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ShinyGuy
04-21-2002, 03:12 PM
I'm working on a dump chamber based marker design and would like to run it at a fairly low pressure ( <200psi ). Operating at this low a pressure allows me to not need separate low and high pressure regulators, be fairly consistant on co2, reduce wear on internal parts (same flow rate with less force), and of course sell the thing to everyone that believes LP is the answear (I would never market anything as being better because it is LP, but it's easier to just say yes when they ask instead of trying to convince them it doesn't matter).

My problem is that every low pressure dump chamber gun I've seen has horid efficiency (shocker, matrix, smart mag). I'd like to know if there is some fundimental problem with dump chamber designs at these pressures or if there's just a reason why it doesn't work well with the above named guns.

AGD
04-21-2002, 11:57 PM
The reason is because you need a longer barrel without holes. Again thats not an easy thing to convince people they need.

AGD

pbjosh
04-22-2002, 09:58 PM
I will go against AGD on this one.

I have tested Dump Chamber designs that use 175 in*lbs of energy at 140 psi.

A 'Mag uses 220 in*lbs of energy at 400 psi.

The main problem with Dump Chamber design has to do with the restrictions in the design. The Shocker for example, is one of the worse designs possible due to large internal spaces matched with flow paths that are large restrictions in the air flow to the ball. Even the Matrix, after the fix of the bolt (It was dumping 1/3 of its energy out the back some how) still has restrictions to the air path keeping it from being as efficient as a mag. In a Blowback type of design, the smaller dump chamber at higher pressure will be more efficient. But other bolt/dump chambers are possible.

Take the Nova. There was a Dump/PEV design that was very effecient. The non-bolt barrel system had some complications that held it back, but for effecientcy the Nova was one of the best.

But the Excalibur is still the best, at 150 in*lbs of energy used, it is about 80-85% effecient.

Josh

AGD
04-22-2002, 11:16 PM
All things being equal lower pressure behind the ball translates into longer acceration distance and thus the need for a longer barrel. Guns in general can very well have different efficiencies for many reasons.

AGD

steveg
04-23-2002, 03:44 AM
(It was dumping 1/3 of its energy out the back some how)
not dumping it out the back, dumping it out of the barrel.the valve between the supply chamber
and dump chamber was incorrectly sized, so that on the forward and back stroke of the bolt,
there was a few millimetres of overlap when the supply chamber was venting down the barrel.

perhaps I'm reading it wrong, but the excalibur is not a dump
chamber marker its more an electo cocker or closed bolt angel

Actually I liked Doc Nickel's explaination that energy is
used (lost to heat) to refill/recompress the dump chamber

pbjosh
04-23-2002, 12:04 PM
Doc is wrong. Sorry to say a friend is wrong on this, but he also still thinks a paintball that DOES NOT Spin is more accurate. He can spell better than me though.

If that is true than using a regulator or a high pressure low volume chamber would have worse efficentcy. Because the temprature difference would be greater. Look at the RT. Filling that fast caused interesting temp changes for a while. If anything, it made the gun run Hotter!

Also if that is the case, a Dump chamber fills up, but even in the case of a Shocker the fill side is HUGE! It fills but doesn't change pressure very much. It is gradual compared to a Reg. In that case his parts 'cocker with AKA guts would never hit 1400 shots because it runs at such a low pressure and the energy loss would be found at the regulator. Sorry I don't buy it. Also the point on the bolt side of a poppet valve would do the same thing. Again. sorry, don't buy it.

As for the efficentcy of a dump chamber or any other design is built into the FLOW paths, not the pressure. The Phantom has a nice clean flow path for the air. So do most pumps. An AKA does also. The only other gun that has a cleaner air path between the release of the Dump Chamber or valve is the Nova.

Now the reason for 400 psi in the 'Mag has more to do with bolt TYPE than best pressure. With a blow forward type of bolt action the the bolt is a restriction, but also built to cycle in accordance with the dumping of the valve. If the bolt cycled seperate than the valve then the valve and bolt could be built for better efficentcy.

OKay, gotta stop now

Later,

Josh

AGD
04-24-2002, 01:53 AM
the efficentcy of a dump chamber or any other design is built into the FLOW paths, not the pressure

PB,

Please explain this in detail and give a simple example of what you are describing. I am trying to understand what you are saying.

AGD

steveg
04-24-2002, 07:24 AM
perhaps not, compared to a phantom but I would say that
both a mag and a matrix have short and smooth air passages

the air in the tank has a fixed energy potential, anything
that robs some of that potential reduces the shot count.

regulators DO in fact use a bit of that potential just as poor
airpath design. any time that you have heat generated, that
is a bit of your energy leaving you.

every time you change the pressure of air (giving a fixed
volume) you either add energy to increase pressure or release
energy when you decrease pressure.

Both my mag and my matrix are sitting beside me without pressure.
the dump chambers are empty, if I were to take a bicycle pump and
pump the air chambers on both (400psi for mag,160psi for matrix),
I doubt that anyone would argue that energy is required to
fill the chambers to operating pressure.

SO now I attach an air bottle to the marker and pull the
trigger a few times empty chamber,fill chamber,etc.
the energy used to fill the chamber is NOT being used to
launch the ball. it is GONE forever.

If you look at the entire system, Anything that takes away
energy, bad air passages, regulators, valves, rams, filling
dump chambers, etc is energy not launching the ball.

(more stuff)

Another thing to consider is how the pressure is released.
for example, if I were to take two identical scuba tanks
with exact fills, and slightly opened the valve on one,
the air would harmlessly excape.
If I took a hammer and knocked the valve off, the results
would not be described as harmless in the coroners report.

a poppet valve struck with a hammer (cocker,phantom,etc)
has a sharp almost instant release of air that is (theoretically at least)
constant in volume and pressure

A dump chamber has a less instant release of air that instantly
diminishes in pressure as it decreases in volume.

Both of course, at the valve.

AGD
04-24-2002, 09:40 AM
Steve,

You had better rethink the popet valve thing.

AGD

steveg
04-24-2002, 09:53 AM
You had better rethink the popet valve thing
which part? the breaking off of the scuba valve;) or the
constant pressure and flow, that would depend on the
resevoir behind the valve (I live near a hydro dam).
in reality it will drop off but never stop so long as the valve is open.

the dump chamber valve need not be slower but for the matrix
it is, thats one of the reasons that Greg (aardvark) placed
a small ridge on his bolt to give a bit more snap to the
valve opening.

pbjosh
04-24-2002, 11:05 AM
Oh man, I had 2+ page reply for you guys and it just got erased! Curse curse curse!

