Chilling down the mag

[xrayhead]

Hi All

 

I did a search for chilling the mag and didn't find anything (very surprising), anyway I have a question regarding chilling down mags before the main fill of Gas. Is this recommended, I've seen a couple of players dumping gas before they fill but only 1 or 2! The reason I ask is many years ago when I marshalled paintball, we used 20oz CO2 cylinders and we would fill them from the main 120L tank.

Before the fill we would hit them with a couple of seconds, then close the bottle valve and open the fill vale to dump out CO2, this chilled the bottle down and allowed liquid into the 20oz. The end result was a far better fill into the bottle. Now I realize that the pistol mags have a different valve design so not sure if the dump method is recommended?

 

Cheers

[bankz5152]

Constantly doing this could potentially damage the rubber o-rings causeing leaks in the future.

 

The idea behind it is sound, in theory this should allow you to get more liquid propane into the mag resulting in more shots. However is the mag is cold it will lead to very poor perfomance.

 

So unless you can chill the mag and then get it back up to room temp pretty sharpish its really not worth doing.

[PureSilver]

This doesn't seem to make a particularly large amount of sense to me. Gravity and pressure, not temperature, is what determines whether liquid or gaseous propane or 1,1,1,2-tetrafluoroethane ends up in the magazine. That's why you hold the fill bottle over the magazine; the liquid will always be at the bottom of the fill bottle and it will always flow downwards regardless of whether magazine is hot or cold. Provided there is sufficient fluid in the bottle, if you fill the magazine fully it should fill completely with liquid regardless of whether it is hot or cold.

 

If the idea behind chilling the magazine is to chill the fluid entering it to make it more dense and therefore squeeze more of it in, I think the fractional difference in temperature imparted by a cold magazine is irrelevant compared to the temperature of the fluid owing to the higher specific heat capacity of the fluid, but I could be wrong.

[Pepperisit12]

The cost of green gas / the smell of propane are the reasons I do not dump out the remainder of the gas before filling.

In theory you would get more gas into the mag and as such a few more shots off, But I top off the gas everytime I fill up the bb's. Each fill gives way more than enough for one set of bb's (TM & HK px4's)

 

Hence you'd only see any benefit if you were reloading the bb's mid skirmish and not refilling the gas

[jv83]

Back in the day. Like way back, when spare gas mags where few and expensive, some people froze the mags in the freezer before filling them with gas. Claiming that this could get more gas into them.

[xrayhead]

My post was not to see if I could get more gas in the mag just a comparison to what we used to have to do when filling the CO2 bottles. The only other reason I asked is because I watched someone dumb and refill there mag this weekend.

 

Also 15 years ago or when ever it was we used to use scales under the bottle when filling, when you had 50 bottles to fill you needed to get the gas in there quick so you could build up the guns! I have a picture somewhere (I'll post it tonight) when we racked over 120 guns in the morning ready for a days rental play!! Needless to say a good pair of gloves was needed to fill 120 CO2 bottles in an hour   Lots of ice on the bottles!!

[Pepperisit12]

You also do the same when filling (or refilling) propane bottles. (or so many internet guides say to do)

[xrayhead]

Dam looked everywhere and cant find that photo of all the guns racked up, if memory serves me correct there was around 120 of them 

 

If I find it I'll scan it in and upload it (old school photo's - pain in the *albatross*)

[Stuey]

This doesn't seem to make a particularly large amount of sense to me. Gravity and pressure, not temperature, is what determines whether liquid or gaseous propane or 1,1,1,2-tetrafluoroethane ends up in the magazine. That's why you hold the fill bottle over the magazine; the liquid will always be at the bottom of the fill bottle and it will always flow downwards regardless of whether magazine is hot or cold. Provided there is sufficient fluid in the bottle, if you fill the magazine fully it should fill completely with liquid regardless of whether it is hot or cold.

 

If the idea behind chilling the magazine is to chill the fluid entering it to make it more dense and therefore squeeze more of it in, I think the fractional difference in temperature imparted by a cold magazine is irrelevant compared to the temperature of the fluid owing to the higher specific heat capacity of the fluid, but I could be wrong.

 

Yes, but pressure is directly affected by temperature. The difference in pressure between the vessels influences when the filling stops; by chilling the magazine you lower the vapour pressure of the gas in there, which allows the higher vapour pressure in the source container to keep pushing liquid in against the lower pressure (as well as gravity).

 

To be honest, I (along with most airsofters) don't fully understand how gas mags work. I'd love to know the exact physics of why the mags stop filling when they do, and how the tube extension thing some fill valves have affects it etc. A clear plastic mag to play with would be fun.

