Simplified Balanced Valve

[oldpro]

Here is a shot string with a 45 gram hammer and 8 lb spring 2800 fill 215 cc air tube unregulated  no ssg
1.861
2.857
3.858
4.886
5.850
6.854
7.855
8.873
9.860
10.846
11.849
12.863
13.868
14.859
15.848
16.856
17.844
18.829       avg 856 fps
                           55   fpe
                          1.56 fpe/ cuin
Not to bad with out a ssg I might have to make one and see

What is your poppet sizes and bleed hole size?

[PikeP]

Congrats mann...very happy to hear more success occurring. I think I've solved a lot of the issues with the closing force over closed force ratio. Before balancing Bob's valve was 10 percent. Which is off the charts meaning tons of hammer energy required for a less than ideal tune range...reducing the force to half doubled that number resulting in a much easier to operate valve..and with getting the chamber filled nearly asap the valve quickly returns to nominal operations of a pcp for the closing event..I think 20% cf ratio is really ideal..likely on full effect at the 25% to 33% of peak dwell mark...

[mann]

Poppet balance part is at .250 bottom is at .375  bleed hole is .052

[mann]

Ported to .200 all the way barrel transfer port and valve

[PikeP]

Here is a draft for small bore...set for wide tuning range pellet shooter. Anyone can feel free to use these or similar dimensions... this is a .25 cal up to 92% bore porting but would work for all small bore...although a .177 really doesn't need balancing even when full bore..and a .22 wouldnt benefit from this design much as the force reduction co.pared to a nominally built unbalanced one is only 15% or so compared to the 35% on the .25 cal.

If anyone has a recommended minimum closing force I can build a version based on that..this one is 100 lbs.

I certainly wont oppose any volunteers with a lathe and motivation to build me a thimble/poppet once a small bore version is set in stone. 😁

[mann]

The ssg is also helping now that I tried it I had a string at 64 fpe at 1.42 fpe /cuin with out much tuning at all really just tossed in Ssg and tried at that power level string is
1.925
2.944
3.944
4.941
5.927
6.931
7.921
8.916
9.915
10.914
11.903
12.896   
I'm going to change out the spring and try it at 55 fpe level which was first string I posted and see how much the ssg has helped

[rsterne]

OK, so first of all, I have an admission to make.... Although the plenum is 108 cc, I forgot to allow for the volume in the microbore hose, gauge and valve, which I now estimate at about 12 cc.... Therefore the volume dropping in pressure when I was calculating the efficiency was wrong, it is about 120 cc, which is the reason the numbers were higher than the should have been.... They are still very respectable, but that 1.74 FPE/CI I thought I had achieved is a much more believable 1.57 FPE/CI.... or thereabouts.... I won't have a final figure until I install the 22 CI bottle, of course, because that will increase the plenum from 108 cc to 460 cc.... I went back and replaced the graph in Reply #340 with a (more) correct version.... 

Anyways, on to todays exciting news.... First thing was I checked a "cold bore shot" of the .357 after storing over night at 3000 psi.... The gauge showed no indication of a pressure drop, and with a 131 gr. bullet the first shot was 914 fps.... I refilled it to 3000 psi and took another shot, and it was 927 fps.... That is only a 1.4% difference, and it is quite possible the gun may have lost 50 psi or less overnight.... So score another victory for the new valve.... stiction is non-existent.... 

I cleaned the .224 and .257 cal. barrels, installed the .224 cal on the receiver, and made a tapered transfer port.... I used a milling cutter with a 7 deg. taper, and made a 7/16" OD port that is 0.328" ID on the bottom and 0.257" ID on the top.... I got the length right for a slight compression fit, and installed the .224 barrel and filled the gun to 3000 psi.... I still had the SSG gap set at 2 turns, loaded a 47.6 gr. bullet that was sized to 0.223", and took the first shot across the Chrony…. The resulting 1022 fps (110 FPE) put a pretty big grin on my face....  …. That is more power than I have ever had before from the .224 cal.... The best I did previously was 106 FPE, but to be fair, that was with a 41.3 gr. swaged RWS bullet at 1077 fps.... Later in the day I tried one of those at this setting and it did (are you ready for this) exactly the same 1077 fps.... This pretty much shows that the gun is (and was) maxed out, because the most restrictive point in the porting system (the chamber where the 0.088" diameter bolt probe restricts the area to the equivalent of a 0.198" hole) hasn't changed.... More to come in a while....

Bob

[PikeP]

The ssg is also helping now that I tried it I had a string at 64 fpe at 1.42 fpe /cuin with out much tuning at all really just tossed in Ssg and tried at that power level string is
1.925
2.944
3.944
4.941
5.927
6.931
7.921
8.916
9.915
10.914
11.903
12.896   
I'm going to change out the spring and try it at 55 fpe level which was first string I posted and see how much the ssg has helped

Very impressed mann... congrats that's a bell curve at over 60 fpe with 8 lb spring and a light hammer...its working, quite well..

