Author Topic: Simplified Balanced Valve  (Read 2322 times)

rsterne

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Re: Simplified Balanced Valve
« Reply #15 on: January 14, 2019, 03:39:45 PM »
Today I removed the .224 cal barrel and installed the .257 cal.... It is a 28" long 14" twist TJ's.... I tethered the gun at 3000 psi and got the following data.... I was getting low on the Lyman 257420s, so I bracketed the weight of that with an NOE 260-63 HP and an RCBS 257-85 HP, the weights are shown on the graph below....



You can see that the gun is not quite reaching the velocity plateau, even at zero SSG Gap.... With the original valve and hammer it peaked at 160 FPE, at zero gap it is 146 FPE with the same bullet.... I don't really care, because I never max. out the gun when shooting anyways, because you get a declining shot string and lousy efficiency.... This could also be due to the small plenum of 108 cc.... I then filled the gun to 3000 psi and shot strings at four SSG Gap settings until the velocity fell 4% below the peak.... The resulting shot strings are shown below.... Remember that the reservoir volume, including the hose, gauge and valve is only 120 cc, when the 22 CI bottle is reinstalled the reservoir volume will be 460 cc, so I should get close to 4 times the number of shots.... depending on the effect of the expected power increase with less pressure loss during the shot from the larger reservoir....



I have not made ANY changes to the .357 cal lower, which has the balanced valve I just built, a 77 gr. hammer and an SSG with an 11 lb/in. hammer spring.... The transfer port is the same tapered one I had on the .224 version (they share the same receiver), the barrel port on the .257 cal barrel is oblong and equivalent to the caliber, and the most restricted point is the chamber, which has the same 0.088" probe as the .224 cal (they share bolts), so the annular area around the probe is the smallest point in the porting system, equivalent to a hole of 0.241" diameter....  I also tested all the different weight bullets I have kicking around, with the SSG adjusted to zero gap.... The results are in the table below....



The FPE was between 145-151 with all bullets tested, peaking with the Lyman 257420 FN at 73.5 gr.... The one low FPE was a cast bullet I got from Doug Noble which had many lube bands.... and despite all bullets being sized the same at 0.256", it had a lower than expected velocity.... I suspect extra friction from all the drive bands was the cause.... One other note.... The 98 gr. bullet I tested was the HP version of my NOE 101 gr. BBT, which is 0.873" long.... Despite my backstop only being at 20 feet, it was keyholing on impact, the holes were about 1/2" long.... This is proof positive that bullet is NOT stable in a 14" twist....

So far, the new valve has worked properly in .357 cal, .224 and .257 cal.... Next I will prep the .30 cal LW barrel I have by enlarging the barrel port, and make a new bolt probe for it that is 7/64" diameter to replace the 0.140" removable probe currently on the .357 bolt.... The .308 and .357 barrels share the same receiver and bolt.... After I have tested that barrel, I will have to do some significant alteration to my 7 mm barrel and receiver to adapt it to the existing lower.... When all is said and done, I will have five calibers that all fit the same lower, using the same valve, hammer and SSG setup.... at least I see no reason now why that should not be possible, since the smallest (0.224") and largest (0.357") both worked properly at the 3000 psi fill pressure I am using....

Bob
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Lob0426

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Re: Simplified Balanced Valve
« Reply #16 on: January 15, 2019, 03:24:48 PM »
It would be interesting to see how the valve acted with the original .032 vent, then the .040 with the reduced spring chamber volume. I suspect the vents would still be too small, but might have been better than they were. The pressure rise would have been faster.

It sounds like moving the .052 vent up and down the stem a bit, to change the timing of its closing, might be worthwhile. Closer to the poppet shorter and further away longer. The question would be which one might possibly increase tunability. You can only go so far towards the poppet before it is obstructed by the valve body. Not that that might not be useful to timing by stopping or severely reducing flow into the port. Pressure would build until the port was occluded then stop. Stopping the valve reaction to full throat pressure. The peak pressure in the chamber would be less than the peak pressure in the throat.

I do not have a real grasp for the math, but great article.

