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Marauder valve lift limiter - Another approach

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ackuric

ackuric

Member
Mar 10, 2017
1,232
61
Colorado, United States
There are many ways to skin this cat. I recently decided to approach this modification for my marauder with two ideas in mine, external adjust-ability, and simple modification. As they say, KISS (keep it simple sillygoose).



This mod can apply to any air gun that has a machinable hammer, and a rear-adjusting hammer spring.


I decided to modify my MDS hammer by simply installing a 3/8" long, 8-32 hex screw / grub screw with an o-ring on its face to allow some buffer and to reduce noise/contact damage.



Pictured below is the face of the hammer, as you can see I run a bolt with a drilled pocket that is then filled with compressed leather for my main striker as I hate the noise of metal or even peek/plastic strikers contacting the valve stem violently upon firing, and this highly compressed leather has held up fine for 2 years, 1000's of shots with 0 issues and is dead silent. The 8-32 screw here doesn't show the o-ring.



1589350411_11834508125ebb900b5e9b56.61049604.jpg




Pictured below here is the back side for adjustment.

1589350433_12069700595ebb9021dba240.14957458.jpg




First tests are promising as the first 8 shots over the chronograph were between 847 and 851 fps with a spread of just 4 fps shooting unweighted 25.4's. Its quite late so I haven't time now to run a full string, and would prefer to weigh some pellets if I were to go to that length, yet lack the proper scale to do so, so until then I'll be happy with my rng luck with pellet weight variance on the 8 shot string I did tonight.



Prior to locking it down around 850~ fps and 40 fpe with the new valve limiter, I was hovering around 900 fps on the same hammer spring setting. I don't know if the current hammer spring setting/valve limiter settings are currently ideal as I haven't tinkered with either being just in a preliminary testing phase, but fwiw I'll leave it be for now and dig into that more later, as it'll be equally important to test its performance both on reg, and off.
 
I'm not quite following either. I first read it after midnight last night and figured I'd come back to it and see if it would sink in but I'm still lost. I get the sense its function is akin to that of a bstaley O-ring buffer and an adjustable striker nose. If so, it's a clever implementation. Is it all about reducing noise, or improving efficiency, or extending shot count, or some combination? And how is the O-ring retained?

 
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The 8-32 hex screw is a secondary striker that strikes the valve body which limits lift. Leather striker contacts valve stem, 3/8" 8-32 hex screw with o-ring on face contacts the valve body.



It works by limiting lift which reduces variation from shot to shot while on reg given the slight variation in pressure from shot to shot, and also limits lift for when shooting off reg while well below the knee so you don't get fps climbing well over an acceptable es range.



For example, I shoot 33.95's, and 25.4's, the 33.95's I shoot around 860-870 fps which is around 4% from my peak. I shoot 25.4's at around 850-860 fps as well, but that is nearly 15% from their peak FPS, which results in quite a decent fps variance from shot to shot, and a large jump in fps when coming off reg...this limiter eliminates those issues. I also shoot the 25.4's at around 750 fps on another tune, which is 25% from peak...and this limiter when set right works as any other 'buffer' or valve lift limiting system.



The o-ring is simply just adhered to the face of the secondary striker / 8-32 hex screw, as the energy left in the hammer contacting the valve at that point is quite small, I used a small dab of industrial adhesive to secure the o-ring to the face of the 8-32 screw, certainly not the most favorable approach but for my personal rifle, it suits me. There are quite a few ways to install and secure a rubber bumper to limit valve lift. The reason I went with an o-ring on the face opposed to just leaving it as is was to kill two birds with one stone, limit noise, and allow some variance in lift depending on remaining hammer energy, or what we call the 'buffer'..



