Just out of curosity what is the reasoning against "flash filling"?

[cockerpunk]

How would there be any measurable difference in efficiency? The compressed air is in a closed system. The thermal energy which is lost to the bath is no different than the thermal energy which is lost to the surrounding air in a normal fill. Even with a slam fill, the thermal energy is the same, and once its dissipated the "efficiency" is also the same.

if you cool a tank without topping it off you lose pressure. so 4500 psi of hot air is probably 4000 psi of that same gass cooled. that energy flows right out of the tank through heat loss. so yes, in a flash fill or a cooled fill the loss will be the same. a slow fill wont have that energy loss.

[nerobro]

The 15 year thing has always puzzled me too. The only thing I could ever think of was that they figured it was used and cared for the whole time, or not used much and its care would be questionable.

The 15 year thing is because the testing method is destructive. Not due to tank condition. Remember, tanks can be retired at any time due to physical damage.

Now, what would have me curious, is how would a tank perform for it's sixth and seventh hydrotests.

[Spider-TW]

The 15 year thing is because the testing method is destructive. Not due to tank condition. Remember, tanks can be retired at any time due to physical damage.

Now, what would have me curious, is how would a tank perform for it's sixth and seventh hydrotests.

Ok. But 3 year and 5 year tanks both have 15 year service lives, don't they? (5 tests versus 3 tests) It also implies a shelf life for a bottle that sat unused for years. It is certainly easier to just say 15 years for all of them, but "easy" is rarely used in a bureaucracy except by oversight.

[nerobro]

Ok. But 3 year and 5 year tanks both have 15 year service lives, don't they? (5 tests versus 3 tests) It also implies a shelf life for a bottle that sat unused for years. It is certainly easier to just say 15 years for all of them, but "easy" is rarely used in a bureaucracy except by oversight.

To get a better measure, you'd need to do something silly, like equip the tank with a strain guage to measure tank stretch, a temperature gauge, and a computer to track changes. ;-) you really don't want that.

[DevilMan]

Well one of the issues I have with the whole process is the "destructive testing" part.

I don't think that testing something should be damaging that object. There should/could be better ways, such as XRay and the like to test the bottles. And they should not be subjected to the 9K PSI that the 4500 bottles are put to... I actually think it's 7K or so. Just the same, how many times has a compressor failed and PUT OUT more than 4500 PSI??? It's not something that works that way. You can't have something under pressure fail and have it output MORE pressure than it has already. Keep in mind I'm not talking about a bottle reg failing and allowing tank PSI into the system but the overall way that compressors work and bottles are filled. How many times have you seen a compressor that can pump up the "test" pressure at a field?

There should/could be much safer and far more sane ways to go about the whole process.

DM

[classicmagplayer]

The idea is, that you burn off the heat immediately by keeping the bottle cool while it's on the fill hose. So you get the true 4500 fill or at least closer than you do when you fill to 4500 and then have a 500PSI loss after cool down. Yes the heat transfer is the same, but the time is reduced. Now if you fill to 4500 in a water bath, and you fill to 4500 open air and you fill them the same time and same rate and remove the one from the water bath at the same time then yes I'm sure you'll see little difference.

It's the matter of leaving them in a system that can cool them back off faster so you get a "complete" fill.

Of course there is always that "all day air" thing to contend with... why do you need a FULL fill when you can go back and get more the next time. Well some argue that it's another trip to the fill station and blah blah....

That's the idea for that... but that's a bit OT. Soooo... back to the "Hazards (or NOT) of Flash Filling" with Mann!

DM

I get the idea of the pressure drop due to internal temperature change, and the difference in specific energy and thermal conductivity of water and air, I was just questioning what cockerpunk meant by a bath system having lower efficiency.

I think the OT is a bit ridiculous. Filling a pressure vessel, probably in close proximity to your body, in an uncontrolled manner is just plain stupid.

if you cool a tank without topping it off you lose pressure. so 4500 psi of hot air is probably 4000 psi of that same gass cooled. that energy flows right out of the tank through heat loss. so yes, in a flash fill or a cooled fill the loss will be the same. a slow fill wont have that energy loss.

Yes a slow fill will have the same energy loss. The energy you are saying is lost, its still back in the fill rig. Its the extra moles of air that couldnt transfer because the pressure was already equalized by the hot air inside the tank. Once the hot air cools, the pressure drops and your left with an under-filled tank. A slow fill allows the thermal energy of the hot air to dissipate, lowering the pressure and continuously equalizing with the fill rig.

