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General Category => PCP, C02, and Helium Powered Airguns => Topic started by: rsterne on December 23, 2018, 01:25:17 PM

Title: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 01:25:17 PM
There is a lot of interest right now in balanced valves for PCPs.... Part of this is because of my recent article in HAM, where I describe a few of the types that have been tried.... https://hardairmagazine.com/ham-columns/balanced-valves-for-pcp-airguns-theyre-here-today/ …. Reading that over will give you a pretty good idea about how they work to reduce the hammer strike required.... Some of these designs, or variations of them, are used commercially, which is why I haven't given any specific details.... However, one design, and perhaps the simplest one to build, I have never seen used commercially....

As you all know, it is my desire to share things publicly, to further the sport of airgunning…. In that spirit, I have drawn up the concept for the next valve I plan to build for my Hayabusa…. I hope to have it work properly from .224 through .357 cal, although it is sized for the .357.... This may be an ambitious project, but I wanted to publish the concept drawing from the beginning, so that you can all share in this project, be it a success or failure.... Here is the drawing....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Simpified%20Balanced%20Valve_zpsvtnfnmnj.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Simpified%20Balanced%20Valve_zpsvtnfnmnj.jpg.html)

The poppet is made from Delrin or PEEK, and is threaded internally with 5-40 threads.... The stem is a piece of 1/8" O1 Drill Rod, threaded 5-40 at the front (the threads secure the poppet to the stem in shear), and drilled lengthwise back into where the exhaust port is, with a small cross-drilled hole, to vent the forward balance chamber of the valve into the exhaust port of the valve.... This means that the balance chamber will start out at atmospheric pressure between shots.... when the valve lifts from the seat and the pressure in the transfer port rises, so will the pressure in the balance chamber.... and when the valve closes again, that pressure will fall back to atmospheric gradually as the pellet moves down the barrel and departs the muzzle.... Since the area of the balance chamber is half the area of the valve seat, it will only take 1/2 the force to crack open the valve, allowing it to open quickly with less hammer strike.... Once open, the rising pressure in the balance chamber will help to shut the valve quickly, and as it takes a short time for that pressure to bleed out through the vent in the stem, hopefully resist any second hammer strike which might cause valve bounce.... At least that is the idea....

Most likely I will drill the lengthwise hole in the stem with a 3/64" (0.047") drill, partly because using a smaller drill it would be so easy to break.... The metering of the airflow through the vent will be done by changing the size of the single cross-drilled hole in the exhaust port area.... Since that is easy to get at, I can start small, at 1/32" (0.032") and go larger if necessary.... I want the hole to be large enough to prevent the valve from "blowing open" on its own, which it can do if the pressure in the balance chamber rises too slowly.... When a balanced valve blows open (like the Cothran valve does), it is impossible to tune with hammer strike, as the valve either works or doesn't.... ie it has a definite "cycle" nearly independent of hammer strike.... I don't want that, I want to be able to tune the valve over a wide range of velocity using only hammer strike.... This will (hopefully) produce a valve that can be used either regulated, or produce a bell curve when used in an unregulated PCP....

For this valve I plan to use a 7/16" OD poppet, made from PEEK, with a 5/16" front section.... That means the front diameter is 71.4% of the rear, so the area is 51%, about as close as I can get to my 50% goal.... The valve throat will be 3/8", which when you subtract the area of the 1/8" stem will leave the throat area the same as a hole of 0.354" (nearly .357 caliber sized).... The exhaust port will be 21/64" (0.328"), which is the same area as the chamber in my .357 Hayabusa which has a 9/64" (0.141") bolt probe.... I will make sure the transfer port and barrel port are also the same area, to insure the maximum possible flow....

One of the advantages of this valve design is that it only needs one dynamic O-ring instead of two like the SS Valve, so less potential for leaks.... The SS Valve is prone to "stiction" problems when the guns sits for a while between shots, and I have a gut feeling that is because at rest the O-rings are loaded in opposite directions and tend to "wedge" inwards towards the center balance chamber.... The front O-ring in an SS Valve would therefore be wedged towards the seat, and opposite to the direction of travel of the poppet when firing.... When you fire the gun after it has been sitting, the front O-ring, which is already wedged into the back corner of the gland, gets pushed even tighter into that corner by the motion of the poppet.... That may be the cause of the low velocity first shots sometimes experienced.... In this design, at rest the O-ring is pushed into the front corner of the gland, and as soon as the poppet moves on firing, it moves back away from that corner into the center of the gland.... I hope that will avoid any "stiction" issue on the first shot after sitting.... Only time will tell....