In its current state its externally adjustable and works as any other 'buffer' system or valve lift limiter, which to say I can limit my valves lift to .04" if I choose, or run it to .12"...which directly effects the amount of air ejected/energy created...eliminating another variable of potential variance. IMO all 'high end' pcp's should have some kind of valve limiting system, which the likes of the fx impact has, and iirc so does the raptor, both of which take entirely different approaches from each other, and myself...fx impacts run a valve limiting system at the poppet end, which limits how much the poppet can lift off the face of the valves seat...both the raptor and I use a system built into the hammer, although approached slightly differently, the end result is identical in that you're limiting how far the hammer can lift the poppet off the seat of the valve. I do not know however if FX uses any type of 'buffer' or material that absorbs energy to limit lift. HTH



FWIW my tunes will still use both different valve limiter settings as well as different preset hammer preloads / spring ratings so that on lower power tunes I am not over driving the valve limiter into the valve body, it's contact will always be after the poppet has already absorbed the majority of the hammer energy...so I expect the o-ring on the secondary striker to outlast the majority of other parts on the rifle. I could have machined a lip or recessed a lip to let the o-ring sit on/in but I feel having it being fully sandwiched between valve and secondary striker upon impact is more desirable. It allows 'maximum' buffer of the small .05" thick o-ring, which I measured around .025". There are quite a few alternative 'bumper' approaches one could take.

-Matt




 
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The popular 'bstaley' mod that puts 2-3 o-rings in between the valve and hammer is quite similar...but not externally adjustable, and better suited for unregulated applications as there is a huge variance of lift between max and min operating pressures for unregulated, and having 2-3 o-rings allows for A LOT of buffer. The end game is 'absorbing' some residual hammer energy or adding an additional force the hammer most over come to create lift, thus reducing the % of difference required to open the valve while the pressure holding the valve shut varies, be it slightly in regulated, or greatly when unregulated.


Fx's iteration of valve lift limitation, the raptors iteration, and mine, are all best suited for regulated applications whereas the bstaley would be more favorable for unregulated.



The buffer built into my iteration and the Raptor iteration can be viewed as an additional 'valve opening force', similar to how heavy valve return springs work that their force remains static regardless of pressure holding the valve closed, reducing the % difference between hammer strike energy requirements as the force holding the valve changes.


The two major impacts this modification or similar have, are ability to limit valve lift which is great for lower power tunes far away from your plateau fps, and a buffer that aids in reducing the difference of energy the hammer has between strikes.

-Matt
 
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Another great thing about this modification is its 100% reversible and can be left installed and still be backed out enough to not limit lift at all.



One downside to this method is it requires access to the rear of the hammer and no blockage between hammer rear and rear adjuster, like some ssg's which would cause an interference of adjustment. Thankfully I run a ssg device that is removable and is not a thru the hammer type, rather a behind the hammer type. Another downside is its another step in a tuning process to 'fine tune' for a particular velocity with a given pellet weight, but to achieve around 1% or less es while on reg regardless of how far down the knee I tune, makes the process worth it. I only run 3 tunes and will only have to remember the 3 settings for the valve lift adjuster as my ssg's are preloaded/preset with their respective tunes.



Additionally I have not done enough research to have an opinion on how much buffer is desirable based on application. I would like to test different tolerances of 'squish' for the buffer provided my current one doesn't prove fruitful, but I have a feeling it'll be fine per my application, when I get the time to test further I'll certainly update here if any major changes take place, as I have another 'bumper' that would have around .06" "squish" opposed to my current .03"~.



I also designed another idea that would encapsulate a spring that can be adjusted, with the face of the hammer having a button with the spring within, any added preloaded on a rear adjuster would allow a greater range of adjustment for a buffer, provided you found a spring that both fit inside the hammer, and had a good range of lbs force. I chose my current route due to simplicity...and due to the doubts that I could source a spring with the desired range of force. Most smaller springs in that size range are of only 2-4 lbs which wouldn't be enough buffer range IMO to consider worthy, where as o-rings seem to have around 10-20 lbs of compressive force in them before seemingly 'bottoming out'.