AGD:

Flowpaths is my term for any place the air has to go to get to the ball.

This is "Paladin" type of thought, so please bear with me. It has no testing with complex computer settings. I am trying to convey internal thoughts on air passages and my intuitive "Force" methods.

As I see it any thing between the valve/dump chamber is a restriction. For the most part this allows the air to get down to an acceptable pressure before it hits the ball. If a 400 psi/ .55 ci dump chamber were to drop all of its air straight onto the ball (using a force field wall of course) the ball would burst. So a restriction to tune the air to the point it doesn’t break the paint is needed.

But look at the Nova. It has a ˝” or so vent on the tip of the piston that is almost touching the ball. It releases the air separate from the bolt/barrel action. It is easy on paint, has great efficiency and very clean “Flowpaths” between the ball and valve. The air dump is nearly instant.

On the flip side is the Shocker. This has the most over-engineered valve in the paintball world. There is nearly another 1 to 1.5 ci of volume between the valve and ball! And the air goes through several passages, and quite a few orifices before it makes it to a ball. All of those are problems in the flowpath ideals I have. They restrict the flow of air. But in the case of a shocker, the restrictions are NOT to slow down a fast high pressure burst of air. They are just from plain lack of maybe not so common sense.

As for thermal energy wasted/used per shot, look at all the restrictions between the tank and ball. Every time the air goes into a larger or smaller chamber, goes through a reg, or expands, there are these problems. And the cumulative affect of this should show up a lot more in a Hp dump chamber or gun due to the drastic change in pressures, and high flow past small orifices. I went through a 68/3000 psi tank in minutes using the cocker set to 18.5 bps. Did the gun heat up of freeze up? Not really. If there is so much air exchange and so much energy wasted in air dumping into a Dump Chamber, then there would be more wasted in a poppet valve design stuck inside the passages of a ‘cocker. Scrap that idea, the total affect is almost to small to measure using HPA. And the Shocker, what part freezes when you shoot a ton of paint on CO2? Yup, the tank. And why? Huge air usage. If the gun was efficient, then the tank wouldn’t freeze. Don’t go backwards on these thoughts, the efficiency of the gun affects the tank usage, not the pressure. Or else an AKA or Nova would be inherently in-efficient. And they are just the opposite.

Okay, I have wasted 3 pages worth of typing to get 1 page out.

Your turn,

Josh

steveg
04-24-2002, 11:58 AM
;) expanding gasses cool, compressing gasses heat. they cancel each other out;)
Don't focus overmuch on the heat it's self

everything contributes to lost energy potential. expanding
into unneccesary volume before it even gets to the ball
(shocker) does that, just as releasing the air/energy against
the ball (nova) uses it more effectively.

regarding what happens to the air before it gets to whatever
valve arrangment (that) fires the ball, it is essentially identical
between poppet and dump chamber markers and therefore a constant

(suppose that anyone has answered shiney's question yet)

I propose an experiment.
A boltless test marker with a poppet valve immediatly
behand the ball.

in one test it is configured as a dump chamber marker, in
the other a (constant source??).

the operating pressures are the same, valve opening the same, and dwell time/volume
are varied to achieve a set velocity.

this would isolate the dump chamber and its effect on energy use

everything else being identical

AGD
04-24-2002, 09:01 PM
I am still not getting the flow path thing. All I know is that when you look at the pressure spike behind the ball you can't tell the difference between a poppet or a dump chamber. (actually I do know more but you guys are doing a great job examining the theory).

AGD

MrMag
04-24-2002, 10:10 PM
wow, i barely understand a thing that u guys r saying, all i do know is that u r arguing w/ the president and maker of automag. just a thought.

RobAGD
04-24-2002, 11:30 PM
Tom I think he is refering to flow energy loss due to change in direction in the air flow. It's all about flow loss due to restrictions and orface changes and turblance.

-Robert

pbjosh
04-25-2002, 12:57 AM
THANK YOU ROB!

I just didn't use the right words, same topic different language!

Yes:

".....flow energy loss due to change in direction in the air flow. It's all about flow loss due to restrictions and orface changes and turblance."

That is what I was trying to show. Sorry I was so long winded about it, I just am not consice enough to get my thoughts out well some times!

So, my basic statement is that a dump chamber valve, with a VERY low flow energy loss due to no change in direction in the air flow, can be more effecient in a LP enviroment than a HP/Low volume design because the HP/LV design will have to have more restrictions to get the air pressure at the point of impact with the ball down.

Josh

ShinyGuy
04-25-2002, 01:27 AM
wow, thank you. Lots of good stuff to think about.

So now the next question. Does the chamber pressure/size matter at all for efficiency? It seems like what you're saying Josh is that a high pressure/low volume gun wil preform exactly the same way as a low pressure/high volume gun with all other factors being equal. Conviently we have a good test case of this with the smartmag/automag/hypermag. In the case of the mag the efficiency improves as it is run at higher pressure. Why?

BTW anyone have a good diagram of a nova. I've never looked at how one works.

pbjosh
04-25-2002, 02:51 AM
Again the issue is what Rob stated:

".....flow energy loss due to change in direction in the air flow. It's all about flow loss due to restrictions and orface changes and turblance."

The 'Mag bolt, because of its design, limits the dump chamber's effecientcy. Very little mind you, but some. IT is designed to drop the pressure of the Chamber enough for it to not break the ball. It is a restriction. The air comes out a .25" dia hole, which has .196 in2 of area, then turns out the tip of the bolt, and through ports to ge to the ball. The pressure of the air drops to 60-70 psi or so AT the ball. Because of restrictions in the system. Designed in to make a Blow-Forward marker work. If there were no restricions, then the bolt WOULDN'T go forward. So the ideas of efficencty from the HyperMag and SmartMag wouldn't work. The bolt and spring are designed to run at 400 psi. Also the 'mag does drop alot of energy out the breech with blow back. Maybe as much as 10-15% (any idea AGD?). So a low pressure Dump Chamber would make the bolt open slower, and the hig pressure Dump Chamber would make the Bolt move faster. The LP mod would slow the bolt as it is opening away from the Dump Cahmber also. The HP mod would cause the bolt to fly forward at nearly twice the pressure. Here are the numbers, the bolt has about a .25" dia face, so the bolt tip has .196 times 300 psi, for a total of 58.8 lbs of force against the bolt tip. At 400 psi you get 78.4, and at 500 psi (hyperMag)you get 98 lbs of force. Which is going to move the bolt faster, and further into the barrel, and hold it there for a longer period of time, and release less into the breech?

