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All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: sobyo1 on March 22, 2012, 06:22:10 PM

Title: How much air pressure in a springer?
Post by: sobyo1 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.
Title: Re: How much air pressure in a springer?
Post by: thekid on March 22, 2012, 06:42:45 PM
I think RSterne came up with an answer to this before.... a little under 3000 psi
Title: Re: How much air pressure in a springer?
Post by: rsterne 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
Title: Re: How much air pressure in a springer?
Post by: thekid 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...
Title: Re: How much air pressure in a springer?
Post by: PakProtector 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.
Title: Re: How much air pressure in a springer?
Post by: rsterne 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
Title: Re: How much air pressure in a springer?
Post by: Tom @ Buzzard Bluff 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
Title: Re: How much air pressure in a springer?
Post by: Scotchmo 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.
Title: Re: How much air pressure in a springer?
Post by: rsterne 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 (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
Title: Re: How much air pressure in a springer?
Post by: PakProtector 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
Title: Re: How much air pressure in a springer?
Post by: sobyo1 on March 23, 2012, 02:11:32 PM
Wow!,talk about a plethora of information! Keep it commin guys and thanks!! That is all.
Title: Re: How much air pressure in a springer?
Post by: Scotchmo 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?
Title: Re: How much air pressure in a springer?
Post by: Tarheel 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
Title: Re: How much air pressure in a springer?
Post by: PakProtector 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
Title: Re: How much air pressure in a springer?
Post by: Jeff on March 24, 2012, 07:44:27 PM
OH-GOD NO!!  More numbers that make my head spin :o :o
Title: Re: How much air pressure in a springer?
Post by: Tarheel 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
Title: Re: How much air pressure in a springer?
Post by: Scotchmo 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.
 
Title: Re: How much air pressure in a springer?
Post by: Tarheel 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
Title: Re: How much air pressure in a springer?
Post by: rsterne 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
Title: Re: How much air pressure in a springer?
Post by: john 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.
Title: Re: How much air pressure in a springer?
Post by: Scotchmo on March 25, 2012, 01:04:42 AM
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
12.578616 fps per cc
At 5fpe/ci, that Hatsan 125 should shoot 11-12gr pellets at 1000fps. That is reasonable but actual FPE would be better than leaving us guessing at the pellet weight. It looks like 5fpe is reasonable for both small chamber volume guns like mine or large volume guns like the Hatsan.

For my use, the peak pressure is less important than the math/model that can predict it. The same model should be able to predict the pressure at any point along the barrel. And from there, the optimum barrel length for a given system. For my current gun, I did a progressive chop until it started to lose power with most types of pellets. By then, I was two inches too short. So I replaced the barrel with one that was two inches longer (though it was 7 inches shorter than stock).
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 25, 2012, 01:50:35 AM
If you know the peak pressure you can calculate the rest, but you will end up using a fudge factor because of the efficiency.... I have a good spreadsheet that calculates the pellet velocity and pressure as it moves down the barrel for a PCP.... but you have to adjust the efficiency and valve dwell until the muzzle velocity and the pressure drop in the tank per shot match your experimental values.... Once you have that, then it does a good job of predicting the velocity with a shorter (or longer) barrel.... or when you change pellet weight, etc.... It's a good tool, but pretty useless for a springer because you are working with compressing air, not just releasing it....

Bob
Title: Re: How much air pressure in a springer?
Post by: Tarheel on March 25, 2012, 09:52:44 AM
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
12.578616 fps per cc
At 5fpe/ci, that Hatsan 125 should shoot 11-12gr pellets at 1000fps. That is reasonable but actual FPE would be better than leaving us guessing at the pellet weight. It looks like 5fpe is reasonable for both small chamber volume guns like mine or large volume guns like the Hatsan.

For my use, the peak pressure is less important than the math/model that can predict it. The same model should be able to predict the pressure at any point along the barrel. And from there, the optimum barrel length for a given system. For my current gun, I did a progressive chop until it started to lose power with most types of pellets. By then, I was two inches too short. So I replaced the barrel with one that was two inches longer (though it was 7 inches shorter than stock).

In another thread, a velocity of 958 fps was posted for 14.3 gr CPHP's . . .

(( 958 x 958 ) x 14.3) / 450240 = 29.148953 FPE

Dave
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 25, 2012, 01:09:51 PM
The swept volume of the Hatsan is 79.5 cc which is 79.5/16.4 = 4.85 CI.... 29.1 FPE / 4.85 CI = 6 FPE/CI.... A bit higher than the 5 FPE/CI that Scotchmo was suggesting as an example to use, but in the ballpark.... One pet peave, if I may.... When one number in a calculation has only 3 significant figures (ie 958), the answer should also have only 3 significant figures.... ie 29.1 FPE.... The extra decimals cannot be justified.... OK, I'm anal and I admit it....  ;D

