Mk 177 mods ? 800+ fps with 7.9g SUCCESS 831 fps @ 16 pumps now 1024 fps @ 20

[K.O.]

Thanks for your time Bob

from your work the other day we have a rough estimate of the flat top pumps efficiency at 1500-1800 psi  @ ~85%~82% respectively and then about 2000-2300 falls to 74%

so a rough estimate (edited to show estimated lower atmospheric pressure along with 14.3 for atmospheric pressure)


942 fps at ~ 1700 psi with a .177 ci valve ( 20 pumps)  ( ~ 1606 psi at 13.2 starting psi)

and

991 fps at about ~2200 psi  same  valve ( 30 pumps)   ( ~2100 psi at 13.2 starting psi)


the mk with the .242 valve and a pump cup it should have been at about 1550 psi at 20 pumps and 80 % efficiency  which is in line with your test... (might have done better because of being warmed?)

so then there is how they dump

I do not  have the concentration to get an idea of the initial charge velocity of the two valves which is very import ant.(could not resist...

I also do not know the porting on yours...  I built mine on the theory that the .23 throat basically was effective in supplying air well enough to overcome the passages 90* turn turbulence  so was almost like directly feeding the .140 transfer port from the valve and that the valves volume helped sustain the velocity of the initial pulse

so in my mind I weigh that against  Higher velocity initially how effected by the turns turbulence (can be thought of as a restriction in my mind)
does it keep up still or make it act like .130 feeding .140?? still the pressure is higher so...

then I look at  how they fill the barrel

next post... in case excel is messy again

[K.O.]

.242 valve  1600 psi (ignoring tport and valve throat)

Barrel Length      0.177      
      Barrel Vol      Barrel PSI
1      0.02459      1452
2      0.04919      1330
3      0.07378      1226
4      0.09837      1138
5      0.12297      1061
6      0.14756      994
7      0.17215      935
8      0.19675      883
9      0.22134      836
10      0.24593      794
11      0.27053      755
12      0.29512      721
13      0.31971      689
14      0.34431      660
15      0.36890      634
16      0.39349      609
17      0.41809      587
18      0.44268      566
19      0.46727      546
20      0.49187      528
21      0.51646      511
22      0.54105      494
23      0.56565      479
24      0.59024      465

[K.O.]

.177 valve 1700 psi (20 pumps) once again (ignoring tport and valve throat)


Barrel Length      0.177      
      Barrel Vol      Barrel PSI
1      0.02459      1493
2      0.04919      1330
3      0.07378      1200
4      0.09837      1093
5      0.12297      1003
6      0.14756      927.
7      0.17215      862
8      0.19675      805
9      0.22134      755
10      0.24593      711
11      0.27053      672
12      0.29512      637
13      0.31971      606
14      0.34431      577
15      0.36890      551
16      0.39349      527
17      0.41809      506
18      0.44268      486
19      0.46727      467
20      0.49187      450
21      0.51646      434
22      0.54105      419
23      0.56565      405
24      0.59024      392

and 30 pumps  2200 psi

Barrel Length      0.177      
      Barrel Vol      Barrel PSI
1      0.02459      1931
2      0.04919      1722
3      0.07378      1553
4      0.09837      1414
5      0.12297      1298
6      0.14756      1200
7      0.17215      1115
8      0.19675      1042
9      0.22134      978
10      0.24593      921
11      0.27053      870
12      0.29512      825
13      0.31971      784
14      0.34431      747
15      0.36890      713
16      0.39349      683
17      0.41809      654
18      0.44268      628
19      0.46727      604
20      0.49187      582
21      0.51646      562
22      0.54105      542
23      0.56565      524
24      0.59024      508

[K.O.]

So guys( and Sensei Bob)  thanks for putting up with all the long winded stuff.

I did this valve on a theory about how the valves handle the turbulence of the 90* turn...

and all that I typed I feel shows that it is very important...

and I still have no real conclusion... just a tantalizing maybe...

[rsterne]

Your table of pressures for each inch of barrel travel is somewhat like how Lloyd's spreadsheet works, except his works by time in 0.00001 second increments.... You might be interested in knowing that the muzzle pressure from Lloyd's is exactly the same as yours (0.242CI valve, 1600 psi), 465 psi, so I would consider your method confirmed.... You need to add a correction factor for the volume between the valve seat and the pellet, and add that into the barrel volume at zero inches of travel to calculate the pressure before the pellet starts to move.... If that volume is 0.015 CI, the pressure before the pellet moves is 1506 psi instead of 1600, and the pressure at the muzzle drops to 457 psi.... At the 12" point it drops from 721 to 704 psi.... Since the initial pressure is much more important in producing acceleration in the pellet, you will be able to see how increasing that volume affects the performance.... Adding just that 1 column/row to your spreadsheet will increase the accuracy.... Measuring the volume isn't so easy, but possible....

Congratulations, you have just added to your own knowledge of what happens inside the barrel after you pull the trigger.... Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well.... 

Bob

[K.O.]

I just realized a mistake I made  I am at an altitude where there is about 14.3 apsi and I did the figures For Bobs extended valve Uber at 14.3 psi... now those test where in Canada  and though  Bob said 13.2 psi for his alt it could have been a period of high Barometric pressure.
So was the test in winter or summer...

atmospheric pressure varies a lot and  it was and is a little higher for now here during my testing(cold dense air) normal barometric pressure is about 29-29.5 in-hg

it has been around 30.9  so I have had a higher starting psi at about   15.1 psi not 14.3 

So maybe we need to look at barometric psi on the days of testing not altitude... So oops  I should back and edit my previous post  to reflect 13.7(?) and 15.1 for starting psi...