Anyways, there is the idea for a simple balanced valve, with minimum parts, that is relatively easy to machine.... By putting this out in the public domain, I hope to encourage others with the skills and equipment to jump on the train and let's get these balanced valves out of the station, and roaring down the track, into the mainstream of PCP airgunning….

Bob
Title: Re: Simplified Balanced Valve
Post by: Alan on December 23, 2018, 02:13:39 PM
A very clever design. I trust you didn't lose too much sleep?

There is another advantage to publishing the design—no one can "steal" it, and call it their own. And, there is no way anyone can claim patent infringement.


Title: Re: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 07:06:03 PM
That, my friend, was the plan....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: tkerrigan on December 23, 2018, 11:32:11 PM
Could a smaller hole be drilled through the peek rather than the stem?  Then use an acetylene tip reamer to adjust the size larger if needed?  Regards, Tom
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 08:18:18 AM
There is not much room between the stem and the bottom of the O-ring groove, which is in the smaller diameter part of the poppet.... If you can get a hole in there without hitting the groove, that will work fine.... You might have to shorten the stem somewhat, to before it gets to the O-ring groove, and drill a second hole on an angle from the front end of the poppet (starting in the middle), on an angle to miss the O-ring groove, and intersect the vent hole between the O-ring, and the end of the stem.... It depends on the dimensions of your poppet, and the CS of the O-ring chosen.... You could use a Metric O-ring with a smaller CS....

Good Luck....

Bob



Title: Re: Simplified Balanced Valve
Post by: rsterne on December 28, 2018, 06:08:37 PM
Now that Christmas is over, I got back into the shop to start on the parts for my new simplified balanced valve for my Hayabusa Mk.II…. Yesterday I roughed out the poppet and stem and assembled them.... The stem is made from a piece of 1/8" O1 Drill Rod.... It is drilled from the front end with a 3/64" drill to a depth of 1.20", which is about 1/4" behind the seat of the poppet, and about in the middle of the valve exhaust port.... It took a while to drill that deep, because the flutes on the drill are only 3/4" long, so after that I could only drill about 0.015" at a time before clearing out the chips.... otherwise the drill would have broken off in the hole for sure.... The front 5/8" of the stem is threaded 5-40, the reason for that size is that you don't have to turn down the shaft, the nominal OD of the threads is 1/8" and the die just screws on.... The new Die Holder I made worked perfectly, and the threads are nice and straight.... The poppet was turned down oversize and then drilled through with a #38 drill, which is the tap size for 5-40 threads.... It was then counterbored from the back to 0.128" for a depth of 0.300", leaving a shoulder inside where the unthreaded portion of the stem will stop.... and then tapped from there to the front of the poppet.... I then coated the inside of the hole in the poppet and the threads with Loctite 638 (green) and assembled the poppet and after wiping off the excess (and making sure there was none inside the vent hole), I left it to dry overnight....

The next step was to make the thimble.... I used a piece of 1144 Stressproof steel that is 1/2" OD, turned the back end flat, centerdrilled it, and then drilled a 1/4" hole 1.25" deep, the front of which is the spring pocket.... I then used a 19/64" drill (1 size under 5/16") and drilled in for the front portion of the poppet to a depth of 3/4", then drilled out the back to 27/64", finishing it to a depth of 0.300" using a 7/16" mill for the pocket to miss the rear part of the poppet.... I then used a 5/16" 4-flute mill to finish the front bore to a depth of 0.830", enough that the finished poppet can go just below flush with the back edge of the thimble without either the front of the poppet hitting the front of the bore, or the spring going coil-bound.... Once the bumper, which is a 7 mm ID x 1.5 mm CS O-ring (10 mm OD), is installed on the poppet, it will stop it 0.050" before anything can come to a crashing halt and get damaged....