Edit: Was the problem with the vent that it restricted the flow of pressure (low) out of the chamber as the poppet was struck? Or was it a restriction of the high pressure entering? It would seem it was more of an impediment to the poppet pistoning into the chamber.
« Last Edit: January 15, 2019, 06:06:18 PM by Lob0426 »
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rsterne

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Re: Simplified Balanced Valve
« Reply #17 on: January 15, 2019, 07:52:53 PM »
It is now quite obvious that the key to getting this balanced valve design to be "tuneable" is to have the smallest possible volume in the balance chamber, and the largest possible vent.... This is to allow the HPA from the exhaust port area to enter the balance chamber and "cancel out" the negative (opening) force imparted by that part of the design as quickly as possible.... Air can only flow from high pressure to low, of course....

The balance chamber reduces the cracking force of the valve by providing a "lifting" or opening force in the opposite direction to the pressure holding the poppet closed, and the force on the stem area trying to close the poppet once it cracks.... We want the pressure in the balance chamber to rise as quickly as possible to the pressure in the exhaust port, hence the need for small volume and large vent, to allow that to happen fast....

Bob
  • Coalmont, BC

rsterne

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Re: Simplified Balanced Valve
« Reply #18 on: January 16, 2019, 05:29:44 PM »
Well, guys, I Rube Goldberged together a method to make direct measurement of the lift on my Hayabusa…. I couldn't do it through the back because the SSG was in the way.... and then in the middle of the night I woke up and smacked myself in the head.... This gun has an EXTERNAL COCKING HANDLE mounted directly on the hammer....  ::) …. All I had to do was make an indicator that showed how far ahead of the rest position (against the valve stem) the handle moves during firing.... Here it is....



The brass tube is sitting against the breech band so it can't slide forward, and held in place by two cable ties and a couple drops of glue.... The aluminum tube slides inside it, and an O-ring slides on that inner tube.... You slide the O-ring forward before you cock the gun, so it rests against the end of the brass tube when the end of the aluminum tube is against the cocking handle, while the hammer sits against the end of the valve stem.... You cock the gun, load a bullet and take aim through the Chrony, fire it, the cocking handle slides the aluminum tube forward, and the O-ring slides back to create a gap (as shown in the photo above) between itself and the end of the brass tube.... You push the aluminum tube back against the cocking handle, which you force to sit tight against the end of the valve stem my putting a turn of preload on the SSG.... Measure the gap between it and the end of the brass tube, and you know the valve lift.... I checked to see if firing a second time slid the O-ring back further and found that it didn't, within my ability to measure the gap.... I was using the 77.2 gr. bullet in the .257 version for this testing.... I was able to measure the lift to the nearest 0.005".... Here are the results....



The lift at 3000 psi went from 0.125" at zero gap down to 0.040" at 6 turns out, and then dropped to zero lift at 8 turns because the gun would not fire at that gap.... The velocities were quite close to my previous data, so the lift indicator device I am using is not slowing the hammer enough to worry about.... Trying a second shot after the O-ring had already moved on the aluminum tube made no consistent difference to velocity or O-ring position.... I then tethered the gun to my other regulator, which is set at 1850 psi, and repeated the tests....

This series was quite interesting.... I expected to measure greater lift, because with only 62% of the pressure, you only have 62% of the opening and closing forces for the hammer to overcome.... That was indeed the case, the lift was 0.190" at zero gap, decreasing to 0.110" at 6 turns of gap, during which time the velocity sat solidly on the plateau at just over 800 fps.... The velocity dropped off over 100 fps to 689, and the lift decreased to only 0.035", during the next 2 turns on the SSG.... This means that the spring I am using for 3000 psi is way too strong at 1850 psi.... I suspect if I used a much lighter hammer spring I would be able to get a decent adjustment range at the lower pressure.... 