A Nova has NO restriction, short of the opening oriface, which is 1/2" or so. If you tried running the Nova at 400 psi you would break the ball. Even if it released the same amount of energy at is does now.

So I am saying a LP system can be more effecient because it doesn't need to put flow restrictions between the valve and ball. But it needs to be designed to be a LP system. If it some hokey SP type of valve with flow restrictions placed in the design, It WILL NOT be efficient. No question. But clean it up like a Nova, and it WILL be effecient.

Please excuse all grammer errors or bad typing in general. It is 2 am again, and time for bed.

Josh

steveg
04-25-2002, 05:41 AM
Tippmanns,
they don't exactly have a tortured air path, and work straight
off the co2 bottle.(as do phantoms) is the need for reducing
the air impulse (vs being beaten to death by the bolt)
being overstated. Admit it they are no more prone to
barrel breaks than any other marker.

The dump chamber is essential to the way a mag works,
the air flow must be cut off for a blow forward marker to work.

But I am beginning to doubt the need of a dump chamber for
it's own sake.
Are dump chambers inherently more consistent than poppet
valves? or are there a bunch of badly tuned cockers out there?

what sort of efficiency would a tippmann style valve operated as a
pnumatic ram instead of blowback get.

as pb stated in another thread there must be almost as
much gas going out the back of the valve as down the barrel

I do agree with pbjosh on the air passages etc. but I'm
not going to back away from the dump chamber using energy
to recharge, if a dump chamber were significantly more
consistant its a worthwhile tradeoff.


best I could find on the nova http://www.petecoffey.com/snova.html

FatMan
04-25-2002, 10:43 AM
I've been reading this thread for days - mostly I've been really confused. Not sure if it's terminology or strange assumptions in the postings.

I think I get what Josh is saying now - and tend to agree that as far as transfer from the dump chamber to the ball, an unobstructed path with no extra work to do (bolt movement) will be more efficient - just as he says. The problem is you DO have to move SOMETHING in order to chamber another round. Most markers have a bolt, the Nova moved the barrel. I order to do that you HAVE to expend some energy - and most markers do that with the primary power source (you could do it electrically with a soloniod, but would probably eat batteries). So, what is the most efficient way to move the bolt? Was the Nova able to cycle the barrel more efficiently than the Mag cycles the bolt? To tell the truth I don't know. My gut reaction would be that moving a much larger object would require more energy. Any good numbers of how many shots a Nova got from a give air source? That's the only thing that REALLY matters with efficiency. Beyond that you are just doing LP for LP sake.

Now, I'm not trying to be mean, but I don't think I understand where Steve is comming from at all! I understand the difference between a poppet valve and dump chamber setup. The poppet valve isn't open long enough to see "continuous" flow from the power source and in the end produces a pressure curve very much like a dump chamber (as AGD has pointed out repeatedly). Poppets are notoriously inconsistent because of the way they operate and the number of variables that effect their dwell time. Even on electronically controlled markers you pretty much universally find them running regulated. Once you put a regulator on the system it runs pretty much like a dump chamber - not exactly, but pretty close.

As for energy expended in recharging a chamber, I doubt that energy loss is significantly different than energy losses with other systems. True, there may be some losses that are unique to that configuration, but then the same is true for any configuration. So far I haven't seen anyone suggest a source of energy loss unique to a dump chamber configuration that would produce a significant effect on efficiency.

What is the net wisdom on a Mag's efficiency? I've never noticed my mag being a whole lot more or less efficient than the other markers I've owned, though I never scientifically tested it. Does someone have specific data to say the Mag is particularly inefficient.

FatMan

pbjosh
04-25-2002, 12:03 PM
Fatman!

Okay, I do have a couple datatables to state energy usage, and backward calculations from a 'Mag using chamber size times the pressure ran. If you look at:

http://automags.org/forums/showthread.php?threadid=18939

We have some of that. As for a bolt moving system, a cocker uses very little air to run the ram. A normal ram has about .1 ci internal volume for each throw, at 50-100 psi. For each shot then the ram uses 10-20 in*lbs of energy. Not to shabby. This is about 5-10% of the shot. If the gun is running at good levels of effecientcy. Since most LP cockers use nearly 300 in*lbs per shot now that means the ram uses only 3-5% or so.

I am not totally sure, but I think the Nova's Barrel mechanism recharges the Dump Chamber.

And a 'Mag is very efficent. One of the best easily. It uses about 220 in*lbs of energy per shot. The only guns that do better are the Nova, and the AKA line. Everything else only comes close. Even the Angels are using 240-275 in*lbs per. And the new Matrix bolt setup uses only 240-250. Alot better. But the AKA sets are only using 150 in*lbs or less.

Josh

steveg
04-25-2002, 12:04 PM
Now, I'm not trying to be mean, but I don't think I understand where Steve is comming from at all! I understand the difference between a poppet valve and dump chamber setup. The poppet valve isn't open long enough to see "continuous" flow from the power source and in the end produces a pressure curve very much like a dump chamber (as AGD has pointed out repeatedly). Poppets are notoriously inconsistent because of the way they operate and the number of variables that effect their dwell time. Even on electronically controlled markers you pretty much universally find them running regulated. Once you put a regulator on the system it runs pretty much like a dump chamber - not exactly, but pretty close.

Not mean at all (lets see now SC isn't that far from New Brunswick and as long as no one warns the border guards)


You guys are doing so well with this I am going to jump in and share some data that I never let out in public. Here is the pressure profile of the Angel that you can use to determine accelleration rates. Virtually all paintgun profiles look like this except for the Matrix and Mag which take longer to get up to pressure. The Y scale is pressure and the X scale is time in tenths of milliseconds so 10 counts = 1 ms.