[PureSilver]

Yes, but pressure is directly affected by temperature.

Correct. However, the temperature of the empty magazine (small thermal mass), as I said above, is more or less irrelevant to the temperature of the fluid in the fill bottle (large thermal mass); chilling the magazine doesn't make much, if any, difference to how much fluid you can fit in there, firstly because the fluid from the fill bottle will quickly impose its own temperature on the magazine. Secondly, remember that if you chill the magazine it will shrink, so it will hold less fluid, which will tend to counteract any miniscule density difference you could impose on the fluid.

 

What you might be able to (stressing the might) is completely fill your magazine, and then chill it in a freezer. That might reduce the vapour pressure of the magazine's contents enough to add in a meaningful amount more fluid from a fill bottle. Bear in mind that as the magazine warmed up during play, without a gas zone to buffer the liquid expansion, it might suffer overpressure problems and would probably vent liquid into the gun's BBU - both of which are deleterious to the gun's performance and/or your health and safety.

 

The difference in pressure between the vessels influences when the filling stops; by chilling the magazine you lower the vapour pressure of the gas in there

If what you mean by that is "when the pressure of the magazine and fill bottle have equalised, filling stops" then yes.

 

by chilling the magazine you lower the vapour pressure of the gas in there

As above, if you chill the magazine by venting it, you're only chilling the magazine itself, as there's no fluid left in the magazine after you vent it to atmosphere and the pressure is simply ambient. You're then relying upon the small thermal mass of the magazine to cool the large thermal mass of the already cold (through adiabatic cooling) fluid as it enters from the fill bottle, which seems unlikely to have a significant effect. If you chill the magazine in a freezer after filling it, then yes, you lower the vapour pressure of the contents relative to the vapour pressure of the fill bottle, and might be able to squeeze in a little more fluid.

 

which allows the higher vapour pressure in the source container to keep pushing liquid in against the lower pressure (as well as gravity).

 

No. The pressure between the fill bottle and the magazine always equalises. If you held the magazine and the fill bottle 'upside down' (that is, with the magazine on top) the pressure would still be identical after filling, it's just that all the liquid would stay in the fill bottle. Gravity is the only thing that draws the denser, heavier liquid into the magazine.

[Rob15]

Dumping gas during a skirmish to try and reduce the temperature of the magazine in an attempt to get more gas in seems a tad daft, by chilling the magazine itself you're only going to compound the cooldown issue which would give worse gas efficiency and counter any potential gains you might make by chilling it before filling.

 

This chilling before filling theory may work with Co2 bottles but the difference is Co2 is a far higher pressure liquid gas regulated down to a lower pressure vapour, it'll take far longer for cooldown to start reducing the output vapour pressure. Standard airsoft gas magazines are affected by cooldown the moment it starts to happen because they don't regulate the gas vapour pressure down at all.

[xrayhead]

Ow no, what have I started....... 

[PureSilver]

tl;dr: Don't chill your magazines.

[xrayhead]

tl;dr: Don't chill your magazines.

 

LOL - seems to be a lot of debate on this. 

[Stuey]

Phew. Just as a preface, I'm going to say that all the conjectural physics in the world doesn't change the fact that this does work. I just want to know why.

 

Correct. However, the temperature of the empty magazine (small thermal mass), as I said above, is more or less irrelevant to the temperature of the fluid in the fill bottle (large thermal mass); chilling the magazine doesn't make much, if any, difference to how much fluid you can fit in there, firstly because the fluid from the fill bottle will quickly impose its own temperature on the magazine. Secondly, remember that if you chill the magazine it will shrink, so it will hold less fluid, which will tend to counteract any miniscule density difference you could impose on the fluid.

What you might be able to (stressing the might) is completely fill your magazine, and then chill it in a freezer. That might reduce the vapour pressure of the magazine's contents enough to add in a meaningful amount more fluid from a fill bottle. Bear in mind that as the magazine warmed up during play, without a gas zone to buffer the liquid expansion, it might suffer overpressure problems and would probably vent liquid into the gun's BBU - both of which are deleterious to the gun's performance and/or your health and safety.

 

You seem to be forgetting that filling a mag has the effect of making it colder. Also, the point of this is not to try to change the density of the liquid.

 

Fill then chill is the better way of doing it, but I won't argue that this whole exercise is waste of time, for gas-in-mag airsoft guns anyway.

 

If what you mean by that is "when the pressure of the magazine and fill bottle have equalised, filling stops" then yes.