Bob
Title: Re: How much air pressure in a springer?
Post by: william71743 on March 25, 2012, 01:39:09 PM
The swept volume of the Hatsan is 79.5 cc which is 79.5/16.4 = 4.85 CI.... 29.1 FPE / 4.85 CI = 6 FPE/CI.... A bit higher than the 5 FPE/CI that Shotchmo was suggesting as an example to use, but in the ballpark.... One pet peave, if I may.... When one number in a calculation has only 3 significant figures (ie 958), the answer should also have only 3 significant figures.... ie 29.1 FPE.... The extra decimals cannot be justified.... OK, I'm anal and I admit it....  ;D

Bob

LOL........I love the last line of this post, sorry Bob.... ;) ....couldn't help myself ! Already told you I read all this kind'of  stuff and enjoy it very much. I don't often say much , don't have any information to add, but if you could comment a little more on barrel length and FPS or FPE ?  ... ???
Title: Re: How much air pressure in a springer?
Post by: Tarheel on March 25, 2012, 02:29:26 PM
OK, I'm anal and I admit it....  ;D

Bob


ROTFLMAO !

Good one, Bob !

Dave
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 25, 2012, 02:41:38 PM
It's pretty well known that in springers most of the velocity happens in the first few inches of travel and that barrel length is relatively unimportant to muzzle velocity.... in fact it can hurt in lower powered guns.... In PCPs, the opposite is the case most of the time, and more barrel length gives more velocity....

I have found that most springers have a "sweet spot" for pellet weight, which increases as the FPE level of the gun increases.... ie low powered guns prefer lighter pellets than magnums.... In PCPs there is a general tendency towards getting more FPE with heavier pellets.... but again it is more pronounced with the more powerful guns....

Bob
Title: Re: How much air pressure in a springer?
Post by: Scotchmo on March 25, 2012, 06:34:15 PM
The swept volume of the Hatsan is 79.5 cc which is 79.5/16.4 = 4.85 CI.... 29.1 FPE / 4.85 CI = 6 FPE/CI.... A bit higher than the 5 FPE/CI that Shotchmo was suggesting as an example to use, but in the ballpark....
I saw a range of under 4fpe/ci to a little over 5fpe/ci but that was for .177 caliber. The .22 caliber tends to be a little more efficient than .177 so that could account for the difference. I would bet that a .177 Hatsan 125 is closer to 5fpe/ci.
Title: Re: How much air pressure in a springer?
Post by: rws45user on March 20, 2019, 07:26:30 AM
If your gun is producing around 900 fps    its  producing around  163 psi  per shot in the chamber . Watch this video https://youtu.be/NrPN1mIVDrM    with a fill up at 3,600 psi  you get  22 shots  so divide 22 into 3,600 and you get  163 psi  per shot .  So a spring that produces  900 fps  is  producing 163 psi with each shot . 
Title: Re: How much air pressure in a springer?
Post by: outdoorman on March 20, 2019, 11:05:56 AM
Indeed! Were it NOT for combustion then we would all be shooting springers that perform like 10 meter guns.

  Not true. I have completely degreased my Diana 34 and only use Krytox lubricant on the piston seal and piston. Krytox cannot cause combustion. I'm shooting 680fps with 16gr pellets accurately out to 50 yards.
Title: Re: How much air pressure in a springer?
Post by: K_sqrd on March 20, 2019, 12:04:17 PM
This was posted on the old Yellow Forum some time ago..

QUOTE:
"...from just two numbers.

ME(fpe) = Muzzle Energy in foot pounds.
SV(ci) = Piston Stroke Volume in cubic inches.

Peak Temperature (Fahrenheit) = Ambient + 520 * (ME / SV)
Peak Compression Ratio = (ME / SV) ^ 2.5
Peak Pressure (bar) = (ME / SV) ^ 3.5

Taking for example an R1 with ME = 17fpe, SV = 3.6ci,

Peak Temperature (Fahrenheit) = 2500F.
Peak Compression Ratio = 48:1
Peak Pressure (bar) = 229bar = 3318psi.

Details

The energy of the spring is transferred to the air.

The core (and obviously only approximate) assumption is that 100% of the cocked energy of the mainspring goes into driving the piston forward in the tube and initially adiabatically compresses the air charge. That is to say, the mechanical energy of the spring is converted to heat and raises the temperature of the air.

1.0 foot-pound of energy will raise the temperature of 1 cubic inch of standard-density air 173F. Therefore if SE = the energy of the mainspring, and SV = the stroke volume of the piston, then the temperature rise of the air when the gun is fired is: Delta_T = 173 * SE / SV.

SV is easy to calculate from bore and stroke (SV = pi/4 * Bore^2 * Stroke), but SE is harder. Fortunately, SE can be inferred from muzzle energy. The Cardews measured a lot of mainsprings SEs and compared them to the MEs of their springers, and found a fairly consistent relationship: ME ~= SE / 3. This is good news, because, if you have a chronograph, ME is one of the easiest numbers to get in all of ballistics.

So substituting 3 * ME for SE gives the more convenient: Delta_T ~= 520 * ME / SV.

Note, however, that this cheap and easy inference of SE from ME only works for a "normally" functioning springer. So you can forget perverse cases like dryfires. 

