GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: rsterne on December 02, 2012, 10:41:59 PM
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I have used an adjustable hammer only once, and that was on my Hayabusa.... The results were somewhat confusing and I didn't find it particularly useful.... I used an MRod adjusting screw threaded into my hammer, and what I found was that over quite a large range of adjustment it made virtually no difference to the velocity.... Only when extended a long ways did it start to reduce the velocity to a significant degree.... I though about why that was occurring, and realized that when you reduced the travel by extending the nose of the hammer, that since the adjuster was sitting on the valve stem when uncocked, the hammer actually moved back, increasing the preload on the spring.... Therefore, even though the travel was reducing, the hammer was seeing a higher average spring force, nearly cancelling the advantage of increasing the hammer travel....
I wanted to increase the travel on the hammer for my new Milleium Pumper project, so this morning I used Lloyd's Hammer Strike spreadsheet to investigate what was happening.... I used a Challenger hammer for the inputs, along with my heavy Disco hammer spring, and came up with the following graphs showing hammer Energy and Momentum.... The adjusting screw is 28 TPI, so each turn of the screw changes the hammer travel by 0.036", and it therefore changes the preload by the same amount.... That information is graphed as "Preload Varies with Stroke".... The second graph was generated with the same hammer travel distances, but is "Preload Constant", set at 10% of the free length.... That value is the same on both graphs when the stroke is 0.58" (the third dot counting from the left).... Both graphs have identical scales, so they are easy to compare, and the lines would cross at that third dot from the left....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/HammerTravel.jpg)
The first thing to note is how little the hammer energy and momentum change with the normal setup.... I didn't look at extending the adjuster out a long ways, because I'm after more travel, not less.... but you can see a slight steepening of the trend on the left side as the travel decreases.... That would be consistent with the way my Hayabusa reacted to decreasing the hammer travel.... little change until you went quite a ways, and then decreasing velocity.... Next you will note the drastic difference in the second graph.... Once you hold the spring preload constant, the Energy and Momentum both increase linearly with increases in travel.... I estimated that the spring would become coil bound if the stroke increased beyond about 0.70", so the last (right hand) datapoint is omitted on the second graph....
Ponder this information while I do the next post about how I built a hammer where the travel is adjustable but the preload is constant at whatever you set using the RVA....
Bob
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I spent the afternoon building a hammer to put what I learned from Lloyd's spreadsheet into practice.... I needed a hammer that would fit into a Disco tube, but had no "waist" as I will be using an MRod trigger group.... I also wanted a bit more weight, so a straight cylindrical shape met all those criteria.... The length and diameter are the same as a 22XX / Disco hammer.... and since I was using a 22XX Crosman steel breech (with the forward breech screw location) I didn't need to relieve the top front portion of the hammer.... I wanted to be able to use the hammer spring from a QB 7X, which is 3/8" longer and slightly bigger in diameter than a Disco spring.... so I made the travel adjuster from a piece of 3/8"-24 NF bolt and threaded the drilled and tapped the inside of the hammer appropriately.... A spring guide was threaded into the travel adjuster, and moves with it.... The hammer spring sits against the back of the adjuster, so the preload doesn't change when you turn it.... What happens is that the front of the adjuster rests against the end of the valve stem, and the hammer moves back and forth over it as you change the adjustment setting.... Since the sear is in a fixed position, the further forward the front of the hammer the further it has to be pulled back to cock the gun.... You therefore have adjustable travel but constant spring preload.... Here are the parts, and the assembled hammer, which weighs 70 gr. including the guide, about 10 gr. heavier than a 22XX hammer....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/IMG_2834.jpg)
In the photo of the assembly, the travel adjuster is protruding beyond flush about 0.1".... It can move back inside the hammer about 0.2" which increases the travel over stock.... Eventually the face of the hammer will hit the back of the valve, and that will be the effective limit of the available travel.... I shortened the threaded adjuster so that the hole in the hammer is deeper to accomodate the extra length of the QB spring without having to make a very long RVA....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/IMG_2833.jpg)
The extended spring guide runs in a hole in the RVA screw.... It will be cut to length so that it protrudes through the screw only when the gun is cocked, acting as a cocking indicator.... The threaded hole in the top front of the hammer is for an 8-32 setscrew pressing on a small piece od Delrin which will act like a brake to hold the travel adjuster from moving.... There will be a screwdriver slot in the end of the guide to adjust the travel.... A standard Crosman cocking pin sits in the back hole on top of the hammer, but it is moved back 1/16" from the stock location so that it won't hit anything at the forward end of it's stroke....
I made a couple of other small mods while I was at it.... I lengthened the front of the cocking slot in the tube about 1/8" so that it is slightly further ahead than the front of the cocking slot in the Crosman steel breech.... I also shortened the back of the bolt 0.110" for the same reason.... The hammer face will now hit the back of the valve before the pin hits anything, and in fact I may turn off a small amount from the back of the valve to get the maximum possible travel possible.... Unless I lengthen the cocking slot in the breech, it (and the back of the valve) becomes the limiting factor on hammer travel....
I will likely just use the adjustment to find the maximum possible hammer travel where the hammer hits the back of the valve, and then set it so that it doesn't quite hit.... That will allow me to get the highest possible hammer Energy and Momentum with the least preload on the spring, and therefore the easiest cocking.... Once that setting is determined I will back off the RVA until I reach the final tune desired.... At least that is how I think the adjustments will be made.... At least now, increasing the hammer travel will have an instant, and definite, affect on the velocity....
Bob
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Yup, Very aware of that issue just recently having to shoot my M-rod in .177 at 12#'s energy.
With my light hammer at Minimal preload ( @ 3/16" ) and travel full long gun was shooting 10.3's @890 fps.
Just going to a 8.4 weight pellet changing nothing else velocity went to @ 1020fps there about.
Staying with the lighter 8.4 pellet it took 13 1/4 turns OUT on travel adjustment to lower velocity to @ 790 fps.
* .036 x 13.25 = .486"
So it took near 1/2 inch reduction in travel to lower velocity and can confidently assume this SAME increase in spring preload raised the DWELL killing the efficiency potential :P
Need to manufacture a new rear cap that allows hammer spring preload values to go back to minimal settings as you back the hammer up reducing stroke.
Or ... fit a spring of equal spring rate thats shorter and fudge the difference seeing if shot count go's up when powers turned down ???
Thinkin out loud ....
Scott
Bob,
you were posting while I was writing ....
Love it !
