Low pressure dump chambers and efficiency

[FatMan]

OK!

Originally posted by FreshmanBob
because the air it's self is causing the friction and turbulance its comming from the energy needed to compress the gas into the large bottle to 5000psi in the first place.

OK, I buy that. So that *would* be a source of inefficiency.

I'm starting to try and visualize this from the molecular level rather than as a continuous thing, and I'm not sure that the explanation I posted a couple days back isn't still sort of correct. I mean, where does the heat of friction come from? I would think that excited molecules slam into the obstruction and impart some of their energy, which takes the form of heat.

I think I'm going to have to go find me a physicist before this is over to get my mind straighted out!

As a side note I have some students working on some molecular dynamics simulations this summer. I wonder if we can simulate this effect? Probably easier than the CFD stuff I proposed earlier (though, we're working on that too).

FatMan

[FreshmanBob]

what you said is basically my understanding of heat and friction. Heat is how fast (or slow) molecules are moving around and bouncing off each other and friction would cause that.

That would be cool if you could similuate the effect to try an see how much energy really is lost.

[fearc7]

i have no idea what yall are saying but yeah...i agree 100% Keep up the good work!

[Vegeta]

Aiiight ima give a shot at simplifying this for those who don't get the heat thing. when a gas expands and compresses, some of the energy is lost as heat and to overcome friction (what little there is) we all know that.
If air is going from a 1/4" dia hose to a 5/8" by 1" chamber, it will expand a bit, and also the gas has to get trhu the hose and hole to the chamber. Then when it goes out of the chamber and out the powertube, it is compressed again, this time into a small dia hole.. i dunno lets say 3/8". The gass compresses, the gas heats up when compressd for the obvious reaons... and you have to push that dense-er air thru that smaller hole now... and theres frictions all over the place there... between the gas molecules and the metal molecules. You tube gets hot... Think of it liek a wire. lets say 4 volts at .5 amps is passed through 6 wires inside a 1/16" wire. easy right? now say that voltage was upped to 12 volts at 1 amp. whew! the wire gets warmer. Why? becuase electrons are getting all bunched up trying to get thru the damn wire. same thing.

Possibly tapering the journet fron the chmaber to the powertube and maybe heat wont be lost as much there. It would make for smoother compression back through hte hole and less resistance friction.

hey thats my shot erh.

[pbjosh]

I realize I didn't make my self clear, but then I am not a clear headed person.

I was trying to state at one point that the energy loss would most likely be greatest at the REG, not the dump chamber. A person could talk about temp diferentials for a chamber that drops incoming gas from 0 to 180 with a large oriface (Shocker), but how about a chamber that drops 4500 to 850 through a small oriface? A person might think that the reg would be the biggest factor of the LP dump chamber being in-efficient. But then the AKA setup is very efficent at very low pressure.

So, what am I trying to say? Only in the case of CO2 usage or high friction (early RT) is there really any inherant change of energy usage due to thermal issues in the gun.

A dump chamber should not be any more efficent due to its pressure, up to certian limits, but due to its design. That and only that. IMHO. Same with airgun design in general. Flame me if you want. A good design will be efficent. Bad designs are not. I have seen effiecient guns at both high and low pressure, both dump and poppet.

Josh

[BlackVCG]

So WHAT is a good design? You've been talking about energy losses due to restrictions in the system and so forth. You've also stated that the reason venturi bolts cause a drop in velocity is because they create a restriction with all the small holes. Well by that same analogy, an 8 hole mod reg. body would lose less energy than a single hole reg. body. That's just not the case. The reason why venturi bolts tend to make the gun shoot at lower velocities is because they aren't providing the needed flow rate that the stock bolt has. You can only flow so much air and it's all dependent on how you match your air passages to the supply source based on how much flow you want. Increasing the powertube on a Mag wouldn't make it any more efficient because the PT size is designed to provide the necessary flow to the bolt and then the ball.

I don't quite get what you're refering to about high friction in the old RT's. The "old" RT valve is the exact same valve in the mechanics as the valve used in the E-Mag, RT-Pro and Retro Valve.

[pbjosh]

BlackVG:

So WHAT is a good design?

The ones that work the best. Excalibur and AKA cockers, Mags, Nova, Phantom, Palmers, etc. They are the most efficient guns.

"You've been talking about energy losses due to restrictions in the system and so forth. You've also stated that the reason venturi bolts cause a drop in velocity is because they create a restriction with all the small holes. Well by that same analogy, an 8 hole mod reg. body would lose less energy than a single hole reg. body. That's just not the case."