Steve"
:UNQUOTE
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 20, 2019, 02:17:01 PM
rws45user.... Sorry, but your statement
Quote
its  producing around  163 psi  per shot in the chamber

is incorrect.... The pressure in the RESERVOIR is dropping 163 psi per shot, but in fact the pressure in the "chamber" (between valve and pellet) creating that 900 fps shot is initially (almost) whatever pressure is in the reservoir (up to 3600 psi), or if regulated the pressure downstream of the regulator (eg. maybe 2000 psi)…. That air pressure, when released from the valve, starts the pellet acceleration, and then after the valve closes, the air continues to expand, still adding to pellet velocity.... In PCPs you are expanding (and cooling) the air, while in springers you are compressing (and heating) it.... This is why springers and PCPs cannot be directly compared....

Bob



Title: Re: How much air pressure in a springer?
Post by: rws45user on March 26, 2019, 07:13:16 PM
If the pcp starts off with 3,600 psi and each shot  puts the pellet out of the gun  at 900 fps after the first shot  you lose  163 psi   so you don't have 3,600 psi  in that tank but the pellet is still going 900 fps  and on the last shot of 22 shots  when the pellet is still going  900 fps  its using 163 psi to make the pellet  travel at 900 fps  or 16fpe  . K-sqrd is saying  a spring gun uses 3,318 psi   to get 17 fpe . If that were true  the pcp would use  its full tank of air  on 1 shot just to get the pellet to 17 fpe . Which you can see is not the case at all . To get a pellet to have 16fpe  you only need to use 163 psi behind the pellet  so why would you think you need  3,318 psi to produce 17 fpe ? 163 psi  is whats  pushing the pellet out of the barrel  at around 900 fps .  It doesn't matter whats producing the air behind the pellet  the fact is  the burst  of air  behind the pellet  can only be 163 psi to produce 16 fpe .  The pcp tank with a gauge to 3,600 psi  and the number of shots 22 ,  it  produces 16 fpe  proves it . For example  lets say the pcp was set to put out  326 psi per shot  you would only get 11 shots and because  of the length of the barrel  you would only gain a few fpe  and the rest of the air would be wasted  because the pellet has left the gun. All you have  to do to prove its only 163 psi thats needed to produce 16fpe  is put a gauge at the end of the  piston cylinder and read it . If you think its going to read 3,318 psi you are out of your mind . It takes a special air compressor  a good 10 minutes to fill up a 500cc cylinder to 3,318 psi  and a foot pump  ,pumped over 100 times  just to fill a 200cc cylinder  to 3,000 psi and you think you can produce 3,318 psi  with a single stroke of a spring  ? if that were true   you could put a line from the  port hole and  connect it to a 500cc tank and fill it up to 3,318 psi  in one shot . No one would ever need a air compressor again  to refill there pcp they just need a springer  and a hose   . Why don't you try that  and see how much air pressure goes into  the 200 cc cylinder . Do you think its going to read 3,318 psi ? No its going to read 163 psi  and you would have to cock and shoot the springer 22 times to fill the tank . Which really  isn't a bad idea . 22 cocks  and shoots from a springer  with a one way valve  to fill a 200 cc tank to 3,600 psi . That might beat using a foot pump .
Title: Re: How much air pressure in a springer?
Post by: nced on March 26, 2019, 08:39:49 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
Years ago I tested out Cardews claim that a piston gun got a high percentage of power from internal combustion.

To test the theory with a modern synthetic sealed .177 Beeman R9 I completely stripped all internal lube with brake cleaner and used powdered graphite (the kind puffed into locks)  for lubing the internals. The result was that my velocity without dieseling using powdered graphite was only 10fps less than when I used molly paste for lube (graphite 900fps vs molly paste 910fps.) For my .177 R9 the velocity gain using molly paste was only about .01% instead of Cardews claim of about 40%.

I do realize the at the time Cardew shot the HW35 in a nitrogen atmosphere for his testing those guns had oil soaked leather piston seals and his reasoning was probably valid, however the test doesn't stay valid with modern synthetic seal piston guns.

Hummm......even in modern guns excess molly paste (or other petroleum based lubes) can add significant gun damaging velocity. I accidentally got molly paste in front of my .20 cal R9 piston seal during a home tune. I had replaced the spring kit with a home rolled one based of a Maccari Tarantula spring (decades ago). After assembly I shot a .20 Beeman FTS pellet over the chrony sensors and along with a loud POW the .20 FTS was clocked at 1100fps! After that shot the gun didn't "act right" and I found that a single molly paste detonation snapped a brand new Maccari spring when the piston rebounded off the detonation.
Title: Re: How much air pressure in a springer?
Post by: K_sqrd on March 27, 2019, 12:31:53 AM
Thank You, nced for your posting. I’ve often wondered and and have done several searches
over the years to see if any one has done a comparison between the Cardew test and an
air gun using a more modern seal. I could never find any definitive info, just anecdotal
results of before and after tunes along with lots of opinions. Makes you wonder about the
wisdom of scoring the compression tube.

