Okay...

In a RT based mag, you will get temperature problems.

When you chrono one, you have to hold back the trigger and do the release/pull very quickly to simulate velocities at high ROF.

The temperature rise of the body and valve isn't due to long strings simply because of sustained fire.

The rise is due to such a quick recharge. The valve recharges at the same rate for 1 bps as it would for 20 bps.

The heat you feel is already in the valve. If you wait, your velocity will be lower than normal.

You can't change the fact that the valve will cool, so materials will only affect how quickly it will cool. If anything, you want the material to be an insulator with poor heat flow so the air can't change temperature/pressure.

How do you remedy the problem? Hold the trigger back between strings, or don't worry about the first shot being off.

[Bront]

Ok, I think I can explain this.

The air in the valve heats up due to compression (Much like a nitro tank warms up when you first fill it) durring it's recharge. From when it recharges to when you fire is when it would have to cool down, and if you are rapidly firing, the air wouldn't have time to drop it's tempurature in any way (less than 1 second, probably closer to .2 seconds or less). It only takes the marker 1-2 seconds to cool back down to normal opperating tempuratures anyway, so it's not that big of an issue (Heat exchange)

Air doesn't need a lot of energy to heat up, nor does it need a lot to cool down. Aluminum needs less than steel, so it does change tempuratures faster, but they absorb and disipate energy at a similar rate, so it shouldn't make much of a difference.

[TheJester]

nippinout, look at it this way, if the metal around the air is warm, it will prevent the air from cooling as well, heat the wall of a tin can, the air in it will heat as well. but if the wall of that same can remains cool, then the air in the can(valve) would be a little more of a consistant temp., and will take less time for the air to cool. now some of you also may see how that could actually cause more drop off, but also look at it this way, if it's cooling off faster, it's staying a little more of a constant temp....a little more consistant of a velocity


Bront, but what if the air didn't heat up as much? now i don't think alm. can dissipate heat that fast, to put this in perspective...say normal operating temp is "cool" air, during fire, it becomes "warm", where in the ss version, it became "hot". and what if instead of the 1-2 seconds from returning from "hot" to "cold" it took 1/2-1 second to return from "warm" to "cool" wouldn't that mean less shoot down, because there is less varience?


i'm more or less just playing the devil's advicate now, i'm pretty convinced that what/if any difference, is for the most part negligable, you guys all have great points, but i think i have some 1/2 way desent points as well

[Conqueror]

In a normal mag, the reg seat opens a few thousandths of an inch to recharge. In an RT assembly, it yawns to nearly 1/8", which is huge in terms of flow characteristics.

The RT recharges so fast that on a shot-to-shot basis the process is essentially adiabatic. The heat that you feel on the valve after is a string is the buildup of heat from numerous shots. Taking a single shot doesn't warm up the regulator. Aluminum does indeed dissipate heat faster than stainless, but in the time frame of a recharging RT valve the difference is totally negligible. In the few thousandths of a second during which the air temperature spikes above normal, the aluminum won't have time to absorb any heat. It's only during prolonged firing that the metal will heat up, and the process will not make the air from any one shot any cooler. Does that make sense?

Additionally, it seems to me that you have the idea backwards... You say that the aluminum will dissipate heat faster, thusly reducing shootdown. It seems to me that if the air is cooler (and thus at a lower pressure), this would increase shootdown. The RT valves actually have "shootup" beyond 25 bps or so, so I think the only effect the aluminum mighht have is to reduce this shootup. It's certainly not going to reduce shootdown, because the RT simply doesn't have any to start with.

CQ

[TheJester]

yea, i def see where people are coming, but i don't think i have the idea backwards, cause it would result in a more constant temp, a smaller range of temps, which would mean a less dramatic change in velocity.

but like i said in my last post, i'm not just playing a devil's advicate, and that what/if any difference there is, is negligable

and when it all comes down to it, i agree w/ poopthatkilledelvis i think too much, but reason i posted this was to get an idea, i'm only 16, and i don't have that much knowledge of matal characteristics, though i am gaining more in my machine shop, so i just kinda threw an idea out to see what people thought