If you look at the lift where the velocity started to drop at 1850 psi, it looks like it was about 0.125".... That is the same as the starting lift at 3000 psi.... This means that if the lift exceeds that amount, you are basically up on the plateau, you get no further velocity increase at either pressure.... That happens to be 1/3 of the throat diameter.... This leads me to conclude that if I allow a maximum poppet travel of 0.150", that should be sufficient.... I currently have 0.250" of balance chamber height in the thimble, so I can put in a spacer to make the volume smaller.... It should make quite a difference in the tuning range of the valve, I would think.... It would also be a good idea if I do that to make sure that the hammer can't drive the poppet into that spacer, as it could break things.... I am going to ponder removing the valve and changing these thing before I fit the .308 cal barrel, which is now ready for testing.... I'll ponder that overnight.... It's nice to know how much lift I have to allow for, and 0.150" should be plenty....

Bob
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rsterne

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Re: Simplified Balanced Valve
« Reply #19 on: January 17, 2019, 11:29:33 AM »
 I took the gun apart and made a spacer for inside the thimble to fill the volume I don't require.... Here it is sitting on the valve spring....



The front part reduces the diameter of the spring chamber from 1/4" to 13/64".... and the flange portion takes up 0.090" of length, to reduce the maximum poppet movement from 0.240" to 0.150".... I determined yesterday that I don't need more than about 1/8" of lift.... This spacer will reduce the volume of the balance plus spring chamber (when the volume of the spring and seat are deducted) from 0.52 cc to just 0.29 cc.... When the poppet is open 0.090", like it is when I have 2 T of SSG Gap, the volume is further reduced by 0.11 cc, which means the balance chamber volume that needs to be filled through the vent drops from 0.41 cc to just 0.18 cc.... nearly a 56% reduction.... This should make a big difference in the tunability of the valve....

I still have to shorten the poppet stem so that the hammer can't drive the poppet into the space and break something.... and I plan to add another O-ring to the flange on the large end as a thicker bumper for added protection....

Bob
« Last Edit: January 17, 2019, 12:07:13 PM by rsterne »
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Alan

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Re: Simplified Balanced Valve
« Reply #20 on: January 17, 2019, 12:07:25 PM »
As I have watched this thread from the start, a reoccurring thought keeps popping into my head.

Assuming some company sets out to duplicate this effort, I suspect their initial thoughts will center around economically manufacturing the valve. So Mr. Sterne, what is your take on someone quantity manufacturing the valve, once the design is stable? Feasible?
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Alan

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rsterne

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Re: Simplified Balanced Valve
« Reply #21 on: January 17, 2019, 09:42:43 PM »
Yep, should be quite feasible.... In fact, I think Travis at JSAR is already doing so....

Bob
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rsterne

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Re: Simplified Balanced Valve
« Reply #22 on: January 20, 2019, 03:25:19 PM »
Well, it's been an interesting and educational couple of days.... The smaller balance chamber REALLY changed things.... I had installed the .308 cal. upper on the gun before testing, even though I know it's not a good idea to make 2 changes at once....  ::) …. I still had the same hammer and SSG spring installed, and with 118 gr. bullets it peaked at 846 fps (188 FPE), which was quite a drop from the 219 FPE I had with the conventional valve, which had smaller ports.... I know I have a much smaller plenum on this gun at the moment, with the tiny tank installed, but that was a big drop in power.... The tuning range, however, was much wider, now up to 200 fps with the smaller balance chamber.... I suspected that perhaps I had cut too much off the valve stem, or stacked too many O-rings on the shoulder on the poppet as a safety bumper, and that the valve was no longer able to "blow open" sufficiently to give me the power I felt I should have had.... I even tried a stronger hammer spring, and all that did was increase the SSG gap required, I could not get the plateau velocity to go over 850 fps.... At small gap settings the velocity dropped, a sign the hammer was bouncing off the back of the valve.... All in all, pretty frustrating....

I pondered it for a couple of days, and then decided that before I pulled the valve out and changed things again, I should try reinstalling the heavier steel hammer, which weighs 123 g. with the cocking handle installed.... With the shortened valve stem, the hammer stroke has increased to 1.18".... I was running low on the 118 gr. bullets, so I grabbed some of the 109 gr. HP version to continue testing.... I tried a shot with the heavy hammer spring and got well into the 900s with a big gap, so I reinstalled the 0.047" wire spring and did some proper testing with the gun tethered at 3000 psi.... Here are the results....



