Tale of THREE BRods - .25, .30 and .357 Completed, Page 19 !

[oldpro]

 That would have been nice to do if I had steeped Carbide bits that small that could bore threw a rockwell 44 hardened valve stem. I used what I had and I can use pressure to verify the effects so no real need to chase 10 steps when I can just figure it out in 2-3 steps.
 heres latest string with modded valve stem on warp with 12" barrel
Latest regulated run from 3k to 2100 Reg was set at 2200. I did get a flyer towards the end on shot 14 but like i say I dont sort or size I just pull from the tin and go.
Created: 02/02/17 08:19 PM
Description: Warp 30
Notes 1: mod TC valve 3k 2100
Notes 2:
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 50.00
Temp: N/A °F
BP: N/A inHg
Altitude: 0.00
#          FPS   FT-LBS       PF
17    726      58.53    36.30   
16    728      58.85    36.40   
15    731      59.34    36.55   
14    757      63.63    37.85   
13    735      59.99    36.75   
12    736      60.15    36.80   
11    741      60.97    37.05   
10    740      60.81    37.00   
9     746      61.80    37.30   
8     735      59.99    36.75   
7     743      61.30    37.15   
6     739      60.64    36.95   
5     740      60.81    37.00   
4     738      60.48    36.90   
3     739      60.64    36.95   
2     738      60.48    36.90   
1     734      59.82    36.70   
Average: 738.0 FPS
SD: 7.1 FPS
Min: 726 FPS
Max: 757 FPS
Spread: 31 FPS
Shot/sec: 0.0
True MV: 738 FPS
Group Size (in): 0.00

[Motorhead]

Who Loves you Buddy  .... We're hopeless enablers seeking your efforts for our benefit    

[oldpro]

 LOL. I still cannot get a good string with a 25 cal no matter what I try it just seems I cant get the dwell down low enough FRUSTRATING!!! AAARRRGGGHHH but I might try putting a sail on the stem or something Im running out of ideas fast. I have a lot of tricks up the sleeve but the sleeve is getting shorter and shorter.

[Motorhead]

LOL. I still cannot get a good string with a 25 cal no matter what I try it just seems I cant get the dwell down low enough FRUSTRATING!!! AAARRRGGGHHH but I might try putting a sail on the stem or something Im running out of ideas fast. I have a lot of tricks up the sleeve but the sleeve is getting shorter and shorter.

All i can offer is Sarcasm ... absolutely clueless on balanced valve tech 

[rsterne]

Yeah, that's what I'm finding.... running out of tricks in the box of tricks.... need a bigger, deeper box.... 

Bob

[oldpro]

 Don never intended the valve to be used on small bores or low power so were really trying to make his POWER valve tame and its proving hard to do really. I have just a few more tricks then Im done trying and will use a self regulating valve for the small bores and Dons for the big bores. I wouldnt actually call Dons valve a balanced valve its actually a hidden poppet valve as there is no equal force that balances out the opening if that makes since.

[rsterne]

Oh, it's balanced, all right.... The "force reduction piston" fastened on the front end of the valve subtracts it's area from the area of the poppet seat.... Only the difference in the two areas is holding the valve closed.... That is why it's so much easier to open....

Bob

[oldpro]

Oh, it's balanced, all right.... The "force reduction piston" fastened on the front end of the valve subtracts it's area from the area of the poppet seat.... Only the difference in the two areas is holding the valve closed.... That is why it's so much easier to open....

Bob

Thats what I'm saying it's hiding the poppet and reducing the poppets picture to the pressure but isn't balanced it's force reduction not using balanced pressure but that's how I see it as opposed to having equal or near equal pressure pushing back or in balance. A true balanced valve doesn't get harder to open with more pressure it stays constant as pressure is opposing. Either way it works well.

[rsterne]

OK, so your opinion is that a "balanced valve" must be 100% balanced, and only held closed by the spring?.... I guess that is one interpretation.... Using that definition, then the balanced valves that Lloyd and Tom use, and any of the other designs I have seen (including the Cothran) are "semi-balanced".... I would respectfully submit that a 100% balanced design (like a symmetrical spool valve, with equal pistons both ends) has zero chance of ever being self-regulating.... so I would prefer a "semi-balanced" design where the opening force is still proportional to the air pressure (just much reduced).... so that we have a chance of it being self-regulating....

