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Efficiency - the maximum potential of a 68/4500


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#1 insixdays777

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Posted 08 January 2009 - 10:53 PM

Punkworks,

What is the maximum efficiency potential of a 68/4500 ci tank? Given perfect circumstances what does the math say the maxium amount of shots of a 68/4500 can be?
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#2 Christopher

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Posted 08 January 2009 - 11:05 PM

Punkworks,

What is the maximum efficiency potential of a 68/4500 ci tank? Given perfect circumstances what does the math say the maxium amount of shots of a 68/4500 can be?


Not even remotely close to what can ever be gained out of it. The average valves used in paintball could probably only get around 60% efficiency per shot. That does not take into account the dead volume in the tank or the air used to re-cock the gun.

I think I have a big non paintball related article explaining some of this somewhere, I'll try to dig it up. This is an important question that needs to be asked when building air cannons. The flow rate of the firing valve will closely correlate to the efficiency of the gun (assuming correct barrel length).

#3 insixdays777

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Posted 08 January 2009 - 11:24 PM

Not even remotely close to what can ever be gained out of it. The average valves used in paintball could probably only get around 60% efficiency per shot.


I agree, This is a very important question, I think efficiency in paintball is the new frontier. I have no math skills but would love to see you punkworks mad scientist work through this.

what does it take to think outside of the adverage valves? What does the math say they need to be like?

Tom Kaye has always hinted that the paintball community has gone about the efficency problem all wrong with the low pressure craze. Does high pressure hold the key to 2500+ shots per tank?

Cockerpunk - what does the math have to say about this. It would be awesome if someone would build a gun working backwards from a theortically perfect efficency stand point.
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#4 cockerpunk

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Posted 08 January 2009 - 11:46 PM

4500 psi = 6.9(4500) = 31026.4078 kpa
68 degree f = 20 degrees C = 293 degrees kelvin
68 cu in = 0.00111432035 m^3

so we look up the enthalpy in the tables -

enthalpy = 2.9343x10^5 J/kg
density = 3.6896ex10^2 kg/m^3

so we have .00111432035 m^3 * 3.6896x10^2 kg/m^3 = .4114 Kg air

that means we have 2.934x10^5 J/kg * .4114 Kg = 120704 J

a paintball at 300 fps has

300fps = 91.44 m/s
.110 oz = 0.00311844754 Kg

Ke = (.5)(3.11844754)(91.44)^2 = 13 J

120704/13 = 9284 shots


that means thermodynamically the guns we shoot are on the order of -

ego, timmy, AKA = 2000/9284 = 21.5% efficiency
modern spools = 1400/9284 = 15.1% efficiency
very bad guns = 1000/9284 = 10.7% efficiency

not terribly surprising. modern electricity is generated at 25-30% efficiency, your car MIGHT be 20% efficient, diesels are a bit better maybe in the 25-30% range too.

maybe snipez can quick check my math. been a while since i took thermo.

Edited by cockerpunk, 09 January 2009 - 01:40 AM.

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#5 brycelarson

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Posted 08 January 2009 - 11:47 PM

I've got say - while the goal of efficiency is noble - it's really a moot point. Unless you're rocking at stock class rig it really doesn't matter. With all day air and more people moving to 4.5k fills most players don't shoot nearly enough in a game to matter.

That said - you can gain %10 or more shots per tank by underboring your barrel. Why do you think that the valves used in paintball are so poor?

I've wanted to do a high / low pressure test on a cocker for a while - maybe I'll get to it this winter.

#6 insixdays777

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Posted 09 January 2009 - 12:09 AM

"that means thermodynamically the guns we shoot are on the order of -

ego, timmy, AKA = 2000/9284 = 21.5% efficiency
modern spools = 1400/9284 = 15.1% efficiency
very bad guns = 1000/9284 = 10.7% efficiency

not terribly surprising. modern electricity is generated at 25-30% efficiency, your car MIGHT be 20% efficient, diesels are a bit better maybe in the 25-30% range too.

maybe snipez can quick check my math. been a while since i took thermo. "

wow that is what I wanted to see, that is very eye opening. I had no idea all guns where that inefficient. Thanks for the quick reply guys!
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#7 Troy

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Posted 09 January 2009 - 12:54 AM

I've got say - while the goal of efficiency is noble - it's really a moot point. Unless you're rocking at stock class rig it really doesn't matter. With all day air and more people moving to 4.5k fills most players don't shoot nearly enough in a game to matter.