See with my custom LW hammers a similar design possible where Spring rests on backside of striker and turning it ( Threaded to hammer ) you just change the valve impact position relative to hammers stroke while the hammer lock point remains constant .... very clever, get right on it ;D
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You would need a T type bolt in the end cap the same size and pitch of the striker pin and a hex hole through it that was the same size as the hex in the pin, so as you turned the pin in or out the bolt would move up or back maintaining the same preload that you had set . I call it a bolt but it would be flat and the same diameter as the spring guide so nothing would tilt. Like a set screw with a washer welded on.
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Just thought I would add the data for extending the nose of the hammer further to reduce the travel more.... As expected, the graph steepens....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/HammerTravel2.jpg)
You will note that the trend is consistent with my experience on the Hayabusa, and what Motorhead mentioned on his MRod.... There is very little effect on hammer Energy or Momentum in the first part of the adjustment, and then once you reduce the travel more it begins to have a noticable effect.... However, the effect is still MUCH less than what it is with my new hammer that keeps constant preload on the spring....
Bob
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Keep up the good work Bob...reading with great intrest.
cheers,
Douglas
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you got me glued to the thread Bob
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Bob, nice work , and a good idea on keeping the spring preload constant while adjusting the stroke length.
The hammer dynamics is a lot more complex than I thought a while ago. Also, the adjustability really has more variables than we normally take advantage of.
You mentioned about seeing what the max stroke you could get out of the Disco style arrangement. I got .90" out of the big valve gun and it required doing all the things you mentioned, including drastically altering the back end of the valve. One advantage to the long stroke is that you don't have to use a real stiff spring to get adequate hammer energy. That can make the gun easier to cock, and easier on the trigger release.
The added adjustability does have a down side..... that is, never knowing if you are actually finished with the testing, LOL.
Lloyd-ss
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Day off ... nutting happening to keep out of the shop ???
MDS Nylon outer hammer threaded 9/16-18 internal
Delrin inner adjuster threaded 9/16-18 external
* 1/4-20 bolt threaded full length giving a head to get an adjustment wrench on, forward tip hits upon valve stem.
A shallow 9/16 counterbore on rear of hammer so I.D. threads won't drag on spring, Spring centering stub on adjustable striker piece.
Combined assembled weight as shown 29g ( target was 28g ... o'well )
So here an M-rod hammer using Bobs idea.
Spring length stays fixed unless preload adjuster is tightened.
Hammer travel has an @ 1/2" travel adjustment range.
* Because of space constraints getting some adjustment distance within hammers I.D. with striker FLUSH with hammers head spring preload is @ 1/4" more than stock hammer provides.
So while not ideal, should give a solid platform for testing ;D
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The only downside of having the preload constant is that at some point in increasing the travel, you may drive the hammer spring into coil bind.... That can't happen when you are adjusting the travel on an MRod style hammer.... Adding travel decreases preload and the maximum compression remains the same....
Bob
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The only downside of having the preload constant is that at some point in increasing the travel, you may drive the hammer spring into coil bind.... That can't happen when you are adjusting the travel on an MRod style hammer.... Adding travel decreases preload and the maximum compression remains the same....
Bob
Bob,
Indeed true about coil bind "IF GUN REQUIRES" a lot of spring pre-load in it's tune.
Got lucky with my Regulated & Light hammer fitted M-rod being able too get all the power wanted on the factory 8# spring at MINIMAL spring pre-load.
My chasing this was for TURNING DOWN THE POWER at times to keep spring pre-load minimal as stroke was reduced .... This Idea you shared does that Exactly !!
Efficiency numbers surely will improve at shorter hammer travels because the dwell is not increasing with high spring pre-load.
This is Cool !!
Thanks Bob !!
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After quickly knocking out the one shared above, thought it over and knew something better could be done with a few design tweaks.
So I did ..... ;)
Increased thread size to 5/8-18 allowing center striker to have full hammer length threading.
Also able to shorten 1/4-20 adjustment screw in the middle to accommodate a full depth counter bore at the same depth as factory hammer keeping the @3/16"
"Min" spring prel-oad setting. ( One above with shorter smaller diameter threads increased it :P )
So ... a final design that is INDEED going into rifle first opportunity ;)
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I don't understand how reducing the hammer travel will increase the efficiency at a given FPE level.... You will have to add preload to the spring to get the energy back.... For a given energy, if you don't change the mass, you have to keep the velocity the same.... To get that velocity, if you decrease the travel you must increase the spring force and vice versa....
Bob
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I don't understand how reducing the hammer travel will increase the efficiency at a given FPE level.... You will have to add preload to the spring to get the energy back.... For a given energy, if you don't change the mass, you have to keep the velocity the same.... To get that velocity, if you decrease the travel you must increase the spring force and vice versa....
Bob
Think I am following you ?
Reason I built hammer was so I can REDUCE power, taking away hammer travel reduces momentum, Spring rate & pre-load remains a constant.
My take at least is based on previous tuning where I reduced power by Lessening stroke because spring pre-load was already dead soft. as stroke was taken away, spring pre-load was increasing the same distance stroke was being reduced.
Am hoping that with spring pre-load remaining constant, backing off on stroke only will have valve able to launch pellet at a reduced velocity and because pre-load is minimal valve will also close faster increasing the efficiency OVER the OEM hammer design where stroke is very short and pre-load very high.
Would ideally like to see subtle stroke changes have a more linear profile in velocity which is WHAT I thought was reason behind this design in the first place ???
** Remember I'm regulated here !
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Having the adjuster NOT affect the preload will make the travel adjustment much more linear, effective, and easier to understand, all good things.... All I was saying is that I don't see how using less travel FOR THE SAME FPE would increase the efficiency (because you have to increase preload to get the velocity and energy back).... Since you are looking to reduce the velocity and energy and you are already at minimum preload, then this new style adjuster should work well for you....
Bob
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Having the adjuster NOT affect the preload will make the travel adjustment much more linear, effective, and easier to understand, all good things.... All I was saying is that I don't see how using less travel FOR THE SAME FPE would increase the efficiency (because you have to increase preload to get the velocity and energy back).... Since you are looking to reduce the velocity and energy and you are already at minimum preload, then this new style adjuster should work well for you....
Bob
Glad that got cleared up .... It's all good Bob.
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I'll still bet on the efficiency going up at low power with a lighter hammer. The new travel adjuster will make it easier to dial in though.
cheers,
Douglas
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Bob,
Got the second version hammer installed this AM & went outside for a spell before heading off to work.
