Simplified Balanced Valve

[PikeP]

I was able to achieve a seal that held 100% overnight and passed a water dunk, so, here is my official toot I suppose.


Below is my hand made balance piston, poppet and stem. The cage was made from a bolt head cut off, crudely rounded, reduced in height, and then tapped 6-32. This arrangement simply fits into the stock marauder valve with the only mod(s) required being reducing the end cap overall length by .1"~ and drilling the spring pocket a tad deeper, otherwise just a drop in to the stock valve. Tolerances were tight but manageable with room to spare. My balance chamber height is adjustable, as I did take it down to .155" from .175" while fixing the leak, (could go further but won't for now), can't give credit to anyone  as I had the idea conceived at the time I made the spread sheet that calculates balance valve fill times, a few years ago, what can I say except great minds think alike. (Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  )



I reduced the hammer to 27 grams and hammer gap to .045 (was 30 gr and .04 before I tore down), fps dropped from 890-900 to 860-870 on a 7 lb spring with barely any preload. Still need to run the valve thru its paces, test for break out friction, and make sure it is reliable from shot to shot, but so far I am impressed overall with the performance, and how much I've been able to reduce hammer weight, I could see going to 10-20 grams on this valve, even in 25 cal doing 60+ FPE. Maybe in time.. as I intend to do a .177/.22 cal upper that will absolutely require a lighter hammer if I only change caliber and hammer spring...

-Matt

As another who whittles on these guns with caveman tools, I have to give credit where credit is due.  At one time creating a peek poppet with Cobra chamber/air valve return spring seemed daunting, but now I have a series of operations where it isn't so difficult.  But a balance chamber and the VENT----I have not even come close to considering such a task...  Great job there.

To dabble in this space I have to use Cothran's as a base.....making Don's stem vent larger than needed, and adding a 6/32 set screw, drilled as a jet to the top of the stem/base of the  balance chamber gives me the ability to play in space of simplified, tuneable balanced valves....

Regarding small stems------I am a firm believer.  On my conventional knock-open valves, I modify most of my guns to accept 2mm stems.  I've yet to bend/break one with valve throats up to .3125....I don't get fancy with the stem/peek interace either.  A tight interference fit is all that is needed.  1/16 predrill of the peek to .375 or so deep, hammer the stem in.  Make sure it bottoms out or it will move and you may end up having to get very creative to degas......

I do appreciate everyone's contributions to this thread, it has been very helpful.

Thanks for the kind words, my caveman methods improve with each daunting task I take on, this certainly was more daunting mentally beforehand than it was when executing it mindfully. I still hate the final step of getting peek or even white delrin to seal under these types of conditions (balanced valve or valves with little force holding poppet closed)

I drilled my poppet to .06" to begin with, made any needed corrections with a small dremel bit, then drilled it to.106" with a jig to ensure straightness, corrected again if it was off a few thou to .115 tops, then with a dab of red loctite hammered the .125" stem in, my depth was quite limited so I only went .165" deep, probably the tightest space constraint in the entire build, the space between stem head and balance chamber is around .07". My vent is a small area ground out from the head of the stem that goes into the poppet, which I then used as a guide to drill thru, starting the hole with a fine dremel bit then graduating to the .047" drill bit.

Its quite easy to get center by hand with the above method, starting with a small hole and making corrections with dremel and caliper, rinse and repeat. My balance chamber is off at most by .002", which for by hand is quite impressive, but with the above methods not too difficult to achieve.

-Matt

[PikeP]

Slightly off topic however I do feel its part of balancing a valve, but speaking about thinned stems and even the use of them in balanced valves had me pondering about my partially thinned stem.

The closing force acting upon a .125" stem at 2030 psi would be about 25 lbs, the force acting upon a .05" stem is only 8 lbs... While the partial stem doesn't cancel or reduce the closing force fully down to that 8 lbs, it does momentarily, even for a fraction for a ms, until the air molecules travel the .4" distance that my stem is slimmed down to. Food for thought on why I favor thinned stems even more, its a fine tuning effect that may not have a large impact, but nonetheless, one can't negate their favorable alteration to valve opening conditions...Air certainly doesn't travel .4" instantaneously...even when adding in upwards of .08" lift the air still must travel .32" before it fully achieves 25 lbs of closing force in a thinned stem arrangement such as mine...

I do think there is an ideal size AND possibly shape to a stem in an airgun (call it another step in tuning)..

Here is a simple graph showing various closing forces at different stem sizes and pressures...and do note, this IS quite a simple way to balance your valve so to speak, as less closing force means your valve is more equalized, favoring a balance between the two forces of open/close...can't personally say where we should draw the line for any particular arrangement (caliber, power output) but I do know a gun operating at regulated 2000 psi with a .125  stem will have nearly the same closure and interaction as a .0984 stem at 3500~ psi
 

[Motorhead]

The stem may fracture DUE TOO Stretch & Not compression.
When the balance chamber become pressurized,  The poppet becomes its own projectile of sorts being literally shot towards the seat.
The head of poppet stops the motion upon seat contact, tho a large if not largest mass is that of the full diameter stem that wants to continue moving towards the retreating hammer.
With the hammer in free flight there is little damping the poppets closing.
Have seen stems get pulled free of the poppet head as well head fractures due to the violent closing nature these valves exhibit.