Title: Re: How much air pressure in a springer?
Post by: robertr on March 27, 2019, 12:46:51 AM
Something for you guys to play with and some info. The pic is interactive, click on the dots.
Add www.
arld1.com/images/swfs/pistonpelletdynamics.swf
Title: Re: How much air pressure in a springer?
Post by: robertr on March 27, 2019, 12:53:13 AM
Can't post link for some reason.
Strange, the link works when I preview my post but when I save it the link disappears.
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 27, 2019, 01:30:24 AM
That 163 psi drop per shot is on the large reservoir volume, not the barrel volume, which is much smaller.... Since the valve closes when the pellet is only a short distance from the breech, the volume is even smaller.... and the pressure even higher....

If you don't believe me, do a simple calculation of F=ma.... You will quickly determine that 163 psi pushing on the back of a .22 cal pellet is not enough to produce 16 FPE in that length of barrel.... If you can do that, you will have achieved more energy out than in.... Voila, perpetual motion....

I repeat.... Removing enough air from a 3600 psi reservoir to reduce the pressure by 163 psi does NOT mean that you are only applying 163 psi of pressure to the back of the pellet.... The pressure in the reservoir after the shot is (3600 - 163) = 3437 psi.... You are using a small sip of air at the average pressure of (3600 + 3437) / 2 = 3519 psi to propel the pellet, but only for the first few inches.... After the valve closes, the air expands behind the pellet and there will still be several hundred psi of pressure when the pellet exits the muzzle....

Pressure times volume is the key.... using one without the other is nonsense....

Bob
Title: Re: How much air pressure in a springer?
Post by: mikeyb on March 27, 2019, 02:26:46 AM
...K-sqrd is saying  a spring gun uses 3,318 psi  to get 17 fpe ...

I was curious to see how the different rate characteristics between a metal coil spring and a compressed gas spring affected a springers shot cycle so I computer simulated a couple different spring piston and gas piston configurations based on dimensions, masses, and spring rates found on a couple sub-$100 Crosman and Hatsan springers. I can confirm that those equations provide numbers that are close to the simulations for those ~17 fpe springers.

... If you think its going to read 3,318 psi you are out of your mind...

Call me crazy then because the physics involved confirm it. If you could get a mechanical gauge to react fast enough (about 0.005 seconds) and "peak hold" the value, it would read pressures over 2000 psi.

... you think you can produce 3,318 psi  with a single stroke of a spring ?...

Yes, because that is exactly how a spring-piston air rifle works. The spring accelerates a heavy piston which compresses the cylinder air into a volume behind the pellet that is over 100 times smaller. Resulting peak pressure is over 100 bar (over 1500 psi). Because this happens in a small fraction of a second, the air undergoes adiabatic heating (https://en.wikipedia.org/wiki/Adiabatic_process (https://en.wikipedia.org/wiki/Adiabatic_process)) which raises the peak pressure behind the pellet even higher.

Something for you guys to play with and some info. The pic is interactive, click on the dots.
http://www.arld1.com/images/swfs/pistonpelletdynamics.swf (http://www.arld1.com/images/swfs/pistonpelletdynamics.swf)

NICE animation and mostly correct. I do question the piston velocity/timing depicted and cannot find what was used as the piston mass. I use a steel piston conservatively weighing 8 ounces and my simulation suggests trigger time to first pellet movement is closer to 150ms. Regardless of which simulation timing is more accurate, the motion sequence and peak pressures are very similar.
Title: Re: How much air pressure in a springer?
Post by: subscriber on March 27, 2019, 09:25:35 AM
Quote
... you think you can produce 3,318 psi  with a single stroke of a spring ?...

Think of your arm as the engine of a Mini Cooper.    The engine can't "push" very hard; but it can get the car up to 100 MPH, after a while.

Now, crash the Mini into a concrete abutment from 100 MPH.  Suddenly the energy that tiny engine stored in the car generates enough force to shorten the car by half.

In the same way, your arm can compress a spring, that accelerates a piston, that stops against high pressure air, squashed against a steel wall, up to a few thousand PSI.  Nothing magical about it:  Simple collision physics...

If you want to gauge the peak pressure of a particular airgun, capture fired pellets in water or cotton wool.  Look at the extent of the skirt ballooning.  The more the skirt is rounded out, the higher the peak pressure was; regardless of platform.  Yes; you need to use a "standard" pellet to make this comparison.

For further reading, see this blog article: https://www.ctcustomairguns.com/hectors-airgun-blog/category/tests (https://www.ctcustomairguns.com/hectors-airgun-blog/category/tests)

(https://www.ctcustomairguns.com/uploads/2/3/8/4/23849268/7735557_orig.jpg)
Title: Re: How much air pressure in a springer?
Post by: Mole2017 on March 27, 2019, 11:22:57 AM
... K-sqrd is saying  a spring gun uses 3,318 psi   to get 17 fpe . If that were true  the pcp would use  its full tank of air  on 1 shot just to get the pellet to 17 fpe . Which you can see is not the case at all . To get a pellet to have 16fpe  you only need to use 163 psi behind the pellet  so why would you think you need  3,318 psi to produce 17 fpe ? 163 psi  is whats  pushing the pellet out of the barrel  at around 900 fps . ...