This is where I was coming from, or trying to go to, at least.To use an analogy, look at a garden hose, turn on the tap
at the house and let the hose fill. turn off the tap, now squeeze the nozzle, a sudden burst of water that immediatelly dies (dump chamber)

Go back to the tap and turn it back on and leave it on.now squeeze the nozzle, sudden burst of water and then continued flow until you release the nozzle. (poppet valve)

(oops forget to have a point) the above statement from Tom shows that there is a difference in behaviors between a dump chamber and poppet valves .
Also, I know from maintaining my matrix, that if the bolt is being a bit slow moving, the velocity can drop to nothing because the air does not come out as a sudden impulse instead it just bleeds out ineffectually.
pb when is the forcefield valve going to be ready?


way up there at the top Tom mentioned barrel length.
I chronoed in at about 270fps with a freak barrel, with
10" tip. I then took the tip off and chrono'd again
240fps. That, I would call an effect. also I tried the
difference between a 10" freak tip and 14" all-american tip
no real difference. I then taped over the porting on the
14" tip 5~10fps increase in velocity and a huge increase
in noise.

ShinyGuy
04-25-2002, 08:05 PM
Thank you Josh. You answeared my question about the smartmag/automag/hypermag perfectly.


steveg -- dump chambers are more consistant than poppet valves since there are fewer things that can effect them. The following factors effect the consistancy of poppet valves;

input pressure
input quality (with co2) (quality refers to the amount of liquid or vapor in a gas)
temperature
friction on the hammer
stickyness of the valve seal
friction of the valve stem
momentum of the hammer (from the player running or moving the gun)
any factors that influence consistancy after the burst of air leaves the chamber

Dump valve designs are only effected by the first 3 and the last factor in that list.

Tippmanns have a long and complex journey around the sides of the valve if I remember how they work correctly. Most 2-tube blowback designs probably have less obstructed airflow. Poppet valves act as a sort of regulator in that they are open too short a time to allow the full pressure behind them to reach the ball. (Not sure how much they drop the pressure. Anyone have good numbers on this?)

All this is not to say that poppets are bad and dump valves are perfect. There are plenty of ways to screw up the consistancy of a dump valve and the inconsistancies of a poppet valve can be minimalized with good design. My personal opinion is just that a dump valve is a slightly better place to start.

BTW-Tom, any way to build a more thermally stable RT valve?

steveg
04-26-2002, 06:20 AM
BTW-Tom, any way to build a more thermally stable RT valve?
make the principle of adiabatic expansion and compression go away.

after you look that up, look up Isothermic expansion and compression. after you look that up, try conservation of
energy. here's is a start. http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html



http://aries.www.media.mit.edu/people/aries/portable-power/node5.html#SECTION00030000000000000000
math for the energy stored in a 68/3000 tank.

FatMan
04-26-2002, 08:42 AM
Josh,

I had forgotten about those (been a while since I read that far back - there is an example of data that would be nice in my proposed repository). That's exactly the kind of data I was interested in - the efficiency of the whole system. How many shots per volume*psi you get with the system. Too bad no Mag data there.

So, I guess what I was trying to get at is if all we do is consider the efficiency of one part of the system, we may optimize that while losing all of our savngs somewhere else. In the end, its how the whole system operates that really matters, not any individual part. Further, I submit that the sum total is a more complex equation than a simple volume and pressure calculation. I'm not arguing that isn't a valid first approximation, but there are a lot of other variables - so again, the real question is how does the whole behave.

I remember when the Nova came out. I thought it was a REALLY cool design. From a strictly engineering perspective it was clean and innovative, and clearly effective. I think the things that have made it a failure (are we agreed it was a failure?) had little to do with engineering, and a lot to do with other stuff - like the horrible "ploop" sound it made when it shot, and the fact that it looked like a gasoline pump nozzle, and the non-standard barrel. I've never seen rate of fire data on it, but I never got the impression it was very fast.

So, I think its interesting to look at that design and ask "what can we (AGD) learn from it?" But we have to keep in mind the WHOLE system because some of the places the Mag (for example) are less efficient, are designed that way for other reasons - which may affect some other aspect of efficiency or other goal of the marker. In the end, as you said, the Mag is really efficient. Way to go AGD! Maybe we can make it a little better - maybe.

Anyway, I think all this puts this thread into a little better perspective for me.

Steve,

I don't know how much you know about SC, but you better know what you're doing before you come sneaking around here! :D

I'm still having trouble understanding exactly what the point you're tring to make is. I understand how dump chambers and poppets work. Your garden hose analogy is OK, except water is an incompressible fluid, and the relative valve open time is really really short by comparison. So, for example, in the case of a dump chamber, the valve closes before the chamber has completely dumped its load - there is still positive pressure in the chamber after the bolt returns and just before the on/off opens. On a poppet valve with a regulator, the regulator doesn't open at the same time as the poppet (and, in fact, if you have TWO regulators, as most well tuned Cockers and electros do the second reg doesn't open at the same time as the first), so the pressure curve is still characterized by a pulse of pressure (as AGD's chart shows) not a continuous flow of pressure. True, the dump chamber profile is not as sharp - though I see that as a benefit, particlularly for consistency, not a drawback.

So, I guess what I'm asking, is what is your conclusion about the difference between a dump chamber and poppet valve? Which is more efficient? My position is that in the end you are trying to produce more or less the same effect at the ball - one like what AGD shows - the difference is in the specific shape of the curve and how it effects the consistency and efficiency of the marker. My conclusion is the dump chamber is very efficient, easier to control, easy to implement, and still yields a high rate of fire. The data seems to support that (though I admit it is spotty at best).

The one thing I have heard that sounds like a drawback is the speed with which the bolt hits the ball - and here it seems AGD may be doing some work to improve that.

So, I'm not sure if you're saying something different from that or not.

I did find your comment on barrels interesting. I have seen where people claim that as soon as the bore increases in a step-bore barrel the gas escapes and the ball no longer accellerates. That never set well with me - even with some air passing around the ball I would think it would still accellerate - but I've never had the data to support that so I've kept my mouth shut. Now the porting, that might have more of an effect. That's basicly why I've stuck with the teardrop tip on my Freak - the porting is bunched at the end.

OK, This one is getting too long, better end it here ...

FatMan

FatMan
04-26-2002, 09:01 AM
Originally posted by ShinyGuy


BTW-Tom, any way to build a more thermally stable RT valve?