If you take a tank and slowly fill, the same amount of heat will be generated as if you took that same tank and dump filled it allowed it to cool and topped it off. Its the huge rate difference thats the problem.

[cockerpunk]

I get the idea of the pressure drop due to internal temperature change, and the difference in specific energy and thermal conductivity of water and air, I was just questioning what cockerpunk meant by a bath system having lower efficiency.

I think the OT is a bit ridiculous. Filling a pressure vessel, probably in close proximity to your body, in an uncontrolled manner is just plain stupid.




Yes a slow fill will have the same energy loss. The energy you are saying is lost, its still back in the fill rig. Its the extra moles of air that couldnt transfer because the pressure was already equalized by the hot air inside the tank. Once the hot air cools, the pressure drops and your left with an under-filled tank. A slow fill allows the thermal energy of the hot air to dissipate, lowering the pressure and continuously equalizing with the fill rig.

If you take a tank and slowly fill, the same amount of heat will be generated as if you took that same tank and dump filled it allowed it to cool and topped it off. Its the huge rate difference thats the problem.

no, its the high flow that generates the heat and cuases the pressure drop. a much slower fill will have less pressure loss and shear heating associated with it. more turbulence = more energy lost through heating.

[DevilMan]

Energy can not be created nor destroyed... only changed forms.

The same amount of "energy" is transferred in and around the system. It's just a matter of how much makes it into the bottle. If you fill a 68/45 bottle and it takes you 1 hour to fill it from 0.00000 PSI to 4500 PSI the same amount of "energy" is lost/transferred in the process. Whether or not that energy is significant is the issue. You take that same bottle and fill it in 5 minutes and the SAME amount of energy is made it's the time that changes. You can "feel" it then, you just couldn't "feel" it before. That doesn't mean it didn't happen.

You then take the same bottle same PSI's and fill it from 0 to 4500 in 1 second and you'll more than be able to "feel" the energy that is transferring out of the process.

The SAME amount is gone for all of them. It's just a matter of where it's "lost" from and how damaging it is when it goes.

DM

[hunter100]

hydro testing is not a destructive test and does not limit the life span of the cylinder. The max psi, test pressure, 5 year hydro requirement, and 15 year life cycle are all based on a statistical analysis of the tank data they had when they wrote the specification (like 10 years ago or so). If you recall back when they first introduced the tanks to paintball, they all had 3 year hydro requirements. But the DOT realized after a few years that all the tanks were good for much longer and raised the requirement to 5 years, even for the previous 3 year tanks (if you got them retested). I wouldn't be suprised if they extend the 15 year service life after they collect more data on the tank reliability past 15 years.

There is no absolute criteria that will cause a tank to fail or not fail, its all statistical in nature. The reason you don't overheat your tank is because it increases the chance of failure, but doesn't guarantee it. Why take chances with your own safety?

[DevilMan]

hydro testing is not a destructive test and does not limit the life span of the cylinder. The max psi, test pressure, 5 year hydro requirement, and 15 year life cycle are all based on a statistical analysis of the tank data they had when they wrote the specification (like 10 years ago or so). If you recall back when they first introduced the tanks to paintball, they all had 3 year hydro requirements. But the DOT realized after a few years that all the tanks were good for much longer and raised the requirement to 5 years, even for the previous 3 year tanks (if you got them retested). I wouldn't be suprised if they extend the 15 year service life after they collect more data on the tank reliability past 15 years.

There is no absolute criteria that will cause a tank to fail or not fail, its all statistical in nature. The reason you don't overheat your tank is because it increases the chance of failure, but doesn't guarantee it. Why take chances with your own safety?

The test is destructive because it's in and of itself straining the tank to limits that do damage to the tank. I'm not saying that 4500PSI does no damage, but I am saying that 7K does a good bit more than 4500 does.

Think of it this way.... if you heat something that has a flash point of say 125*F to 120*F over and over and over... it may not like it and it may cause it to weaken. BUT if you heat it to 126*F and the conditions are right, you just ignited the substance. That changes the whole aspect as to what it was to begin with.

It is said that the reason that the tanks are 15 year tanks is because of the expansion/contraction of the tank due to it's life. Yet we all know that there are tanks that get filled and emptied sometimes every weekend and several times that weekend, and others that get used a few times a year. So who is it that came up with the 15 year rule? They said it was from the testing that compromises the structure of the tank that they are only good for X amount of times. I do think that's one of the reasons it changed from 3 to 5... because people got wise with the... "It can only take 2 (5 year tank) tests before it goes bad, but then this tank can take 4 (3 year tank), so what gives?"

