How much air pressure in a springer?

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Offline sobyo1

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How much air pressure in a springer?
« on: March 22, 2012, 06:22:10 PM »
Okay okay. Doing some thinking and was wondering. Lets say we had a pressure gauge screwed into the compression chamber of an average springer. What kind of a spike would we see? How many psi are developed just before pellet lets go? In a pcp if we have a disco pumped to 2.5kpsi,do we actually have a very low volume at 2.5kpsi pushing the pellet out? If so whats going on inside of a springer...pressure wise?That is all.

Offline thekid

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Re: How much air pressure in a springer?
« Reply #1 on: March 22, 2012, 06:42:45 PM »
I think RSterne came up with an answer to this before.... a little under 3000 psi

Offline rsterne

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Re: How much air pressure in a springer?
« Reply #2 on: March 22, 2012, 08:35:46 PM »
IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion (note, not dieseling) is taking place.... which according to them is common in springers shooting over about 600 fps....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline thekid

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Re: How much air pressure in a springer?
« Reply #3 on: March 22, 2012, 09:00:10 PM »
IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion (note, not dieseling) is taking place.... which according to them is common in springers shooting over about 600 fps....

Bob

Thankyou...

Offline PakProtector

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Re: How much air pressure in a springer?
« Reply #4 on: March 22, 2012, 09:29:40 PM »
IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion (note, not dieseling) is taking place.... which according to them is common in springers shooting over about 600 fps....

Bob

hey-Hey!!!,
What else but Dieseling would you call it? This is afterall ignition of the fuel by compression heating. That is good old Rudolph Diesel and nothing else but. I suspect this is a matter of degree for the reference quoted in the quoted post.
cheers,
Douglas

any shooters do Diesel for increased power or does it wreck things too quickly? Now if it were possible to do a precise measure of fuel( say oil damp cotton ) crammed into the pellet skirt, and not a big measure either...it could be less damaging.
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Offline rsterne

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Re: How much air pressure in a springer?
« Reply #5 on: March 22, 2012, 09:51:29 PM »
Sorry, I should have said "note - not detonation".... we tend to use the terms dieseling and detonation interchangably in airguns.... What Cardew's were making the distinction between was controlled, consistent burning (combustion) rather than uncontrolled detonation which can do severe damage....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline Tom @ Buzzard Bluff

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Re: How much air pressure in a springer?
« Reply #6 on: March 22, 2012, 11:48:57 PM »
IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion---is taking place....which according to them is common in springers shooting over about 600 fps....

 Indeed! Were it NOT for combustion then we would all be shooting springers that perform like 10 meter guns.

 Target guns must be utterly repeatable in velocity as well as all other aspects of performance. Therefore combustion must be eliminated from their firing cycle in order to reduce its' inconsistent effect. We are not so limited in our sporter guns so slight velocity variations are accepted in order to achieve the far higher velocities resulting from semi-controlled combustion of the minute quantities of petroleum lubricant introduced to the compression chamber by the seal scavenging the compression chamber walls
on firing. The resulting combustible super-lean fuel/air mix is what makes the difference between target velocities and hunting capabilities.

 Few tuners---and virtually NO owner/tuners---understand that complex relationship between piston seal and compression chamber that controls that super-lean fuel/air mix that must be not only the right mix but infinitely repeatable to achieve consistency.

 I'll be the 1st to admit to being conflicted by numerous aspects of it. It verges on 'black magic' to my simple mind so I rely on proven methods and techniques like almost everyone else.

 I suspect there are a very few---such as Watts & Macarri---who have a better grasp of that greater scheme of things but I also suspect that they too are only a few steps ahead and also largely in the dark.

 Ultimately the art of tuning springers is just that---more art than science---and the few artists among us achieve legendary status largely by default.

 Or that's the view from the Bluff anyway.  Tom
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Offline Scotchmo

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Re: How much air pressure in a springer?
« Reply #7 on: March 23, 2012, 01:42:16 AM »
If we ignore dieseling (unless all guns diesel a significant amount):

A piston gun might give 5fpe per cubic inch (swept volume) of air.

We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?