The velocity peaked at 938 fps at 2 turns of gap on the SSG, which with the 109 gr. bullets is 213 FPE, pretty close to what I had previously, with the full size bottle in place.... The fall off with less gap is because the hammer is bouncing off the back of the valve.... The big surprise was the HUGE increase in tuning range with the small balance chamber, about 300 fps....  8) …. This pretty much proves that the small balance chamber, along with a generous vent, is the key to a wide tuning range.... However, it does need a heavier hammer to create the dwell needed to get maximum power.... The valve is operating like a balanced valve on opening, but a conventional valve on closing, so you need hammer momentum to fully open the valve and keep it open long enough to get maximum power.... The efficiency is pretty decent, I have no problem with those numbers.... certainly a huge improvement with the balanced valve and the SSG.... I ran some short shot strings (still with the tiny tank, remember), as follows....



You will note the nice bell-curves, and that the fil pressure drops as the velocity decreases, just as it should.... I didn't stop the last string (in red) until the pressure was down to 1300 psi, so the valve is perfectly stable, with no sign of hammer bounce.... I also tested the maximum velocity with 4 bullet weights at 2T of gap on the SSG, as follows....

79.5 gr.... 1047 fps (194 FPE)
98 gr..... 958 fps (200 FPE)
109 gr.... 938 fps (213 FPE)
118 gr.... 899 fps (212 FPE)

To put this performance in perspective, compared to the 154 gr. bullet in the .357 cal, the 118 gr. bullet is a slightly higher SD, and yet it is shooting faster in the .308 cal, 899 fps instead of 883 fps.... so I certainly don't seem to have lost any performance with the smaller balance chamber and larger vent.... I think before I try the 7 mm upper I will reinstall the .357 upper, just make sure.... All in all, I am very pleased with the way this balanced valve has turned out.... It is MUCH easier to cock than the conventional valve, I can run an 11 lb/in hammer spring instead of the 15 lb/in spring I had previously.... with a lighter hammer, less travel, and the cocking force has dropped from 23 lbs. to just 13 lbs.... Yes, I had to reinstall the steel hammer from the .224/.257 cal version instead of the MDS hammer, but the range the valve can be tuned over is now double what I started with (actually, the original version of this valve was not tuneable at all)…. I would say this valve is a screaming success....  8)

Bob
  • Coalmont, BC

rsterne

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Re: Simplified Balanced Valve
« Reply #23 on: January 21, 2019, 12:44:40 PM »
One of the tests for a tunable valve is to turn down the pressure and use a lighter bullet and see if it is still tuneable.... I tethered the .308 Hayabusa with the balanced valve at 1850 psi, and used a 79.5 gr. BBT to test it, and here are the results, plotted on the previous graph with the 109 gr. bullet at 3000 psi....



Note that the curve is moved to the right because it takes less hammer strike to get to the velocity plateau, in this case the maximum is at 8 turns of gap instead of just 2 turns.... After that, the velocity drops in a nice smooth curve, as you would expect, and is still reasonably stable 300 fps below the peak.... At that point, the SSG gap is 14 turns, or 0.7" (the spring is only being compressed another 0.48" to full cock), so the free flight of the hammer is longer than the acceleration.... I am sure that with a lighter hammer spring and/or hammer the consistency even at these low velocities could be improved even more.... I have no doubt that using this valve in a regulated PCP would achieve good stability and efficiency.... I shot 4 different weight pellets at the maximum velocity setting of 8 turns of gap, with the following results....