The next step was to finish machining the poppet.... I ground the stem off flush with the front end of the spring seat in the poppet and cleaned up the end of the vent hole with a tiny center drill.... With the stem of the poppet in the lathe chuck, and the front running on a live center in the tailstock, I finished the poppet to size and machined the O-ring groove for the 5 mm ID x 1.5 mm CS 70D O-ring (8 mm OD).... It's nice doing it this way as it ends up machined true to the stem.... The last thing on the poppet was to drill the cross vent hole in the stem on the exhaust port side of the seat.... I used a 1/32" drill for that.... I have a selection of small drills coming, as the next size up I have currently is 0.040".... I can go all the way to 0.047" to match the 3/64" hole in the stem if necessary.... That is about 2.3 times the area of the current 0.031" vent hole....

The last thing to do on the internals of the valve was to finish the thimble.... I finished the length to 1.90", the same length as the previous SS valve thimble I made, so that if this new valve doesn't work I can make SS internals to fit the valve body (which I still have to make)…. I then drilled the front end to a depth of 1/2" and tapped it 8-32.... I turned the OD of that portion to 0.290" OD so that it will have lots of clearance in the 5/16" milled shoulder I will machine in the perforated front mounting wheel.... The center hole in that wheel will be 3/16", which will be a loose fit on the 8-32 screw used to mount the thimble.... I turned off the last 1/8" of threads on the mounting screw, so that it can be tightened up against the bottom of the threaded hole without damaging the threads.... When it is tight there is 1/4" of space between the head and the end of the thimble, so that I can set the end play to just a few thou and yet have lots of radial play so that the thimble is self-aligning with the poppet.... The last machining on the thimble was to cut a 10 deg. taper joining the two ODs.... Here is what all the parts look like....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Mk%20II%20New%20Valve%20Parts_zpsrcn09wtn.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Mk%20II%20New%20Valve%20Parts_zpsrcn09wtn.jpg.html)

I know for a fact that the O-ring doesn't leak, at least at low pressures, and yet slides easily.... If I slide the poppet into the thimble without the spring in place (with the vent hole plugged), it compresses the air in the thimble and the poppet pops back out from that tiny bit of pressure.... With the bumper O-ring in place the poppet stops with about 1/32" showing behind the back of the thimble.... I will set the back of the thimble 1/4 from the seat of the valve and that will give me about 0.220" of lift before the bumper touches inside the thimble.... The stem of the valve, however, will only protrude 0.200" behind the back of the valve body, so the hammer cannot drive the poppet far enough to make it crash inside the thimble....

Next step is to make the valve body, and the perforated wheel that mounts the front of the thimble....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 06:23:17 PM
I finally got back into the shop today and finished the new valve.... Here is the front end, showing the perforated mounting wheel for the thimble....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zpsvof6r32i.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zpsvof6r32i.jpg.html)

The thimble is free to move radially about 0.020" where it fastens to the center of the wheel, so that it can self-align with the poppet.... The back end has a much larger port than the previous valve.... You can see the vent in the stem down inside the exhaust port....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve_zps82u60mav.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve_zps82u60mav.jpg.html)

The throat is 3/8", and the stem is 1/8", so the area is the equivalent of a hole measuring 0.354", or almost bore area for the .357 cal and larger than all the other calibers that can fit on my Hayabusa Mk.II…. The exhaust port is 0.328", and the transfer port for the .357 will be the same size.... For the smaller calibers I will match the transfer port to the caliber.... The OD of the transfer port has increased to 7/16", so I had to drill the hole in the main tube out to match that....

On first assembly I had a small leak, so I took the valve apart, ran a 1/2" end mill (by hand) up against the seat, undercut the PEEK poppet by 3 deg. so that it only touches around the outer edge, and then lapped it with Solvol Autosol, cleaned everything and then burnished the poppet against the seat.... It sealed up just fine.... I started at 500 psi, there were no issues getting it to seal, and I dropped the hammer down the tube a few times to get it to burp.... It still wasn't leaking, so I filled it to 1000 psi, then 1500, 2000, 2500 and finally 3000 psi, which is the MSWP of this PCP.... Each time I dropped the hammer down the tube to fire the valve, and as expected as the pressure increased it took more hammer strike to get the valve to "pop".... There was no tendency for the valve to burp at pressures over 1000 psi, just a nice clean pop, and if I launched the hammer a bit harder, a very loud "BANG".... I am delighted that the valve seals up fine, and look forward to getting the gun built up so that I can test further....