I suspect there's a misunderstanding of some principles here. No problem though. With each shot, the pressure in a PCP tank does go down by a small amount. For comparison to that 163 PSI number, it's probably about 25 PSI in mine, a little more or less at the extreme ends. (3300 PSI to 1500 PSI is about 70 shots for me, give or take a few.) If your tank is bigger or smaller, or you system more or less efficient, the numbers will be different.

Now back to the principles. Consider a 1377 (multipump) pistol. 10 strokes gets you up to about 900 PSI, all of which is lost on the shot unless you have valve problems. What happens is that with each stroke of the pump, the pressure in the plenum of the valve body increases, representing a certain amount of work that can be done to accelerate the pellet. The plenum volume is constant, but the amount of air stored--and the energy available for the shot--with each stroke increases. Shoot a 1377 with only a few pump strokes and you get a very slow shot (and use all that air too). The situation is similar in CO2. In PCPs, air is drawn off from the main tank to an intermediate chamber (plenum) at high pressure. Firing the shot uses that air and the valve closes again before much more air gets out of the main tank through the regulator, if there is one, and plenum. The path to the plenum is through narrow ports, with or without a regulator, and it takes time for the plenum to get back up to pressure for the next shot. Not much time, but just enough that the valve will close first, allowing us to have PCPs that aren't regulated and still function well. We'll ignore hammer bounce for now.

Consider also the fire piston. By striking it with one's hand, pressure and temperature go high enough to ignite combustible materials. The pressure is low (a couple hundred PSI), but imagine what would happen if you had a much higher compression ratio and a really big hand, i.e. spring driven piston. Here's an interesting discussion with calculations of that final pressure given an ignition temperature: https://survivalschool.com/how-a-fire-piston-works-boyles-law/ (https://survivalschool.com/how-a-fire-piston-works-boyles-law/). (You'd use different calculations to actually find the temperature, but it gets a little harder to sort out--this is the minimum pressure and temperature case for now.)

My understanding of fire pistons is that when fully compressed, there is still a small void for the combustible material, hence the known compression ratio. In a springer, there isn't much space left unless you set your pellets deep or have a strange breech like the Gamo CFX/CFR/ACCU. In that case, a ballet of sorts ensues: the piston starts ramming the air and at some point the pellet starts to move. But the pellet doesn't move quite fast enough before the piston almost bottoms out and a very high pressure is developed. With tuning, you can maximize the timing of the pellet movement, peak pressure, and final muzzle velocity.

Come to think of it, the CFX is a nice example. Someone can do the calcs for us, especially if you have better numbers than I'm about to pull from memory:
The piston is about 1" in diameter and travels maybe 5 inches. The breech block has a .177 bore that is about 7/8" long, and then you get to the pellet. (Interestingly, the port is the same size in both the .177 and .22 CFX, only the barrel bore changes.) If the pellet doesn't get moving by the time the piston bottoms out, that's about 182:1 compression ratio even with my guesses at numbers. Can someone here do the peak pressure and temperature possible if the pellet stays in the breech right to the end of the piston stroke?

Title: Re: How much air pressure in a springer?
Post by: nced on March 27, 2019, 11:38:09 AM
Thank You, nced for your posting. I’ve often wondered and and have done several searches
over the years to see if any one has done a comparison between the Cardew test and an
air gun using a more modern seal. I could never find any definitive info, just anecdotal
results of before and after tunes along with lots of opinions. Makes you wonder about the
wisdom of scoring the compression tube.


"scoring the compression tube"
Crosshatching?
I've read for years that folks have crosshatched their receivers with the explanation that the groves provide "lube reservoirs". IMHO, the notion that piston gun receivers need cross hatching is the fact that automotive cylinders are cross hatched. Automobile cylinders are indeed cross hatched to provide "lube reservoirs" for the initial seating of the steel piston rings. Well, piston gun receivers aren't like auto pistons and I'm of the notion that crosshatching only provides channels to "pump" lube (especially excessive lube) in front of the piston seal to diesel. Since most piston gun lubes are "diesel prone petroleum based" they should be very sparingly to minimize shot to shot velocity inconsistencies. LOL....seems that one of the benefits of "molly paste" is that after the reserve of "diesel prone petroleum dinosaur oil carrier" is "burnt up", there is the residue of molly powder packed into the voids to still provide som "metal to metal separation". Myself.......I prefer to use non-dieseling Dupont Krytox GPL205 which is the "Plain Jane" variety without "wear and corrosion additives". While "less is better than more" with Krytox, it's been my experience that internal lubing with the "space station lube" is much less tedious than when using petroleum based lubes because Krytox doesn't diesel if a bit migrated past the piston seal. Here is a factory HW95 piston seal after testing using Krytox GPL205......
(https://i.imgur.com/oJW4NcVl.jpg)

   

