Simplified Balanced Valve

[mann]

It says balance chamber od is .315  I don't see the dimension of the balance part of the poppet

[PikeP]

It says balance chamber od is .315  I don't see the dimension of the balance part of the poppet

The balance part is the entire ID of the chamber as you have to keep it sealed with oring on the poppet so the force is applied to that whole area.

[mann]

Yeah I figured it had to be close to .315 to get the seal

[rsterne]

Mark, I drilled the balance chamber in the poppet just under 5/16" and then finished it with a 5/16" end mill and then polished the bore with 220 and then 400 grit paper.... The finished ID was 0.315", which is 72% of the OD of the large end of the poppet.... I used a 5 x 8 mm O-ring (1.5 mm CS = 0.059")…. I turned the groove in the poppet 0.100" smaller than the 0.315" bore, so 0.215".... This gave a crush on the O-ring of 15%, and I used a 70D Buna-N O-ring, lubricated with Dow 55.... The small end of the poppet was turned to be a sliding fit inside the 0.315" bore, so about 0.312".... When you are calculating the area so you can get the correct force, you use the ID of the bore, which is the OD of the installed O-ring....

Mike, I noticed a couple of small errors.... The Hammer Gap is only 0.10", not 0.42".... The spring is preloaded 0.31" on the SSG, and then there is a gap of 0.10" (at 2 turns) between the end of the stopped guide and the inside of the hammer.... When the hammer first touches the SSG guide on cocking, it is 0.10" from the valve stem, and the spring at that point has a preload of 3.4 lbs.... In addition, the valve spring when the poppet is on the seat is compressed 0.35" and the load is 5 lbs.... In addition, I would estimate the Wasted Transfer Port volume at about 2 cc, including the chamber in the barrel....

Bob

[rsterne]

Travis, the small end is 5/16", big end 7/16".... nominal diameters....

bob

[PikeP]

Bob, iirc you had more gap earlier and less hammer pl, but I could be mistaken. I'll correct all those figures. What's your estimated valve dwell and lift with those figures based on Lloyd's info so I can try to match that data as closely as possible as I haven't formulated that part of the model particularly well. Itll certainly help keep all the other data more accurate.

[MJP]

Nice work Bob, achieving what you wanted in a valve.
The port can be too big for a given hammer, closes off too quick if you have bigger balancer piston.
All you get is a small pop and that's it.

Marko

[rsterne]

Mike, you are correct, I was running more gap earlier, because the valve was blowing open.... Now that it is better controlled, more hammer strike is required, and when you vary it, you get a velocity change (as it should be) instead of just a change in air use.... I tune regulated PCPs about 3-5% below the plateau (maximum) velocity to get decent efficiency.... 2 turns of gap is about 97% of maximum, and that is the 0.10" gap (the adjuster is 20 TPI)…. In order to get a bell-curve in an unregulated PCP, you need to be about 10% below the plateau, and somewhere between 7-9% will often give you a couple of equal shots.... 5 turns of gap is about 91% of maximum, and produced a decent bell-curve with the 131 gr. bullet.... Heavier bullets need a bit more hammer strike, of course, as you can see I can't quite max. out the 154 gr. with the 11 lb. hammer spring, even with zero gap on the SSG....

I set up Lloyd's spreadsheet for the new, higher efficiency with the 154 gr. bullet, and it says the dwell is likely about 2.2 mSec. with the valve closing when the bullet is about 9" from the breech.... Here is the output from his spreadsheet at these settings....



That is for the first shot in the string, of course, at 3000 psi.... SSG at 2 turns of gap.... 858 fps (252 FPE).... 1.46 FPE/CI (380 psi drop, 173 std. CI of air used)…. 13.7 cc of air at 3000 psi.... The lift would only be slightly less than before, but your current 0.085" is probably in the ballpark....

Bob

[rsterne]

Just to give everyone an idea of what I started with.... my .357 Hayabusa Mk.II had slightly smaller ports (0.281") and a bit smaller throat at 0.328" (1/8" stem) and a 3/8" poppet.... With the same 154 gr. bullet, the gun maxed out at 866 fps (257 FPE), at 0.74 FPE/CI.... basically using twice the air it does now per shot for the same velocity.... When tuned for a 6 shot bell-curve it averaged 824 fps at 1.13 FPE/CI.... It was using a 145 g. hammer with 1.45" of stroke, that took 23 lbs. to cock....

With the new balanced valve, it maxes out at about 890 fps (271 FPE) because of the larger ports.... With the new balanced valve I am now using a 77 gr. hammer and an SSG with a much lighter spring and just under 1" of stroke, and the cocking force is down to 13 lbs.... It can be tuned to the same velocity that it maxed out at before, using about half the air.... so the efficiency has roughly doubled.... and so far I have only been testing with my "tiny tank" and a total reservoir volume of 108 cc instead of 460 cc.... 

I fully expect the maximum velocity and energy to increase when I fit the 22 CI bottle.... because the pressure drop during the shot will be a lot less.... I hate making predictions, but 300 FPE on 3000 psi is not out of the question, according to Lloyd's spreadsheet.... 