I would say we need a lot more than 1500psi at the pressure peak.
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Offline rsterne

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Re: How much air pressure in a springer?
« Reply #8 on: March 23, 2012, 02:28:08 AM »
Here is a spreadsheet that gives, among other things, the peak pressure inside a springer.... http://www.prosperousa.com/resources.html

Click on the "Internal Ballistics Calculator" link.... The default numbers (8.4 gr. pellet at 750 fps) show a peak pressure of only 60 bar (870 psi).... I have no idea how accurate the calculator is, but it's one more piece of information.... I checked in my Cardew's book and the example they cited gave a peak pressure of 1366 psi and a peak temperature of 816 *F....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline PakProtector

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Re: How much air pressure in a springer?
« Reply #9 on: March 23, 2012, 07:10:10 AM »
hey-Hey!!!,
That question of peak pressure is best taken up with some good numeric methods programming. Having written some rudimentary stuff like that, I would offer that the boundary conditions considerations( and the 'shape' of the equations they relate to ) will be a large factor in the accuracy of the result.
cheers,
Douglas
  • Ann Arbor, MI
1990 D250, NV5600, Luk 05-101, 16cm housing, TST Kit KDP tab, 366 spring, Powr-Lok'd 3.07, HX35...IC soon

She wasn't built to travel at the speed a rumour flies

Offline sobyo1

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Re: How much air pressure in a springer?
« Reply #10 on: March 23, 2012, 02:11:32 PM »
Wow!,talk about a plethora of information! Keep it commin guys and thanks!! That is all.

Offline Scotchmo

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Re: How much air pressure in a springer?
« Reply #11 on: March 23, 2012, 08:47:01 PM »
...
I would say we need a lot more than 1500psi at the pressure peak.
I studied this a little more. I oversimplified. The rise/drop in pressure as the gas is compressed/expanded is not linear. With a peak of 1500psi, the average pressure could be higher than I originally thought. Time to rework my oversimplified model. Any thermodynamics experts here? Any recent ME grads?
« Last Edit: March 23, 2012, 08:48:50 PM by Scotchmo »
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Offline Tarheel

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Re: How much air pressure in a springer?
« Reply #12 on: March 24, 2012, 06:21:14 PM »
If we ignore dieseling (unless all guns diesel a significant amount):

A piston gun might give 5fpe per cubic inch (swept volume) of air.

We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?

I would say we need a lot more than 1500psi at the pressure peak.

A Hatsan 125 has a swept volume of 79.5 cc and generates 1000 fps in .22 caliber . . .

1000 / 79.5 = 12.578616 fps per cc

Dave
Even with the finest pellet rifle in the world, shooting the most accurate pellet in that particular rifle, and sighting through a perfectly-adjusted scope with the world's finest optics, it all still boils down to the person holding the rifle . . . !

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Offline PakProtector

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Re: How much air pressure in a springer?
« Reply #13 on: March 24, 2012, 07:18:02 PM »
If we ignore dieseling (unless all guns diesel a significant amount):

A piston gun might give 5fpe per cubic inch (swept volume) of air.

We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?

I would say we need a lot more than 1500psi at the pressure peak.

A Hatsan 125 has a swept volume of 79.5 cc and generates 1000 fps in .22 caliber . . .

1000 / 79.5 = 12.578616 fps per cc

Dave


That needs more boundary conditions; my generator has 25 cubic inches per cylinder and if you hook a 22 parrel to its spark plug I guarantee it won't spit out the pellet at anything near 1000 fps. We need compression ratio, and time to do the compressing. If it is too slow we just modify the compression ratio by slowly shoving the round down the barrel. Soooo...figure the two extremes, one the pellet does not move before the piston is at the end of its travel, and the other where it  gets half way down the barrel. What are the peak pressures then?

What we'll actually see will ov course be somewhere in the middle...and we do need to worry about gamma changing across this compression. Even a 6:1 change in volume is enough for the variation of gamma to effect the calculation...:)
cheers,
Douglas
  • Ann Arbor, MI
1990 D250, NV5600, Luk 05-101, 16cm housing, TST Kit KDP tab, 366 spring, Powr-Lok'd 3.07, HX35...IC soon

She wasn't built to travel at the speed a rumour flies

Offline Jeff

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Re: How much air pressure in a springer?
« Reply #14 on: March 24, 2012, 07:44:27 PM »
OH-GOD NO!!  More numbers that make my head spin :o :o
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Offline Tarheel

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Re: How much air pressure in a springer?
« Reply #15 on: March 24, 2012, 08:05:20 PM »
If we ignore dieseling (unless all guns diesel a significant amount):

A piston gun might give 5fpe per cubic inch (swept volume) of air.

We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?

I would say we need a lot more than 1500psi at the pressure peak.

A Hatsan 125 has a swept volume of 79.5 cc and generates 1000 fps in .22 caliber . . .