 Over a decade ago I started questioning this procedure when I started replacing my HW piston seals with home turned oring sealed piston caps. For the oring seals to be reliable in my HW springers I would first hone my receivers (comp tube for the HW77k) to remove any compression area constrictions or "ovality". To test for "receiver ID abnormality I first tested the receiver with a homemade gage like this...........
(https://i.imgur.com/JjxZu5Wl.jpg)
If the gage didn't freely pass through the receiver tube I used this "hone" to relieve the constriction/ovality..............
(https://i.imgur.com/Gsa7pdll.jpg)
The "hone" is made by machining a piece of PVC pipe so the OB is straight and allows a wrap of oiled 500 grit "wet-or-dry" to slide into the receiver with a bit of friction. This simple "contraption" will also hone all the way to the transfer port unlike a $35,000 Sunnen hone that can't hone to a blind end. Initially I tried to hone using a "three stone brake cylinder hone" but found that they didn't play nice with receiver cocking shoe slots. The continuous "PVC pipe hone" od will bridge the cocking shoe slot so the whole length of the receicer can be honed. This "feature" is especially helpful for opening up the receiver ID at the end plug where the punching out of the holes has reduced the receiver tube relative to the rest of the tube. This pic shows the "receiver end" punch outs and holes that tend to constrict the receiver........
(https://i.imgur.com/ezK0Mull.jpg)

Here is a pic of a HW95 receiver tube where a constriction was reduced (not removed) to the point that my gage would pass............
(https://i.imgur.com/sImpGWkl.jpg)

More to the "crosshatching" comments.............
As mentioned I need the receiver to be relatively smooth and round to function well with the 1/16" nominal cross section orings I use so the receiver is honed with oiled 500 grit wet-or-dry abrasive.

Evidently, the late model CNC HW receivers aren't honed like they were decades ago. A couple decades ago I've had HW receiver tubes that were so "over honed" at the  transfer port "blind end" that the ID was belled to the point that an oring wouldn't seal if the oring would slide through the rest of the receiver. I'm assuming that the cause for this was the mechanic "falling asleep" when the hone was at the blind end.  ::)

Anywhoo....my HW receivers, after prepping for an oring seal, was considerably smoother than the cross hatched surface before the honing. Well.....evidently HW has also minimized the amount of receiver crosshatching based on the appearance of my newest HW springer, a HW95 bought a few years ago. Here is a pic of that HW95 receiver that was untouched straight from disassembly...........
(https://i.imgur.com/svbiK3Ml.jpg)
Yep, bright and shiny like my receivers after fitting an oring seal.

 
  use a home made receiver hone 
Title: Re: How much air pressure in a springer?
Post by: rws45user on March 27, 2019, 01:53:41 PM
If you pump the pcp gun thats in the video above  up to 163 psi  and stop  it will send a pellet out of the barrel at 900 fps . It will only fire one time because the tank will be empty .    900 fps is 900 fps  no matter if its comes out of a spring gun or a  pcp.  The pressure  behind the pellet as it leaving the barrel  is going to be the same amount of pressure  if the same weight  pellets  chronys  at 900 fps  . If you chrony the  lets say 10 grain pellet  from a spring gun and it reads 900 fps  and then you  shoot a pcp  charged up to 163 psi and  the chrony reads 900 fps  with the same  pellet weight   that means the the spring  gun  is  sending the pellet out of the barrel   with the same exact amount of  psi as the pcp  . If the psi was higher in the  barrel the  pellet would  come out faster  . If the  pellet was coming out slower it would be less psi . So since we can measure  on a gauge  how much pressure is in the pcp ans we know its  charged to 163 psi and it sends the pellet out at 900 fps   we  know is a springer  sends the pellet out at the same  900 fps  we know  the springer   has the same amount of  psi  behind the pellet . It doesn't  matter how much psi the cylinder  is producing  all that matters is  how my psi  is in the barrel behind the pellet  and that's 163 psi   if the  gun is chrony at 900 fps with a 10 grain pellet  and the pcp with a gauge proves it . The question was How much air pressure in a springer ?  The answer would have to be   Its according  to  what the crony fps  reads with a certain  weight pellet .  So for example  if the springer  that used a 10 grain pellet  chronyed out at 900 fps  the answer would be  it takes 163 psi in the barrel  to achieve 900 fps with a 10 grain pellet .  If someone ask that same question about a pcp you would have to give the same answer . Its really as simple as that .
Title: Re: How much air pressure in a springer?
Post by: Mole2017 on March 27, 2019, 02:31:31 PM
If you pump the pcp gun thats in the video above  up to 163 psi  and stop  it will send a pellet out of the barrel at 900 fps . It will only fire one time because the tank will be empty .    900 fps is 900 fps  no matter if its comes out of a spring gun or a  pcp.  The pressure  behind the pellet as it leaving the barrel  is going to be the same amount of pressure  if the same weight  pellets  chronys  at 900 fps  . If you chrony the  lets say 10 grain pellet  from a spring gun and it reads 900 fps  and then you  shoot a pcp  charged up to 163 psi and  the chrony reads 900 fps  with the same  pellet weight   that means the the spring  gun  is  sending the pellet out of the barrel   with the same exact amount of  psi as the pcp  . If the psi was higher in the  barrel the  pellet would  come out faster  . If the  pellet was coming out slower it would be less psi . So since we can measure  on a gauge  how much pressure is in the pcp ans we know its  charged to 163 psi and it sends the pellet out at 900 fps   we  know is a springer  sends the pellet out at the same  900 fps  we know  the springer   has the same amount of  psi  behind the pellet . It doesn't  matter how much psi the cylinder  is producing  all that matters is  how my psi  is in the barrel behind the pellet  and that's 163 psi   if the  gun is chrony at 900 fps with a 10 grain pellet  and the pcp with a gauge proves it . The question was How much air pressure in a springer ?  The answer would have to be   Its according  to  what the crony fps  reads with a certain  weight pellet .  So for example  if the springer  that used a 10 grain pellet  chronyed out at 900 fps  the answer would be  it takes 163 psi in the barrel  to achieve 900 fps with a 10 grain pellet .  If someone ask that same question about a pcp you would have to give the same answer . Its really as simple as that .