I will be building a new SSG for this gun, it never had one.... Once that is done I will be able to find out how tuneable the valve is.... I have my fingers crossed....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 04, 2019, 07:06:56 PM
The valve is still holding air fine after 24 hours, so I guess I got the leak fixed.... I spent the day today making/modding the rest of the parts to assemble the .357 version of my Hayabusa Mk.II using this new valve.... The first thing to do was to modify the receiver to accept the new 7/16" OD transfer port, and then drill out the port in the receiver to 0.328" to match the exhaust port in the valve and make the new transfer port from a piece of Delrin rod.... I then milled out the barrel port, leaving it 0.280" wide but increasing the length to 0.380" and blending that into the diameter of the transfer port.... This insures that the barrel port is at least as large as the transfer and exhaust ports, and also the same area as the chamber minus the bolt probe.... The ports are now all 0.328", compared to the 0.281" they were previously....

I have two hammers for this version of the Hayabusa…. The .224/.257 hammer weighs 123 gr. including cocking handle, and had a stoke of 1.2".... The .284/.308/.357 hammer weighs 147 gr. including cocking handle, and had a stroke of 1.45".... The new valve is 0.10" further back in the tube, so I lose that much stroke, and I decided to try the smaller hammer, even though the valve is larger than the .357 valve I had before.... I am confident that the balanced valve will at least make up that much difference.... I had a look at all the hammer springs I have to choose from, and decided to use the original spring from the .357 for my initial testing.... It is a McMaster Carr spring that is 3" long, 0.36" OD, made from 0.051" wire and rated at 15 lbs/in.... although once I set it, the length decreased by 0.1" and the rate was only 14.1 lbs/in.... The .357 originally took about 23 lbs to cock with this spring, at the 1.45" cocking distance.... With the SSG, using this spring, I have set the preload at 0.30" (4.2 lbs), and with a small gap between the SSG and hammer, and the new 1.10" cocking distance, the maximum cocking force will drop to about 19 lbs.... I suspect this will still be more hammer strike than I need for the new balanced valve, but I have two 3" springs with lower spring rates, of 0.047" and 0.049" wire, to reduce the hammer strike further if required.... I also have some 3.5" springs, but the spring rates are similar, and I have enough cocking distance without reaching coil bind with the 3.0" springs, so unless I need to increase the cocking distance, I should be able to stay with the 3.0" springs.... Here is what the new SSG looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20SSG_zpsm7lifdbl.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20SSG_zpsm7lifdbl.jpg.html)

If I end up needing a heavier hammer with more stroke, I can revert to the other one I have.... but for now I will use this one from the .224/.257 version....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/SSG%20with%20257%20Hammer%20and%20TP_zpsfxwjeytc.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/SSG%20with%20257%20Hammer%20and%20TP_zpsfxwjeytc.jpg.html)

You can see the new, larger transfer port in that photo as well.... This is as big as I can go with the current valve and bolt probe design, it is 92% of the caliber, at 0.328".... I put the .357 barrel into the receiver before dinner.... and tomorrow I hope to finish the assembly and test this new valve in the .357 Hayabusa….

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 05, 2019, 01:13:04 PM
Before removing the trigger group and stock from my .457 Hayabusa Mk.III (those are shared between all the versions), I thought I would perform a test to see if "stiction" was an issue with the SS Valve I recently built and installed in it.... The gun has been sitting for weeks, and still had over 3200 psi sitting in it, but I topped it up to its usual 3600 psi fill and fired 4 shots through the Chrony…. They were 962, 973, 978 and 973 fps.... That means the first shot was less than 2% below the peak, so stiction is NOT an issue for that valve....

I then assembled the .357 Hayabusa Mk.II, using the new simplified balanced valve I have been working on.... The first shot was with the 0.051" spring with 4 turns of gap, and with a 131 gr. bullet it screamed across the Chrony at 955 fps.... That is more power than I have ever had before, which is attributable to the larger port, of course.... I backed out the gap a couple of turns at a time, and the velocity didn't drop until I was 12 turns out, at which point it tanked to 275 fps.... I then reduced the gap to zero, and the gun was only slightly louder than with 10 turns of gap, and absolutely NO sign of hammer bounce or machine-gunning.... So, the initial test was successful on every count but one.... the valve acts like a Cothran valve, either it cycles or it doesn't....