Kept spring preload full soft ( @ 3/16" pre-load ) Took hammer travel adjustment progressively shorter and like a linear graph velocity dropped away very evenly with each turn. Velocity over the Chrony was rock steady staying within 2-3fps for every string of 5 shots done at each stroke reduced position.
Got us a keeper .....
Thank You once again for sharing your design ideas ;)
Scott
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On the efficiency 'thing', it is the momentum the valve puts back into the hammer on close that the travel adjustment can't change; only the hammer mass will have an effect on that. Making the lift high, but dwell short is where hammer mass comes in. For 12 FPE energy levels, I suspect a lighter hammer will get what you want. Considering the ease of hammer swapping, it looks like a fine exercise to try. say maybe 20-23 grams? It looks like a max efficiency for your set up will occur at a maximum spring/minimum hammer mass scenario.
going to try a few shims on the two o-ring/light hammer 2263. Shoot for an 880-900-880 tune across __ shots( should be 30 plus as I am at 30 now with 50% more spread ).
cheers,
Douglas
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On the efficiency 'thing', it is the momentum the valve puts back into the hammer on close that the travel adjustment can't change; only the hammer mass will have an effect on that. Making the lift high, but dwell short is where hammer mass comes in. For 12 FPE energy levels, I suspect a lighter hammer will get what you want. Considering the ease of hammer swapping, it looks like a fine exercise to try. say maybe 20-23 grams? It looks like a max efficiency for your set up will occur at a maximum spring/minimum hammer mass scenario.
going to try a few shims on the two o-ring/light hammer 2263. Shoot for an 880-900-880 tune across __ shots( should be 30 plus as I am at 30 now with 50% more spread ).
cheers,
Douglas
Douglas,
No need to go lighter yet on hammer IMO.
Earlier tests on hammer weight was to find an optimum hammer weight ( Mass ) and balance it to the available 8# OEM spring energy looking for the peak in delivered kinetic energy at valve stem.
So one would think even at reduced travel distances the hammers ability to accelerate remains constant having only it's potential energy at valve being reduced with less stroke distance being achieved.
Not saying set up is ideal for LOW POWER ( Think an even lower spring rate and lighter hammer would be best keeping stroke long )
But ... have no desire in swapping out parts for each caliber / pellet weight and tune :P
Even before this latest hammer, Rifle changing NOTHING but hammer stroke and a tad bit of pre-load ( less than 2 turns ) can shoot from 35 ft lbs in .22 cal to 12 ft lbs in .177 On the SAME VALVE ... SAME TRANSFER TUBE ... SAME HAMMER SPRING
* Efficiency numbers above 1.15 ave-fpe/cu in per shot in all tunes so far with room for improvement now with the latest hammer design installed.
Pretty dang K.I.S.S. tuning in any ones book ;D
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You never know what path you wil take until you get there.... Nothing could be more true of this adventure into airgunning Nirvana.... What started out as a new way to adjust the hammer travel has suddenly taken an abrupt right turn (or is that left?).... When I installed my new adjustable travel hammer into my Millenium Pumper I really didn't expect anything unusual to happen.... I figured that increasing the stroke would mean I could reduce the hammer spring preload, or maybe even fit a weaker spring, making the gun easier to cock.... and for the most part, that is exactly what happened.... However, when I adjusted the hammer for maximum travel (about 0.2" more than a stock Disco) and ALSO used a lot of hammer spring preload, I actually LOST velocity.... HMMMMMMMMMMMMM.... DOES NOT COMPUTE !!!
I intuitively figured the face of the hammer had to be hitting the valve body, limiting the lift, and that was causing this effect.... It required taking quite a few data points at different pressures and with different springs for this idea to gel in my mind so that I could wrap my brain around it (I'm slow sometimes!).... I can hear bstaley laughing, he already knows what's going on here.... It turns out that the valve stem in my Disco sticks out 0.30" from the back of the hammer.... At the maximum travel setting, the face of my hammer is recessed 0.20".... Therefore, when the outer face of the hammer hits the valve, the MOST it can lift the valve is 0.10" (the difference).... If I don't have enough hammer spring preload to lift the valve that far, you don't notice anything unusual, because the hammer face never hits the back of the valve.... However, at maximum preload, the hammer WANTS to lift the valve more than 0.10".... and IF it could, the velocity would increase (or at least not drop off).... Now for the "lightbulb moment".... When I recess the "travel" adjustment far enough, it is no longer a travel adjustment - it is a LIFT adjustment....
Lots of precedence here, I'll mention two that I am aware of.... One is the bstaley mod for the MRod, where he uses O-rings against the back of the valve to limit the hammer travel and turn the stroke adjuster into a valve lift adjuster.... I never really grasped this until he wrote up an excellent thread on how it works, which you can read here.... http://www.gatewaytoairguns.org/GTA/index.php/topic,37695.0.htm (http://www.gatewaytoairguns.org/GTA/index.php/topic,37695.0.htm) .... My compliments to bstaley on figuring this out and implementing it.... The idea (to paraphrase) of not affecting the first part of the shot string, while limiting the lift (and possibly also the hammer bounce) in the second half of the shot string are a perfect example of critical thinking followed by a simple solution, and I congratulate him for it....
The other place I have seen this used is in the Korean rifles which have a power wheel that adjusts the valve lift.... They use a metal block between the back of the valve and the hammer, which can be moved back and forth by a rotating adjuster on the side of the gun.... When you rotate the adjuster, it in turn rotates this block, which is threaded, and it's fore-and-aft movement changes how far the hammer can travel.... This, in turn, directly alters the lift of the valve.... less lift, less power.... There are probably other examples of this that I am not aware of, and if so, please accept my ignorance, I'm not trying to slight you in any way.... I'm going to post this and take a breath here.... lots to think about....
Bob
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OK, to continue.... Let's assume for a minute that my new style "travel adjuster" is now a "lift adjuster".... How is it different than the bstaley mod?.... Well, for one thing, it is recessed into the front of the hammer instead of the way the MRod (or Challenger) adjuster sticks out the front.... This INCREASES the available hammer travel instead of decreasing it.... Secondly, it has a spring guide attached to it.... How about the lloyd-ss "long stroke hammer"?.... Lloyd of AirGun Lab has been using hammers with a hollow front for quite a while to increase the stroke, a simple and effective method.... He takes that a step further by machining the back of the Disco valve to shorten it, allowing even more hammer travel.... I believe he leaves a central "stub" on which he mounts an O-ring to seal the stem, perhaps he will chime in with the details....