Bob

[oldpro]

 That is not what I said at all your misinterpreting what I posted but it doesnt really matter anyway lets get on to business. Im going to pull Dons valve again and try a few different things today and see If I can get the dwell short enough for a light bullet. Fingers crossed as this may be my last attempt unless I dream up something else soon. 

[grand-galop]

.. I would respectfully submit that a 100% balanced design (like a symmetrical spool valve, with equal pistons both ends) has zero chance of ever being self-regulating.... so I would prefer a "semi-balanced" design where the opening force is still proportional to the air pressure (just much reduced).... so that we have a chance of it being self-regulating....

Bob

Not to interfere in your developper brainstorm, but i`m really interested in what you just say there Bob.. SO!! BY DEFENITION=A balanced valve would have a spool valve with equal piston at both end..  Can someone elaborate in this mather? I`m really interested of KNOWING what is happening with this type of valve..  Thanks guys..

[rsterne]

To visualize a spool valve, think of a spool of thread in a tube with two open ends.... One end of the tube is the barrel, and there is a side port in the tube supplying HPA, that when the valve is closed is in between the two ends of the spool.... Since there is equal pressure on both ends of the spool, it has no end force and happily sits there, and no air moves from the side port into the barrel....

Through the hole in the middle of the spool is a piece of string, hanging out the other end of the tube.... To fire the valve, you give a tug on the string.... As soon as the other end of the spool clears a small part of the side port, there is now air pressure on the barrel end of the spool, which forces it fully open, emptying the HPA reservoir out the barrel....

Without some other mechanism to close, or reset the valve, it dumps ALL the air in the reservoir in one shot.... That is how a basic spool valve works....

If the two ends of the spool are different diameters, then when you pressurize the middle of the spool, you create a force on the spool towards the larger diameter.... This can be used to hold the valve closed against a seat.... Instead of having the HPA between the ends of the spool, you could also have the pressure on the ends, and the exit (exhaust port) in the middle.... kind of an "inverted" spool valve.... but the concept is the same.... To fire such a valve, you need to overcome the force holding the spool against the seat....

In a conventional poppet valve, the force against the seat is the area of the seat, times the air pressure (plus any valve spring)..... In a spool valve, the force against the seat is the DIFFERENCE in area between the seat and the balancing part of the spool, times the air pressure.... You are using air pressure against one end of the spool to reduce the force against the seat at the other end.... and therefore reducing the hammer strike required to open the valve.... When I talk about a "balanced valve", I would almost always be referring to one that is "semi-balanced" where the spool reduces, but does not completely eliminate the force holding the valve closed.... because if the balancing force is equal (or greater), the valve will usually become a "dump valve" and will lose any capability to self-regulate as the pressure changes....

If you want to see an example of a dump valve, triggered by a smaller pilot valve.... look at Reply #61 here.... http://www.gatewaytoairguns.org/GTA/index.php?topic=119234.60 .... In the case of the Lane Cartridge, the spool valve is larger at the balancing end, and once the small HPA chamber on the back side of it is dumped, the spool moves back under the influence of the internal pressure, dumping all the air in the cartridge....

HTHs....

Bob

[grand-galop]

Thanks for the precision..   I will wrap my head around it more... That bring a new perspective in my knowledge and understanding of some principal behind the heart of the pcp..

[rsterne]

Today, after much prompting by Travis, I started modifying my Cothran valve, to try and improve it's efficiency in my .25 cal regulated BRod.... It is important to realize that these changes may not work (in fact are unlikely to work) in an installation that is prone to hammer bounce.... In my gun, I have an energy absorbing bumper made from "Iso-Damp" on the back of the valve, an extremely light MDS hammer of only 28 grams, a recessed striker that only pushes the valve stem about 0.050", and an SSG.... This allowed me to consider removing the small metering rod (counter-piston) which lives inside the valve stem.... There is a debate as to the purpose of that device, but I believe it to be to prevent the valve from re-opening on a second, or subsequent hammer strike, by acting as a "leaky check valve", slowing the HPA that fills the poppet head during the cycling of the valve from dumping back too quickly into the exhaust port.... I have been told that removing it will cause everything from uncontrollable hammer bounce, to various burps or flutters, to extreme air use, to even destruction of the valve itself.... However, since Travis agreed to supply me with any parts I destroyed I decided to remove it.... I tethered the gun at 1900 psi and started testing.... What happened?.... Exactly NOTHING.... Zip.... NADA....