Uhm, I don't know if I can dignify this with a responce. The eight hole mod has 8 holes the size of the same 1 hole mod. Of course it flows better. But in a bolt where there are 8 tiny holes trying to flow the same air a 1 big hole there is a difference. Didn't aligning the main hole with the top hole into the power chamber make the reg work as fast or faster than the 8 hole mod? So by making 1 hole a bit larger and aligning it the reg flowed better. You made MY point.

"The reason why venturi bolts tend to make the gun shoot at lower velocities is because they aren't providing the needed flow rate that the stock bolt has. You can only flow so much air and it's all dependent on how you match your air passages to the supply source based on how much flow you want. Increasing the powertube on a Mag wouldn't make it any more efficient because the PT size is designed to provide the necessary flow to the bolt and then the ball."

Again, the bolt venturies were designed to lower the air pressure on the ball. By restricting the flow. Thats all I am saying. I didn't say increase the power tube size on a Mag. I said a LP Dump chamber gun can be as efficient as a Mag or better not depending on the pressure ran, but the design of the gun. Efficentcy is NOT a value of pressure ran, but gun design. A Mag will not run effeciently at 95 psi, but a Nova does.

"I don't quite get what you're refering to about high friction in the old RT's. The "old" RT valve is the exact same valve in the mechanics as the valve used in the E-Mag, RT-Pro and Retro Valve."

Sorry my mistake. The internal working of the original RT Mag caused some friction due to the design. It was fixed. I was using it as an example of a gun that was affected by thermal issues in the HPA enviroment.

Josh

[BlackVCG]

What I just don't buy into is your whole thing about "clean flow paths" and such relating to efficiency.

As for lining up the reg body hole with the front valve body hole, all that did was increase the flow rate. It had no effect on efficiency.

The way I see it is it doesn't matter what goes on in the valve, it's an issue of how much pressure you're putting on the ball, how much volume you're releasing and how long you're releasing it. Matching all of these things to the system are what make it efficient. How the air gets to the bolt, I believe, has nothing to do with efficiency.

One of the reasons the Mag isn't the most efficient design is because it of blowback. The current dwell time is rather long, thus leading to blow back and wasted energy.

[pbjosh]

"What I just don't buy into is your whole thing about "clean flow paths" and such relating to efficiency."

No problem, I am not selling. These, like everybody else's, are my opinions and ideas from what I have witness and worked on my years in paintball. I have tested and figured most out myself. As almost everybody here has.

Back to my first comment. I was talking about how a Dump Chamber can be as efficient either at high or low pressure. That the pressure is not the variable in a effecient design, the design is. The Reg that supplies the pressure is where the Thermal Issues would take the most affect. The Shocker had horrible flow paths in-between the valve and the ball in the gun. A Nova has good flow paths. A Mag does also.

"As for lining up the reg body hole with the front valve body hole, all that did was increase the flow rate. It had no effect on efficiency"

Yikes! flow rate=flow path! You are making this hard on yourself. But if you used either method to deliver air to the ball, the single lined up hole would do it faster, making the system more efficient. What I was stating is exactly that, that the lined up ports and pathways are what makes a gun more efficient. A smooth transition from Valve to Ball.

"The way I see it is it doesn't matter what goes on in the valve, it's an issue of how much pressure you're putting on the ball, how much volume you're releasing and how long you're releasing it. Matching all of these things to the system are what make it efficient."

Yes, I thought I was saying the same thing. All points betweent he valve and ball, if they are not lined up, and cleanly ported have a ton of constrictions etc, that affect the efficeintcy. The Shocker is badly matched. The Mag is well matched.

"How the air gets to the bolt, I believe, has nothing to do with efficiency."

Sorry, wrong. You want to look at ALL areas between the BALL and valve. Take a batch of different bolts and you do exactly that. How come 10 bolt will have ten different velocities? How come hoggng out a guns valve and body make it flow more, and more efficient. I understand what your saying, but I think you are missing the point of my original comment. The Shocker has a ton of choke points. A Nova has almost none. Which is more efficent?

"One of the reasons the Mag isn't the most efficient design is because it of blowback. The current dwell time is rather long, thus leading to blow back and wasted energy."

Yup! The mag is very effecient. I never said the Mag wasn't efficent! It is still one of the worlds best! And if you cured the blowback it would be even more effecient. Or built a valve that had a separate action between the dump valve and bolt. I think I said this also.