-Matt




 
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Another interesting note. To generate the 40 FPE, my valve limiter was sticking out roughly .09"...my leather striker is recessed .03", my valve stem protrudes roughly .165" from the valve, which makes it so I am limited to roughly .135" lift. This means the poppet only needs to lift around .055"~ (.045" + some from oring squish, estimating at around .055"~) to generate the 40 fpe in my current configuration. (.225 ports / 19.5" barrel / 53 cc plenum / ~1950 psi), which is roughly what my current spreadsheet predicts. Wild that so much occurs within our air rifles, in such little time, with such small windows such as .055" lift and roughly 1 ms of valve dwell.



-Matt
 
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Any chance you could get a pic of the o-ring installed? I am having a hard time visualizing how that is placed per your description.
Click to expand...



Do not have one currently sorry, but I just adhered it using industrial strength adhesive that doesn't dry brittle but rather dries with some flex. This allows maximum 'squish' of the o-ring buffer as its dual purpose, noise reduction and excess hammer energy dampening from pressure differential holding valve shut, any other attempt at retaining the o-ring would create quite a bit less available buffer which I personally wanted to maximize.


Here is a picture of the o-ring. Its tiny at .059" CS / thick and .17"~ OD. Its the smallest o-ring I had laying around at the time I was tossing this together so I ran with it. To be able to retract the valve lift adjuster fully into the hammer for max lift I had to recess a bit more on the striker bolt, and the tapped 8-32 hole as this o-ring was a tad big (near identical od to the 8-32 hex screw, but slightly larger (8-32 is .164")



1589420982_6491345515ebca3b67ce2e4.29668908.jpg




One could go as far as creating an encased sliding 'piston' that allows the oring(s) to reside in much like a regulator, that retains them very efficiently and provides maximum buffer similar to how belleville washers work, although having a lathe would likely make said job much easier working with such small confined space and small parts, I am not too confident I can come up with something on the fly, nor can I really push it to the 10-32 OD that would greatly benefit from this approach. You can see in the picture I am butted up to both the hammer inner wall and the main strikers threads, and creating a sliding piston with internal oring's with a .164" work area would be quite the challenge, but still doable provided a lathe and a good set of eyes. If I find myself seeking more and more 'buffer', I may have no choice but to run a setup that retains 2-3 orings similar to what I am referring to here. Although I don't find that likely as the current o-ring has around .03"~ "buffer" which should suit me.


 
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Found an alternative solution for a valve buffer using the small 8-32 screw. A 1/8 ball (.125) would work great. I need to source these either locally or on the internet cheaply. I would drill a pocket roughly .05~ deep and 3/32 wide, and with a drop of adhesive the ball should 'squeeze' fit in and hold in place, allowing at least .03 - .04" buffer. I'll have to see if ace hardware carries anything of the like...



1590721768_3347688445ed07ce8ab4af2.69533715.jpg




As of now I have been side tracked making a new moderator and brain storming. No other major testing of my current integration done other than casual plinking, otherwise its holding up fine but I would like a more robust valve stop thats secured a bit better than my current one. Just need to get on the ball (pun intended)
 
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Fantastic results! That looks great.

That’s a nice tune for the heavies. Any chance you’re ready to call it done or is there another mod in the works?
Click to expand...



Thanks brother. Whats even better is my new retractable (6", extendable to 9") moderator didn't even budge during the entire shot session being retracted to its 6" position, it just took those 60 fpe shots and kept on chugging without extending itself whatsoever.



Honestly, a precision match grade barrel would be a nice addition, this valve would knock the socks off of anything in .22 cal being slightly over full bore ported, so that would be fun...I would love a thimble with a .22/.25 cal quick change setup. This GM barrel works great with 33.95's at its 17.5" twist so its hard to deviate away from it until I decide if I want to start on a new gun/project to fill the .22 caliber hole, or go the thimble route for quick changes. The work involved for the thimble route deters me, as well as the cost, which would likely rival the price tag of a new gun. 



I am considering a pp750 once they hit the shelves, as it comes from the factory with an uncanny resemblance to my rifle being they use similar retractable stock configuration and grip/frames. a .177 that makes between 12-20 fpe would be pretty ideal for my low power needs while keeping a flatter trajectory than shooting 25.4's at ~500 fps....but I have been known to do that too so who knows!
 
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