The valve functioned exactly as before, the same velocity, sound, air use, everything.... I was shocked, but it does reinforce my belief that its primary purpose is anti-bounce.... which I have already addressed by a combination of four different methods.... I did notice one thing that changed, if I leaned on the hammer strike by adding preload (instead of gap) to the SSG.... thereby vastly overdriving the hammer.... the velocity DROPPED slightly, accompanied by a high-frequency "flutter".... I don't know how else to describe it.... It sounded like hammer bounce, but much faster.... The strange thing was, it didn't use more air.... As I said, removing the metering rod may not work in many installations, if they have any possibility of hammer bounce.... but in my gun, set up the way it is, it made no difference, when the SSG was adjusted normally, with a bit of gap.... The velocity was stable until you got to the cliff, and then dropped like a stone, same as always....

OK, so the other thing Travis (and others) have tried is drilling out the tiny vent hole in the valve stem.... This hole lives in the exhaust port, and allows the hollow head of the poppet (which is the diameter of the "force reduction" piston attached to the front of the valve) to be at atmospheric pressure between shots.... This "blanks off" the equivalent area of the poppet, drastically reducing the opening force required to crack the valve.... When you fire the gun, the pressure in the exhaust port rises, HPA flows through that hole, through the valve stem (past the metering rod) and pressurizes the inside of the poppet, providing a greatly increased closing force for the valve.... Without this vent, the valve would stay open, and likely vent the entire reservoir.... With it, the valve cycles in a timely manner, allowing lots of air to escape and produce copious amounts of power.... The way Don builds the valve, I would estimate the dwell time at roughly 2 mSec.... and if you have way too much hammer strike, it can be even more.... Limiting the valve lift keeps that more constant, preventing the valve from being a real air-hog, which is why I like that modification....

In stock form, that vent hole is tiny, only about 0.020".... Logic dictates that enlarging it will make the valve close faster, reducing the dwell.... and that should lead to increased efficiency.... The stem is HARD, and Travis warned me not to try drilling it, and I didn't have small enough drills anyways.... so I did like he did, and used a thin pointed diamond burr in my Dremel and "countersunk" the hole, gradually opening it up at the same time.... The smallest diameter, doing it this way, is just at the very inside of the vent hole, and I found I was causing tiny burrs inside the stem, which I had to keep cleaning out with a #31 twist drill (0.120"), turning it by hand.... I did this in case I had to drop the metering rod (0.118" diam.) back in the hole, I didn't want it to get stuck.... Anyway, I used a couple of sewing needles with the points ground off as go-nogo gauges, and when one that was 0.028" would fit through the hole (but one measuring 0.030" wouldn't) I quit grinding.... I chose 0.028" because it has TWICE the area of the original hole.... I have no idea it that is optimum, but I wanted to start smaller than what others had used, which was 1/32" (0.031") or larger.... I left the metering rod out, reassembled the gun, and repeated my testing.... All I can say is WOW !....

First of all, it took a bit more hammer strike to open the valve.... not a lot, but a couple of turns less gap on the SSG.... Secondly, instead of a completely flat plateau, with only a few fps drop just before you got to the cliff, and then nothing.... I actually saw a "knee" on the curve.... It wasn't long, the sensitivity to SSG gap was still there, but compared to stock it was day and night.... Here are my results....



Note that the blue (stock) and black (no metering rod) lines virtually lie on top of each other.... At 3 turns of gap on the SSG, the velocity is at maximum, at 4 turns, it has only dropped a few fps, and shortly after that the velocity became unstable (400-500 fps ES) and at 5 turns out it was in the basement.... With the larger vent hole, compared to the velocity at zero gap, there was about a 10 fps loss at 1 turn out, and then about another 15 fps in the next turn.... At 2 turns of gap, the velocity was 25 fps below the peak, and the ES was still less than 1%.... At 2.5 turns of gap, the average velocity dropped another 40 fps, to what in a conventional valve would be the middle of the knee, but the ES had increased to about 2%.... At 3 turns of gap, the velocity was down 200 fps, but the shots were all over the place, with an ES of over 5%.... The valve was becoming unstable, although nowhere near as bad as a stock one.... At 4 turns out, the valve was no longer cycling properly, it was in the basement....