What I've done here is to combine several good ideas, none of which I can take credit for.... However, the result is a hammer for the Disco that first of all increases the stroke, secondly provides adjustability for the valve lift, and thirdly incorporates a spring guide / cocking indicator.... I believe I first saw that idea used by Ribbonstone although his simply sat in the hammer, held in place by the spring.... There is even a fourth possibility, and that is adding a cocking knob to the end of the spring guide (which Lloyd and I and others have already done).... That would additionally add mass to the hammer, and could be turned to adjust the lift.... Lloyd uses a captive O-ring on that shaft as a visual indicator of the valve lift, enabling direct measurement of that difficult to ascertain measurement....
Anyway, there you have it.... I'll be doing a bit more work on this over the next few days, trying to develop it and optimize it.... I am hopeful that the result will be a hammer that not only increases the potential FPE of the Disco, but provides easier tuneability and hopefully even an increase in efficiency and/or shot count....
Bob
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After writing the previous two posts, I went out into the shop, pulled the hammer out of my Millenium Pumper, and modified it slightly.... I removed 0.040" from the back end of the adjusting screw to allow one more turn of travel.... I can now recess the hammer 0.25" from the front face, reducing the maximum valve travel to 0.060" at the point the hammer face impacts the valve body.... I set the RVA to a whisker short of coil bind on the 2.00" x 0.045" hammer spring, maxed out the travel, and took a shot at 1800 psi, recording the velocity.... I repeated this, adjusting the position of the travel/lift adjuster.... I then decreased the hammer spring preload a turn at a time and did everything again.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/MilleniumPumperHammerLimiting.jpg)
If you look at the curve for the hammer spring near coil bind (blue line, reading from right to left), you will see that as you increase the hammer travel (and hence the Energy and Momentum) the velocity increases and then plateaus.... This is the expected reaction to increasing hammer strike, as I've demonstrated many times on regulated guns (ie at constant pressure, in this case 1800 psi).... However, the last 2 turns of travel show something different happening.... At about 1 turn out, where the valve lift can no longer exceed about 0.10" without the hammer hitting the back of the valve, the velocity starts to decrease.... In that last turn of travel (1/24th of an inch = 0.042") it drops like a stone.... This is clear evidence that the hammer is hitting the valve, and that the loss of valve lift is killing the velocity.... At 2 turns out, we see the same pattern, with the velocity dropping off during the last turn of adjustment.... At 3 turns out, the dropoff doesn't occur until the lift is less than about 0.080" (1/2 turn out).... and at 4 turns out it doesn't occur at all, with the maximum velocity occurring at maximum hammer travel.... That tells me that at 850 fps, the valve is only opening 0.060" or less at 1800 psi....
Sooooooooooooooo.... the facts fit with the theory.... I can now adjust the valve lift providing that I am running lots of hammer spring preload.... There is one problem, however.... The adjustment, even using 24 TPI (0.042" per turn) is VERY finicky.... One turn (with the spring at coil bind) is over 250 fps.... Considering that, it remains to be seen if there is any practical application.... It will depend on whether or not I can achieve better efficiency running on the "left side" of the curves (where the velocity is determined by valve lift directly) compared to on the "right side" where the velocity is determined by spring preload (and it's effect on lift and dwell).... More experimenting is called for.... and the Millenium Pumper may not the the ideal candidate for that....
Bob
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sure wish i had a drawing of the parts to better follow your description.
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There is a photo and description of the hammer at the top of the thread....
Bob
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Lots of precedence here, I'll mention two that I am aware of.... One is the bstaley mod for the MRod, where he uses O-rings against the back of the valve to limit the hammer travel and turn the stroke adjuster into a valve lift adjuster.... I never really grasped this until he wrote up an excellent thread on how it works, which you can read here.... http://www.gatewaytoairguns.org/GTA/index.php/topic,37695.0.htm (http://www.gatewaytoairguns.org/GTA/index.php/topic,37695.0.htm) .... My compliments to bstaley on figuring this out and implementing it.... The idea (to paraphrase) of not affecting the first part of the shot string, while limiting the lift (and possibly also the hammer bounce) in the second half of the shot string are a perfect example of critical thinking followed by a simple solution, and I congratulate him for it....
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I think you give me more credit than I deserve. I came up with the idea while attempting to tune my p-rod, which was only my 2nd pcp. My only prior tuning experience was installing an RVA on a disco. Beginners luck more than anything.
It's only after learning more about how pcp's work, by reading posts by yourself, the others you mentioned in that post, and many others, did I really start to understand how and why it works as well as it does....and I'm still learning.
Looking forward to your experimentation with this, and would buy one of those hammers from you in a second if you decide to sell them!
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A lot of folks have contributed a lot of good ideas on this forum, and many of those ideas are coming together in this thread. Bob has already mentioned a lot of the people. I think Bob is planning to combine those ideas into an ultimate... airgun device, what ever it may turn out to be.
To digress a little, I used the recessed hammer face on my first version of the Disco Double, in Sept 2011,
http://www.gatewaytoairguns.org/GTA/index.php/topic,17637.60.html (http://www.gatewaytoairguns.org/GTA/index.php/topic,17637.60.html)
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/hammer-faces-1.jpg)
There is a series of pics in about the middle of the thread that show the hammer and cocking rod. Bob has now added adjustability to the actual striker, and that is a good thing.
Bstaley has added the o-rings to limit, and tame, the hammer stroke, and that is also a good thing.
But, there may be another material choice that has better characteristics than the usual o-rings to limit the hammer travel. Back when I was first working on mustang Mike's carbine, I again used the recessed hammer face, but I also added an impact absorbing pad between the hammer and the back of the valve.
The energy absorbing material takes a little thinking to understand. It is an elastomer, it has some hardness to it, and can absorb
quite a bit of energy. I have been using energy absorbing elastomers for years to protect delicate equipment during shock events. They work well when chosen correctly for the application. Elastomers all have elasticity, but just HOW elastic they are that makes the big difference. Imagine hitting a golf ball that is laying on the floor with a hammer. Major bounce-back. Now take that hammer and hit a memory foam mattress. Almost No bounce-back. They are both elastomers, but the speed at which they release the energy that has been imparted into them is very different. The impact absorbing pad is like a very dense version of that memory foam. The hammer bounces back very little, and at a much reduced velocity. The yellow impact absorbing rings fit around the gland nut on the valve, and snub the hammer when it is an over-travel condition. Hammer bounce is virtually killed.