Been there FYI .. 

[sb327]

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

[Motorhead]

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.

[PikeP]

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

+1 Strongly agree, the balance chamber does NOT shoot out the poppet into a throat, physics won't allow it. Your balance chamber NEVER exceeds the pressure of that in the valves plenum or the throat, only equal or less than, therefore no shot. Valve closure events are not that violent, or we wouldn't use soft plastics to seal them

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.

Any pressed in home made poppet is prone to losing its stem from a sudden stop, but that is so unlikely and would take an incredibly lose fit, I've never had that happen out of the half a dozen stems I personally made...

The poppet stem is not stretching when it comes to a stop, and certainly isn't failing in such manner even if it were. The young modulus would have to be so low for that material to stretch in such event, that it would flail. The collision event from our valves closing is not stretching valve stems, even when thinned to 1-2mm...and again, I highly disagree that this is more stressful on a valves stem area then the opening event of a valve, neither being catastrophic in the event of failure

[PikeP]

I'll additionally say, long before a piece of hardened steel stretches, an interference fit of metal to plastic (stem into poppet) will fail, meaning  as I said before, there will be other failure modes before this stem area in my application, fails. Toss this stem into a gun with 200-300+ lbs of force holding it closed, and it will likely fail upon attempting to open said valve before it fails on a closure event...

-Matt

[mackeral5]

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

+1 Strongly agree, the balance chamber does NOT shoot out the poppet into a throat, physics won't allow it. Your balance chamber NEVER exceeds the pressure of that in the valves plenum or the throat, only equal or less than, therefore no shot. Valve closure events are not that violent, or we wouldn't use soft plastics to seal them

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.

Any pressed in home made poppet is prone to losing its stem from a sudden stop, but that is so unlikely and would take an incredibly lose fit, I've never had that happen out of the half a dozen stems I personally made...

The poppet stem is not stretching when it comes to a stop, and certainly isn't failing in such manner even if it were. The young modulus would have to be so low for that material to stretch in such event, that it would flail. The collision event from our valves closing is not stretching valve stems, even when thinned to 1-2mm...and again, I highly disagree that this is more stressful on a valves stem area then the opening event of a valve, neither being catastrophic in the event of failure

Valve closure events are not that violent.........I think you may rephrase that as "should not be that violent" when designed and built to not be. 

I do not think it was just airflow that did this.  And let me assure you, it was a bit on the violent side....

[PikeP]

Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

[Motorhead]

Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out
 

[PikeP]

Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out

I'm no teacher here, rather a student, but care to show your work or how you arrive at such conclusions? Because you're speaking a foreign language to me and possibly others. Clarity on what your trying to convey certainly doesn't hurt to ask for...


The force you're speaking of that I am familiar with is what allows us to simply tune the valve so it doesn't remain blown open until pressure drops enough for the valve to shut itself, not so much a destructive force that slams the poppet into the seat any more than a conventional valve...add to that, how much inertia or momentum do you think a 2 gram poppet can build up traveling within the .05-.09" or 1-2mm journey back to the seat? Lol, I laugh because you clearly haven't done that math, and I have...

[sb327]

Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out

You are correct in that the force pushing against the poppet from the inside increase. But the force can only rise to the same level of force that is pushing from the outside of it (which is the blow open effect). Once the pressure inside the balance chamber equals the plenum pressure, the force opening vs closing is neutral.

According to your thoughts, a balanced valve simply laying on a bench, atmospheric pressure inside and out, would push itself apart. We know that doesn’t happen.

Also something to consider, I float my balance piston, if what you say is correct, my system would spit my piston out. It does not.

Laughing at someone is an insult, something that doesn’t promote progress or learning for anyone. It tends to show one’s true colors during a conversation.

As far as the ‘figure it out’, you have offered nothing to make me re-think the way I have already figured it out.

Dave

[PikeP]

I semi - float my balance cage, its under slight tension from spring while under no pressure...HPA definitely changes that dynamic within the valve. A fully floated piston would destroy itself if what Scott said is factual.

The "I'm right, and you're wrong" attitude, with no other constructive contributions is certainly revealing, and while it is an attempt to insult, I find myself chuckling at how low people go..

[mackeral5]

Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet. 

[PikeP]

Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet.

Yea I didn't imagine you'd make a poorly designed conical, so my original assumption was spot on! Lol, a spring wedged under a poppet head, jack hammering into a seat sounds like a nightmare. Cothran valves are definitely different animals.