[PikeP]

Ughh bob I put 120 cc into your plenum volume...changed caliber, portsize and pellet weight. The current formula spit out this...off by 2 fps 

Also not sure why others thought Bob would need more hammer strike going down in caliber..that's the opposite to how physics works.

[rsterne]

Mark and Mike.... nice progress.... I like the design for a .25 cal pellet valve, Mike.... Notice how close your 109 FPE prediction was for my gun in .224 cal?.... 

Note the plenum volume remains at 108 cc, the additional 12 cc only affects the pressure reading once it equalizes after the shot, that air is NOT available within the very brief shot cycle....

Bob

[PikeP]

Mark and Mike.... nice progress.... I like the design for a .25 cal pellet valve, Mike.... Notice how close your 109 FPE prediction was for my gun in .224 cal?.... 

Note the plenum volume remains at 108 cc, the additional 12 cc only affects the pressure reading once it equalizes after the shot, that air is NOT available within the very brief shot cycle....

Bob

Here is 108cc available. With 2.2 cf. The 109 was honestly with a 2.3 cf I was testing and forgot about, but feel 2.2 is where a 28 inch barrel belongs...roughly

2 fps off the other way 😂

Estimated within .195%...

[PikeP]

Think I found a way to formulate approximate dwell based on power levels...it requires metering air flow through a given port size and the required time to flow the avg air required for said energy...

I see a trend of achieving half the ports potential flow over the entire valve open event..although this may be closer to 45 percent which would add more valve duration.

If we assume 28% of energy making it to the pellet as a baseline then we can approximate the length of time your port at 45% to half its peak flow has to be open..

If my ports max flow is 980 mg a ms, and I pump 800 mg of air through it, that means my dwell time is approximately 800/(980/2)..
 1.63ms...or at 45% 1.85 ms...

It's probably not 100% accurate but a good approximation. Just like how I calculate lift..

Say Bob's valve moved 3725 mg a ms and his 250 fpe shot was roughly 3300 mg. That means 3300 / (3725/2) = 1.8ms or at 45% 1.96 ms...

Opinions Bob?

Here is what I got after completing the above formula for your 250 fpe shot.

Seems good enough for ball park to me.

[rsterne]

So here is the meat and potatoes of today's testing of the .224 cal Hayabusa Mk.II based on the .357 cal. version.... Remember, all I have done is replaced the upper, nothing in the lower tube has been touched, and the SSG gap settings are still the same as on the .357 version.... I was using a 47.6 gr. "Bowman" bullet, which is a scaled down version of the Lyman 257420, made by Arsenal, which is designed to be stable in the 14" twist TJ's barrel.... With 2 turns of gap on the SSG it shot at 1020 fps (110 FPE) and peaked at 1035 fps (113 FPE) at zero gap.... Here is a plot of velocity and efficiency vs. SSG gap.... I had a usable tuning range of about 140 fps with this (admittedly oversized) valve in the .224 cal....



I also tested some lighter bullets, just a few shots to see what velocity they reached.... At 2 turns of SSG gap, the bullet I used previously in this gun, the 41.3 gr. swaged RWS that is virtually identical to a .22LR bullet shot 1077 fps (106 FPE).... I have some of the NOE version of the Lyman 225107 which weigh 38.3 gr. and they shot at 1116 fps (106 FPE).... and were just supersonic at zero gap.... I also have some of the swaged NAA 30.6 gr. bullets which are similar to a .22 Short, and they went 1195 fps (97 FPE), still at 2 turns of gap on the SSG.... The two cast bullets I tested I sized to 0.223", the swaged were nominally 0.224" and I did not touch them.... Now that I have NOE sizing bushings in various sizes, I find that the 0.223" chambers a lot easier than the 0.224".... At 0.225" you nearly have to beat on the bolt handle to chamber bullets in this barrel....

The next step was to see what kind of shot strings I could get at various SSG gap settings.... Remember, I only have a 108 cc plenum (120 cc including the valve, gauge and hose), so these shot strings are only about 1/4 as many shots as they will be once I install the 22CI bottle.... Anyways, here is the results, all shots over 96% of the peak velocity are shown....



At zero gap I have a declining shot string.... With 2 turns of gap, the first 2 shots were within 1 fps, and the velocity then dropped 2.5% for the 3rd shot, and the 4th was down more than 4%.... At 5 turns of gap, I was starting to get a nice bell-curve, the first 4 shots were within a 15 fps ES (1.5%), so the gun is tuned right at the top of the bell curve.... The average over those 4 shots is 983 fps (102 FPE)…. At 7 turns of gap the first shot was about 6% below the peak, so it isn't shown, and the bell-curve starts at 2850 psi.... 7 shots later the 4 % ES ends, the average velocity is 924 fps (90 FPE), and the pressure is down to 1870 psi.... That is nearly a 1000 psi pressure range within a 4% ES, which is very good.... With the 22 CI bottle installed I should get about 4 times the shot count.... although that may be slightly less as I expect the FPE to increase because of the higher average pressure during the shot with 460 cc on tap instead of just 108 cc.... The string I didn't shoot, at 6 turns of gap, looks to be the one that will start right at 3000 psi and still be within a 4% ES.... I'm guessing it would have been 6 shots at about 950 fps average (96 FPE) at around 1.25 FPE/CI.... If that comes to fruition, that will be more than a 50% increase in shot count from my previous .224 cal version, with the conventional valve....