Ah, but my PCP is right around 25 PSI per shot and launches a 10 grain pellet at 900 FPS too. But that is because my tank is much larger than that on the Seneca and holds more compressed air--and thus more energy for more shots per fill--for the same pressure--200 cc vs..what, 20 or 30 cc (Anybody know this number? I can't find it anywhere). These results also depend on the pellet--for some reason one of the ones I tested recently was much slower than others that weighed nearly the same (all were just over 10 grains).

However, consider again how a multipump rifle behaves. One pump, you might get a pellet stuck in the barrel. Two or three pumps, you might get off a slow shot. Do the proper 10 (if that's what yours takes) and you get closer to its maximum FPS.


We're trying to get across that the velocity and the pressure needed to get off a desired shot will vary with available volume of air. Consider this: would you be willing to sit in a chair over a small pill bottle configured to "explode" at 50 PSI? No big deal. Would you sit on a truck tire an let it explode at 50 psi? You'll die trying. The difference is not the PSI--which is only the pressure--but the volume and the corresponding energy stored.

Regarding springers, we can calculate it and get close, but there are enough variables that real-time pressure measurements would certainly be the last word.
Title: Re: How much air pressure in a springer?
Post by: superchikn on March 27, 2019, 03:02:11 PM
If you pump the pcp gun thats in the video above  up to 163 psi  and stop  it will send a pellet out of the barrel at 900 fps . It will only fire one time because the tank will be empty .    900 fps is 900 fps  no matter if its comes out of a spring gun or a  pcp.  The pressure  behind the pellet as it leaving the barrel  is going to be the same amount of pressure  if the same weight  pellets  chronys  at 900 fps  . If you chrony the  lets say 10 grain pellet  from a spring gun and it reads 900 fps  and then you  shoot a pcp  charged up to 163 psi and  the chrony reads 900 fps  with the same  pellet weight   that means the the spring  gun  is  sending the pellet out of the barrel   with the same exact amount of  psi as the pcp  . If the psi was higher in the  barrel the  pellet would  come out faster  . If the  pellet was coming out slower it would be less psi . So since we can measure  on a gauge  how much pressure is in the pcp ans we know its  charged to 163 psi and it sends the pellet out at 900 fps   we  know is a springer  sends the pellet out at the same  900 fps  we know  the springer   has the same amount of  psi  behind the pellet . It doesn't  matter how much psi the cylinder  is producing  all that matters is  how my psi  is in the barrel behind the pellet  and that's 163 psi   if the  gun is chrony at 900 fps with a 10 grain pellet  and the pcp with a gauge proves it . The question was How much air pressure in a springer ?  The answer would have to be   Its according  to  what the crony fps  reads with a certain  weight pellet .  So for example  if the springer  that used a 10 grain pellet  chronyed out at 900 fps  the answer would be  it takes 163 psi in the barrel  to achieve 900 fps with a 10 grain pellet .  If someone ask that same question about a pcp you would have to give the same answer . Its really as simple as that .

I think that what may be the simplest way to illustrate the error of this logic is my CO2 rifle tethered to a regulated HPA bottle.
The rifle with CO2 which we know accelerated the pellet with approximately 800 to 900 psi with many variables and my pellet leaves the barrel a hair under 700 fps.  It is .22 caliber.
When I tether the same rifle to a tank filled with 3,000 PSI of air and a regulator set to 850 PSI the same pellet leaves the same rifle at approximately the same speed as with CO2.  I know that the air going into the gun is 850 psi because I can put a gauge on it and read the pressure.
The 3,000 psi in the tank is reducing by a very small amount which I cannot read on the gauge I have but it is certainly less than 163 psi.
The point is that regardless of the psi drop in the tank the pressure acting on the pellet is still 850 psi.
Title: Re: How much air pressure in a springer?
Post by: rsterne on March 27, 2019, 07:10:39 PM
Quote
If you pump the pcp gun thats in the video above  up to 163 psi  and stop  it will send a pellet out of the barrel at 900 fps .

Rubbish....  ::)

I have a bottled QB79 that will deliver 25.5 FPE (15.9 gr. pellets at 850 fps).... I get 78 shots from 3000 psi down to 1200 (a drop of 1800 psi), which is 23 psi per shot.... That does NOT mean that 23 psi will push a 15.9 gr. pellet in .22 cal at 25.5 FPE.... The regulator is set at 1200 psi, and THAT is the pressure it takes to hit 850 fps with a 15.9 gr. pellet in a 20" barrel....