I took the SSG apart and installed the lightest spring I have of that size, made from only 0.047" wire, with a spring rate of only 11 lb/in.... The velocity was essentially unchanged (a few fps less), and it still showed no signs of adjustability.... With 10 turns of gap it was 950 fps, 940 fps at 11 turns, and 270 fps at 12 turns of gap.... I spun the adjuster back in to 4 turns of gap and fired a few 154 gr. bullets through the Chrony and they were 892-894 fps (273 FPE).... Did I mention that this valve is INCREDIBLY STABLE for velocity?....  ::)

So, I have drained the air from the reservoir, and will be pulling the valve and drilling the vent out to 0.040" to see if that makes any difference.... If not, then I will go all the way to 0.047", which is the size of the hole through the stem.... Bottom line at the moment is that I am quite pleased with the new valve, it does 90% of what I wanted.... I have increased the size of the valve throat from 0.328" to 0.375", and the poppet from 3/8" to 7/16".... The hammer weight has been reduced from 145 gr. to 122 gr. (and can obviously be much less) and the hammer stroke from 1.45" to 1.09" (much less with the large SSG gap)…. The cocking force has gone down from 23 lbs. to about 9 lbs.... The shot cycle sounds crisp, with no sign of hammer bounce.... The ONLY thing I have not achieved so far is tunablity…. We'll see if that can be achieved or not.... If not, at least I have still produced a simpler balanced valve that yields big power for low hammer strike....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 05, 2019, 06:18:23 PM
This valve is obviously "blowing open" like a Cothran valve does.... I tried increasing the vent diameter from 0.032" to 0.040" (a 56% increase in area, possibly double the flow because of friction affects)…. and it made NO difference to the way the valve operated.... Same velocity, same cliff, at the same SSG gap.... I then made an MDS hammer to replace the steel one.... I kept the same 1.09" stroke but the hammer with handle weighs 1/3 as much, 42 g. instead of 123 g.... The only way the gun would fire with the light 0.047" spring was with the SSG gap set to zero.... With just 1/2 turn of gap the velocity dropped to under 200 fps.... BTW, as Travis requested, I tried some preload with this setup, by turning the SSG in a couple of turns, to give 4 lbs. of preload.... The velocity remained the same as with zero gap, the bark was a little louder, and there was still no sign of hammer bounce....

I tried the original 0.051" spring with the light hammer and it would fire properly (955 fps) with 1 turn of gap, but at 2 turns of gap it was inconsistent in velocity, shots varying from 450-950 fps.... (I saw similar things with the Cothran valve when it was right on the edge of the cliff, the ES went through the roof.... So, for that matter did the original SS valve I got from Travis, which had only about 100 fps of adjustability and then a cliff).... Anyways, I can either use the light hammer and the heavy spring with 1 turn of gap on the SSG.... or the heavy hammer and the light spring with about 8-10 turns of gap.... With the light hammer and heavy spring set to 1 turn of gap I checked the pressure drop.... With the tiny tank fitted my total volume is only 6.6 CI (108 cc) way too small for proper performance at 265 FPE (0.4 cc per FPE)…. Filled to 3000 psi, the pressure drop was 498 psi (measured with a digital gauge) for a shot of 956 fps with the 131 gr. bullet (266 FPE)…. That works out to 1.17 FPE/CI.... pretty respectable for this much power with way too small a plenum.... The normal volume available for a shot is 28 CI, which means that I should only see a pressure drop of about 120 psi instead of 500, and with the average pressure increasing from 2750 to 2940 the FPE should increase nicely as well, hopefully with an increase in efficiency too....

Obviously, neither current hammer solution is the best.... The next time I have the valve apart I will drill the vent out to 0.047", even though I don't expect that to make any difference in the tunability.... The next step is to get the hammer weight somewhere in the middle, so that I can use the light spring (hopefully) but with about 4 turns (0.20") of gap before it falls off the cliff.... To do that, I  will make a brass or steel insert for the MDS hammer, drill it out and press in the insert.... I think about double the weight I am now, which is 2/3rds what I started with, should be about right, but that is really just a guess, so I will try and hit about 80-85 g.... With 3 springs to choose from, I should be able to get it about right....

