Low pressure dump chambers and efficiency

[ShinyGuy]

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]

The reason is because you need a longer barrel without holes. Again thats not an easy thing to convince people they need.

AGD

[pbjosh]

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]

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]

(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]

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]

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]

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]

Steve,

You had better rethink the popet valve thing.

AGD

[steveg]

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]

[steveg]

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]

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]

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]

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