I beg to differ. Less air consumption means less air needed to be pulled through the reg, which means faster recharge rates and higher rates of fire without shootdown... theoretically. It also means that dump chambers and volumizers can be smaller, thus decreasing the size of the marker.
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#8 Lord Odin

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Posted 09 January 2009 - 01:19 AM

Very cool, guys. Stuff like this makes me want to take Thermodynamics just for the fun of it. :D

#9 cockerpunk

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Posted 09 January 2009 - 01:37 AM

Very cool, guys. Stuff like this makes me want to take Thermodynamics just for the fun of it. :D



have fun with that ...

lol

actually thermo was not that bad of a class, rather interesting.
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#10 Snipez4664

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Posted 09 January 2009 - 11:58 AM

You're not using the heat energy to do any useful work, so it's strictly PV math, and dimensional analysis will suffice...

68 cubic inches*4500 pounds per square inch

=306,000 pound-inch force

=34,573 Joules

And then we simply divide by 13 joules per shot (At 300 fps, lowering fps has a HUGE effect on efficiency and is the root cause of many unbelievable claims IMO)

=2659 shots

This is BEFORE cooling effects are taken in to account @ the tank - only really significant if you try to do it all at once IMO, although when you flow the denser air (at a given P) you do waste more potential, since you won't get as much pressure BACK when you warm it up (non fixed ratio)

A well set up paintball gun is actually pretty good - the amount of air used to cycle is <10% of what the ball sees. Valving in paintball is actually pretty good - it's almost always overdwelled conditions or retarded dump chamber metrics (I would never design a gun with a dump chamber per se but that's another story) that lead to gross inefficiency.

The expansion is pretty complete too, if our breech pressure power pulses can be trusted. Car Engines are heat engines, and are therefore subject to Carnot efficiency - pneumatic systems are much more efficient. As an aside, that is why higher compression produces higher efficiency in cars, and therefore why diesel or cars running premium fuel are more efficient. (The energy in heat is huge compared to mechanical energy)

Edited by Snipez4664, 09 January 2009 - 11:59 AM.

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#11 cockerpunk

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Posted 09 January 2009 - 12:14 PM

You're not using the heat energy to do any useful work, so it's strictly PV math, and dimensional analysis will suffice...

68 cubic inches*4500 pounds per square inch

=306,000 pound-inch force

=34,573 Joules

And then we simply divide by 13 joules per shot (At 300 fps, lowering fps has a HUGE effect on efficiency and is the root cause of many unbelievable claims IMO)

=2659 shots

This is BEFORE cooling effects are taken in to account @ the tank - only really significant if you try to do it all at once IMO, although when you flow the denser air (at a given P) you do waste more potential, since you won't get as much pressure BACK when you warm it up (non fixed ratio)

A well set up paintball gun is actually pretty good - the amount of air used to cycle is <10% of what the ball sees. Valving in paintball is actually pretty good - it's almost always overdwelled conditions or retarded dump chamber metrics (I would never design a gun with a dump chamber per se but that's another story) that lead to gross inefficiency.

The expansion is pretty complete too, if our breech pressure power pulses can be trusted. Car Engines are heat engines, and are therefore subject to Carnot efficiency - pneumatic systems are much more efficient. As an aside, that is why higher compression produces higher efficiency in cars, and therefore why diesel or cars running premium fuel are more efficient. (The energy in heat is huge compared to mechanical energy)


why would it only be a PV term?

hummm ... total energy isn't it becuase the system is obviously flowing, are you basically using head as your energy?

your the chemE, i defiantly concede the point, im wondering why im wrong.

EDIT - what if i subtract off the energy of ambient air ... at STP.

im basically using a turbine expatiation type model when i look at this kind thing, is that just simply wrong?

Edited by cockerpunk, 09 January 2009 - 12:43 PM.

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And yes, Gordon is the sexiest manifestation of "to the front."


#12 Z3R0

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Posted 09 January 2009 - 12:17 PM

So you're saying 2600-2700 shots is mathematically what we should be expecting from a 68/45 on a marker with perfect efficiency?

Vikings aren't all too far off from that number if well tuned... and modern Egos, Timmies, and Cyborgs aren't all too far behind, either. Interesting.

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EDIT: "I would never design a gun with a dump chamber per se" - EigenGat hint? :P

Edited by Z3R0, 09 January 2009 - 12:19 PM.

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#13 Snipez4664

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Posted 09 January 2009 - 01:10 PM

Enthalpy has a specific definition of E+PV

where E is internal energy

and PV is pressure * volume.


When you look at the states, the internal energies cancel out (or very very close to it) in the balance.


Subtracting the value of air at STP (depending on the Standard they use, lets call it ambient 60F standard rather than the 0C standard) will have the same effect and be more accurate, but should yield a similar result.
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#14 cockerpunk

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Posted 09 January 2009 - 01:19 PM

Enthalpy has a specific definition of E+PV

where E is internal energy

and PV is pressure * volume.


When you look at the states, the internal energies cancel out (or very very close to it) in the balance.