 

I guess. I'm not 100% convinced that's the only factor though, different mags have the tubes on the fill valves, and WA seem to be able to accurately determine how much liquid will go into their mags (NLS system).

 

As above, I don't see why you're trying so hard to disprove this, it's a well known effect that can exploited when transferring gases around. Those who refill those Coleman tanks know that the Coleman bottle can be left in the freezer for a while to get a more useful fill in them, and/or the safety vent can be opened during filling - both achieve the same thing: lowering the pressure in the bottle to allow more liquid in.

 

 

 

Here's a fun question: if the pressure in the two containers is equal, but one is physically higher than the other (i.e. has gravity on it's side), why does the transfer stop?

 

 

LOL - seems to be a lot of debate on this. 

 

Well, there's no debate that it works. It's almost certainly not worth the faff, but the effect is there, just like with your CO2 bottles.

[BaBaBooey]

Sorry, I haven't read all the posts above.

 

My own personal opinion, it's not really a good idea to go messing around with magazines or you might open up a black hole, which will suck down the entire universe into nothingness. Just because Joe on the internet said frozen magazines are awesome doesn't necessarily mean you'll have the same results (even if everything on the internet is true).

 

They are relatively expensive (at least more than the usual AEG magazine) and fragile to being with. Just based on my own experience, standard Marui P226R magazines can hold about 12g, the E2 a bit more about 15g, of 143a at room temp...your mileage might vary.

 

Trying to charge a few additional g's won't make a significant difference and will just increase the likelihood of failure.

[renegadecow]

You can chill propane bottles when filling from a larger tank to squeeze more liquid in. The mechanism of this is lowering the temperature of the vessel which will lower the temperature of the contents and as far as refrigerants are concerned, lowers pressure in effect. The same works for mags, but the extra amount you get isn't all that much more so it's not really recommended. Venting gas to lower temperature is even far less recommended as mentioned the o-rings can freeze and crack.

[scorch]

If you're getting so few shots per fill that this is looking a worthwhile option to you, may I humbly suggest fixing your gun.

[PureSilver]

You seem to be forgetting that filling a mag has the effect of making it colder.

 

Filling the magazine has the effect of making it colder, yes. But filling the magazine makes everything colder; what's happening is adiabatic cooling, and that is completely inevitable and therefore totally irrelevant, insofar as I can tell.

 

I'm not 100% convinced that's the only factor though, different mags have the tubes on the fill valves, and WA seem to be able to accurately determine how much liquid will go into their mags (NLS system).

 

Equilibrium is the only factor. The gas in the magazines is the same propane as the liquid; as the pressure inside the magazine climbs (as it fills) the gas will quite happily condense, just as the liquid will quite happily evaporate when the pressure falls. If the pressure in the fill bottle is sufficient, the entire volume of the magazine should be able to fill with liquid; not that that is necessarily a very good idea; the systems inside the magazines may be designed to ensure that pockets of gas remain as an expansion buffer zone should the magazine heat up.

 

As above, I don't see why you're trying so hard to disprove this, it's a well known effect that can exploited when transferring gases around. Those who refill those Coleman tanks know that the Coleman bottle can be left in the freezer for a while to get a more useful fill in them, and/or the safety vent can be opened during filling - both achieve the same thing: lowering the pressure in the bottle to allow more liquid in.

 

You're confusing different issues here. Jacking open the safety valve uses exactly the same principle as shotgunning a beer or non-silent-fill valves. It allows the gas inside the receptacle to escape as it is displaced by the liquid, rather than waiting for the gas to condense as the pressure builds. All you get is a faster fill, not a more complete one, not to mention you're wasting a fairly significant amount of fluid (the escaping gas) doing so. The only exception is when the bottle is full of something that isn't the fuel you want (e.g. it's a new tank, and is full of air) in which case you would fill the receptacle as normal, then vent it partially to allow the evaporating fluid to push the air (which is lighter and remains at the top of the receptacle) out, before refilling it as usual.

 

Cooling the receptacle is a completely different issue to that. The "well known effect" seems to be used only when filling small CO₂ tanks without the aid of a pump, and even then only to reduce the pressure of the receptacle below 800psi to allow a faster fill unaided by gravity. That isn't how airsoft magazine filling works; it is aided by gravity and doesn't need to have internal pressure decreased, as the gas will quite happily condense or be displaced around a non-silent-fill valve as gravity drags the liquid into the magazine.

 

Here's a fun question: if the pressure in the two containers is equal, but one is physically higher than the other (i.e. has gravity on it's side), why does the transfer stop?