Here are the pics of valve and hammer and parts and pieces of that make up that high powered set-up.
Notice also in that pic where I borrowed Bob's Disco valve idea of the one-piece front end.
(http://i226.photobucket.com/albums/dd79/loyd500/mustangmike/DSCN2173.jpg)
Lloyd-ss
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Got to shoot my M-rod with the hammer design shared earlier in this thread over the weekend ... Was not charting shot strings but did fool around throttling up and throttle down the power by ONLY changing travel ( kept same spring preload ) and found gun to shoot Very very well keeping shot report extremely quiet telling me dwell is staying very low. Air usage indeed seemed to be just sips at all power settings.
* Do need to remove a tad of my hammers inner sleeve length on back end so contact surface can be drawn further back increasing travel further yet.
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OK, guys.... here is a question for you.... Have a look at the velocities at maximum hammer travel, where the valve can only be opening about 0.060".... ie the very left hand side of the graph above.... Look at the velocities for the four hammer spring preloads (and I'll add one not on the graph)....
Coil Bound ~690 fps
1 turn out (not on the graph) ~720 fps
2 turns out ~740 fps
3 turns out ~780 fps
4 turns out ~ 850 fps
There is clearly a trend opposite to what you would expect.... More spring preload (and a higher force driving the hammer) is producing less velocity.... However, the distance the hammer travels from being released by the sear until it hits the valve stem is the same for all.... In addition, the valve stem can only be pushed 0.060" before the hammer hits the back of the valve.... so the lift is limited the same for all....
Anybody want to have a stab at explaining why?....
Bob
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OK, guys.... here is a question for you.... Have a look at the velocities at maximum hammer travel, where the valve can only be opening about 0.060".... ie the very left hand side of the graph above.... Look at the velocities for the four hammer spring preloads (and I'll add one not on the graph)....
Coil Bound ~690 fps
1 turn out (not on the graph) ~720 fps
2 turns out ~740 fps
3 turns out ~780 fps
4 turns out ~ 850 fps
There is clearly a trend opposite to what you would expect.... More spring preload (and a higher force driving the hammer) is producing less velocity.... However, the distance the hammer travels from being released by the sear until it hits the valve stem is the same for all.... In addition, the valve stem can only be pushed 0.060" before the hammer hits the back of the valve.... so the lift is limited the same for all....
Anybody want to have a stab at explaining why?....
Bob
Sounds like the carnival sledge and bell ....
A fast glancing blow sends the weight up striking bell.
A solid hard hit only jumps the weight a bit.
Kinetics at work here and honestly don't have a clue ... tho likely one of our resident brainy aches will enlighten us ???
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perhaps the harder the hammer hits the valve face, the faster it rebounds, reducing dwell.
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perhaps the harder the hammer hits the valve face, the faster it rebounds, reducing dwell.
Bstaley, that sounds like a reasonable explanation to me.
Bob,
Now that we know more or less know what is happening with the hammer and valve travel in the graph at the top of this page, and you have indeed described it in your text, I have to say that I think the graph is misleading. The sharp downturn at the left introduces another variable: limitation of maximum valve lift. Also, I would think that the downturn is actually a sharp downturn, not gradual as the curve smoothing implies. Once the valve travel limitation eliminated, I think all the curves might look somewhat similar to the 4-spring-turns-out curve.
Nice work and a good discussion.
Lloyd-ss
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I think Mr. Staley has it in a nutshell. The reduced preload stroke will leave the valve opening and closing more slowly; the high preload gets the valve open quite quickly, and then the valve starts closing. I'm ready to bet heavily that the high preload, low velocity shot is going to be more efficient than a comparable velocity shot done with reduced preload.
cheers,
Douglas
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I think Mr. Staley has it in a nutshell. The reduced preload stroke will leave the valve opening and closing more slowly; the high preload gets the valve open quite quickly, and then the valve starts closing. I'm ready to bet heavily that the high preload, low velocity shot is going to be more efficient than a comparable velocity shot done with reduced preload.
cheers,
Douglas
Douglas,
X2
I like what you said in your last sentence.
Lloyd-ss
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Yes, while metal on metal is very different than using o-rings or some other material as a buffer, using this method to limit power should be more efficient than transfer port restriction also. Restriction results in an attenuated, longer duration pressure pulse because it reduces the closing forces on the valve. Limiting valve lift does not attenuate the pulse until the hammer hits the buffer (quicker rise time than restriction.....the most important part of the impulse). It also does not reduce the closing forces(for any given lift), so dwell is shortened rather than lengthened as restriction would do.
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OK, enough answers that you all agree with my (unstated) premise that DWELL is the only possible answer.... The higher preload is driving the hammer faster, it's hitting the back of the valve harder (and in a shorter period of time) and rebounding quicker.... thus the total dwell and hence (since the lift and pressure are fixed) the total amount of air released is less.... Makes perfect sense, and I alluded to that in my Millenium Pumper thread when I first mentioned this phenomenon....
bstaley, you mentioned metal on metal.... Well, guys, I left out (on purpose) one important bit of information until Lloyd posted about the energy absorbing elastomer.... The initial testing in the Millenium Pumper was metal on metal.... However, when I pulled the gun apart to modify the hammer adjuster to allow another turn of throw, I machined 0.100" off the back of the valve (leaving a 1/4" diameter stub around the stem) and fitted a washer of Lloyd's yellow elastomer to the back of the valve.... Therefore, the graph at the top of this page was done with the elastomer in place.... I agree with Lloyd's comments that I probably shouldn't have used "curve smoothing" on the graphs, there should be a (more or less) sharp discontinuity at the point where the hammer begins to contact the elastomer / back of the valve....
Any more comments, now that you know there was an energy absorbing bumper in place for the hammer to hit?....
Bob
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How thick is the washer then...0.10? The thickness and elastic properties of the buffer material will have a significant effect on hammer and valve response. I believe that having a somewhat thicker, compressible buffer does help improve the length of a shot string, but perhaps with a bit more ES, as a result of allowing lift to vary a bit more over the string.
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The 3 o-ring stack comes into play gradually across 1/2-3/4 quarter of the shot string and is deflecting much further in the last quarter. For a maximum rate open and close I find the metal-metal striker/valve contact hard to beat conceptually. For a max efficiency reg'd rifle I would want a monster valve, a strong hit and a travel limited opening. Hammer will bounce fairly effectively on metal and the poppet will only have its own mass do deal with on close. Can tune this system with a bit of damper material and a minimum mass hammer( I for one have no issue with a nutty cocking effort ) to incease dwell at max opening.
cheers,
Douglas
also, can get direct valve lift measurements to simulate an unreg'd system response and get a fine idea of exactly what's going on in order to develop a set of adjustments that will let you shoot through a 2x spread in tank pressure v. an open loop operation.
