Author Topic: Simplified Balanced Valve (Read 116342 times))

rsterne · « **Reply #440 on:** January 14, 2019, 03:42:05 PM »

The average speed of air molecules at room temperature is ~1650 fps, independent of the presssure.... At high pressure, you just have a lot more of them colliding with the walls of the container.... At very high pressures, they are also colliding with each other more frequently, which actually reduces the pressure, but they are packed more tightly together (less vacant space between), which increases the pressure.... These two factors are taken into account in the VanDerWaal's equations, which is the reason that pressure builds faster than density above about 3000 psi for air.... It is no longer acting as an "ideal gas" like Boyle's Law is based on....

That explanation just gave me an idea that may explain partly why you were able to exceed my 50% rule of thumb.... At 4500 psi, you are getting more force from less mass of air being expelled (accelerated) out the muzzle.... Just like in using Helium (a lower mass gas), you get a similar (but much reduced) effect.... While very high pressure air loses shot count compared to 3000 psi air.... it should actually gain velocity....

At 4500 psi, the air "pushes" on the bullet with 50% greater force than at 3000 psi... However, it only has a density 38.7% higher.... That should give about an 8% advantage to 4500 psi air in my "lofty goal" equation, compared to 3000 psi (which I am used to working with, and used when I made that approximation).... When we incorporate the VanDerWaals correction, it makes your results make sense....

Bob

mann · « **Reply #441 on:** January 14, 2019, 06:09:28 PM »

Got the ssg made using tss end cap and a 13 lb flat spring may have to thread it some more once I get it set up and need to drill a hole in my transfer port thinking about try around a .150 to hole

oldpro · « **Reply #442 on:** January 14, 2019, 06:32:28 PM »

triggertreat · « **Reply #443 on:** January 14, 2019, 06:51:58 PM »

WOW Travis...That's very impressive!!! You know I/we want that for sure. Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve. Can't wait to get back to easy cocking and no stiction. Thank you for all you do for us!

oldpro · « **Reply #444 on:** January 14, 2019, 06:59:26 PM »

Quote from: triggertreat on January 14, 2019, 06:51:58 PM

WOW Travis...That's very impressive!!! You know I/we want that for sure. Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve. Can't wait to get back to easy cocking and no stiction. Thank you for all you do for us!

Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.

rsterne · « **Reply #445 on:** January 14, 2019, 07:41:21 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

rsterne · « **Reply #446 on:** January 14, 2019, 07:49:30 PM »

Well done, Travis.... It looks like a pretty sudden increase in velocity from 521 to 669 in 1/4 turn, as we would expect somewhere in that range.... but still lots of adjustment either side of that.... Looks like you are getting about 250 fps in the upper range.... Good job !!!!

Bob

triggertreat · « **Reply #447 on:** January 14, 2019, 07:59:12 PM »

Quote from: oldpro on January 14, 2019, 06:59:26 PM

Quote from: triggertreat on January 14, 2019, 06:51:58 PM
WOW Travis...That's very impressive!!! You know I/we want that for sure. Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve. Can't wait to get back to easy cocking and no stiction. Thank you for all you do for us!
Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.

That's great Travis! I have been following along and could tell the Python wasn't happening. Have fun at the Shot Show and be safe. I'm looking forward to seeing whatcha got to show us.

oldpro · « **Reply #448 on:** January 14, 2019, 08:13:03 PM »

Quote from: triggertreat on January 14, 2019, 07:59:12 PM

Quote from: oldpro on January 14, 2019, 06:59:26 PM
Quote from: triggertreat on January 14, 2019, 06:51:58 PM
WOW Travis...That's very impressive!!! You know I/we want that for sure. Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve. Can't wait to get back to easy cocking and no stiction. Thank you for all you do for us!
Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.

That's great Travis! I have been following along and could tell the Python wasn't happening. Have fun at the Shot Show and be safe. I'm looking forward to seeing whatcha got to show us.

The Python works awesome its just not what your looking for at your power level. Im going to make both valves eventually.

oldpro · « **Reply #449 on:** January 14, 2019, 08:36:19 PM »

Quote from: rsterne on January 14, 2019, 07:49:30 PM

Well done, Travis.... It looks like a pretty sudden increase in velocity from 521 to 669 in 1/4 turn, as we would expect somewhere in that range.... but still lots of adjustment either side of that.... Looks like you are getting about 250 fps in the upper range.... Good job !!!!

Bob

I went and reran it and used 1/8 turns and I get a 300 fps window which I think is plenty in most applications. I have to tell you I have been working off and on with this for 3 months now and until you guys made the spread sheet I was getting nowhere. The secret for me was reducing the area in the vent chamber to as small as I could get it and that made it work I was nearly twice the size it is now before. MUCH Thanks Gentlemen.

rsterne · « **Reply #450 on:** January 14, 2019, 09:42:52 PM »

I agree, 300 psi is lots for a tuning range.... more than I have seen on any balanced valve....

Just think when we started playing with these, there was NO adjustability unless you changed the pressure (Cothran)…. We've come a long ways since then....

Bob

PikeP · « **Reply #451 on:** January 14, 2019, 10:03:03 PM »

Update to where sheet currently is. It's basically done once I run numbers on more versions, calibers, and energy levels.

