Thoughts on Hammer Travel Adjustment

[Motorhead]

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 ?   

[bstaley]

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.

[Motorhead]

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

[rsterne]

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

[bstaley]

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.

[rsterne]

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

[bstaley]

..., 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.

[rsterne]

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

[bstaley]

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. 

[lloyd-ss]

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.

[Bill G]

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 

[Bill G]

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

[Bill G]

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

[PakProtector]

..., 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

[Motorhead]

..., 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


 

[rsterne]

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

[PakProtector]

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

[bstaley]

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.

[Bill G]

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

[bstaley]

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