44.8 gr.... 1076 fps (115 FPE) with JSB .30 cal. Exact
59.2 gr.... 1000 fps (131 FPE) with NOE Magnum Hunter (light)
65.7 gr.... 958 fps (134 FPE) with NOE Magnum Hunter (heavy)
79.5 gr.... 885 fps (138 FPE) with Accurate 31-079A BBT

Keep in mind that this performance level is being achieved with only 1850 psi and a 108 cc plenum.... I also did a short shot string with the SSG Gap set to 11 turns, filling to just 1800 psi.... With the 79.5 gr. BBT the velocities were 799, 812, 794 fps (average 113 FPE) and the end pressure was 1300 psi.... That means that the efficiency for that very flat 2% ES was 1.35 FPE/CI.... I'm very pleased with how well this valve performs when dialed back.... With that velocity stability over a 500 psi range, it should be great in a regulated PCP.... It is hard to imagine a .30 cal regulated PCPs spitting out Magnum Hunters in the 900s with an 1800-2000 psi setpoint....  8)

Bob
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rsterne

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Re: Simplified Balanced Valve
« Reply #24 on: January 22, 2019, 04:13:42 PM »
With what we have learned since I introduced this thread, I thought I would put all the ideas together in a drawing, and add one thing I thought about a week or so ago.... Instead of having the thimble extend down over the OD of the larger part of the poppet, I wondered about shortening it and fitting a spring over the outside, instead of having the spring inside the balance chamber where it increased the volume.... Note that this has NOT yet been tried, but it should work just fine.... I also incorporated the idea of a shorter balance chamber, with enough depth to safely allow the poppet to travel 1/2 the throat diameter.... In addition, I shortened the stem, since it is no longer needed to create a spring seat on the front of the poppet, and drilled a hole in front of the stem, slightly larger than the vent diameter, to keep the resistance to the airflow filling the balance chamber, and the chamber volume itself, to a minimum.... This stepped hole helps avoid too little room between the OD of the stem and the bottom of the O-ring groove.... Here is the drawing with all those changes.... It is "generic" in that the proportions are basically correct, but no dimensions are shown....



I feel that the range of balance chamber diameters that will work OK are from 60% to 72% of the diameter of the outer sealing edge of the poppet.... With all the changes we have made, you might even get to 75%.... I would still use 71% as my goal, which means that the cracking force of the valve is reduced by half.... The back of the poppet is undercut slightly (about 5 deg.) to insure a narrow seal, right at the outside edge.... Here is what the cracking force is, as a percentage of what it would be without the balancing chamber, relative to the diameter of the balance chamber as a percentage of the seat diameter....

60% balance chamber diameter reduces the cracking force by 36%
66% balance chamber diameter reduces the dracking force by 44%
71% balance chamber diameter reduces the cracking force by 50%
75% balance chamber diameter reduces the cracking force by 56%

Here are some examples for the dimensions you might like to try for a valve for a full power .257 cal. bullet shooter.... (could also be used for smaller PCPs)….

Throat ID 0.312"
Stem OD 0.125" (using 5-40 threads on the forward 1/4" to provide shear strength)
Vent Hole ID 0.052" (hole forward of stem 0.062" ID)
Exhaust Port ID 0.257"
Poppet OD at Valve Seat 0.375"
Balance Chamber ID 0.250"
Balance Chamber Length (ahead of poppet) 0.170"
Poppet Travel Before O-ring Bumper Contact 0.156"
Stem Protrusion Behind Valve Body 0.150"
The length of the larger part of the poppet would be about 0.25"
The length of the smaller part of the poppet would be about 0.50"
The front OD of the thimble is 0.250" and threaded inside 8-32
The overall length of the thimble would be about 1.00"
The center of the perforated mounting wheel is drilled 0.187" and counterbored 0.281" for the front of the thimble
This assures a loose fit between the thimble, thimble screw, and the supporting wheel to allow some radial movement for self-alignment
The thimble is secured to the perforated wheel with an 8-32 screw cut to length to give minimum end float when tightened
The OD of the thimble, the poppet at the spring seat, and the spring would be about 0.42" minimum (matching the spring OD)
A good spring would be the Century #71332, which is 1"LOA, 0.42" OD, 0.038" wire, 0.344" ID, 11 lb/in, and 0.26" length at coil bind
Nearly identical is the McMaster Carr # 9657K307, same specs except the wire is 0.039", 0.342" ID, and 0.29" length at coil bind
The ID of the valve would be about 0.625" minimum, and larger is better, to provide double the throat area past the poppet, thimble and spring
You would want 8 holes of 0.156" min. ID in the front mounting wheel, to provide double the throat area into the valve
That means the mounting wheel needs to be 0.75" OD or larger, it is retained with a circlip
That circlip groove OD in turn dictates the minimum OD of the valve body, in the case of a 0.75" front wheel, the valve must be at least 0.875" OD
The overall length of the valve would be about 2.75"

I hope this will give you a basic "road map" to follow if you want to try a balanced valve....