Bob

[Brian W Cook]

 I dug out my oldest poppet i made with the piston on the end . At the time i wasn’t worried about how fast the high pressure air would get back to the “chamber”.
Hence the minimal exposure of the hole . 
Doing one now i would football shape the piston around the Oring to minimize any drag and probably use a square bottom Oring grove to allow a bit of movement.   

[rsterne]

Thanks for sharing that, Brian....

Mike, I have a question for you.... I have a smaller OD spring here that will fit in a 13/64" hole (0.203") instead of 1/4".... It weighs 0.71 g. (so almost the same)…. I would have to turn the spring seat down to 0.130" from 0.160" OD to fit inside it.... I am pretty sure I can use it with no other changes required.... That would make the spring cavity only 2/3rds the volume it is now.... Based on my previous calculations, I think that brings the total chamber volume down to 0.453 cc, less the 0.109 cc from the poppet lift, which would mean the chamber at 100% fill would only be 0.344 cc instead of 0.444 cc.... I think that brings the fill time down to 1.05 ms.… Could you check these figures and comment please?.... I think it may be worthwhile to stuff the front spring hole and try the smaller OD spring....

Bob

[PikeP]

Here is the current and modified spring chamber approximations as requested. I think I can scale required hammer spring energy to the fill times as now it's just final closing force and opening force. I think I'll need to determine the ideal timing first for our bell curve based on required dwell for  a particular arrangement.

[oldpro]

Here is the current and modified spring chamber approximations as requested. I think I can scale required hammer spring energy to the fill times as now it's just final closing force and opening force. I think I'll need to determine the ideal timing first for our bell curve based on required dwell for  a particular arrangement.

I wish I had this a few years ago!!! Awesome mike just awesome.

[rsterne]

Thanks, Mike.... I agree with Travis, awesome job.... How do you determine the "optimum fill times" at the various percentages

If I could suggest that you change the vertical scale on the right hand side to -200 to +100.... then the numbers would be on the lines, instead of drifting away from them....

Bob

[oldpro]

 Bob any noticeable stiction yet? Also do you think it will be stable with a loaded hammer?

[rsterne]

No stiction that I have noticed.... I fired the gun set up for 3000 psi down to less than 1000 psi with NO hammer bounce.... Also, a couple days ago, per your request, I preloaded the SSG against the hammer 2 turns, which was 5.6 lbs. of preload, and all it did was get louder.... Reply #184, with the smaller vent in place.... The only thing I haven't tried is preloaded and way less pressure, but I am confident preloading will not be an issue.... However, with the efficiency I am getting with this valve with an SSG, I may never find out.... 

Bob

[oldpro]

No stiction that I have noticed.... I fired the gun set up for 3000 psi down to less than 1000 psi with NO hammer bounce.... Also, a couple days ago, per your request, I preloaded the SSG against the hammer 2 turns, which was 5.6 lbs. of preload, and all it did was get louder.... Reply #184, with the smaller vent in place.... The only thing I haven't tried is preloaded and way less pressure, but I am confident preloading will not be an issue.... However, with the efficiency I am getting with this valve with an SSG, I may never find out.... 

Bob

I can test it tomorrow I did put the old valve back together and ran a string to verify my original string. I will add additional vent hole and see what happens tomorrow time permitting as were really busy getting ready for shot show. I didnt have any 34s like in original strings but same effect is noted.

Created: 01/10/19  1:06 PM
Description: test balanced valve
Notes 1: 25.4 Jsb
Notes 2:
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 25.40
Temp: 59 °F
BP: 29.79 inHg
Altitude: 0.00
#          FPS   FT-LBS       PF
10    1001     56.52    25.43   
9     795      35.65    20.19   
8     634      22.67    16.10   
7     609      20.92    15.47   
6     485      13.27    12.32   
5     517      15.08    13.13   
4     446      11.22    11.33   
3     402      9.12     10.21   
2     434      10.62    11.02   
1     384      8.32     9.75   
Average: 570.7 FPS
SD: 196.8 FPS
Min: 384 FPS
Max: 1001 FPS
Spread: 617 FPS
Shot/sec: 0.1
True MV: 571 FPS
Group Size (in): 0.00

[mann]

Bob how do you keep the threads from causing inconsistency on your ssg do you only use a minimal amount of threads on them

[PikeP]

Bob right now I have optimum fill time set to a factor of dwell and balance ratio in Hope's this will scale well...of course that ratio can be modified provided fine tune it or throw in another variable. If I reduce dwell time to 1.2 seconds the recommended optimal fill time drops to .8 ms. If I take that same 33 gr hammer and put the balance ratio to 82% I go back up to 1.5ms optimal fill time...for example.

Here is the current formula in use.

Dwell * (reduced force % / 100) * correction factor

I also re did the above graphs to reflect minor changes as well as the scaling on chart Bob recommended. I get slightly less air ejection and use than what you're getting of course I'm just predicting it out of thin air so I will have to fine tune that as well as other things I'm sure.

[PikeP]

Here is some more data reflecting potential changes based on barrel length alone, port size alone, plenum size alone, and projectile weight alone. This may give a good look into what kind of energy is possible with each change for the configuration being built.

Also modified air usage...was using full 3000 psi opposed to average pressure for air mass ejected. And 1.45 instead of 1.46 fpe/ci