As for not buying my train of thought, I have a feeling you think the same way I do. We may not be using the same words, but we are saying the same thing. IMHO.

Josh

[FatMan]

Since you two are both saying the same thing, I'm not jumpoing in on either side - OK?

A couple of comments - since the efficiency of the maker is defined by how much pressure is released and for how long - and the "flow path" effects how fast pressure flows from one place to another - then it stands to reason that the flow path from valve to ball DOES have an effect on efficiency indirectly in that a restricted flow path forces the design to release the pressure for longer in order to get the required pressure curve behind the ball. This explains why bolt design - by affecting flow - can also affect efficiency.

Now, the 1-hole, 8-hole, 1-hole-aligned issue is NOT a valve to ball flow issue. That is reg to dump chamber - that path does not come in to play during firing thus it affects recharge time but not efficiency.

On a completely different issue - we were talking about the issue raised previously by Steveg that a dump chamber was inherently less efficient than a poppet valve. I think there IS a case for that based on thermal issues (which, by the way, are STILL an issue with the RT valve as far as I know). However, it has not been shown that that effect is particularly significant in the overall efficiency equation. I don't think anyone has stated anything about whether or not you can build an efficient or in-efficient marker with dump chamber or poppet valve designs. I feel fairly certain you can do both (as Josh has pointed out).

So, I think the question remains - is there any inherent efficiency factor in a low versus a high pressure design - or is the efficiency really dependent on something else? Anyway I *think* that's the point of this thread and yet there seems to be no glaring evidence to support or deny this.

FatMan

[Redkey]

Flow Paths and Efficiency.

Say you have a marker shooting 300 fps with the stock bolt. If you were to replace the stock bolt with a snazzy bolt with lots of little holes instead of one big hole and then re-chrono... what happens? Your velocity will be lower... why? because of the flow restrictions associated with the new bolt. So... to increase the velocity you turn up the pressure or increase the tension on the hammer spring. Turning up the firing pressure means you are dumping more air through the gun. Increasing the hammer spring tension means you hit the valve harder causing it to stay open longer which uses more air.

In either case you are using more energy per shot and will get fewer shots per tank of air.

I suppose in some bizzare case the velocity could increase.... meaning you would have to decrease the amount of air used per shot to maintain the 300 fps velocity. In which case, you have improved the efficieny of the gun.

[BlackVCG]

PBJosh-

I was about to put in my last post that I thought you and I were kinda thinking along the same lines but just not using the same words. Now I see we are basically saying the same thing, but with a few differences.

What I don't believe is that a lot of twists and turns in the system cause inefficiency just because they are there. What I think is it's a matter of setting up the system with all flow paths matched and the bolt system setup to work in rythm with your valve pressure to deliver the air at the proper rate and volume. I think there's a lot more to it than just making the air paths smooth and straight. I think you could have a very inefficient gun even if the air basically took one 90 degree bend into the valve and then went straight to the ball. That's what I'm trying to get at with all that I'm saying. Everything needs to be working in accordance with the rest of the system. Designing based on static pressure rather than dynamic pressure and focusing on making the flow "smooth" is what I see is the key to an efficient system.

Anyway, I hope I'm making myself a bit more clear.

[pbjosh]

DAMN STRAIGHT!

yup, thats what I was so badly stating all along! or at least in my own head!

And IMHO the deal with low pressure dump chambers effecientcy has almost everything to do with designs. I feel that in a LP design there needs to be a cleaner air path because the LP air, as it transfers throught the points between valve and ball, seems to be more suseptable to restrictions,

Josh

[Redkey]

Now That We Have That Cleared Up.....

BlackVCG... I'm not sure I understand the designing to static pressure comment. I define static pressure as unchanging pressure... ie you gas up a marker and let it sit. I would think that any efficiency design work would involve working with dynamic pressures.

Also... Do you agree that twists and turns in the flow path will reduce the flow rate?

PBJosh... are you headed to STP this saturday?

[AGD]

You guys have to remember that this stuff is a continuum. If you have extra large dia flow paths turns will make little to no difference. If you have minimum holes, turns make a much bigger difference.

Static pressure can involve moving air. For the airfoil to work it needs moving air but the lift is provided from the static pressure.

Maybe one way to describe it is like this. If you had a basket of corn kernels pour out on your head you would be annoyed but ok. If you tried to stick your head into a basket of corn it would be a tough task.

AGD