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Why not just place a thin washer/spacer made of delrin, hard polyurethane or a rubber washer up against face of valve to give just a tad bit of shock absorbing and set up so hammer DOES BOTTOM OUT every shot and JUST ADJUST lift for power ya want ??
Dial in to much lift and have hammer no longer bottom out ... add some more spring tension.
This ONLY for a regulated gun .. But another way to fix valves flow so it does EXACTLY the same thing shot to shot ???
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bstaley, yes the washer is about 0.110".... actually the piece Lloyd sent me was squashed? in the middle and varied from about 0.080" to 0.120".... The whole point of this material is that IF the hammer hits it, it should, at least in theory, decelerate it quickly and not cause it to bounce.... pretty much the opposite of a stack of 3 O-rings, I would think....
Doug, I would think that metal to metal would have a VERY elastic collision, and coupled with any push from the valve stem the hammer would have the biggest possibility of bounce you could give it for that combination of air pressure, hammer strike, and springs.... It does make sense that the dwell of the valve would be much less, as once the hammer impacts the valve, it is no longer being pushed by the hammer (so it should stop sooner and reverse quicker), and if the hammer has rebounded from the metal valve body, it can close quicker as well (no hammer to accelerate).... Sorry, I don't understand your last paragraph....
Motorhead, that's kind of where I was going with this idea.... I was thinking of tuning the gun on the "left side" of the curve (which appears to be pretty much a straight line of velocity vs. lift).... You would select the hammer spring preload that allowed maximum lift (and velocity) to occur with the hammer still in contact with the valve body.... However, the adjustment required to dial in the velocity you want is VERY sensitive, in this case about 250 fps per turn on 24 TPI.... Using the "coil bound" example (the blue line), pretty much the entire range of velocities is available, zero to maximum, within about 2.5-3 turns on the adjuster.... At the very minimum, a finer thread is in order, IMO, to make this practical....
Bob
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hey Bob,
I was thinking of gettimg empiracal valve lift v. velocity but that would only be applicable to a certain kind of collision( and that ov course dependant on the type of any damper material used if any). Was recalling discussion from a while back egarding hammer behavour and valve opening and thought to use this one as a test bed. It could yeild non-impact data if you ran over the hill past the collision-induced knee for any given preload, you'd know the lift to within a few thou if the velocity discontinuity were sharp enough.
cheers,
Douglas
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Only issue coming to mind in using a semi rigid plastic / rubber capable of offering some energy absorption qualities, it's resiliency changes with temperature most likely ?
Maybe just a single Polyurethane O-ring would work well as a full time contact bumper ?
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bstaley, yes the washer is about 0.110".... actually the piece Lloyd sent me was squashed? in the middle and varied from about 0.080" to 0.120".... The whole point of this material is that IF the hammer hits it, it should, at least in theory, decelerate it quickly and not cause it to bounce.... pretty much the opposite of a stack of 3 O-rings, I would think....
Regardless of which material is used, I think the valve stem is the more likely to cause the hammer to bounce, not the buffer......but there are many variables.
.... At the very minimum, a finer thread is in order, IMO, to make this practical....
Or a valve design that changes the ratio of flow to lift.
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Or a valve design that changes the ratio of flow to lift.
Like our conventional poppet with a twist ... A tapered throat and tapered stem behind sealing face perhaps ?
Like a mechanical needle valve orifice
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I see what you're saying, Doug.... If you took enough measurements (velocity vs. lift) and determined the exact position of the "knee" (ie discontinuity) in the curve, you should then know exactly where the hammer came in contact with the valve.... Since you can calculate the lift (knowing the limiting lift and the thread pitch) you could plot velocity vs. lift.... Clever idea, but I don't know what you could do with that information.... It's a lot easier to just let the spring guide stick out the back, slide an O-ring on it, and measure the lift directly.... Accurate and works like a charm....
Regardless of which material is used, I think the valve stem is the more likely to cause the hammer to bounce, not the buffer
If that is true, then the valve should stay in contact with the hammer at all times.... The only time it wouldn't is due to it's own (very small) momentum.... If the hammer is being thrown back clear and ahead of the valve stem after colliding with the valve body (or buffer) then by definition the hammer is recoiling faster (and with more energy) than it could if propelled by the valve stem.... This argument is only valid for the hammer hitting the valve body or buffer, not in comparison to a valve without one.... If the buffer was removed, and if the valve then opened further, the extra distance to (re)accelerate the hammer would alter things....
Motorhead, Lloyd likely has the information on how the energy absorbing elastomer varies in performance with temperature....
Bob
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Regardless of which material is used, I think the valve stem is the more likely to cause the hammer to bounce, not the buffer
If that is true, then the valve should stay in contact with the hammer at all times....
I would be very surprised if that were not the case! I doubt that any of the buffer materials mentioned, other than metal on metal perhaps, would cause the hammer to rebound faster than the valve stem could keep up with.
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I would agree with that.... Soooooooooo.... that begs the question.... Does the buffer (assuming not metal to metal) make ANY difference to hammer bounce?.... I'm particularly interested in what Lloyd has to say, as he's been playing with the energy absorbing elastomer for some time....
How about it, Lloyd?.... Is the valve stem the culprit in propelling the hammer backwards?.... If your elastomer IS reducing bounce (in those cases where the hammer is hitting it, obviously).... is that due to the elastomer, or the valve stem travelling less and therefore having less distance to reaccelerate the hammer backwards?....
Note, I'm not asking if the hammer is bouncing off the elastomer.... I'm asking if it makes any difference to hammer rebound off of the valve stem/buffer combination....
Bob
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..., or the valve stem travelling less and therefore having less distance to reaccelerate the hammer backwards?....
In my opinion that is exactly how a buffer would reduce hammer bounce. The choice of buffer material will have some effect on net bounce as there will no doubt be some portion of the energy it absorbs returned to the hammer before the stem pushes it off of the buffer.
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So, bstaley, you feel that there is less energy being put into the valve stem, so less is available to bounce the hammer?.... seems reasonable.... Particularly in the case of an energy absorbing elastomer?....