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

[K.O.]

Your table of pressures for each inch of barrel travel is somewhat like how Lloyd's spreadsheet works, except his works by time in 0.00001 second increments.... You might be interested in knowing that the muzzle pressure from Lloyd's is exactly the same as yours (0.242CI valve, 1600 psi), 465 psi, so I would consider your method confirmed.... You need to add a correction factor for the volume between the valve seat and the pellet, and add that into the barrel volume at zero inches of travel to calculate the pressure before the pellet starts to move.... If that volume is 0.015 CI, the pressure before the pellet moves is 1506 psi instead of 1600, and the pressure at the muzzle drops to 457 psi.... At the 12" point it drops from 721 to 704 psi.... Since the initial pressure is much more important in producing acceleration in the pellet, you will be able to see how increasing that volume affects the performance.... Adding just that 1 column/row to your spreadsheet will increase the accuracy.... Measuring the volume isn't so easy, but possible....

Congratulations, you have just added to your own knowledge of what happens inside the barrel after you pull the trigger.... Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well.... 

Bob

I actually made the spreadsheet back when I started my 1325 project to see just how much air hungrier the .22 and .25 barrels are compared to a .177 barrel.

I did the measurements for the air passage and agree that they should be a part of the spreadsheet. part of the reason I chose to open the area behind the exhaust poppet was it only cost about 4 psi over stock at 1500 psi...

"
Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well.... 
"

Done


 

[K.O.]

.177 ci valve at 2100 psi (30 pumps @ 13.2 psi starting psi)

Barrel Length      0.177      
      Barrel Vol      Barrel PSI
1      0.02459      1844
2      0.04919      1643
3      0.07378      1482
4      0.09837      1350
5      0.12297      1239
6      0.14756      1145
7      0.17215      1065
8      0.19675      995
9      0.22134      933
10      0.24593      879
11      0.27053      831
12      0.29512      787
13      0.31971      748
14      0.34431      713
15      0.36890      681
16      0.39349      652
17      0.41809      625
18      0.44268      600
19      0.46727      577
20      0.49187      556
21      0.51646      536
22      0.54105      518
23      0.56565      501
24      0.59024      484

[rsterne]

I was searching around in my old data and came up with some volumes for the area from the valve seat to the base of the pellet.... These are for stock valve and transfer ports.... They are calculated from measurements and allow for the volume displaced by the valve stem and pellet probe in the barrel.... and assume the pellet is loaded just ahead of the barrel port (using an average pellet base hollow)....

1377 - 0.018 CI
1322/2289 - 0.021 CI
Disco .177 - 0.018 CI
Disco .22 - 0.021 CI

You would think that the larger diameter valve in the 22XX / Disco would have larger volumes because the exhaust ports are longer, but in fact the 5/32" stem eats up more of the 0.219" throat than the 1/8" stem does of the 0.203" throat on the 13XX valve.... which evens up for the longer exhaust port.... I also have figures for Disco valves that are opened up for more power....

Disco .22 with 0.234" throat and 0.125" stem and 0.166" exhaust, transfer, and barrel ports - 0.028 CI
Disco .25 with 0.250" throat and 0.109" stem and 0.188" exhaust, transfer, and barrel ports - 0.036 CI

If you add a line in your spreadsheet entitled "0" for the pressure at the instant the valve opens and before the pellet moves, and use those volumes, you will correct for them....

Bob

[K.O.]

Hey Bob the stock 13xx/760/2100 valves I have  are .2 throat so are the Mk. valve... 

I measured with the shank portion of a 13/64 drill bit it just fits...

?

I think I did only measure 1377 And 2100 valves though...

[K.O.]

I have to go shopping but will be back in a couple hrs.

[rsterne]

Yes, the 13XX throat is 0.203", I transposed the numbers and have corrected it above (I had typed 0.230").... 0.203" was used in the calculations....

Bob

[K.O.]

hey guys I am an Idiot... ( notice the capital I)

it is not a fluke and it should be repeatable just not practical...

what happens when you stuff 75* F air at 1500-1600 psi in a .242 ci valve that has been warmed to 95*-100*F you get a psi boost... 

that is why it only lasted 3 shots... the valve cooled while I was trying to figure it out  I was so focused on the pump cup that I just shut off my brain...

[rsterne]

Glad you figured it out.... but if you do the math you will find out the pressure rise shouldn't have been enough to make much difference, unless the temperature difference was quite a bit higher than you thought.... The pressure rise is proportional to the ABSOLUTE temperature.... eg. 75*F is (75+460) = 535*R and 95*F is (95+460) = 555*R.... The pressure rise should only have been (555/535) = 3.7%, or about 60 psi....

Bob

[K.O.]

well you are right it was a bigger difference I was just making an estimate air temp could have been as low as 65*F and as high as 75*F  it was probably  65-70...
and before I finish this post I will have measured the oil filled heaters temp with my cooking thermometer

I did not bother with the ideal gas law because I was pretty sure it was what happened...

so it sat on the oil filled heater(on low heat) for about 5-6 min and the pump tube did make good contact...  and it looks like the pressure rise could have been about 10%...

[K.O.]

Man I hope the manufacturers are not looking all they need is another way of inflating fps...

But I am still happy because my figures are with a 16.75" barrel with some leakage and still 898 fps (cold) in 22 pumps and I plan on a 19"-22" .22 barrel. 850+ fps?

A 24" .177 barrel well about 960-970 fps?(cold)

[K.O.]

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[Matt15]

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