So I have accomplished all the goals, except tunablity…. This valve would be a sweet setup tethered to an adjustable regulator.... Since this version of my Hayabusa will primarily be shot tethered, I will likely leave this valve in the gun until I can come up with something better.... The alternative would be to make an SS valve with the same proportions and try that.... Before I go that route, I think I will fit the .224 cal barrel and receiver to this gun and see what happens, and what changes I might have to make for that huge caliber change.... If that works out OK, then I will complete the conversion for the other 3 calibers, .257, 7mm and .308.... Lots of fun ahead....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 02:24:15 PM
I rebuilt this valve yet again, drilling out the vent to 0.052" and fitting a bit heavier valve spring.... The valve is now adjustable, and incredibly efficient.... Here are the results, using the SSG with the 11 lb/in spring and 3.5 lbs preload, with the gun tethered at 3000 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg.html)

The valve is working about the same as an SS valve in terms of adjustability.... The hammer spring is perfect for the 131 gr. bullet, it is solidly on the plateau at over 950 fps with 2 turns of gap.... With the 154 gr. bullet it needs a slightly heavier spring or more preload to reach the plateau, which would be at about 890 fps.... However, since I never tune my guns to shoot on the plateau because it is quite inefficient, this SSG spring setup is just fine.... The cocking force is just 13 lbs. instead of the 23 lbs. with the smaller, conventional valve.... I tried a couple of short strings just to prove that I can get a bell curve, but bear in mind this is with the tiny tank fitted, and a total reservoir volume of only 108 cc....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg.html)

With the 154 gr. bullet I had the SSG adjusted with 2 turns of gap, for about 3% below the plateau, and got a declining shot string, although the first 2 shots were within 15 fps (2% ES)…. With the 131 gr. bullet, I used 5 turns of gap on the SSG to produce a nice bell-curve at about 9% below the plateau.... The first three shots had an ES of only 8 fps, which is less than 1%.... Bear in mind that with the 500 cc tank fitted, the total air capacity is 460 cc, which will give over 4 times the shot count within the same ES....

I need to brag about the efficiency for a minute.... What I got for each of the 4 shots with the 131 gr. bullet is plotted on the dotted line above.... The first shot only used 284 psi from my 108 cc reservoir, or just 129 CI of air to produce 216 FPE, for 1.67 FPE/CI.... That is definitely off the scale compared to any other Big Bore PCP I have ever shot, or am aware of.... The average over those 4 shots was 1.53 FPE/CI....  :o

To say I am delighted with where I am would be a complete understatement.... It was difficult to get here, requiring several changes to the valve.... but it turns out that the large vent through the stem was the key.... We have to get a high enough flow rate through the vent to keep the valve from blowing open.... Once that is achieved, the valve is definitely tunable, and capable of producing a bell-curve.... I am just over the moon the way this worked out.... My thanks to all those who provided input along the way, and in particular to Mike, who by quantifying the fill time for the balance chamber led me in the right direction....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: Alan on January 09, 2019, 03:14:34 PM
And the saga continues!

I have often wondered what airgun engineers go though when designing something new. I'm sure they think their efforts were rewarding, at least monetarily. But you, Mr. Sterne, it isn't money which drives you. Rather it is the perfection of the art, and the thrill of accomplishment we all strive for. Thank you for showing the rest of us, how it is done!
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 04:28:00 PM
After the gun sat overnight, I shot the pressure down using 68 gr. roundball, starting from 3000 psi.... It took 11 shots to get down to 270 psi.... The first shot was supersonic at 1160 fps, the 2nd shot was 1108, and it progressed down to 446 fps for the 11th shot, taken at only 315 psi.... There was NO sign of hammer bounce, regardless of how low the pressure got.... the gun just got quieter and quieter as the velocity dropped.... I then refilled it and cranked in 2 turns of preload on the SSG, so that there was 4.7 lbs. of preload against the stem.... I was finally able to get the valve to dump the tank down to about 300 psi in 1 shot by doing that.... Now, you would never tune the gun this way, because you are wayyyyyyyyyyy up on the plateau and the efficiency would be terrible.... but there you go, Travis, I forced it to machine-gun for you....  ::) …. I really doubt it would ever do this with any kind of a tune you would ever use, but if you insist on running lots of preload against the stem, you may be able to create a tank dump....  ;D

After draining the tank I pulled the valve out yet once more, because I had a smaller poppet spring I wanted to install, and then sleeve down the spring chamber to reduce the volume and speed up the pressure rise in the balance chamber.... I made a Teflon sleeve to fit inside the 1/4" bore of the 0.40" deep spring chamber, and drilled it out to 13/64".... This reduced the volume of the chamber from 0.55 cc to 0.44 cc, and I was curious what effect that would have on the tuning range.... I put the gun back together, and this is what I got....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve2_zpsyty6gnro.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve2_zpsyty6gnro.jpg.html)

NOTE: When calculating the efficiency, I forgot to include the air in the hose, gauge and valve.... I have estimated that at 12 cc, making the total 120 cc instead of 108.... This reduced the FPE/CI numbers to more realistic values, shown on the corrected graph above.... I still won't have the actual numbers until I install the 22 CI bottle....