Bob
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All I can say with any certainty at all is that adding a hammer buffer to the equation seems to yield measurable efficiency gains and the gains seem to be larger the more you limit valve travel. Whether the gains are a result of reduced hammer bounce, more efficient impulse waveforms, some combination of the above, or other properties yet to be discovered is still mostly conjecture as far as my understanding goes. I have my ideas, but without some way to observe and measure these reactions.....that's all they are.
The elastomer would probably be superior with regards to hammer bounce, but I also think that a more compressible material (like the o-rings) may have advantages in improving self regulation and shot string length in non regulated guns. There are always tradeoffs in any component selection.
I'm just hoping to learn more from everyone's experimentation, much of which I do not have the resources to do. ;D
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A multitude of great thoughts going on here and I am trying to muddle through them. Bstaley, I think I agree that the o-rings add little of the bounce of the hammer. I like to think of the valve stem as being spring loaded. At max air pressure and a valve lock situation I think you have an almost fully elastic collision, with the hammer bouncing back from a solid valve stem. There is probably a lot of hammer bounce, but it can't open the valve. As the pressure drops, the valve stem (spring) becomes softer, and bounces the hammer less elastically. But at some point the rebound is able to re-open the valve and the hammer bounce results in a loss of air. Then the ultimate hammer bounce is the soft spring on low air pressure that gives that flabby machine gun bounce. It seems that bstaleys method brings some control to the harmful bouncing situations.
Bstaley, do you use different types and hardnesses of o-rings?
Motorhead, the variable stem/throat seems like a good idea for tuning air flow. How would it work, though. When would the maximum flow occur?
Motorhead, Yes, the performance of the elastomers are temperature dependent, but some of them have a very broad temperature range. In general, they become harder and more elastic (bouncy) when cold. The loss factors of these materials varies less within its operating temperature range, and can be pretty predictable. Bob has a softer (less elastic) blue material, that should perform differently. Both absorb the same amount of energy, but the harder material takes good hammer hit to absorb maximum amount of energy. The blue material is softer and can control a lighter hit better.
I don't know if I really said anything, LOL.
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Where to start? Great exchange here! the designs that you all have been trying are a great idea. The lift adjustment concept is how I had been viewing the B-staley set up all along. The part that played havok with the visualization is the fact that the hammer throw changed when ever you adjusted the lift expectation. This seemed to cause a loss in velocity at fill but streched velocity over a wide smooth curve. With a high spring tension and hi lift adjusted, I could get high velocity with very tight ES for10-11 shots. (this is in referance to stock .25 valve) I haven't tried it since I made the valve mods. Try this thought out. If you are to choose a min operating psi for a desired velocity, like in a regulated gun. But instead of a reg, you are using the new hammer design to adjust lift. The hammer throw will be the same and you will still retain the ability to adjust spring tension, causing more linear predicability since momentum won't be adjusted in a give or take manner. I say give or take because, the old way allowed change in momentum do to the distance the hammer had to travel changed with stroke adjustment. At the low psi, you would increase stroke until desired velocity is reached. If the adjustment in lift is greater than the length of the valve stem, then preload in too low, adjust until desired velocity is reached. Once this has been achieved, fill the gun and shoot a few shots. If the velocity is too low, I'll bet it is safe to say that psi is too high. At this point, adjusting the lift would seem to be pointless because the hammer couldn't possibly open the valve to full stroke with a high fill. It would seem logical to say that when the velocity reaches the same as it was at low fill, that would be a good fill psi. The valve would be ballanced and and velocity ES would be suitable. I think it is safe to say that if one chose to increase spring tension instead of decrease fill psi, efficiency would go up. With that in mind, you would have to consider shortening the lift to maintain a lower ES but at higher avg velocity. With this tool box of manipulators, it would seem that the only thing left to consider is, what size ports do I need to increase the operating psi range, thus increase shot count with acceptable ES.
Thinking out load and trying to catch up
Bill
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Addressing hammer bounce. Oh boy, we're asking for it there. Ive often visualized the hammer bouncing off the valve stem at fill psi because of the hi closing force on the poppet. Like a Newtons craddle but one ball has less mass than the other. The larger ball (poppet) will move but less distance and with less velocity. With the hammer, once impact occurs, it doesn't just stop because the hammer spring is still imparting itself on the hammer. Each time the larger ball moves, it in essence looses mass for the next impact. At some point the force is low enough that the hammer and poppet have matching force or better yet, reverse rolls. I imagine this is when the burp occurs, causing extreme reservoir dumps. To keep this from happening the valve spring comes to play. Another thing that I've often contemplated. Could a chosen valve spring be too strong? If the ports are large enough to flow the required vol at psi to achieve a desired velocity but never seems to reach the potential, could it be the valve spring? If the valve spring is that stiff, could it induce bounce by imparting it's energy back on the hammer?. This takes me back to the discussion on sine wave valve opening. It seems that this is worth contemplation in the way of, Why isn't it a sine wave? Hammer hits the poppet stem and beginns to open. The valve opens more and more untill it is decelerated and returns. I don't imagine that the hammer maintains contact with the valve stem the entire cycle. I'd say it hits, the stem beginns to accelerate much faster than the hammer decelerates and then recontact again. If the spring tension is really high and momentum are high, we get longer durations or poppet bouncing off the hammer. perhaps an unnecesarily long duration (waste). The force on the poppet opening and closing would look like a sine by nature I would think. Force closing poppet decreases as the valve opens ever wider until psi equalibrium is reached at which time direction is changed and force closing the poppet begins to increase as the valve get nearer to closing. As the pellet beginns to move the diferential in psi begin to re-occur. Since the force is ever decreasing on the popper shot after shot, the plateau of the sine wave gets longer. I guess that would be ideal. But then you throw the valve spring into the mix. I imagine this would take the sine out of the wave. This has lead me to wonder if the valve spring should be absent or better yet, mached to the hammer energy and momentum. If so, thats gonna be a pain in the rear. I know Lloyd and Bob have had great success with springless valves and achieving great efficiency. That's probably true to spring as well as spring less. Wonder which is most consistant in regard to velocity v.s. efficiency?
Bill
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another consideration. What about using something like derin as the contact face of the hammer/lift adjuster. this would allow an impact that would perhaps minimize the bounce/seperation between hammer and stem at initial contact. This could give a move smoothe driven motion, especialy since the spring is still driving to some extent.
Bill
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..., or the valve stem travelling less and therefore having less distance to reaccelerate the hammer backwards?....