1000 / 79.5 = 12.578616 fps per cc

Dave


That needs more boundary conditions; my generator has 25 cubic inches per cylinder and if you hook a 22 parrel to its spark plug I guarantee it won't spit out the pellet at anything near 1000 fps. We need compression ratio, and time to do the compressing. If it is too slow we just modify the compression ratio by slowly shoving the round down the barrel. Soooo...figure the two extremes, one the pellet does not move before the piston is at the end of its travel, and the other where it  gets half way down the barrel. What are the peak pressures then?

What we'll actually see will ov course be somewhere in the middle...and we do need to worry about gamma changing across this compression. Even a 6:1 change in volume is enough for the variation of gamma to effect the calculation...:)
cheers,
Douglas

Douglas,

Agreed . . . I merely threw a "starting point" out there !

For Compression Ratio, we need to know the precise Stroke Length, as well as the "Deck Height" ( in "Hotrodder" terminology, I was young once ) . . . Maximum Cylinder Volume, divided by Volume at "Top Dead Center" (max piston travel ) should give us that number.

Piston Velocity, while easy to compute in a car engine ( based on Stroke Length and RPM ), is difficult, at best, to compute in an airgun tube.

Of course, no two pellets have the same, identical fit and barrel friction either.  So, this will likely never get better than a "ballpark number".

Dave
Even with the finest pellet rifle in the world, shooting the most accurate pellet in that particular rifle, and sighting through a perfectly-adjusted scope with the world's finest optics, it all still boils down to the person holding the rifle . . . !

Crosman Nitro Venom .22 (Wood Stock)

180 BAR GAS RAM - HATSAN (Coming Soon )

Offline Scotchmo

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Re: How much air pressure in a springer?
« Reply #16 on: March 24, 2012, 08:46:37 PM »

... be somewhere in the middle...and we do need to worry about gamma changing across this compression. Even a 6:1 change in volume is enough for the variation of gamma to effect the calculation...:)
cheers,
Douglas
PakProtector,
The simple way would be a completely isothermal model. The other extreme would be a completely adiabatic model. It is somewhere in between and probably mostly adiabatic. Lets calculate both ways and then at least we will know what the range of pressures needed to get 5fpe/ci.

For isothermal we can ignore gamma (gamma = 1?). For adiabatic use a gamma of 1.4 which is about right for air.

Some simplifications:
Let's ignore barrel friction and just say that all the energy from the compressed air is transferred to the pellet.
The compression will be just enough to get the 5fpe. So the piston bottoms out with only head space remaining to contain all of the air at the peak pressure. At that instant the pellet starts to move and absorbs all the energy. I guess that means we have a very long barrel. That is OK for the first pass. Let's ignore everything else for now.

So we have 1 cubic inch of atmospheric air. We input/extract 5 ft-lb of energy. What is the peak pressure the air will see?

Isothermal compression/expansion - peak pressure?

Adiabatic compression/expansion - peak pressure?

Will this get us the two extremes?

How is your calculus/integration? I can't solve it but I did do a rough numerical integration of the isothermal model and I got over 3000psi. I suspect that the adiabatic model will be closer to 1000psi.
 
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Offline Tarheel

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Re: How much air pressure in a springer?
« Reply #17 on: March 24, 2012, 11:07:52 PM »
How is your calculus/integration? I can't solve it but I did do a rough numerical integration of the isothermal model and I got over 3000psi. I suspect that the adiabatic model will be closer to 1000psi.

My Calculus bit the dust years ago . . . LOL !

Dave
Even with the finest pellet rifle in the world, shooting the most accurate pellet in that particular rifle, and sighting through a perfectly-adjusted scope with the world's finest optics, it all still boils down to the person holding the rifle . . . !

Crosman Nitro Venom .22 (Wood Stock)

180 BAR GAS RAM - HATSAN (Coming Soon )

Offline rsterne

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Re: How much air pressure in a springer?
« Reply #18 on: March 24, 2012, 11:18:27 PM »
I can see quoting an FPE value per CI of swept volume.... but what is the point of using fps unless you specify the pellet weight?.... it's apples and oranges....

Is there a particular reason people don't want to use Cardew's numbers?.... just curious....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline john

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Re: How much air pressure in a springer?
« Reply #19 on: March 24, 2012, 11:47:12 PM »
It's all about peer review. Time for me to reread Chapter 7 of The Airgun from Trigger to  Target.
« Last Edit: March 25, 2012, 01:14:50 PM by john »
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