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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"
Retained air in a pumper rifle
Nvreloader:
Last 4 tests, before M test,
Test L1 L2 L3 L4
1= 272 - 252-232-295
2= 351 - 377-354-433
3= 436 - 426-429-439
4= 482 - 465-459-457
5= 511 - 495-482-495
6= 541 - 531-501-511
7= 577 - 567-565-544
8= 593 - 583-705-611
9= 639 - 597-761-757
10= 662- 613-823-800
11= 688- 626-836-849
12= 754- 643-866*-853
13= ------651-900*-870*
14= ------661-------915*
15= ------672-------948*
* = air retained in valve after shot, 1st time ever
(L1 test)
Used a valve with Peek air inlet seal and Peek poppet, .145" air inlet hole,
this air check seal had a .135" Dia x .370" long nose that fit into the inlet hole,
this nose was flush at the face of the valve. TP hole =.145", .156" bbl hole.
OEM valve spring and Valve stem length .180" from rear of valve,
Same test format as above tests, Alum Hammer, Flat wire hammer spring,
airways opened up to .145" Dia. 14gr Crosman ammo.
No air left after any shot.
(L2 test)
Used a valve with Peek air inlet seal and Peek poppet, .156" air inlet hole,
this air check seal had a .145" Dia x .370" long nose that fit into the inlet hole,
this nose was flush at the face of the valve. TP hole =.156", .156" bbl hole.
OEM valve spring and Valve stem length .180" from rear of valve,
Same test format as above tests, Alum Hammer, Flat wire hammer spring,
airways opened up to .156" Dia. 14gr Crosman ammo.
No air left after any shot.
(L3 test)
Used a valve with Peek air inlet seal and Peek poppet, .145" air inlet hole,
this air check seal had a .135" Dia x .370" long nose that fit into the inlet hole,
this nose was flush at the face of the valve. TP hole =.145", .156" bbl hole.
OEM valve spring and Valve stem length .375" from rear of valve,
Same test format as above tests, Alum Hammer, Flat wire hammer spring,
airways opened up to .145" Dia. 14gr Crosman ammo.
*Air left after shot.
(L4 test)
Used a valve with Peek air inlet seal and Peek poppet, .156" air inlet hole,
this air check seal had a .145" Dia x .370" long nose that fit into the inlet hole,
this nose was flush at the face of the valve. TP hole =.156", .156" bbl hole.
OEM valve spring and Valve stem length .375" from rear of valve,
Same test format as above tests, Alum Hammer, Flat wire hammer spring,
airways opened up to .156" Dia. 14gr Crosman ammo.
*Air left after shot.
Bob,
Here is the last 4 tests, before the "M" test, with the notes for each test listed.
I have changed nothing, the pump rod and head "O" ring were oiled
at the start of the L1 test.
Because of the Peek seal/poppet, I did pump to 10 pumps and left it over night,
then fired that shot and checked for retained air, there was none.
I then started the "M" test, as I wanted the info on the retained air shots to explore.
The L1-2 tests were with the OEM .180" length valve stem,
.145" air passage ways then .156" air passage ways,
the L3-4 tests were with the .375" length valve stem,
.145" air passage ways then .156" air passage ways,
Bbl hole is .156"
Using a Flat wire spring, 2.500" long, weight = 8-9#'s, .415" O/S Dia, .265" I/S Dia,
.022" thick Flat wire, 25 coils, Alum Hammer weight at 533grains. 14 gr Crosman ammo.
The spring was set several times before use, and is the same spring used thru all the tests.
https://www.gatewaytoairguns.org/GTA/index.php?topic=195725.500, all tests are listed here.
James,
Yes, I have gone to 20 pumps, but stop when there is no gain in the fps, for any test,
any test with -------- indicates there was no fps higher.
Sam,
same pellet weight used all thru the 20+ tests.
Thanks all,
Your thoughts or suggestions.......
Don
Blowpipe Sam:
Just musing here but it seems that (theoretically) with the right combination of hammer/spring, TP diameter, poppet, and pellet you could tune a modern pumper to be a two shot repeater. Finding the sweet spot where the two shots will fall within 20% (or better!) of each other as regards velocity seems to be the biggest challenge.
I know Airguns of Arizona was marketing an air conserving pumper based on a Benji 392/397. I have no idea what the efficiency or the consistency was like and they don't seem to be offering it anymore. Probably an indication that it didn't work that well.
Good luck! As a pumper enthusiast I'm hoping you succeed.
Nvreloader:
--- Quote from: rsterne on May 30, 2023, 10:16:26 PM ---Retained air can be increased by reducing the hammer strike, or deceased/eliminated by increasing the hammer strike.... If you are experiencing it now and not previously, did you increase the hammer strike to the point of setting the spring?.... When I am setting up a retained air pumper, I try and get 2 shots of the same velocity, or very close, so you have 1 and a follow up.... Bob
--- End quote ---
Bob
Per the above information on increasing retained air, I have only 3 ways to allow this,
1. Reduce the Hammer weight,
2. Reduce the hammer spring weight,
3. Or a combo of both?
Or change the valve stem length as per the testing results I have done?
I DON'T like the hammer smacking the rear of the valve, with the .180" OEM stem length.
The best tests have been with the .375" length of valve stem,
with NO hammer strikes.
Am I correct in this line of thinking? I am in uncharted waters here,
as I have no experience, yet of doing this.
I have done these calculations, for the top 3 reading of 13-15 pumps, M test,
the average of the top 3 fps = 886fps av,
the av of the 3- 2nd shots = 639fps av,
886 - (minus) 639 = 247fps difference,
1/2 of 247 = 123fps,
886 - (minus) 123 = 763 fps
639 + 123 = 762 fps,
I know, I can't get this close of (762/3)fps readings, but if I am between 750 to 775fps,
this should be close enough to average around 763fps,
for any of the top end readings that retain air?
Am I correct in this line of thinking??
Sam
I am in uncharted waters for me, but I'll attempt to do the best possible,
providing I can figure out the best way to do it.
As I do want the second shot backup when needed, for this pumper.
Then I see what the best pellet is for this demented Dragon Fly II 22 cal is, I hope. ::)
Thanks Guys,
Your thoughts and suggestions are greatly appreciated,
Don
splitbeing:
Following
rsterne:
I very much doubt that you are using even 0.180" of poppet travel, more like 0.05-0.10" for most valves that are operating efficiently.... Dump valves, of course, may travel further, and I do agree with you that having the hammer hit the back of the valve is not great.... It gets unpredictable, as the hammer bouncing off the back of the valve can reduce the dwell, even though you were striking it harder....
Hammer energy (valve lift) can be increased by increasing the (average) spring force and/or the travel (compression) distance.... The momentum (valve dwell) can be changed relative to the energy by changing the hammer mass, which changes the ratio of lift to dwell....
Bob
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