So when that happened it went to all 5 year tanks to keep the standard "logical"

Just my .02 on the matter.

DM

[halB]

This is only sorta correct. You need to consider the fatigue limit of the material you're working with. If the stresses you put on the material are below the fatigue limit, there will be no damage done.

If you only bend the paperclip a little, you can bend it back and forth forever, without it breaking. However, once you exceed the fatigue limit, you start getting hardening, and cracking, and eventually failure of material.

Carbon fiber has effectively an infinite fatigue limit. Aluminum however, has no fatigue limit. That means if you don't exceed the fail strength of carbon, it will bend back and forth like a spring, forever, without failing. (this does depend somewhat on the binding agent used..) And aluminum, no matter how little you bend it, will accumulate stress and start cracking eventually.

Carbon also has other things to consider. It does not handle heat well. Temperature is the concern here. The epoxy used with carbon fiber does not transfer heat well. And it loses strength quickly with temperature. While a bottle might just feel "warm" to you on the outside, the inside is going to be a WHOLE LOT hotter.

To put that in perspective, find someone who's got a steel 68/3k, and try to even HOLD the bottle after a fast fill. You won't be able to do it. You get the same heat in a fiber bottle too, just you're insulated. The heat is kept within the tank, cooking the aluminum and epoxy.

I remember the first time I had my Maxflow filled. 114ci 3k tank, fiberglass wrapped. Fiberglass tanks are thicker than carbon, by some 1/4" IIRC. That bottle was beyond "warm to the touch" for a good 45 minutes. The tank lost 400psi cooling. I'll bet we can calculate how hot the tank was internally if we were so curious.

It's not leaving a clip loaded or unloaded that fatigues the spring, both being under the fatigue limit, it is the constant loading and unloading. To use an analogy.

[MANN]

Good articles.

I concur. I read that the upper limit for temperature is 120 for any hp bottle in service. I would like to see what fill rate coincides with this temperature.

[DevilMan]

I concur. I read that the upper limit for temperature is 120 for any hp bottle in service. I would like to see what fill rate coincides with this temperature.

Get a small transmitting thermometer and put it inside of the tank... put on reg and do your fills. Have it transmitting from the get go. Keep an external one as well and keep them sync'd and see what you come up with.

Because you know finding an itty bitty thermometer that can transmit and all as well as fit through a 3/4" hole as well as withstand 4500PSI atmospheric pressure is just as easy as going to Home Depot or Lowes or Radio Shack...

DM

[OneUp]

When flash filling, you are compressing the air so rapidly that there is a (intense sometimes) build up of heat. That heat, combined with the oxygen rich environment of compressed air, is 2/3 of the ingredients for a single stroke single cycle diesel engine (i.e. tank goes boom). If you have volatile vapors in your tank (caused by using inappropriate lubricants), then it could be very very bad. The less dangerous, but more annoying on a daily basis problem, is that as the tank comes back down to ambient temperature, the pressure drops as well. You can flash fill to 4,500 psi and be left with 3,500 psi in the tank after cooling (with no leaks).

just don't use lube or let an airsmith work it. pv=nrt equation means that normally nonvolatile lube will still be volatile in your tank.

[Spider-TW]

Get a small transmitting thermometer and put it inside of the tank... put on reg and do your fills. Have it transmitting from the get go. Keep an external one as well and keep them sync'd and see what you come up with.

Because you know finding an itty bitty thermometer that can transmit and all as well as fit through a 3/4" hole as well as withstand 4500PSI atmospheric pressure is just as easy as going to Home Depot or Lowes or Radio Shack...

DM

I would be surprised if the carleton guys didn't at least have a fill head with a pair of solid wires epoxied through it for a temperature probe.

I think that is the only way to know for sure. How about that for a senior project? Anyone?

Like cockerpunk says, the friction generates heat. At normal conditions and low flow rates, you can call it ideal gas and trade pressure for temperature. Generally however, you can say that the more violent the transfer, the less reversible the process is (isentropic). Stirling engines are a good example of the highly reversible end. If everything was ideal, and you very carefully (think insulated, for days) let your air roll over from the 70F 4500psi storage tank to your empty 70F bottle, you should have no heat generated. As an integral, you let down the pressure on some air, but then you squeezed it back up.

You could probably measure the heat generation of a fast fill with a calorimeter setup (back to the water bath!). A small styrofoam ice chest might work...