Bob
« Last Edit: January 23, 2019, 04:03:41 PM by rsterne »
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rsterne

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Re: Simplified Balanced Valve
« Reply #25 on: January 24, 2019, 09:23:38 PM »
I reinstalled the .357 cal barrel this afternoon on the Hayabusa with the balanced valve, now with the smaller balance chamber volume and the heavier hammer.... The velocity peaked at 883 fps at 2 turns of Gap on the SSG, exactly the same as the previous peak.... However, I was able to tune the velocity down lower.... ie the tuneable range of the valve has definitely increased with the smaller balance chamber....

I then milled out the receiver for the 7 mm, made a stepped transfer port (I had to because of the way it fits to the barrel in that version), with an ID tapering from 0.328" at the valve to 0.281" at the barrel.... The barrel has an oblong, full area barrel port, and this version has a flat nosed, retractable bolt.... I tried a few shots, tethered at 3000 psi, and the velocity was virtually the same as what I had when maxed out with the conventional valve, with both the 96.5 gr. BBT FN bullets and the 91.0 gr. HPs.... The gun peaked at 190 FPE....

I have been contemplating stripping the valve out of the gun and machining a bit off the end of the spacer and removing an O-ring from the bumper, to allow the poppet to move a bit more.... but the gun is shooting so well I think I will leave it alone.... I never shoot my PCPs maxed out anyways, they just use too much air that way....I am getting very close to installing the 22 CI bottle so that I can test the gun with the full size reservoir, and as that will increase the average pressure during the shot, I may have to use a bit less gap anyways.... Just tuning by reducing the preload on the SSG spring, or maybe reducing the hammer weight a bit, may be all I will need....

Bob
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rsterne

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Re: Simplified Balanced Valve
« Reply #26 on: January 26, 2019, 04:39:51 PM »
I installed the 22 CI bottle today, along with the .357 cal. barrel.... The final version of the valve has the internal spacer to reduce the balance chamber volume and the 0.052" vent.... along with a reduction in stem length to limit the travel to 0.125".... This means that when the SSG Gap is set to zero, the hammer bounces off the back of the valve and the velocity drops a bit below maximum.... However, I never shoot my guns maxed out anyways, because they waste air and end up with a Korean Cliff tune.... so the fact I have to run a bit more SSG Gap is not an issue... I am running the steel hammer, which weighs 113 gr. including the cocking handle.... The SSG is using an 11 lb/in. spring with 0.30" of preload (3.3 lbs) and with 2 turns of gap it takes 15 lbs. of force to cock the gun, which is wayyyyy less than the 23 lbs. it required with the conventional valve.... At 8 turns of gap, the cocking effort is less than 12 lbs.... Here is how the velocity works out at various SSG Gap settings....



As you can see, the tuning range is much increased with the small balance chamber volume and larger vent.... The gun can be tuned over a 300 fps range, which is way more than I would ever need.... The maximum velocity occurs at 2 turns of gap (260 FPE), at which point the efficiency is 1.09 FPE/CI.... With the conventional valve, at slightly less FPE, I was only getting 0.74 FPE/CI.... At 5 turns of gap (240 FPE), which is about 3% below the peak, the efficiency has increased to 1.19 FPE/CI, and with 8 turns of gap it is up to 1.36 FPE/CI, and the gun is still producing 210 FPE.... At a similar power level the original version of the Hayabusa was getting 1.13 FPE/CI, so I am getting the same power on 17% less air.... Here are some sample shot strings....