I then tethered the gun to my 500 cc bottle, regulated at 1800 psi, for some efficiency testing.... I left the bottle connected to the gauge on my Great White (valve closed) so I could record the pressure drop for a 8-shot mag. and tested each half turn out, starting at zero gap.... At that setting, the velocity was maximum for this pressure, at 968 fps, and the drop 280 psi, for 0.97 FPE/CI.... This was basically the same as I had before, with the 34 gr. JSB Heavies.... At 1 turn out, the velocity was 962 fps (220 psi) and 1.22 FPE/CI.... At 1.5 turns, 951 fps (210 psi) and 1.24 FPE/CI.... and at 2 turns of gag, 943 fps (200 psi) and 1.28 FPE/CI.... This is far better efficiency than I have ever had before with the Cothran valve in my .25 cal BRod.... At 2.5 turns out, the velocity (809 avg.) was becoming unstable, and it was much worse at 3 turns out (701 fps), so I didn't record the efficiency, figuring it was meaningless....

So, what are my conclusions?.... Well, for one thing, if you have cured all chance of hammer bounce, I think you can try removing the metering rod, I don't think it is necessary.... Secondly, doubling the area of the vent hole, by increasing the diameter to 0.028", decreases the dwell at a given hammer strike, and creates the beginning of a knee to the velocity vs preload/gap curve.... It gives you significantly more control of the velocity just above the cliff, and softens the cliff into a usable, although sensitive knee.... While the operating pressure is still by far the dominant factor in the velocity, you can now detune the velocity just a bit, saving air in the process.... I haven't got all the answers, but I think we're on the right track....

Bob

[oldpro]

Excellent work as usual and I'm confident that if you make the hole slightly larger .035-.040 and put the pin back in but upside down with a spring below it you will get to 1.50 efficiency. The rod is in there to fill the area above the poppet  without it the lock time(dwell) increases due to HP air feeding threw a small hole at high speed then spews into a big void slowing and filling the area now with the pin in it fills up all that void and having the spring in there also fills in the area and also the rod doesn't have to move and this adds to lock time. So put pin in upside down with very small spring below holding pin up and your dwell will again be cut in half and your ES and effecincy will both be much better and it will add another 50 FPS of adjustment below the knee.

[grand-galop]

Even at 1.28 FPE/CI is a respectable number..  If ever Travis is right, at 1,50 FPE/CI would that be one of the most efficient valve out there??

[rsterne]

I am pretty happy to get 1.28 FPE/CI at 68 FPE, or 1.22 FPE/CI at 70+ FPE.... particularly from a 23.8" barrel at only 1800 psi.... Remember that the higher the FPE output, relative to the barrel length and pressure, the tougher it is to get great efficiency numbers.... If I reduce the dwell more, then I will also, automatically, be reducing the velocity, and have to increase the pressure to make up for that to get back to 70 FPE.... The increase in efficiency will have to come from a higher setpoint, which means less overhead (pressure range between fill pressure and setpoint).... which will eat into shot count.... The choice then becomes simply a matter of how much air you have to put into the tank to top it up, not how many shots you can get.... I should currently be on track for about 48 shots at 68 FPE, or about 44 shots at 70 FPE, per fill....  .... If I raise the setpoint to 2000 psi, I will need to increase the efficiency to 1.46 - 1.54 FPE/CI to break even.... If I have to increase it to 2200 psi to make up for the reduced dwell, I would need 1.83-1.92 FPE/CI to get the same shot count.... I have my doubts, but I've been wrong before.... 

Bob

[oldpro]

 Yes youll lose a little headroom but you wont have to move your reg pressure that high I believe. I dont mind loosing a few shots to get better efficiency as it lowers the guns report and thats a big concern for me, I know your running with no shroud or moderator so for you the lower set point and higher shot count is probably a better set up. Also the higher reg pressure will also reduce dwell as well so for me its a win win but for you maybe not so much. You should try just for posterity reasons. 

[WyoMan]

Bob, thanks for performing that test. It's always nice to get some confirmation. It does seem that a larger vent will help close the valve faster... improving the  self-regulation.
Your .028" vent sounds good for HPA. The vent I'm using for co2 is .031"  - makes sense that the vent for HPA should be smaller.
I'm glad I found this thread - had no idea from the title. Well done! 

Wyo

[rsterne]

I would like to try and come up with a combination for the Cothran valve that will work in both .25 and .30 cal, regulated at 2000 psi or less.... and shooting heavy pellets in the mid 900s.... with the option of shooting slightly heavier bullets without having to get rid of the regulator.... I know, dream on !!

Bob