The maximum velocity stayed the same at 955 fps, but the velocity dropped off faster as I increased the gap, as I expected it might.... Instead of a range of about 120 fps before the valve quit working, that range increased to 180 fps.... The velocity was still very stable when tuned below 800 fps, whereas with the larger spring chamber I couldn't even tune it that low.... Being able to tune it down that far allowed the efficiency to reach even higher than yesterday, I got to 1.57 FPE/CI at 864 fps (217 FPE)…. With my old conventional valve at the same power I was getting 1.13 FPE/CI, which I thought was pretty good at the time.... I'm now using 2/3rds of the air for the same power....  :o

Decreasing the balance chamber size by 20% certainly widened the tuning range.... However, it really only made about 1 turn difference in the SSG gap for the same velocity.... That means the valve is taking the same hammer strike to open, but with the pressure in the balance chamber rising faster, a bit more hammer strike is needed to get the same dwell.... It was definitely worth changing to the smaller poppet spring and making the chamber smaller.... Once again, it seems obvious that you want the smallest balance chamber you can achieve, with the largest vent.... That definitely seems to be the key to getting this valve tuneable....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 03:49:58 PM
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 above 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....  8)

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....  ;D …. 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

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 04:39:11 PM
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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zps9g5whedg.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zps9g5whedg.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Strings_zpsxhj6xe6d.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Strings_zpsxhj6xe6d.jpg.html)

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....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Valve_zpspxfpqaej.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Valve_zpspxfpqaej.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Strings_zpsizgrffwu.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Strings_zpsizgrffwu.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/257%20Hayabusa%20Balanced%20Weights_zpstzcnoeou.png) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/257%20Hayabusa%20Balanced%20Weights_zpstzcnoeou.png.html)

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
Title: Re: Simplified Balanced Valve
Post by: Lob0426 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.
Title: Re: Simplified Balanced Valve
Post by: rsterne 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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Lift%20Measurement_zps3rlqrkr2.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Lift%20Measurement_zps3rlqrkr2.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Lift_zpsjcfxjdbb.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Lift_zpsjcfxjdbb.jpg.html)

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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Poppet%20Spacer_zpsxpqhyf7e.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Poppet%20Spacer_zpsxpqhyf7e.jpg.html)

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
Title: Re: Simplified Balanced Valve
Post by: Alan 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?
Title: Re: Simplified Balanced Valve
Post by: rsterne 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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Valve_zpsdehvbvfz.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Valve_zpsdehvbvfz.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Strings_zpsqp9tvesw.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Strings_zpsqp9tvesw.jpg.html)

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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Bal%20Vlv%201850_zps5db6cxui.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Bal%20Vlv%201850_zps5db6cxui.jpg.html)

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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png.html)

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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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
Title: Re: Simplified Balanced Valve
Post by: rsterne 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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20Final%20Velocities_zpsnwhkxqxt.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20Final%20Velocities_zpsnwhkxqxt.jpg.html)

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....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20Final%20Strings_zpsqvplxbwk.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20Final%20Strings_zpsqvplxbwk.jpg.html)

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

Title: Re: Simplified Balanced Valve
Post by: Alan 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.
Title: Re: Simplified Balanced Valve
Post by: rsterne 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
Title: Re: Simplified Balanced Valve
Post by: Alan 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.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 27, 2019, 07:10:32 PM
The cocking effort on my .357 has dropped from 23 lbs. to 12-15 lbs, depending on the SSG gap....

The Daystate 2-piece "Slingshot" hammer is great for valves that open easily.... Before balanced valves, that meant relatively low powered PCPs.... The SSG works in a similar manner, but instead of stopping most of the hammer mass and letting only a small portion open the valve.... it just stops the spring.... This means that more of the spring energy goes into opening the valve.... plus it's easy to make for the home tinkerer.... Both work to help stop hammer bounce and save air....

Bob