Lots of approximations going on so dont nitpick..added a lot of metric conversions for outputs but inputs are still mostly imperial. Sorry Marco..

rsterne · « **Reply #452 on:** January 14, 2019, 10:28:39 PM »

The spreadsheet is looking great, Mike.... Nothing wrong with approximations, particularly where they make the results agree with the testing.... As long as you don't have to make drastic changes in those assumptions when you change the test criteria (eg. caliber), that's the important part.... When you are happy with it, I would love to see the inputs use my spring chamber and spring (diam. = 0.203", height = 0.40", spring vol. = 0.09 cc; hammer sprung travel 1.09 max. - 0.1 gap = 0.99"; port = 0.328", throat = 0.375",)…. Some of your values have drifted a bit from what I have (in the interests of optimizing the design, I realize that)…. One other thing, the barrel, from the base of the bullet to the muzzle, measures 27.5", not 28".... At that 2T Gap setting the velocity with the 154 gr. bullet is 860 fps.... efficiency is 1.33 FPE/CI....

Once you have that, I would love to see the other calibers input (just changing the specs. on the upper) and see how close the outputs are to my measured tests.... If it doesn't require tweaking between calibers, that would be a pretty good indication you're there....

Bob

oldpro · « **Reply #453 on:** January 14, 2019, 10:42:11 PM »

Quote from: rsterne on January 14, 2019, 09:42:52 PM

I agree, 300 psi is lots for a tuning range.... more than I have seen on any balanced valve....

Just think when we started playing with these, there was NO adjustability unless you changed the pressure (Cothran)…. We've come a long ways since then....

Bob

That’s a fact Bob! We’ve moved the needle a bit. Now we’ve found a way to make a trouble free adjustable valve the sky’s the limit my friend.

PikeP · « **Reply #454 on:** January 15, 2019, 12:14:57 AM »

So after studying dwell some I believe 1/2 barrel is 1.0 fpe per ci, 1/3rd is roughly 1.43 fpe/ci..and 1/4th is 1.85 fpe/ci....thats with a projectile that is 1/2 gr per fpe or greater, peller mass certainly effects the above..I dont know how well that holds up universally but I think Bob has always advocated about barrel distance for valve closure closely relating to volumetric efficiency..I certainly agree and have finally understood the connection myself..

Attached is the same graph as above but with a recorded efficiency of 1.0 fpe/ci

rsterne · « **Reply #455 on:** January 15, 2019, 01:46:39 AM »

I think your FPE/CI vs the dwell is a bit optimistic, but then I could be wrong about how short I think the dwell is on the really efficient shots.... We both agree that there is a direct relationship between where the valve closes and the volumetric efficiency....

I have a question about your valve dwell lift in the lower left corner.... Is that the "effective" dwell, taking into account curtain limiting.... or do you think that is how high the poppet lifts from the seat?.... I ask because you only have a 0.002" difference in the lift, even though the dwell increases from 2.11 mS to 2.79 mS.… I don't see any difference in the hammer strike, so I don't see how all those factors can interrelate.... With the same hammer mass, the relationship between lift and dwell is somewhat proportional, and governed by hammer velocity.... Lift should increase with the square of residual hammer energy, and dwell in proportion to the residual momentum.... at least that is my understanding.... How can you get a 1/3 increase in dwell without a corresponding large increase in lift?....

Bob

PikeP · « **Reply #456 on:** January 15, 2019, 02:18:14 AM »

Bob I added a valve close checker...it verifies close distance based on your formula that I've modified down to within 1% accuracy based on a given barrels length volume...then you match your volumetric efficiency until your thermally projected FPE output matches...once both figures match you should know approximate close distance and efficiency...

rsterne · « **Reply #457 on:** January 15, 2019, 12:20:07 PM »

HI Mike....

It is cool to see the volumetric efficiency being tied into the valve dwell, and the point where the valve closes as the pellet moves along the barrel.... Lloyd's spreadsheet, once set up for the known quantities, ends up with two numbers that must be changed to come up with the observed FPE/CI.... One is the valve dwell, and the other is an overall "efficiency factor" that can run anywhere from 50-80%.... There is only ONE combination of those two inputs that will produce the observed FPE/CI at the observed velocity/energy.... By using Thermodynamics, it appears you have eliminated the "fudge factor" (always a good thing)…. I am wondering, however, it that is still there to some degree in your choice of 28% thermal efficiency.... Surely not all airguns have that same value?.... I assume if you change that, then the relationship between dwell, FPE and efficiency all changes....

Still, I am delighted to see that the relationships between FPE and barrel length, port size, plenum volume, projectile weight and caliber are being clarified, as I knew they would.... If each of us can come up with small pieces of the puzzle, and we all keep an open mind, we can accomplish a lot....

Bob

mann · « **Reply #458 on:** January 15, 2019, 02:40:38 PM »

Ok I have a question . Won't changing the transfer port to a smaller size make the chamber fill faster

PikeP · « **Reply #459 on:** January 15, 2019, 03:40:26 PM »

Bob the 28% rule only applies when operating at peak efficiency and power combined...imo..for example your 274 fpe shot was in the neighborhood of 22%..and the 250 fpe shot was probably 27%or so..

28% is just a baseline to want to be at..which translates to roughly 1.4 fpe/ci which I think you can agree is a good place to tune for both air use and power.

I think I figured lift and dwell to some degree...at least getting within spitting distance. I think the valave opens up 10% or so more than what an equivalent port would flow...

Bob, can you for a giggle run a simulated 150~ fpe shot with the 154 grain through Lloyd's spreadsheet so I can see where I currently stand in comparison on lift and dwell? It's really hard to solve for x and y when you only know the median of z..but I think it's possible. I get around 1.5 to 1.8 ms dwell depending on efficiency but I haven't found a way to modify your formula for less than peak performance ie low lift conditions..if I figure out that solve I'll be golden..lift, dwell and volumetric efficiency is all I need to compare. Thanks.

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Simplified Balanced Valve

Author Topic: Simplified Balanced Valve (Read 116342 times))