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Mapp gas characteristics

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Mapp gas characteristics

Unread postAuthor: BigBang J » Sat Jan 15, 2011 10:32 pm

Hey guys,

I am having some trouble finding information on map gas characteristics.
I am specifically wondering if mapp is a refridgerent gas like propane?
In that the pressure decreases as the temperature drops. I am pretty sure it is a liquid in the cylinder and flashes to a vapor, is this correct? And what is the pressure of the gas, is the presure majorly affected by temperature like propane is?

Thanks guys.
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Unread postAuthor: Technician1002 » Sun Jan 16, 2011 1:32 am

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Unread postAuthor: mark.f » Sun Jan 16, 2011 9:37 am

Just a tip, it's harder to find actual MAPP gas these days. You're more than likely finding a gas like MAP/Pro, which is about 99.9% propylene.
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Unread postAuthor: BigBang J » Mon Jan 17, 2011 7:59 pm

O.k, Here is where I am.
I am building an airsoft gun using QEV and 3 way valve.
I was planning on using propane for a propellant but it would only be fine for summer play. Even at 60 degreese or so the pressure drop to far.
So I am looking for another propellant, I thought mapp gas might be a better alternative.
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Unread postAuthor: Lockednloaded » Mon Jan 17, 2011 8:03 pm

whats wrong with air? how high could you compress it in an air chamber
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Unread postAuthor: ramses » Mon Jan 17, 2011 8:44 pm

propane is liquid at reasonable temperatures and pressures. That saves him dealing with high pressure CO2 or air..

as far as I know, all gases have a lower vapor pressure as temperature goes down.

I recommend a mix of propane and butane. You could reach the sum of their vapor pressures at a given temperature because of partial pressure.
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Unread postAuthor: Technician1002 » Tue Jan 18, 2011 1:44 am

ramses wrote:I recommend a mix of propane and butane. You could reach the sum of their vapor pressures at a given temperature because of partial pressure.


This vapor pressure does not raise the boiling temperature of the two liquids involved. It means that vapor will continue to evaporate from the surface when the vapor of the other gas is in contact with the surface lowering the local vapor pressure. In a high supply demand situation, the concentration of Propane vapor over the propane liquid pool and vise versa will limit the effect of the total combined vapor pressures.

Relying on surface evaporation to generate the required combined vapor pressure works, but takes time and a fair amount of heat input to the liquids to supply the latent heat required.
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Unread postAuthor: DYI » Tue Jan 18, 2011 10:50 am

My solution to the problem was a tank of warm water surrounding the propane tank. You can reach ~200 psi without much in the way of safety concerns, and the heating occurs much faster than it would were the tank sitting in air of the same temperature. This may, however, be a bit unwieldy for your application.

Another possibility is, as Tech suggested earlier, heating the tank using combustion of the fuel it contains. It's certainly possible to achieve here, but surely even less practical than the first solution.

The heat of vaporization problem is going to exist with *any* liquefied gas that isn't supercritical. CO<sub>2</sub> is useful in this respect, in that its critical point is just barely above room temperature, meaning that the energy required to boil it off is normally quite low (non-existent, if it's above 31°C).

HPA tanks work just fine for paintball guns in all weather conditions. Unless you need a much higher quantity of gas for some reason, they're probably your best option too.
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Unread postAuthor: Ragnarok » Tue Jan 18, 2011 10:54 am

ramses wrote:I recommend a mix of propane and butane. You could reach the sum of their vapor pressures at a given temperature because of partial pressure.

Unfortunately not. I had suggested this as an idea previously, but I had overlooked the fact propane and butane are mutually soluble, so their vapour pressures do not stack.

Propane/butane mixes have a vapour pressure somewhere between that of their two components.
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Unread postAuthor: ramses » Tue Jan 18, 2011 5:13 pm

Ragnarok wrote:
ramses wrote:I recommend a mix of propane and butane. You could reach the sum of their vapor pressures at a given temperature because of partial pressure.

Unfortunately not. I had suggested this as an idea previously, but I had overlooked the fact propane and butane are mutually soluble, so their vapour pressures do not stack.

Propane/butane mixes have a vapour pressure somewhere between that of their two components.


poop. I didn't see that one coming. Does this also preclude 320x hybrids?
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Unread postAuthor: Fnord » Tue Jan 18, 2011 6:39 pm

poop. I didn't see that one coming. Does this also preclude 320x hybrids?


Well, 320x with propane anyway.

With gasses like hydrogen/oxygen would probably be possible, but who goes that high?

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Unread postAuthor: BigBang J » Tue Jan 18, 2011 8:42 pm

Well Guys you see I want this gun to be very practical, very simple and very convenient. I have tried setting the propane tank in the sun to warm up and then using it, this seemed to work fine for a little while, till the tank started to cool because of vaporization of the liquid, and this would not work well for cooler days. I have recently acquired a mini fridge that does not work anymore (it wont get cold) So I am going to rip out the compressor and convert it to compress air, hopefully to 700psi, and use that to fill up an expired paintball c02 tank and use that as my propellant. I think it should last a good long time since I will be regulating it down to around 100 psi, and airsoft doesn't require very much air.
C02 would work well but it wouldn't be convenient for me to get refill.
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Unread postAuthor: Lockednloaded » Tue Jan 18, 2011 10:22 pm

you can calculate how many shots per fill you can get with a simple P*V of your tank/P*V of your chamber
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Unread postAuthor: Ragnarok » Wed Jan 19, 2011 10:06 am

ramses wrote:I didn't see that one coming. Does this also preclude 320x hybrids?

Via that method, yes. However, there are a lot more ways than just that.

Still, I have been thinking about whether the 200-220x we think of as the propane/air limit is the real limit.
As far as you can force a lean combustion, you should be able to cram extra propane/air into the chamber (even if the propane is condensing). The enthalpy of combustion is considerably in excess of the energy needed to boil excess liquid propane.

As the LEL of propane is half that of stoichiometric, it may be possible to achieve combustion in a propane/air mix at ~6000 psi pre-ignition pressures with sufficiently energetic ignition.
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Unread postAuthor: BigBang J » Mon Feb 07, 2011 8:58 pm

Hi guys, I have finally decided to go high pressure compressed air regulated down from 1000psi to 100psi. The change coming from the fact that I obtained a fridge compressor.

SpudFiles Forum Index » Construction Materials/Ammo Discussion » 1000 psi Air compressor project!!


http://www.spudfiles.com/forums/1000-ps ... 22296.html
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