Bob
Title: Re: How much air pressure in a springer?
Post by: subscriber on March 27, 2019, 09:20:27 PM
rws45user,

There is a  minimum pressure below which the pellet will not even leave the barrel, no matter the air volume behind it. 
In fact, there is a minimum pressure to get the pellet to start moving:  The way a typical PCP seats a pellet with a probe, means that its "threshold pressure" is usually lower than with a springer. 

A springer needs the pellet to be held in the breech cone, until the pressure has built many times higher than the pressure to overcome friction once travelling down the barrel.  Else it is not going to shoot very fast.  This is similar to holding a jet plane on the brakes when on a short runway, until the engines spool up to near full thrust, before letting the brakes go.

If you multiply 163 PSI by its effective area on a .177 pellet, the resultant force is 4 lb.  That is without taking friction between the pellet and barrel, or in the air stream into account. 

Now, applying a full 4 lb over the length of a 24" barrel will yield a maximum of 8 ft.lb. 
From: Energy =  Force x Distance

8 ft.lb with a 10 grain pellet is just over 600 FPS.  Quite far off from 900 FPS, or 18 ft.lb.  Note that springer barrels tend to be a lot shorter than 24"...

While energy stored in compressed air is proportional to pressure times volume; the max theoretical 8 ft.lb cannot be exceeded.  It does not matter if you have a cubic foot of air at 163 PSI; as you will only use one barrel volume full.  Any air that leaves after the pellet clears the muzzle cannot possibly accelerate the pellet. 

Practically speaking you won't achieve near 8 ft.lb in .177 on 163 PSI out of a 24" barrel - no matter the available volume.  Much better efficiency will result when using a small volume of air that starts at somewhere between 1000 and 3000 PSI;  achieved by "crashing" a piston into a column of air in a closed cylinder, or by taking a sip from a large reservoir, via a fast acting valve...

If you want to use air pressures well over 3000 PSI, diabolo pellets are probably going to distort too much, with grossly ballooned skirts.  The heads would also tend to be blown off the skirt.  If the muzzle pressures were anywhere near 3000 PSI, the skirt could end up mushroomed or inverted as it clears the muzzle, due to a lack of barrel support...  Better results would be achieved with solid "slugs" at such pressures.
Title: Re: How much air pressure in a springer?
Post by: rws45user on April 08, 2019, 11:32:14 AM
I think anyone can do this test that has a pcp .  Fill a empty cylinder to 163 psi put a 10 grain pellet in it and do a chrony test and see what happens .
Title: Re: How much air pressure in a springer?
Post by: Mole2017 on April 08, 2019, 11:58:09 AM
I think anyone can do this test that has a pcp .  Fill a empty cylinder to 163 psi put a 10 grain pellet in it and do a chrony test and see what happens .

I might be able to do that test for you as I plan to run my R10 without its regulator for a little bit, but perhaps data for a multi-pump air rifle/pistol would do in the meantime.

From a thread on the Green Crosman Forum, we have this chart for pressure built up in a 1377 style pumper per stroke of the pump (red line and red axis):
(http://realm.tapatalk-cdn.com/realm/Realm/pneuguy/walts2289.GIF)
source: https://www.tapatalk.com/groups/thegreencrosmanforum/any-idea-of-the-air-pressure-steve-nc-inside-t27103.html (https://www.tapatalk.com/groups/thegreencrosmanforum/any-idea-of-the-air-pressure-steve-nc-inside-t27103.html)

Looks like one stroke of the pump lands you just under 200 PSI. From a post on the same forum a few years later, a modified 1377 (longer barrel and some valve work) they give us this data:
1 pump 226 fps
2 350 fps
3 435 fps
5 549 fps
6 600 fps
10 707 fps
15 783 fps
20 828 fps
source: https://www.tapatalk.com/groups/thegreencrosmanforum/just-wondering-about-1377-velocities-t42365.html (https://www.tapatalk.com/groups/thegreencrosmanforum/just-wondering-about-1377-velocities-t42365.html)

So, it's like we've been saying: the pressure of the air pushing the pellet does affect the speed. Most people take the manufacturer advice to stop at 10 pumps, but this one has been hopped up to (a) develop somewhat higher pressures per stroke and (b) dump all or most of the air at 20 pumps--they can't all take 20 pumps and work right without some modifications. My 1377 got something in the 500s FPS for 10 pumps, depending on the pellet.
Title: Re: How much air pressure in a springer?
Post by: rsterne on April 08, 2019, 12:51:30 PM
rws45user.... Since you don't believe those with experience, I would suggest that it is up to you to prove your theory.... Using a pumper would be the easiest.... I have a similar graph showing pressure vs. number of pumps....

(https://oi378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg.html)

On a stock 13XX/2289 you get about 100 psi per pump at the beginning, before the pump cup starts to distort.... Try 1 or 2 pumps and see what you get for velocity from 200 psi.... With a 2289 (14" barrel) I got 230 fps at 2 pumps with a stock piston and valve.... and even with a flat-topped piston and modified valve that only went up to 242 fps....

Bob