Valve 2100 vs 13xx

[K.O.]

Ok so we answered your original question,

"I wonder why the 2100 would have the smallest valve volume and yet perform much better than a 13xx?"

Now the thing is if you have the high pressure and the larger valve and enough barrel    !


I have to say all this is greatly simplified to the point of not being accurate to actual results but does show the concepts and gives a pretty decent

approximation of what is going on.

I was told that in this next part Sectional density is what I should use but I have never seen it used in internal ballistics, only external and terminal.

I should also state that my brief survey of ballistics was long ago...

so this next part is my method and I winged it   you will need to substitute 14.3g and convert to what you prefer I chose grams because I can

visualize  grams being pushed by foot pounds easier than  .00sumthin pounds being pushed.


so you take the numbers from developing the index and they are one leg of the graph and the barrel length is the other

and you will have an approximation of the acceleration curve of the pellet.


you can stop at knowing there is this much force on this much weight at a given length into the barrel...

the index thing is just a way to compare different calibers and weights of pellets...


All this is vastly simplified  but does help build an understanding of what is going on...

and the surface   area acted on is just found by  the area of a circle/caliber

http://www.gatewaytoairguns.org/GTA/index.php?topic=59377.20

[K.O.]

"HOW CAN THE VALVE VOLUME POSSIBLY BE RE-ADDED FOR EVERY CONSECUTIVE PUMP CYCLE (AS PART OF YOUR "TOTAL VOLUME")? PLEASE EXPLAIN"


Hi Davio  if you look it is not...

It is just used to get the pumps  starting to ending ratio.

and then that is used as the multiplier of atmospheric pressure...

[Davio]

I see that, but the valve itself is isolated (mechanically by the spring pressure on the check valve) from the amount of air being pushed into it. I consider the valve the receiving vessel only and again isolated from pump stroke calculations. What do I know? 

And Pi R not square!  They are round. 

[K.O.]

K.O.
I got it now. Thanks,

You know what, kids that are good in

maths and algebra              become accountants
maths, algebra and physics become engineers
physics, chem and bio         become doctors
BS                                     become lawyers
Bullying                              become cops

I fell short of physics


LONG a** story  but  just a misfit who's kids survived him and are crazy enough to still love him...

Did do a internship  cobol/cics using vsam and os-jcl  at Tacoma public uttil.
Most of my math was self taught and am just falling behind my math major daughter  on (Ring theory)

Honestly this is the easy stuff and I can still get things wrong  I have some brain probs(concentration) now  (to many concussions?)

[K.O.]

I see that, but the valve itself is isolated (mechanically by the spring pressure on the check valve) from the amount of air being pushed into it. I consider the valve the receiving vessel only and again isolated from pump stroke calculations. What do I know? 

And Pi R not square!  They are round. 

You cannot look at it that way  were does the air go...

It adds that much air (at a certain efficiency which probably falls as pressure rises) every stroke but the ratio stays the same and the check valve just keeps it contained in the valve.

this is just a basic model and leaves out a lot butcan show ballpark figures.

[Ryan]

so by Boyle law means  we can take atmospheric pressure of say  14.3 psi x 7.53 and learn we get about 107.67 psi per stroke

K.O.

I always go back to refresh myself after leaning something new, just to make sure I flow through with the logics. I now understand the principles behind the Boyle's law, but where does the 14.3 psi come from? Is this the weight of a .22 pellet? Thanks,

[K.O.]

K.O.

I always go back to refresh myself after leaning something new, just to make sure I flow through with the logics. I now understand the principles behind the Boyle's law, but where does the 14.3 psi come from? Is this the weight of a .22 pellet? Thanks,

Ryan I just pulled that figure out of the air(pun intended)...

but it is a very likely number...

http://en.wikipedia.org/wiki/Atmospheric_pressure

[Ryan]

ok, now I can put the various attributes together. The 14.3 is the link between the volume and atmospheric pressure. It is close enough to 14.696 psi per unit of atmospheric pressure. Thanks,

[K.O.]

that pressure varies from day to day with the weather and at differing altitudes


http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

[Ryan]

Now that I know the inter-relationship between the valve and swipe volumes, I have to figure out a way to get the best of both worlds.