With the 131 gr. bullets tuned at 8 turns of gap, to peak just below 850 fps, I am now getting 13 shots per fill averaging 202 FPE.... compared to 8 shots previously.... Not only is the new valve more efficient, I can also shoot down to 2000 psi and stay within a 4% ES, whereas before I had to stop at 2200 from the same 3000 psi fill.... At 5 turns of gap, I am getting 6 shots in a nice bell curve within a 4% ES at 240 FPE with either bullet.... If I choose to tune for maximum power, at 2 turns of gap, I am getting 260 FPE, but after 3 shots the ES drops more than 4%.... While this is OK for hunting, dialing the power back to 4-5 turns of gap gives nearly the same FPE and more velocity except for the first 2 shots....

Something interesting, and a bit unexpected occurred when I fitted the 22 CI bottle instead of the tiny tank.... I had expected a bit of a power increase, but basically it didn't occur.... It appears that with the higher efficiency the 108 cc plenum, which was only 0.42 cc per FPE, wasn't really costing me any significant FPE.... This could be because this balanced valve is opening very quickly, while the pressure is still high in the plenum.... Certainly, compared to a conventional valve, where you can continue to get a small amount more FPE by keeping the valve open a long time, that isn't happening here.... I'm not complaining, mind you.... I'm getting more power and using less air....  8)

This concludes the development of this new balanced valve design.... I had a few nay-sayers at the beginning, but I had a gut feeling this valve was going to work, once I found the right combination.... As with any balanced valve the devil is in the details.... It was really interesting to see that Brian built one of these over 17 years ago.... My gut feeling about what was required to get this valve to work was beautifully calculated by Mike (aka Matt/akuric) in his spreadsheet, and I really do have to thank him for quantifying what was happening inside this valve.... When he showed that the flow rate into the balance chamber, relative to the volume of that chamber, was allowing the valve to "blow open" for more than 50% of the dwell, it became crystal clear that reducing the balance chamber volume and increasing the vent diameter was critical to getting the tuning range we all desired.... So, thanks to Matt for his help....  8)

There you go, guys.... A simplified balanced valve that works, is easy to cock, tunable, and efficient.... Have fun !!!

Bob

« Last Edit: January 26, 2019, 05:42:48 PM by rsterne »
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Alan

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Re: Simplified Balanced Valve
« Reply #27 on: January 27, 2019, 05:29:20 AM »
Okay Mr. Sterne. Do you want to try to design an electrically-operated valve like the Daystates use?

I better explain myself here.

The Daystate unit incorporates a whole lot of technology to measure the pellets speed, chamber pressure, driving an LCD screen, etc. It doesn't use a regulator, nor does their SlingShot hammer design. However, what I'm proposing is an electrically, solenoid-driven hammer without all of the fanciness. Using one with you regulated valve design, would result is almost no cocking force, save for reloading the pellet via the magazine. It would take some thought, but building the circuitry isn't all that difficult.
« Last Edit: January 27, 2019, 05:44:52 AM by Alan »
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I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: Simplified Balanced Valve
« Reply #28 on: January 27, 2019, 11:26:45 AM »
Hey, Alan....

I'm not a solenoid guy, but if you are talking a regulated PCP, then you don't need all the fancy bells and whistles, because the solenoid, once programmed for the pellet and velocity you want (ie how much hammer strike), it doesn't need an algorithm to change that as the pressure drops, because it doesn't....  8)

At it's simplest, I can imagine a potentiometer to vary how hard the solenoid hits the valve.... Tune it like you would a preload adjuster on a hammer spring for your operating conditions.... and leave it alone.... My question would be, since we can achieve the same thing with a simple spring, why would you bother?.... Would you get a more consistent hammer strike, and therefore improve the ES?.... I doubt it, because our simple mechanical systems are capable of less than a 1% ES now, if it is larger than that, it is likely pellet variation....

Bob
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Alan

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Re: Simplified Balanced Valve
« Reply #29 on: January 27, 2019, 03:35:51 PM »
The only advantage I see, really, is less cocking effort. I don't know what the cocking effort on your set up is, but I'd like to know?

Another thing I'd like to know, deals with Daystate's floating, two-part hammer design. Airguns so equipped, don't use regulators. But, based on the on-line data, I think the resulting velocity curve would be a bit straighter. good discussion material if nothing else.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.