 

Because the lower container is full, such that trying to force more fluid into it would result in a higher pressure in the lower container than in the upper, which would then push the fluid back up into the upper container. That's equilibrium; it's simple.

[TB-Stalker]

Seriously, the man above knows his stuff, for a much easier life, take the advice given by PureSilver and don't ask for the scientific explanation behind it, because, let's face it, he knows it, will write it out and a good chunk of it will go over your head.

 

My opinion.

[BaBaBooey]

“Asking questions is a great way to figure out whom to listen to as well when you’re in a confusing situation like you are now—some of those people will have sound rationale for what they’re saying and it will be obvious, and others will very quickly demonstrate that they have no idea what they’re talking about. Immediate red flag if one of them gets defensive, can't, or doesn’t want to explain it to you.”

 

If the answer to a question is too complicated to understand, even if the response is correct, the question still remains unanswered.

 

"Chilling" magazines is not generally recommended.

[Stuey]

 

Seriously, the man above knows his stuff, for a much easier life, take the advice given by PureSilver and don't ask for the scientific explanation behind it, because, let's face it, he knows it, will write it out and a good chunk of it will go over your head.

 

My opinion.

 

Speak for yourself. I don't want an easy life, I want to understand the physics, and what PS is saying doesn't seem consistent to me.

 

Filling the magazine has the effect of making it colder, yes. But filling the magazine makes everything colder; what's happening is adiabatic cooling, and that is completely inevitable and therefore totally irrelevant, insofar as I can tell.

 

It's completely relevant; if the gas is colder, its vapour pressure is less, there is a pressure difference between mag and bottle, encouraging flow into the mag.

 

 You're confusing different issues here. Jacking open the safety valve uses exactly the same principle as shotgunning a beer or non-silent-fill valves. It allows the gas inside the receptacle to escape as it is displaced by the liquid, rather than waiting for the gas to condense as the pressure builds. All you get is a faster fill, not a more complete one

 

I would have thought if you can prevent the pressure from building you could in theory fill the tank completely with liquid.

 

Because the lower container is full, such that trying to force more fluid into it would result in a higher pressure in the lower container than in the upper, which would then push the fluid back up into the upper container. That's equilibrium; it's simple.

 

But you just said that gas can escape through the fill valve if the pressure increases, so why doesn't it keep going until the mag is full of liquid?

 

This is at the crux of what I'm trying to figure out: as soon as there is liquid in the mag, the pressure will be whatever the vapour pressure at that temperature is i.e. the same as the pressure in the source bottle. Now you say, correctly I believe, that when you add more liquid, some of the gas condenses to keep the pressure the same. I want to know why this process doesn't continue until the magazine is completely full of liquid.

 

 

Cooling the receptacle is a completely different issue to that. The "well known effect" seems to be used only when filling small CO₂ tanks without the aid of a pump, and even then only to reduce the pressure of the receptacle below 800psi to allow a faster fill unaided by gravity. That isn't how airsoft magazine filling works; it is aided by gravity and doesn't need to have internal pressure decreased, as the gas will quite happily condense or be displaced around a non-silent-fill valve as gravity drags the liquid into the magazine.

 

As I said in my last post, regularly used by people refilling propane tanks.

[PureSilver]

Speak for yourself. I don't want an easy life, I want to understand the physics, and what PS is saying doesn't seem consistent to me.

 

OK, then I'll keep trying.

 

It's completely relevant; if the gas is colder, its vapour pressure is less, there is a pressure difference between mag and bottle, encouraging flow into the mag.

 

No, the fact that you noted ("filling a mag has the effect of making it colder") is completely irrelevant.

 

What you are trying to establish is a pressure differential; lower pressure in the magazine than in the bottle, encouraging flow from the higher-pressure area (the bottle) to the lower-pressure area (the magazine). The reason that filling a magazine makes it colder is irrelevant is that what is making the magazine colder is adiabatic cooling, which starts in the bottle, not the magazine, and affects all the fluid in the bottle. The part that is getting cold is the fluid in the bottle (where the pressure is dropping), not the fluid in the magazine (where the pressure is increasing). The cold you're feeling in the magazine is simply due to fluid, cooled by adiabatic cooling in the bottle, draining into the magazine. The bottle is just as 'cold' as the magazine, though with a larger volume to 'absorb the cold', you won't notice it as much. Therefore, even though the magazine may be cold when you're done filling it, that doesn't mean that it is now at a lower pressure than the bottle; there is no pressure differential.

 

I would have thought if you can prevent the pressure from building you could in theory fill the tank completely with liquid.