My ideal is to lengthen the stroke length with an adjustable piston, a hybrid valve which is a cross between a 2100 and a 13xx's and to make use of a 13xx trigger frame.

I don't think the 2100 tube would let me do it. I may have to find a new tube with the same id and to machine the slots and holes into the new tube. I will shorten the pump arm slot in order to lengthen the pump stroke with an adjustable flattop piston. In order to make use of the 13xx trigger frame, I will also need a new flattop valve head with a sold internal so that the valve cavity will remain slightly larger than that of a 2100 valve. I may have to machine a check valve with a long pin attached to it as Wyo has just suggested to reduce the head space loss.

Just dreaming for now. I will get there once I have a little peace of mind and time... may be after April.

[Ryan]

Given the weight of a pellet, is it possible to translate a barrel psi into FPE?

I realize the fpe could be determined by putting the gun through a chrony. It would be nice if it could be established by blending the barrel psi with the weight just so that the desired fpe could be pre-determined.
Am I asking for too much?

[K.O.]

You can form an educated guess but it takes building a data base for that gun all this is just to get a theoretical  psi each pump is going to be slightly to very different in how efficient it is especially once it starts building high pressure .

Quoting Big Bore Bart from a GTA thread

" The math is standard compression ratio stuff, and it works better in metric. :   (Pump area x stroke + valve volume)/(valve volume - headspace) =CR.    CR x 14.7 = pressure rise in the valve per stroke.  P/R x # strokes = theoretical valve pressure.  Theoretical pressure x pump efficiency = valve pressure.    I personally use ~65% as a pump efficiency fudge factor.    Calculating the actual pump efficiency is not doable with out a gauge in the system. "

I like Decimal more than metric just the way my mind works. (besides the point)


but

Pre charged pneumatics have a pressure gage and you can build a good understanding but it has to be for each gun. and then with pellets well there are variations of up to .3 grains or so in weight also variations in head size.

I am giving a slightly educated guess about my projects estimated fps/fpe  but it was not the math that guided my choices as much a my experiences and then the math helped bolster my opinion.

But so much rides on pump efficiency that in the end that will decide what I get.

[Ryan]

Let me take my time to digest this. Thanks anyway.

What I was thinking is if I wanted a 9 fpe with a given pellet weight and if there was a relationship between fpe and the barrel psi, I could then reverse engineer the 9 fpe into the optimum valve and stroke volume ratio, etc. Wouldn't that be nice?

Re" Quoting Big Bore Bart from a GTA thread

" The math is standard compression ratio stuff, and it works better in metric. :   (Pump area x stroke + valve volume)/(valve volume - headspace) =CR."

What is CR? 

[K.O.]

Re" Quoting Big Bore Bart from a GTA thread

" The math is standard compression ratio stuff, and it works better in metric. :   (Pump area x stroke + valve volume)/(valve volume - headspace) =CR."

What is CR?

  1.13 / .15 = 7.53...  ending volume is this much smaller than beginning volume. (7.53 is the CR, compression ratio)

What I was thinking is if I wanted a 9 fpe with a given pellet weight and if there was a relationship between fpe and the barrel psi, I could then reverse engineer the 9 fpe into the optimum valve and stroke volume ratio, etc. Wouldn't that be nice?

The easy way is to read how others have achieved  their level of performance  and understand the whole system.

I get about 10 fpe out of my 1322 @17 pumps with 14.3g pellets, it is a balance of valve volume, # of pumps, hammer and valve spring balance to dump it, port size, pellet caliber/weight and barrel length.

It is the system as a whole and how you want to get there...

I can not resist here are a couple port size threads to fry our brains just a touch more...

http://www.network54.com/Forum/275684/message/1386883683/Noodling+about+transfer+ports+and+supersonic+flow.

http://www.airgunhome.com/agforum/viewtopic.php?p=78260

[Ryan]

KO, Thanks for all the heads up. I think I have a pretty good grasp of the msp logistics by now. Work is getting pretty thick in the office. I will have to wait till early spring to do some real modding.