In my opinion that is exactly how a buffer would reduce hammer bounce. The choice of buffer material will have some effect on net bounce as there will no doubt be some portion of the energy it absorbs returned to the hammer before the stem pushes it off of the buffer.
Just to examine the bugger o-ring behaviour in a Marauder. Hammer hits the rings and seals up a chamber between it and the valve. At this point the valve is open and leaking past its stem into this chamber. It puts out enough air to spray valve stem grease up against the hammer in small specks.
cheers,
Douglas
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..., or the valve stem travelling less and therefore having less distance to reaccelerate the hammer backwards?....
In my opinion that is exactly how a buffer would reduce hammer bounce. The choice of buffer material will have some effect on net bounce as there will no doubt be some portion of the energy it absorbs returned to the hammer before the stem pushes it off of the buffer.
Just to examine the bugger o-ring behaviour in a Marauder. Hammer hits the rings and seals up a chamber between it and the valve. At this point the valve is open and leaking past its stem into this chamber. It puts out enough air to spray valve stem grease up against the hammer in small specks.
cheers,
Douglas
Douglas,
That effect is Real enough IF THE LEAKING of HP air is sufficient to actually fill the space & create some pressure within the minimal time hammer spends up against the o-ring stack ?
While stem grease / oil indeed gets blown out against hammer, really doubt the volume of HP air is sufficient to give a "Blow Back" effect.
Seen this ON PURPOSE done with blow back auto cocking semi auto paintball guns ( Spyders etc ... ) and to impart the blow back takes some pretty good size vent holes off the transfer passage.
Understand we are not talking sufficient energy to re-cock but only talking enough air to create more rebound energy, still personally feel you would need to have a REALLY loose fit stem to valve getting enough air to pass in the fraction of a second the pressure pulse is happening.
Lloyd-ss ...
Motorhead, the variable stem/throat seems like a good idea for tuning air flow. How would it work, though. When would the maximum flow occur?
Bear with me NOT being a math guy ...
A tapered seat like a needle valve, a carburetors float valve or metering needles pending degree of taper where both Male and Female counterparts share a common taper Exponentially increase there area as the are drawn further apart. Shallower the taper shallower the curve, steeper the angle steeper the curve.
* So my take at this early stage knowing / understanding our conventional valves DO NOT open very high so a Tapered throat / stem would require a VERY steep angle that changes area REALLY quickly to work.
My thoughts are REDUCE the poppet head diameter subjected to HP pressure within valve, still use the time tested flat / semi seat, but design valve to have Greater stroke.
Understand greater poppet stroke is going to return greater bounce energy potential to hammer ? ... but then again a tapered throat would also have poppet self damping upon closing do to progressively lowered flow further it get towards closing ???
Just sharing thoughts here ....
Scott
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Understand we are not talking sufficient energy to re-cock but only talking enough air to create more rebound energy, still personally feel you would need to have a REALLY loose fit stem to valve getting enough air to pass in the fraction of a second the pressure pulse is happening.
My Hayabusa would beg to differ.... I had a poor stem fit and a good hammer fit, and the first time I fired it, it emptied the reservoir and sounded like a machine gun.... The cure was to drill a 3/16" hole in the tube immediately behind the valve to vent the air being compressed by the hammer and/or leaking past the stem.... I never did figure out which was the culprit, the fix was soooooooo easy....
Bob
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hey-Hey,
I think the re-opening bounce is a closer thing than we realize, and taking out energy is a good thing. Now one way to do it is to have the air spring of two different k's opening v. close...and that is usually done by strangling the transfer port. How strangled is a variable thing.
The stem leakage when running Mr. Staley's o-rings has got to be putting some energy back into the hammer. How effectively is open to discussion; they seem to work pretty well. I have been giving a stem o-ring install a bit of thought. Can probably get away with extending the valve backwards a bit, as well as shortening the body. Goal being to install a plate with a chamfer, and chamfer the back of the valve. Probably secure it with two counter sunk 4-40's. Off to the o-ring charts...:)
cheers,
Douglas
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There is precedence for installing a buffer on the stem instead of inside the tube. "Rich. from Mich." posted on the yellow chinese forum that he as been using a length of silicone tubing on QB valve stems for years to help flatten the shot string. I installed an o-ring + plastic spacer buffer on the stem of my Windy City with nice results.
Also the AF guys have been sticking a o-ring under the tophat for years too. I've also had hood results with that on my .25 Talon SS
Only problem is that with the buffer on the stem, you lose the adjustability that you get from an adjustable striker.
Lloyd - I have really only used 70 Duro o-rings, but would be interested in a comparison of different values and how they affect the shot string......just never got around to it.
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I have been doing some thinking ans came across a question that one of you may be able to help me with. I'm currently doing some tests with my Marauder and would rather not tear it down. Do any of you know the active coil count of the valve spring? This would be very helpful and save me time.
Thanks Bill
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I have been doing some thinking ans came across a question that one of you may be able to help me with. I'm currently doing some tests with my Marauder and would rather not tear it down. Do any of you know the active coil count of the valve spring? This would be very helpful and save me time.
Thanks Bill
about 7.5
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Lloyd-ss ....
Where are you ?
Could use ya again in this think tank discussion.
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I have been doing some thinking ans came across a question that one of you may be able to help me with. I'm currently doing some tests with my Marauder and would rather not tear it down. Do any of you know the active coil count of the valve spring? This would be very helpful and save me time.
Thanks Bill
Bill,
I have it as .0445" wire, with 7.5 coils, OD .336", with free length of 1.391".
Best Regards,
Douglas
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Thanks Douglas. I'm gonna guess that the modulus of rigidity is 30,000,000psi? If that is true, the rate would be 84lbs. Wow!
I'm using k=Gd^4/[8nD^3]
k=spring constant
D=mean coil diameter
d=wire diameter
n=number of active coils
G= modulus of rigidity
Am I on to the right formula? that seems a bit high.
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I got 28.5 lbs with a quick run through the calculator below. Yeah I'm lazy.
http://www.efunda.com/DesignStandards/springs/calc_comp_designer.cfm#calc (http://www.efunda.com/DesignStandards/springs/calc_comp_designer.cfm#calc)
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Bummer this thread has fizzled out .... the possibilities were just starting to take shape :P
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I just woke up. Had to re-read what I could. Have been working with M-Rod, lengthening the stroke to get more usable power without having to use a heavy spring or heavy preload. It seems to be working. There are a lot of restrictions inside the M-Rod that make getting the full potential out of it a bit of a chore.
Data coming.
Lloyd-ss