WA's on propane

[Crunchmeister]

Originally Posted by Thenooblord

heh, guess we differ like that, I cant stand to have any gun in my collection un gamed, I'd rather devalue it, because in my mind its worthless if you cant shoot it, so not shooting it is just making it worthless WITHOUT me breaking it xD

Well, all my guns are gaming guns except that one. Looks just like the Beretta in your sig with the white grips. I love that gun, but I want to keep it pristine.

[MadMax]

Originally Posted by Guges Mk3

While there is a phase transition, due to the chemical make up of the gas being used. the pressure we derive from a magazine is founded on the gas in the magazine and not the liquid.

Sure our guns work on gas from our mags. Gas which is at equilibrium conditions with the liquid phase which is a non ideal condition.

Consider this 2 phase situation:

A syringe filled to half it's volume with only liquid butane with it's end plugged and a force holding the syringe piston from moving. If you allow the piston to move back under pressure slowly, liquid evaporates and creates some gas space. If you move the piston slowly then the internal volume of the syringe increases with no decrease in pressure so long as you allow heat to warm the liquid and maintain a constant temperature. This is very non ideal behavior. Volume goes up with no change in pressure.

If you allow the piston to move fast, the temperature of the liquid drops as liquid boils off (energy is involved in the phase transition from liquid to gas). The pressure drops until the liquid warms up to it's original temperature (equilibrating once again with the room temperature).

PV <> nRT (on the left, pressure is constant, volume increases. On right nRT is constant)

Carl,
you seem to forgot about all those Version 1&2 prokillers and infinity parts from me, they are all victim of propane on stock slides even the red hybrid Vreaker or what ever they call it all the slides went to heaven even after your V1 restrictor

With all the parts given to you i think you made like 3 prokillers and some infinity

Yeah, I can't remember if your slides were the heavy weight slides or light ones. Not all Prokillers got light slides. I've seen a lot of variation in that model. If I recall, you Vreaker was a heavyweight model. The flow restrictor ended up causing a misfire so we removed it in the end.

I'm not saying that all WA slides are propane tolerant. I'm just saying that the few lightweight slides I've seen and run (and run alot) seemed to have been ok with propane, but all of the slides I've replaced for my own guns or others (maybe a dozen in my time) were all heavyweight slides.

[Guges Mk3]

You draw a valid example with a syringe, but a gas mag is not a syringe and the volume is fixed. Which makes it a constant. In addition gas properties vary by gas type.

[MadMax]

Dude, you're dead wrong in asserting ideal gas behavior.

For instance when we shoot we let out some gas which is replenished by liquid evaporation. The ideal gas model would have the pressure drop steadily with each shot. The fixed volume example does not hold in our mags because we let gas out into the environment which lets "n" go down. In this situation we let "n" reduce as we allow some fractional mole of gas out of the container. If internal volume of the mag is constant (it is because it has non moving walls) and we allow temperature to remain constant (allow the mag to warm a bit between shots) then it would follow that pressure would have to drop unless you want to allow a change in the Boltzmann constant.

pv cannot equal nRt if only "n" changes. Therefore situation non ideal.

The ideal gas law neglects molecular size and molecular interactions which only holds as long as the average distance between molecules is large compared to molecular size. This breaks down considerably when you reach condensation conditions and molecules eqilibrate across a phase transition. In this condition molecular interactions are not negligible and even become dominant in dictating behavior.

Of course gas type will affect pressures. It will have a stronger effect under non ideal conditions than under ideal conditions because of molecular interaction. For instance a liter of gaseous air or propane or HFC134a at 1atm will all have similar behaviors when compressed to half a liter. Take a liter of any gas far from condensation conditions at STP conditions and compress them to half their volume and you'll get two atmospheres pressure. It's only when you get closer to condensation conditions for particular gases will they star to exhibit significantly different behavoir (other than other chemical characteristics like combustion). It is because we have non ideal conditions in our GBBs that we can switch propellants to achieve different operating pressures.

[Thenooblord]

wait... so what does this have to do with WA pistol slides....

[Thenooblord]

on the topics of properties of gas, this M9 i got will only get 10-12 shots off on propane, but the previous owner claims it could get a mag and a half on duster, is there any rationale for this?

[Guges Mk3]

Originally Posted by MadMax

Dude, you're dead wrong in asserting ideal gas behavior.

pv cannot equal nRt if only "n" changes. Therefore situation non ideal.

Every Gas follows ideal gas law at some point or another for a limited time.

Again you cite an accurate example of gas changing from liquid to gaseous state. However your arguments are to literal and not practical and you one factor that makes your argument invalid. A Siphon tube in a gas magazine.

Take some active chrono readings some time with a gas magazine that has a siphon tube, the key here is the Siphon tube. This maintains a constant volume inside the magazine for gas phase development. It prevents over filling of the magazine with liquid. It helps maintain a minimum volume for gas inside the magazine.

Take 5 shots. After five shots in said magazine with a siphon tube fps will drop. Pressure dropped due to two factors changing on the other side of the equation. n and T. Literal application of the Ideal gas law is followed.

