Should you purge your gas magazines?

[The_Lord_Poncho]

I've come across posts (generally not on this forum mind) which indicate that you can get air trapped inside your GBB magazines, and to remedy they advocate purging them.  Usually via a process of depressing the knocker valve for a few seconds as you fill them.  Is this really a 'thing'?

It seems surprising to me that air can become trapped in a magazine - and that it wouldn't as a matter of course vent out when you fire a few shots. Without knowing anything about how gases behave, I would also naturally assume that when you fill a mag, the liquid gas you are injecting falls to the lowest point, and any air that is trapped, rises to the highest point - in which case, with the mag inverted how would depressing the knocker valve release anything other than liquid gas?

I'm not trying to start a debate for the sake of a debate - after the second fill of my hicapa magazines the other night, I only managed  a few lacklustre shots out of each. Almost certainly because it was pretty cold + the gas can i was filling from was the same temperature as the mags; but I'm wondering if in parallel there could be other things that I could do to help. 

 

[Khyber]

I have recently heard about this. I think there may be something in it. I am experiencing the same with my MWS. I weigh the mags empty and full and cant get more than around 7-8g of gas in some mags wheres before I could get up to 20g. Get a few shots then it vents. Haven't had chance to see if this purge method remedies it. 

 

[Adolf Hamster]

It seems surprising to me that air can become trapped in a magazine - and that it wouldn't as a matter of course vent out when you fire a few shots. 

it'd only be actual air if the mag had been completely emptied and left open to air before filling (eg first fill after a rebuild), otherwise by "air" whats really meant is the gaseous portion of the mags contents.

Without knowing anything about how gases behave, I would also naturally assume that when you fill a mag, the liquid gas you are injecting falls to the lowest point, and any air that is trapped, rises to the highest point - in which case, with the mag inverted how would depressing the knocker valve release anything other than liquid gas?

that's exactly what happens.

there is logic to venting the gaseous portion of a mags contents as its being filled, it keeps the pressure of the mag lower than the fill bottle hence ensuring it keeps flowing regardless of how full or empty the bottle is.

however as you summise, it's pointless to vent from the bottom as that'll just dump liquid out, it's gotta vent from the top (which when filling is the fill valve).

tm are the main manufacturer for using vented fill valves, although i have seen them elsewhere (eg airsoft innovations 40 mike and derivatives), idea being you fill until you get liquid spew from the valve.

for non vented fill valves you can pulse when filling, but this risks overfilling (this is how i'd refill a lighter as it doesn't matter so much if there's no gas portion)

 

[EDcase]

I've tried the purge method on a couple of mags that didn't seem to hold the same amount as previously and it seemed to improve them.  Not empirically tested tho.

Its very easy to do so may as well give it a try (and report your experience)

 

[Sewdhull]

Filling a pressurised container from another pressurised container requires that there is a pressure difference.

All that purging will do do is reduce the temp of the magazine allowing the gas to transfer, because the pressure reduces in the mag. There is some small temperature reduction from general filling which is soon offset by the valve spring requiring a bit more pressure.

Liquid to liquid transfer does not alter the temp.

With cooled magazines i have never had issues filling them.

Its hard to know how much gas a mag will hold. It would be useful to know.

If you do something expecting an improvement you will probably see one...

 

[Shamal]

If you do something expecting an improvement you will probably see one...

Not true.

I bought Mrs Shamal a cook book last Christmas.

Nothing has changed. ??

 

[The_Lord_Poncho]

Thanks all for your thoughts. Actually, i hadn't considered that venting the mag a bit would help it cool, and create the necessary temperature difference to assist filling. That would actually have been quite useful for me to do the other evening when i had the mag filling issue, and possibly goes some way to explaining why people feel there is some truth in the 'air bubble/lock' issue - if the 'remedy' is actually solving a different problem they didn't realise they had!

I think i need to resolve the lack of temperature differential in other ways too - I might need to sew up an insulated sleeve for the gas bottle, within which i can chuck in a disposable hand warmer on cold game days.