OK, I'm going out on a limb here. I've studied the ReTro Valve with great interest ever since it came out. I have some theories about how it works that may be right, may be wrong - not sure if AGD has ever made these details clear. So here I go, and if I'm out to lunch, by all means, tell me ...

So, I don't think one can reasonably expect to make a "more thermally stable" valve. Any system that involves transfer of air pressure is going to have thermal issues and heat loss. The real issue is why the heat loss in the RT causes a drop in pressure in the chamber. Why doesn't the reg open up and restore the pressure?

The answer, I think, is that the RT valve actually OVER charges the chamber by a small but consistent amount. This happens because of the restricted route of the air to the controlling surface of the reg. Unlike a regular Mag valve the air at the input that passes the reg seat is not the air that controls the reg - the air must pass down past the on/off valve and then back up the regular pin (which you will note is hollow in an RT) to the reg piston.

This is a restricted path, so by the time the increased pressure has reached the piston, the pressure in the chamber is actually a little higher than that at the piston. The reg shuts off and the pressure balances - now the chamber is a little over-charged. As the air cools the pressure reduces, but not enough to let the reg open again. Hence the drop in chamber pressure and velocity.

This also explains why the input pressure has an effect on consistency at slow rates of fire. A lower input pressure doesn't overcharge the chamber as much, so the pressure difference is less. Again, because of the way the air is routed to the piston, while the trigger is held back and the on/off is closed, the air to the piston comes only from the chamber, which has been dumped, thus the reg is open and the full input pressure is allowed into the valve all the way up to the on/off. When the trigger is released you have a fairly high pressure there ready to quickly fill the chamber - thus the RT's fast recharge (on the old valve you have to wait for the reg to open after the trigger is released). Once again this is why you must have regulated air for an RT, or things don't go well.

Anyway, I think the thermal/pressure issues of the RT are an artifact of the design. If you want a more stable valve, you can go back to the old Mag valve, or use a lower input pressure. About the only other thing that would work would be to build the valve from a perfect insulator that doesn't allow the heat to escape - but I don't see that happening any time soon.

FatMan

Redkey
04-26-2002, 09:46 AM
However, I have no idea how a mag works. Heck, I've never even shot one before.

Could someone please send me one so I can play with it? That way, when I contribute my mindless drivel to this topic I'll at least look like I know what I am talking about.

steveg
04-26-2002, 06:39 PM
Gee, come on in the waters fine here Redkey.

Garden hose, better to have used air hose but, the water hose
expanded with pressure and returns that when you open the nozzle.

Point One. as suggested elsewhere by Doc Nickel, the dump
chamber has to be raised from 0 psi to whatever
the operating pressure is. this takes energy (my bicycle pump) A poppet valve does not.

Point Two (this one is loosing steam with me too so lets forget
this one after this O.K.;) )
as illustrated by Toms data the pressure spike happens later
than with a poppet valve.
The matrix bolt has it's dump valve 4" away from the tip
the mag dump valve is 1 3/4' but has the stem in the way

The maximum pressure impulse will happen at valve opening
and drop quickly, this happens before it gets to the ball
thus the later spike on Toms graph.

This implies some of the fixed (dump chamber) energy is already gone.

The poppet valve has the entire bottle behind it
(or at least as fast as the regs let it through) so the impulse of
air is much less diminished when it reaches the ball,
therefore the earlier pressure spike.

My totally ungrounded assumption is that the earlier pressure impulse just takes less air.

(the problem with this sort of speculative, mindless drivel
is that it is a one sided conversation, not the best way for ideas
to conveyed and mistaken assumptions corrected or correct
assumptions to be confirmed)

The phantom and nova release their pressure right onto the
ball. no air wasted in filling passages.

all other things being equal dump chambers are less efficient.

OK Tom whats the real answer

Vegeta
04-26-2002, 06:58 PM
Josh now knows i am a new fan of poppet valves, after my last attemp at new valve design.

Poppets are not fully consistant throughout their cycle. When the hammer hits, its starts to open. At first it is not open a whole lot and therefore large voulumes of ait connot pass through them. Then it gets more wide open as the hemmer's momentum keeps pushing it, and the gap becomes bigger, and mroe air is let through. Then the bolt's momentum reches a standstill with the valve in its wide open position. in a blowback marker, this is where the blowback gas's energy is at an equilibrium with the power of the bolt drive spring. Then the blowback gas (or a ram, depending on what kinda system is going here) starts to push back the bolt, and the poppet valve starts to close, again slowing and restricting the air flow, cuaseing a bit of fluxuation in the consistaeny. Of course this will not effect the ball's fps consistency that much if at all.

I will continue to read on this... while working on my long awaited (for me) new design, after the old one was horridly shot down.. i really should have looked at that better!

Vegeta
04-26-2002, 07:00 PM
And I also agree on the flowpath ideas. The more corners and routes the gas has to take from the time it is released from the valve to the ball is a set back.The smoother the flow, the better.

FatMan
04-29-2002, 09:13 AM
Steve,

I think I'm getting you now. No diss to Doc Nickel, but I don't see that charging a dump chamber is any more of an issue than charging the area behind the ball when the poppet opens, or charging the chamber behind the poppet after a shot. Any time the air is transferred from one place to another friction and heat loss result in some energy loss, but that's going to be true for just about any marker, poppet or dump chamber.

OK on dropping point 2.

The pressure spike is later, but why does that imply a loss of energy - rather than just a timing of when the energy is applied? I think its that totally ungrounded assumption that I take issue with.

I'll give you that a dump chamber might be a little less efficient - though I'm not entirely sold on that. On the whole though, the complete system seems to be very efficient.

I guess what I've always wondered is how much energy is being wasted out the end of the barrel after the ball has left. What I think is GOOD about the dump chamber arrangement is that there is a single burst, and once the ball has left the barrel there isn't more pressure comming down the tube, where as it seems like a poppet valve which is "open to the bottle" more or less, is still pumping pressure in behind the first pulse - pressure which isn't really effecting the ball, only being spent down the barrel.

This is sort of related to the stuff AGD posted over the weekend - though not exactly I admit.

Anyway, I'm glad we've managed to communicate on this - you're right this isn't the most efficient communication, but then if it weren't for this we wouldn't HAVE this conversation and noone else would have heard it (and potentially learned something).

