Low pressure dump chambers and efficiency

[pbjosh]

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]

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]

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]

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]

Think I'm getting it.

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]

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/showthrea...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]

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]

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]

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]

OK.

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!

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]

Thermo-nuclear RT valves

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]

I would love to comment on this.

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]

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]

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]

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.