Carbon Tanks and Elevation Changes

[rbmyeet]

I've been filling my FX Bobcat .25 cal with a hand pump and after almost a year of doing so, I'm ready for an upgrade. I live in a rural area at about 6k feet elevation, and regularly hunt anywhere from 3k feet to 12k feet elevation. I want to get a large-ish carbon tank to bring with me on longer trips to refill the gun easily and quietly. Will my abrupt elevation changes be a cause for concern? It only takes me about 15 minutes to get to 11k feet elevation, if that's relevant.

Thanks guys. I'm new to the forum and still figuring this PCP thing out

 

[bchannell]

Welcome to the forum.
You will lose 400 or so psi from 3000ft to 12000ft. BUT, you can fill most air cyls 10% over, to account for the heat of compression etc. so, unless you're running close on air, it won't be a problem.

 

[Gerry52]

what he said.

 

[AlanMcD]

With all due respect ot @bchannell and @Gerry52 , I completely disagree . . .

Higher elevation leads to lower atmospheric pressure, and secondarily usually also lower temperatures - but not always.

As far as the change in atmospheric pressure goes, you can pretty much ignore it for any impact on air pressure in your gun or tank. Normal pressure at sea level is 14.5 psi, and in space is zero - so the max swing you can get there at any elevation is ~15 psi, but you are likely only dealing with about 8 psi. That won't even show up on your gauge. Now, filling your tank with a compressor at elevation is another matter - the air going into the compressor or hand pump is less dense, so it will take longer to fill the tank, but that is not what you asked about.

As for the impact of changes in temperature, that is more impactful. Your reservoir pressure will drop about 2% for every 10 degrees F change in temperature (or rise if the temperature goes up). That can add up to ~10% or more if you go from summer-like conditions to winter at elevation . . .

 

[JimD]

I respect Alan and I like his analyses but I see no cause at all for concern. The factors he mentions are real and should be kept in mind but taking a SCBA tank up and down hills all day isn't going to hurt anything. The differential pressure across the walls of the tank will vary but by less than the 14.5 psi atmospheric pressure so no concern. Getting the tank hotter or colder will change it's pressure but not by enough to be a concern. The biggest effect will be on the rifle's velocity. It will decrease with temperature. But in terms of safety, you have a green light. It will not damage you, the tank, or the gun.

 

[Dstrac]

I've been filling my FX Bobcat .25 cal with a hand pump and after almost a year of doing so, I'm ready for an upgrade. I live in a rural area at about 6k feet elevation, and regularly hunt anywhere from 3k feet to 12k feet elevation. I want to get a large-ish carbon tank to bring with me on longer trips to refill the gun easily and quietly. Will my abrupt elevation changes be a cause for concern? It only takes me about 15 minutes to get to 11k feet elevation, if that's relevant.

Thanks guys. I'm new to the forum and still figuring this PCP thing out

Carbon fiber scba tanks are hydrostaticly tested every 5 years to over 7000psi. The tanks are over built, they can safely handle changes in pressure.

Have you picked out a compressor?

Amazon.com: TUXING Pcp Compressor,4500Psi/300Bar/30Mpa,High Pressure Compressor with Double-Cylinder Mini Portable Air Compressor for Scuba Tank Pcp Air Rifle Paintball Gun Inflation : Tools & Home Improvement

Amazon.com: TUXING Pcp Compressor,4500Psi/300Bar/30Mpa,High Pressure Compressor with Double-Cylinder Mini Portable Air Compressor for Scuba Tank Pcp Air Rifle Paintball Gun Inflation : Tools & Home Improvement

a.co

 

[AlanMcD]

I respect Alan and I like his analyses but I see no cause at all for concern. The factors he mentions are real and should be kept in mind but taking a SCBA tank up and down hills all day isn't going to hurt anything. The differential pressure across the walls of the tank will vary but by less than the 14.5 psi atmospheric pressure so no concern. Getting the tank hotter or colder will change it's pressure but not by enough to be a concern. The biggest effect will be on the rifle's velocity. It will decrease with temperature. But in terms of safety, you have a green light. It will not damage you, the tank, or the gun.

I agree with Jim's point, and hope I did not convey concern about taking a tank up to altitude - my intent was completely the opposite . . . .

I was trying to show that the altitude change itself is essentially meaningless, and that a big temperature change is noticeable but manageable (and not the least bit unsafe).

You'll have nothing to worry about in taking your tank and gun to higher altitude.

 

[F6Hawk]

Welcome to the forum.
You will lose 400 or so psi from 3000ft to 12000ft. BUT, you can fill most air cyls 10% over, to account for the heat of compression etc. so, unless you're running close on air, it won't be a problem.

How did you come up with 400 psi differential? I'm seeing that at 3000 ft, standard pressure is approximately 13.2 psi (ignoring temps), while at 12,000 feet it's about 10.9 psi, for a differential of 2.3 psi.

 

[Aimright]

Just curious what do you hunt at 12,000 ft?

 

[Avator]

At 12k ft. I'd be hunting for my lungs.

 

[rbmyeet]

Carbon fiber scba tanks are hydrostaticly tested every 5 years to over 7000psi. The tanks are over built, they can safely handle changes in pressure.

Have you picked out a compressor?

Amazon.com: TUXING Pcp Compressor,4500Psi/300Bar/30Mpa,High Pressure Compressor with Double-Cylinder Mini Portable Air Compressor for Scuba Tank Pcp Air Rifle Paintball Gun Inflation : Tools & Home Improvement

Amazon.com: TUXING Pcp Compressor,4500Psi/300Bar/30Mpa,High Pressure Compressor with Double-Cylinder Mini Portable Air Compressor for Scuba Tank Pcp Air Rifle Paintball Gun Inflation : Tools & Home Improvement

a.co

I haven’t picked one out yet, my buddy is a firefighter and said I could come by the station to fill it up whenever I want

 

[rbmyeet]

Just curious what do you hunt at 12,000 ft?

sage hens and squirrels mostly, I personally don’t like hunting anything much bigger than a jack rabbit with an air rifle but there are coyotes and red foxes as well

 

[DesertSilver]

How did you come up with 400 psi differential? I'm seeing that at 3000 ft, standard pressure is approximately 13.2 psi (ignoring temps), while at 12,000 feet it's about 10.9 psi, for a differential of 2.3 psi.

That's what I would like to know?

 

[Aimright]

sage hens and squirrels mostly, I personally don’t like hunting anything much bigger than a jack rabbit with an air rifle but there are coyotes and red foxes as well

Phew…I was worried you were going elk hunting with the .25 FX and I was going to tell you were under-gunned a tad. We have Dusky Grouse here in Arizona (we used to call them Blue Grouse until the biologists determined they needed to divide them into two distinct species) that will get up to about tree line here at around 11000 ft.

By the way I regularly take my scbas between 1200 and 8400 feet elevation, no issues other than losing a little pressure in the tanks due to the cooler temperatures. One thing I thought worth mentioning that you may already be familiar with is that your trajectory will be slightly flatter at the higher elevations. You might need to account for that particularly if you are taking distant headshots on those sage grouse and squirrels.