FatMan

steveg
04-29-2002, 09:23 AM
English Canadian joke:
How do you gag a Frenchman?
Tie his hands behind his back.

steveg
04-29-2002, 10:09 AM
Going back to the Tippmann (model 98 valve)

The velocity adjuster is a setscrew placed in the airflow
after the poppet valve.
By turning the screw in and out the velocity lowers or raises

More obstruction=lower velocity
less obstruction=higher velocity

Soooo the question is; Is the lower velocity a product of
the same volume(quantity) of air being slowed down
and therefore imparting less energy or momentum to the ball
or is it a product if an obstruction in the path of the
air allowing less air out of the valve?

FatMan
04-29-2002, 12:53 PM
I think clearly it slows the air going past the valve, thus less air gets past the valve.
Less air past the valve is less energy expended. I don't think the rate of the air itself is much of an issue (within a range). Unless you slow the rate of increase WAY down, that's not what's going to control the velocity. Its the total energy transfered, not the rate of transfer that is critical.

FatMan

bjjb99
04-29-2002, 01:20 PM
I agree, the set screw in the Tippmann restricts the airflow, so less air gets released in the forward direction. Incidentally, some fraction of the air that doesn't make it towards the ball due to the restriction actually goes towards throwing the hammer back for the next shot. This can be seen when pressures start to drop in a Tippmann, screwing in the velocity adjuster can cause the gun to recock when leaving it open would result in the blowback's characteristic low-gas runaway burp.

You see the same effect in some blowbacks when firing with no paint in the barrel. The slight difference in airflow when a ball is not there results in the hammer not being thrown back far enough to catch the sear.

BJJB

FreshmanBob
04-29-2002, 03:53 PM
someone needs to convert a shocker(or any dump valve) into a pump and compare it to a well tuned (*cough*Palmer) sheridan pump. Using co2 and N2 may also produce slightly different results because the dump valve has to completely refill each shot, which might need more expansion energy(im not sure, but its possible). That means less liquid co2 is expanded an you may shoot more liquid than with a poppet valve.

Doc Nickel
04-30-2002, 02:49 PM
Hey guys? Please don't put words into my mouth, okay?

The loss of energy of the compressed gas is minimal, but it does exist. I posted that in the Guild as an example of a factor, not as an explanation for the entire cause.

And yes, the expansion/recompression of the gas does indeed cause a loss of energy. Josh stated it himself in the first post when he mentioned the RT's chamber heating problem- that heat came from somewhere

If you compress a gas, it warms, if you allow it to expand, it cools. The energy that does the work we're doing- firing a paintball- comes from the potential energy created when the gas was compressed. At any time after that, if the gas is allowed to expand and at least partially recompress, as in filling a "dump" type chamber, some of that energy is irrevocably lost.

I'm surely no expert on physics, but that's the root concept of entropy at work.

Poppet type valves see only a small drop in pressure, so there's minimal recompression at work. Dump chambers see a far larger drop, so there's more loss. But again, that's just one factor, not the entire explanation.

As for dump vs. poppet, keep in mind dwell times and the pressure rise times have a lot to do with it as well.

Carry on.

Doc.

FatMan
04-30-2002, 03:28 PM
Hey Doc,

Nice to see you here. I didn't intend to drag you into this, your name was thrown around and I hadn't seen your post - so I wasn't arguing with you. Sorry.

Anyway, I'm also not a physicist, but I do know something about it. From what I do know there's nothing inherent in compressing or expanding a gas that causes energy loss. In a perfect universe with perfect insulators and no friction you should be able to compress, expand, and recompress gas all you want without energy loss - the energy is simply transferred from place to place. Or am I missing something (wouldn't be the first time :rolleyes: )

Of course, we don't live in a perfect universe. When we compress a gas we lose some of the energy in heat loss as the gas cools. When the gas escapes it has to overcome some friction - which can also cause heat that is lost, thus in practice the effect you noted.

I guess what I'm not seeing is why transferring a gas from one chamber to another, and then out the barrel is all that different for a poppet valve versus a dump chamber? In both we will see a cavity that has its pressure reduce and then increase. Granted the rates are a little different, the specific pressures and volumes are a little different, but I still don't see an *inherent* difference.

Anyway, I realize the discussion may be academic, as these losses probably pale in comparison to other factors that affect efficiency, but I'm actually interested in the subject - and since we're discussing it ... well ...

So, if you want to just let this go, that's fine but if you have some insight I'm missing I'd like to hear about it - as long as we're on the subject.

;)

FatMan

BlackVCG
04-30-2002, 05:48 PM
Originally posted by pbjosh
The air comes out a .25" dia hole, which has .196 in2 of area.

The pressure of the air drops to 60-70 psi or so AT the ball. Because of restrictions in the system. Designed in to make a Blow-Forward marker work. If there were no restricions, then the bolt WOULDN'T go forward.


Your math is wrong. The I.D. of the PT tip is .25" so you need the radius squared times pi. Not the diameter squared times pi. A = piR^2 gives us an area of .049in^2.

How does a "restriction" in the system drop the pressure? I'd have to argue it simply relates to the relationship of pressure and volume. You're releasing a fixed volume of air at 375psi in a controlled manner and due to volumetric expansion, the pressure decreases. Also, you say if there were no restrictions, then the bolt wouldn't go forward. I'm assuming you're saying that the power tube is the restriction. I guess if you want to look at it that way, then the bolt certainly wouldn't move because you have to have some way to build up pressure behind the bolt. You have to have that "restriction" there in order to make it practical. The only way you couldn't have that "restriction" there is to make an erroneously large bolt the size of the dump chamber. It's just not practical and pointless.

Furthermore, I don't think anyone has really discussed it yet, but the way you'd lose energy in a system from the dynamic flow is due to turbulent flow. When you have turbulent flow making sharp turns and entering smaller orfices, it forms small eddies at the transition point, which equates to a lose of pressure downstream and therfore a lose of energy. This is more applicable when you're dealing with liquids in a constant flow system, but I'd have to argue that in a pneumatic valve for a paintball gun, which is a non-constant flowing system, there is no energy lose do to turbulent flow created by sharp bends and reductions in orfice sizes throughout the airflow path of the valve. In aerodynamics it's a whole different issue. You're dealing with constant flow, so losses do to turbulent flow are an issue. Which is why they design planes and such to get the Nr below 2000 and thus have laminar flow.