Subtracting the value of air at STP (depending on the Standard they use, lets call it ambient 60F standard rather than the 0C standard) will have the same effect and be more accurate, but should yield a similar result.


yeah, that sounds like my error. makes sense.

i knew enthaply would be used, and it makes sense then we need to subtract off the ambeit air energy. simply bad problem solving on my part there.

damn doing thermo at 11:30 at night ... damn you!
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And yes, Gordon is the sexiest manifestation of "to the front."


#15 Troy

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Posted 10 January 2009 - 08:23 AM

Valving in paintball is actually pretty good - it's almost always overdwelled conditions or retarded dump chamber metrics (I would never design a gun with a dump chamber per se but that's another story) that lead to gross inefficiency.


OK, now that the op's question is answered, can you expand on this point (in stupid person terms please :P )... color me, very interested.
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#16 LieutenantDan

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Posted 10 January 2009 - 04:49 PM

I've got say - while the goal of efficiency is noble - it's really a moot point. Unless you're rocking at stock class rig it really doesn't matter. With all day air and more people moving to 4.5k fills most players don't shoot nearly enough in a game to matter.

That said - you can gain %10 or more shots per tank by underboring your barrel. Why do you think that the valves used in paintball are so poor?

I've wanted to do a high / low pressure test on a cocker for a while - maybe I'll get to it this winter.



Not true! Although many have access to all day air. Many others would greatly benefit from a marker that has higher efficiency. For example, scenario players. They participate in games that last upwards of 6 hours. It would be much easier to not have to fill up that much, and they could hold more paint because they will not need to go with a rediculous 114 CI tank! Also, outlaw ballers would love a super-efficient marker, since one tank is all they get!
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#17 chewiestmonkey

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Posted 10 January 2009 - 10:14 PM

thats something ive alwaysss wanted to knoww

so happy we have punkworks :tup:
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#18 Snipez4664

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Posted 10 January 2009 - 10:20 PM

Valving in paintball is actually pretty good - it's almost always overdwelled conditions or retarded dump chamber metrics (I would never design a gun with a dump chamber per se but that's another story) that lead to gross inefficiency.


OK, now that the op's question is answered, can you expand on this point (in stupid person terms please :P )... color me, very interested.


On what, specifically?
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#19 dave3066

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Posted 10 January 2009 - 10:24 PM

this thread just fried my brain
and i think i brained my damage
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#20 Troy

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Posted 11 January 2009 - 08:20 AM

Valving in paintball is actually pretty good - it's almost always overdwelled conditions or retarded dump chamber metrics (I would never design a gun with a dump chamber per se but that's another story) that lead to gross inefficiency.


OK, now that the op's question is answered, can you expand on this point (in stupid person terms please :P )... color me, very interested.


On what, specifically?

What do you have against dump chambers?
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#21 Snipez4664

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Posted 11 January 2009 - 05:29 PM

What do you have against dump chambers?


The simplest way to say it is that the entire dump chamber volume is added to the pre-expansion volume for efficiency purposes. Sealing dump chambers pretty much just stems the bleeding from the system, you ideally always want to meter out a set amount of air to the ball and let it expand (entirely post valve). Not to mention you lose recharge from the reg.

In the age of all day air it doesn't really matter.
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#22 cockerpunk

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Posted 11 January 2009 - 05:31 PM

What do you have against dump chambers?


The simplest way to say it is that the entire dump chamber volume is added to the pre-expansion volume for efficiency purposes. Sealing dump chambers pretty much just stems the bleeding from the system, you ideally always want to meter out a set amount of air to the ball and let it expand (entirely post valve). Not to mention you lose recharge from the reg.

In the age of all day air it doesn't really matter.


except in terms of recharge.

i have herd, only herd, many spools have issues with recharge. never had a chance to test them myself.


another reason for looking at efficiency as a good thing even if we usually use free all day air, is two fold.

1. a more efficient gun can use a smaller, lighter tank.

2. tune for efficiency, gain consistency.

and by that i mean inefficiency is caused by chaotic flows, flows that are more chaotic are less efficient, and by their nature, less predictable and harder to normalize. this means that by the properties of fluid mechanics, less chaotic flows means more efficiency and also more predicable and more normal flows.

so, within a type of gun, or a gun design, making that particular setup more efficient makes the fluid flow more normal, makes it more consistent.

now, thats not to say that a more consistent gun is more consistent then a less efficient gun. but if we take one gun, and run it inefficient, we should see it shoot also less consistently. the transverse is also true, a more efficient operating method or tuning for a gun should make it more consistent.

Edited by cockerpunk, 11 January 2009 - 08:21 PM.

The ultimate truth in paintball is that the interaction between the gun and the player is far and away the largest factor in accuracy, consistency, and reliability.

And yes, Gordon is the sexiest manifestation of "to the front."


#23 chewiestmonkey

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Posted 12 January 2009 - 12:46 AM

palmer's says that too, he said he noticed that the more efficient he got his guns to be, the more consistent and accurate they got.
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