 

What? You can't "prevent the pressure from building"; pressure is the only thing that's keeping the fluid liquid. The pressure in the magazine builds to equilibrium with the bottle; then the filling stops.

 

If you would like to fill the magazine completely with liquid, you can do it in two main ways:

• You allow displacement to occur. Here you allow gas to escape from the magazine as it is displaced by liquid, which is pulled in by gravity from the bottle, until the escape route (typically in magazines, a leak around the inlet valve) begins to spit liquid instead of hissing gas. That indicates that the magazine is now overflowing liquid rather than gas. This is how you fill a magazine anyway.
• You force condensation to occur. Here you don't allow gas to escape from the magazine as it fills with liquid, which is pulled in by gravity from the bottle. As the weight of the liquid presses into the magazine, it increases the pressure inside the magazine until the gas trapped inside condenses into liquid. This takes longer than the above method (unless you're using a pump, as most CO₂ retailers do these days) but the magazine will still be full of liquid by the time you're done. This is how you fill a magazine with silent-fill valves anyway.

Either of these will fill a container with liquid fully as long as you have gravity (to draw the liquid) and time (to allow the containers to reach equilibrium) on your side. If you are filling a lot of containers rapidly (e.g., commercially) and/or you don't have gravity on your side you can speed the filling up in a few ways, all of which involve increasing the pressure differential between the bottle and the container:

• Impose additional pressure through temperature. This would involve heating the bottle above ambient temperature to increase its pressure, which increases the pressure differential between the bottle and the container, and speeds filling up. This is prohibited under every health-and-safety statute you can think of in commercial settings and not used anywhere.
• Imposing additional pressure mechanically. This involves increasing the pressure of the fluid using a pump. This is fast, but dangerous; you can overfill gas bottles up to 20-30% this way, and leave them with no expansion (gas) space. In that situation the fluid no longer behaves in a Newtonian way, and can cause the bottle to explode - this is why CO₂ bottles are filled by weight, not pressure, and why they are fitted with burst discs. This is typically used where the receptacle is higher than the bottle (and therefore gravity cannot draw the liquid into the bottle) and where speed is important.
• Reduce the container's pressure mechanically. This involves venting the receptacle to atmosphere, which increases the pressure differential between the bottle and the container, and speeds filling. Almost all commercial CO₂ filling stations used to do this; not to squeeze more fluid in, but to speed filling.
• Reduce the container's pressure through temperature. This involves chilling the receptacle in a fridge or freezer (or by venting), which increases the pressure differential between the bottle and the container, and speeds filling. Most commercial CO₂ filling stations do this these days, because it is cheaper than wasting whatever remains in the container by venting it. Again, this doesn't allow you to get more gas into the container; it just makes it faster to get the fluid in.

But you just said that gas can escape through the fill valve if the pressure increases, so why doesn't it keep going until the mag is full of liquid?

 

It does keep going until the magazine is full (or very nearly full) of liquid. If you'd like I will film me filling a P226 magazine up, and you can watch it spitting fluid at me as it begins to overflow.

 

This is at the crux of what I'm trying to figure out: as soon as there is liquid in the mag, the pressure will be whatever the vapour pressure at that temperature is i.e. the same as the pressure in the source bottle. Now you say, correctly I believe, that when you add more liquid, some of the gas condenses to keep the pressure the same. I want to know why this process doesn't continue until the magazine is completely full of liquid.

 

You're absolutely correct. As soon as there is liquid in the magazine, the pressure inside is the vapour pressure for the temperature of the fluid. That is an equilibrium of its own. As gravity pulls more of the denser liquid from the bottle into the magazine, more of the space inside the (fixed) internal volume of the magazine is occupied by liquid, which reduces the space available for the gas (compressing it). As the gas is compressed, it passes the vapour pressure and condenses, reducing the pressure of the gas zone and again reaching equilibrium. If you fill it indefinitely (and in the absence of designed-in safety measures), the magazine will eventually completely fill with liquid.

[renegadecow]

I want to know why this process doesn't continue until the magazine is completely full of liquid.

 

The temperature of the system isn't low enough to decrease the pressure of the gas pocket in the mag to shrink enough that all space will be filled with liquid. Get everything cold enough and you should be able to transfer fluids like it was tap water in a canteen.

[Im going space]

as a side note:

Your GBB runs off of pressurised gas, not the liquid. it is better for efficiency to NOT completely fill the mag, and to leave room in it for expansion. 4-5 seconds is all it needs, not till it sprays out BC the mag is 'Full'