Originally posted by FatMan

Anyway, I'm also not a physicist, but I do know something about it. From what I do know there's nothing inherent in compressing or expanding a gas that causes energy loss. In a perfect universe with perfect insulators and no friction you should be able to compress, expand, and recompress gas all you want without energy loss - the energy is simply transferred from place to place. Or am I missing something (wouldn't be the first time :rolleyes: )


You are correct, this is known as an adiabatic system. In an adiabatic system the Work (W) = 0; Energy transfer by heat (Q) = 0; and so therefore the change in Internal Energy is = 0.

FreshmanBob
05-01-2002, 07:15 AM
When it comes to turbulance, your talking such a small space that the air is moving through i really doubt it could make that large of an impact. If we were dealing with much larger systems, not channels through guns 1/8th of an inch wide i could see your point but i doubt the energy loss is substantial

FatMan
05-01-2002, 10:44 AM
OK, so all of this really has had me thinking a lot about pressure and energy and all that. So here is an interesting questions:

Suppose I have a large steel tank of N2 at 5000 psi with an even temperature throughout the gas and tank. I also have a steel bottle at 0 psi (OK, its actually at sea-level atmospheric pressure, but you know what I mean) and it is also at the same temperature. Now, I connect the two with a hose, and I open the valve long enough to fill the bottle to 2500 psi. The tank is much larger, so its pressure drops, but not so much.

Now, the interesting thing is this: the N2 in the bottle is now at a lower pressure than it was a moment ago. All the same, the gas and the bottle have heated up. The tank should be cooler than it was a moment ago - which makes sense as the gas is at lower pressure. Given time, the excess heat in the bottle dissipates into the room, and some heat from the room warms the tank, with corresponding adjustments in pressure - in the ideal case no energy is lost.

Why did the bottle heat up? yes the air in the bottle is under higher pressure than before, but most of the air in the bottle came from the tank and was at a still higher pressure before. If anything I would expect the heating and cooling to cancel out.

So, I don't know the answer to this question, but I suspect it has something to do with something AGD brought up in another thread - so called dynamic pressure. Could it be that when gas is released, more than just gas molecules is lost? Does some of the engergy in the remaining molecules transfer to the leaving molecules in the form of motion - and dynamic pressure - that converts back to stored energy in the form of heat in the bottle? Thus the resulting cooling of the tank and heating of the bottle?

If this is the case, then one would expect that the faster you fill the bottle, the warmer it would get (and the cooler the tank would get). My experience says this is true, though I don't know this any better than the original question.

Now, if all of this is true, then to answer my own question from a couple posts back - the inherent loss in a dump chamber comes in the fact that by storing the charge momentarily we convert the dynamic energy to heat, which can be lost through dissipation. Of course, that will depend on the recharge speed which would imply it is more of an issue on an RT (which recharges fast) than a standard AIR valve (which recharges slower) and thus represents a trade-off (which can only be evaluated in terms of the whole system).

So - am I out to lunch on this? Is this even close? Gee, I ought to go back and get another PhD in Physics! :D

Until next time,

FatMan

steveg
05-01-2002, 10:50 AM
Ah-ha starting to come around arn't you;)
By the way which of you Guy's are putting words into Doc's mouth;) ;)

AGD
05-01-2002, 11:03 AM
The little bottle heats up for two reasons. First when the air is flowing through the hose to the small tank it is at much lower pressure. The lower pressure automatically means lower temp (below ambient) so during transistion the air picks up heat from the suroundings and when recompressed to the same pressure, has more BTU's per cubic inch = hotter. The second thing that happens is the flowing air has turbulence and friction which also serves to heat the air. THe faster you transfer it the more heat it generates. The RT valve gets most of it's heat from friction in the recharge flow.

AGD

FatMan
05-01-2002, 01:01 PM
Originally posted by steveg
Ah-ha starting to come around arn't you;)
By the way which of you Guy's are putting words into Doc's mouth;) ;)

Well, actually Steve, you were the one who invoked his name way back at the beginning of the thread. I don't know anything about his mouth - I try to stay away from that! ;)

AGD, so I was dead and completely wrong! Cool!

OK, so heat picked up from outside the system during transfer and later lost in the dump chamber doesn't count as lost energy.

The turbulence and friction - where does that energy come from? Is that energy previously stored in the system as pressure that is converted to heat and lost, or is it energy picked up from outside the system that temporarily increases the energy in the system until it is dissipated?

FatMan

FreshmanBob
05-01-2002, 05:04 PM
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.

FatMan
05-02-2002, 08:19 AM
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
05-02-2002, 03:27 PM
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
05-03-2002, 08:42 AM
i have no idea what yall are saying but yeah...i agree 100% Keep up the good work! :D ;)

Vegeta
05-03-2002, 04:32 PM
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
05-07-2002, 02:10 PM
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
05-07-2002, 02:38 PM
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
05-07-2002, 05:37 PM
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
05-07-2002, 08:04 PM
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
05-07-2002, 10:48 PM
"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
05-08-2002, 03:24 PM
Since you two are both saying the same thing, I'm not jumpoing in on either side - OK? :rolleyes:

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
05-08-2002, 04:02 PM
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
05-09-2002, 09:16 PM
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
05-09-2002, 10:35 PM
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
05-10-2002, 12:54 AM
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
05-10-2002, 02:32 AM
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

pbjosh
05-10-2002, 04:49 AM
Redkey-

I am with my wifey this weekend, she had an Ectopic Pregnancy, and ruptured her falopian tube while I was at Vegas. So I have relocated to my house with everything to help her heal from surgery.

Maybe next time, I have some ACE Racers built that just ROCK and I want to show them off!

Josh

Redkey
05-11-2002, 10:59 PM
ugh! Man that sucks.

I hope she gets better soon.

pbjosh
05-14-2002, 12:17 PM
So how was STP, I heard it went very well.

Josh

Redkey
05-15-2002, 10:04 AM
Ended up staying at home and working.

A bit more productive. Not quite as fun.

How is your wife doing?

Vegeta
05-15-2002, 06:28 PM
Originally posted by AGD:
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.

OK we have hit a low point! corn kernels? (whistles.....)

OK so big paths w/ corners = little diffrence.
Small paths w/ corners = diffrence. We also have to think about cycle time along with velocity here folks. The more turns the air has to take from valve to ball may not make a big diffrence when firing slow. Take it this way.