Now take a magazine that has no siphon tube and you will get readings all over the spectrum. First 3 shots will most likely be low until enough liquid is vented to allow the liquid to gas phase to develop inside the magazine. Then FPS will increase and then start dropping as the magazine empties.
++++++++++

Thenooblord

Yes there is. The gas properties are different between hfc134a and propane. 134a has a lower pressure to gas phase rating. So you can put more liquid 134a in a magazine over propane. More liquid in magazine leads to more "gas" to fire your gun

[Thenooblord]

you mentioned htat the siphon prevented overfilling, so i took it off the mag, and now it can atleast get 15-16 shots off, but i still think it should be easily able to cycle a plastic slide 30+ times

[MadMax]

Nooblord: what make and model GBB are you using? Not all models have two port valves in their mags. KJW for instance does not have overflow ports so they can sometimes take a short shot of propellant. Do you get a leaking sound of propellant while filling and a spurt of visible white mist when the mag is full? Are you filling a lower capacity single stack mag? Is the rubber bit at the top of your magazine torn? I recall that many WA mags slowly destroy this rubber bit on propane. If it's badly torn it will allow a lot of gas to leak out when firing.

Back to the threadjack:

Yeah, I made a post about the siphon tube a bunch of years ago. It has little to do with the pneumatics in a GBB while shooting. All it does is assure a measured shot of liquid into a mag. When you turn the mag upright, it does not siphon liquid out of the mag while shooting. The situation in a mag is a two phase saturated single component system not too unlike what you have inside of a refrigerator except we let the stuff escape when we shoot.

The temperature drop you see is due to heat being used to boil liquid into gas which results in a colder liquid temperature. This has nothing to do with the ideal gas law which does not address phase changes or evaporation. Just for kicks, look for a temperature-pressure phase diagram for HC-290 (it happens to be the refrigerant definition for propane).

http://www.engineeringtoolbox.com/pr...re-d_1020.html

If you were to measure the pressure in a propane filled mag at room temperature (~20C or 293K) you'd get a pressure around 125psia. Cool things down to about -3C/270K and you get pressure at around 62.5psia. So you have a temperature drop of only 6.5% but you get a pressure drop of 50% which is very non ideal behavior. Don't forget to add 15psi to the psig numbers because the ideal gas law only applies to absolute pressure so you need to add one atmosphere of pressure which is about 15psi at sea level on our planet.

The temperature pressure behavior of the propellants we use in our typical conditions is governed by the equilibrium conditions which exist between liquid and gaseous phase in our mags. Not by the ideal gas law which works at lower pressures. Our propellants start to behave like ideal gas laws somewhere after exiting the barrel and exhaust ports outside of the gun when they drop to lower pressures far away from condensation conditions.

The Ideal Gas law is pretty much as far as High School goes. It's not a bad law, but it has significant limitations on where it's valid that teachers don't seem to be doing a good job of communicating. It's actually nearly as important to know where one's knowledge applies as to have knowledge. In a sense, systems of knowledge are like tools in a toolbox to apply to understanding or modeling the physical world. Some tools seem generally quite useful, but there are special conditions where they are wholly inappropriate. Kind of like knowing when one should use a voltmeter or an oscilloscope or a spectrum analyzer.

[Thenooblord]

its a WA magna M9, yes the rubber is slightly torn I noticed that the other day, but its not bad, and there is no puff of smoke or evidence of excessive gas useage

its the same type of valve as TM, not the shitty silent fill ones

[MadMax]

HFC134a has a higher expansivity than propane, but you should still be able to get about two mags of bbs out of a WA M9 mag if you don't shoot too rapidly (say a shot per 2s) on propane.

A torn mag rubber will not spew huge clouds of vapor, but it will still adversely affect efficiency. When your gun is in recoil mode, the valve is held half open by the valve lock on your mag. This keeps the valve open, but I think it reduces the flow rate while the gun is recoiling. You get a wide open valve while the firing pin opens it up during firing mode, but the valve closes to half mast when the slide begins to recoil and lifts the hammer off the firing pin.

A torn valve rubber allows some gas to leak between the mag and the nozzle body so it consumes more gas during the recoil phase.

Another thing you could check is the piston oring on the nozzle body. If it's very dry it can stick in the cylinder and make the recoil more sluggish which keeps the mag valve open longer. If it's nicked or otherwise damaged, it could allow gas to leak out of the blowback assembly and reduce efficiency.

[Thenooblord]

theres no damage to any of the seals or orings, and like i said, theres no vapour at all when if fires, if you say it should get 2 mags off and I get 15 shots, that would have to mean its using 3x as much gas, so there would have to be vapour

[MadMax]

No, not necessarily. Propane evaporates pretty damn fast. It can transition from liquid mist to invisible gas inside the gun. If you have many places for the gas to escape from (say out the mag well, chamber cover, and gaps in the slide) visible vapor can significantly evaporate before escaping.

Try pushing the mag up in the magwell a bit while shooting. If this fixes your problem, then you might have a worn mag catch which allows the mag to sit low so the rubber can't get a good seal.

[Thenooblord]

pushing as hard as I can i got 30 shots off
no wear on the mag catch though

[Crunchmeister]

That's odd. My WA M9 (also Magna) gets almost 3 mags on 1 fill of 134a, and an easy 2 mags (with gas to spare) on propane. You definitely have an issue with your gun or mag. I would have also suspected the mag catch as well, but seems like you've ruled that out.