[rsterne]

The pressure in the balance chamber starts at atmospheric, leading to a "blow-open" effect until that pressure rises through the vent from the throat.... Since there must be at least a few psi loss past the poppet and through the throat, the pressure in the throat cannot exceed that in the valve, and likewise the pressure in balance chamber cannot exceed that in the throat, so until the pellet leaves the barrel and the valve closes, the pressure in the balance chamber cannot cause the valve to slam shut.... If the valve is still open at that point (this would only happen in a valve intended to blow open and stay there, with a large balance chamber and small vent), then as the pressure in the barrel suddenly drops, the pressure in the balance chamber could indeed slam the valve shut.... as would the pressure in the valve itself....

In conclusion, it is possible to design a valve that will blow open and stay open until after the pellet has left the muzzle (a Cothran will do that in a short barrel), and that will deliver maximum power for that barrel, at the expense of being very inefficient.... However, most of this thread has been devoted to developing a semi-balanced valve that can be tuned to be not only easy to open, but one where the dwell can be tuned through hammer strike, and improve efficiency.... This means, of course, that the valve must be closing while the pellet is still in the barrel, in which case the balance chamber pressure will never exceed the pressure inside the valve, and it will not slam the poppet closed.... In a properly tuned "semi-balanced" valve, once the pellet is travelling down the barrel, the main closing forces on the poppet are the throat pressure working on the stem area, the valve spring, and the "drag" on the poppet head due to air rushing past it, and causing a pressure differential across it.... Since the pressure in the balance chamber does not exceed the pressure inside the valve, in fact it is still countering that closing force to a small degree....

Bob

[mackeral5]

Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet.

Yea I didn't imagine you'd make a poorly designed conical, so my original assumption was spot on! Lol, a spring wedged under a poppet head, jack hammering into a seat sounds like a nightmare. Cothran valves are definitely different animals.

If I would have made a spring I can assure you it would have been poorly designed.  I would have no idea where to even start....  The spring was original to the valve.   IIRC, I seem to recall it was pulled down over itself, top to bottom, like pulling down a sock from the top.   

Regarding the uniqueness of a Cothran valve, I still cannot fathom how/why Don arrived at the rod/leaky check valve vs what is described in this thread.

[sb327]

Bob,

An eloquent way of trying to save face for someone but in the end, M-head is wrong.

 
M-head,
Seriously, the kind of snobbery by you and the ‘my way or the highway’ bs is what drives others away from sites such as this. I’m not a punk or some idiot, I came here to learn and share ideas. Laugh at me on the internet….you prove who you are. Not very gentlemanly for sure. That keyboard sure makes some folks big n bad, at least in their own minds.

Dave

[PikeP]

(Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  )



-Matt

Bob,

An eloquent way of trying to save face for someone but in the end, M-head is wrong.

 
M-head,
Seriously, the kind of snobbery by you and the ‘my way or the highway’ bs is what drives others away from sites such as this. I’m not a punk or some idiot, I came here to learn and share ideas. Laugh at me on the internet….you prove who you are. Not very gentlemanly for sure. That keyboard sure makes some folks big n bad, at least in their own minds.

Dave

Not only that but this thread took a derail trying to understand the mode of failure Scott was attempting to proclaim (a thinned stem made with hardened steel stretching during valve close). Clearly he didn't read the above bold text...

I as well am here to live, learn and share ideas/concepts in a hobby I thoroughly enjoy. I know my thinned stem can and under certain circumstances absolutely will fail, circumstances outside of my use case...that applies to nearly everything we do though, we design within our safety factor / limitations, be it thinned walled tubes, thinned stems, or thin walls on entry points for connectors ect...thinned balanced valve cages that fail (ahem), the list can go on...it simply boils down to personal grievances / differences that spill over into a forum that should only contain discussions in good nature, even when heeding caution to fellow members, such as voicing ones concerns over a design or idea.

Balance valves, in their worse design, blow OPEN, not closed, and when designed as we intend here, operate nearly identical to conventional valves with the benefit of reduced pressure holding it shut and for the first few fractions of a ms. Even a Cothran style valves, an over vented valve with too large of a balance chamber should not SLAM shut, because it will have lost so much pressure in the system to remain open, that there won't be enough force TO slam it shut...

The most vicious close cycles I can think of are, such as mackerals, with a spring underneath your poppet head, which is obscure but certainly a possibility in a really overdriven valve, or one that is jack hammering over and over repeatedly with excessive lift (clearly in this situation excessive lift is most likely, allowing more inertia and momentum to build between each strike than a situation with nominal lift...) which is an entirely different mode of failure

[mackeral5]

Matt, there is no value in continuing to attempt and rub Scott's nose in it. You have to acknowledge that you, as well,  have a history of let's just say not playing very nice with others at times.  Examples lie in this particular thread....

You like to poke the bear, and I get it.  But it is not necessary to continue beating this particular drum so to speak..... 

Not everyone has been around long enough to know  that you are here under at least your second profile, largely due to taking things like this a bit too far, IIRC???

Each of you greatly contribute greatly to the community, there is no reason for either party to try and belittle the other. 

Being "right" isn't the most important thing in life.