I couldn't be happier with the results.... I had hoped I could just swap calibers without any other change, but there were times I thought that was a pipe-dream.... It turns out it wasn't a dream at all, but a reality.... 

Bob

PS.... Mike, now that you have a complete second set of data for the same valve in a MUCH smaller caliber, I suspect you will find that some things meet your expectations while others don't.... Chew on this for a while and see what you come up with.... BTW, the .224 cal barrel is 29" long, not 28" like the .357 and others.... I haven't run the data through Lloyd's spreadsheet, but "in theory" I think the dwell should be the same as on the .357 for each SSG gap setting.... At least I don't see why it should change, do you?....

RBS

[PikeP]

Dwell is entirely measurement of the duration it takes to flow x amount of air through an expanding and contracting orifice..it will change based on the demands you place on it, at peak operation going up in caliber requires more dwell because you have to flow more air and the port flow rate cant keep up with the demand for more air...its subtle but there. More so increasing barrel length and higher  pellet sd effects dwell because this allows the use of more air ejection..which adds more valve duration. This is why you need much heavier ammo and longer barrels when you increase caliber to achieve their optimal energy levels...ie more dwell to allow more air ejection




29" barrel...any other changes...like port size?

[mann]

My hammer and spring set up while on the ssg I can't get lower than the 930 area with out being a cliff if I go back to before with out the ssg I can remove more preload and get it down to the 55 fpe range with about 1.5 efficiency I'm going to give that a try in my brod tube and see what happens it regulated at 2100 

[PikeP]

My hammer and spring set up while on the ssg I can't get lower than the 930 area with out being a cliff if I go back to before with out the ssg I can remove more preload and get it down to the 55 fpe range with about 1.5 efficiency I'm going to give that a try in my brod tube and see what happens it regulated at 2100

You need to slightly decrease chamber volume to open up the tuning range...while you have it out I would try...keep up the good work. A lighter hammer or spring might work if your ssg is simply too heavy or over sprung

[mann]

Yeah I'll have to try a lighter hammer I'm going to give it a run in my brod and see how it goes

[rsterne]

I have had somebody ask what my "tiny tank" is.... Here it is on my 6mm Regulated PCP, with my digital gauge in place as well....



It is just a piece of 1" CRS drilled and tapped the same as the threads on a bottle (either 5/8"-18NF or 18mm x 1.5mm), plus a shoulder for the O-ring, with minimal internal volume (just a few ccs)…. I originally made them to use when testing and adjusting regulators, so that I didn't have to waste a bunch of air every time I took the reg. apart.... It turns out that replacing the bottle on a PCP with one has the same benefit when you are working on it.... You don't blow of hundreds of ccs of HPA every time you have to tear the gun apart to work on the valve.... You just remove the tank, and screw on its tiny replacement.... After your development is finished, you swap them back again....

Bob

[rsterne]

Mike, the valve is the same, but the transfer port tapers down from 0.328" to 0.257" (so I can use it for the .257 barrel, which fits the same receiver)…. Then the barrel port tapers from the round 0.257" hole to an oblong port measuring 0.180" x 0.270", which is the equivalent area to a hole of 0.230" (just over bore size)…. All my Hayabusas use a probed bolt (except the 7mm), the one on the .357, which is 0.140", brings the total annular area of the chamber down to the equivalent of the 0.328" transfer port.... In the .224 and .257 cal bolt, the probe is 0.088", so the equivalent annular area is the same as a hole of 0.206".... Therefore, that is the most restricted part of the porting system on the .224 cal.... Note the bullet I am testing with is 47.6 gr., not 46.7 gr. as per your Reply #393...

On the .257, the same thing applies, with the smallest point again being the chamber around the probe, and the equivalent hole is 0.241".... The .257 barrel, which I hope to test tomorrow, is 28" long....

Bob

[mann]

Well I got about 5 more shots with the Cobra valve but I was at 820 ish fps this valve was at 855 most of the time high of 865 es was under 20 until the last couple shots last shot of 67 was at 835. I was using the same spring but way less preload on 13 lb flat spring which was cocking super easy I'm pleased about the same amount of shots with more power I'll do some more tuning tomorrow and if I can hit 100 shots at 50 plus fpe and with es at 15 or less it would be great