Lets say we haev a seupt where there is two turns hte air has to make from the valve to the ball. Now it takes say 15 seconds for the air to get from point A to the ball, going around the corners. Now if hte gun starts to shoot faster, that air will have to be moving thru there to keep up with the bolt, or else the golt will be hitting the ball, and startign to return before the air has completely exited the bolt, and therefore cuaseing the seal between barrel/botl to break and the left air to leak up the feed tube and bobble your balls. The FASTER the air can get out hte bolt, the better, especially durign high feeding rates.

Am I on track here? I have nothing to expiriment or see this on.. just going out on a limb.

Josh is having a heated discussion here, and I am right now behind his story.
He is a damn good designer, and I have seen his new gun, I belive he calls the 'Shiva' project am I right?
Josh im sure we'd love to see some more details on that thing.. maybe it would help in this discussion?

pbjosh
05-16-2002, 05:11 PM
Vegeta-

The 'Shiva' was mostly a test mule. I haven't been able to kill the blow-back, and have tabled it for a bit. Sorry. But what I did do is prove my hypothosis that a LP dump chamber gun doesn't need to be in-effecient. So I am happy for a while. And that was with a Dye Boomstick boys, not some long barrel. In fact I needed much more energy to shove a ball out of a 14 j&j than a dye boomer. 240 in*lbs per shot on the 14" compared to 175 in*lbs on the Boomer. Eat that one up you doubters.

As for internal speeds in paintball guns, most of the air is gone in 3-8 milliseconds, ask AGD, he knows. In 1-2 ms the air is at the ball and moving it for the most part.

Josh

Vegeta
05-17-2002, 05:11 PM
Hmm.. ok i dont relly know about the times it takes for things to move/flow andall.. I wish I did. 1-2ms wont hurt anything.

echoes
05-17-2002, 11:05 PM
One thing to keep in mind is that a dump chamber may be more susceptible to a change in pressure than a poppet valve would be. For example, if you fire your cocker at a high ROF and pressure to the valve drops, dwell will increase slightly helping to compensate. But I can't think of anything like that on the mag or any dump chamber design.

By the way, to whoever it was that said that they didn't think the novas are fast; they are very fast. I've heard that they can even cycle faster than RTs. I don't have any numbers to back that up, but I've owned two novas and it seems possible.

pbjosh
05-18-2002, 12:25 PM
One thing to think about with dwell compared to pressure in a poppet is that all the parts have to be balanced, so, if you are not feeding the poppet enough air the valve can open a bit longer and cause a more air to release. That is part of the reason you are suppose to tune your 'cocker to the 'sweet spot'. If you tune over the sweet spot, and then out shoot the reg, then you can shoot hot.

As for the Nova, I am fairly sure it wasn't just a dump chamber design. I took a good look at it, and I think It really shoots from a Poppet Valve Emulator (PVE) style. The Piston would go forward as the reg recharged and before all the pressure would leave the Chamber. Part of the reason for the large port in the front I think might have to do with back pressure on the piston, from the ball as it exited, helps hold the piston open.

If somebody wants to send me a Nova ET I can set it up with a Morlock and Warp, and we could see how fast it really will go!

ES13Raven
05-19-2002, 02:15 PM
Originally posted by pbjosh
If you tune over the sweet spot, and then out shoot the reg, then you can shoot hot.Can you further explain that to me?

pbjosh
05-19-2002, 11:04 PM
The 'Sweet Spot'

Oh boy, I will keep this decent and on topic :)

I am not to good at describing these things sometimes. The sweet spot is a point of balance in the valve of a 'cocker or similar gun that the most air flow can run through the gun. It is a balance between the air pressure behind the cup seal and the spring as it acts against the force of the hammer. As you increase pressure into the gun (again, 'Cocker types) you will see the velocity rise, until it gets to a point, then it starts to decrease, and then after a bit more pressure is added, the velocity starts to rise again. The first point that the velocity rises, right at its peak, is the sweet spot. Tuning the gun to a point above that (higher pressure than the sweet spot) allows you to have the velocity increase as you fire at a rate above what your regulator can supply, so you end up with less pressure, making your gun run in the sweet spot, hence shooting higher at times. I hope this answered your question.

Josh

ES13Raven
05-23-2002, 05:30 PM
I understand the sweet spot being the point of highest flow and balance between spring tension and pressure.... acts like a bell curve with velocity.

What I don't understand is if you run a higher pressure than the sweet spot, how you could "fire at a rate above what your regulator can supply"?

Wouldn't a higher pressure recharge the valve chamber quicker using the same reg?

Vegeta
05-23-2002, 08:53 PM
"The Sweet Spot" - Great explanation.

There are just so many variables here.. whoo!
And just think if people were to be able to tune the spring inside the valve (blowback-type) with a screw on the outside of hte gun just like you would to turn up velocity. More spring bound = diffrent sweet spot.it would peak before the bolthits the all the way mark. Also would result in shorter dwell? Hmmm this takes some thinking. less bound/more rebound of hte spring equals longer dwell time? possible bottom out? more volume? And what if this was implemented on a cocker type valve?

pbjosh
05-24-2002, 12:57 PM
ES13Raven-

Quite a few regs just are not that good. Look at AGD's testing of the Govnair, 20 seconds to fully recharge. I had similar issues with a Stab at 180 psi. It took a while to recharge. You could take a Govnair, run it at 300 psi, but have the valve tuned for sweet spotting at 260. Then at high rates of fire, you wouldn't supplying the gun with a full 300 psi. Funny how that works, eh?

Vegeta-

There used to be that adjustment on the Spyder. You could adjust your front screw in or out to adjust valve spring pressure, and the original ones also had a screw on the body where the valve dumped into the bolt to act as a choke to adjust velocity.

Also several other guns had that also, including an adjustment for the F1's (aftermarket) and a couple others. The Original 'Blade' (heavy F1 clone) also came with one. We had one of those. We played around with the front screw alot to figure out how the balance of it all was. Kinda of a cool design in some ways.

I have a CADed cocker body with an adjuster in the front for the valve. It would be involved, but could be done.

Josh

Vegeta
05-31-2002, 12:54 PM
I dont know about this WDP reg, but Tom and a guy did soem 'informal' reg testing one time, and posted the results here in deep blue. They tested an RT against an Angel reg i belive. All I can remeber abot it was that the angel's reg (Angel AIR it was?) recharged much slower than the RT.