Going to extremes with balanced valves

[Stubbers]

The following was performed on a heavily modified 25 cal marauder.

I got around to testing my new balanced valve in my marauder, it is a drop in that replaces the end cap, however this version uses a 2mm valve stem so requires the stem bore be sleeved down. The poppet is made from peek (very fun to get sealed with only 60 lbs of force holding it shut) with a balance ratio of around 60% (60% reduction). The valve stem 2mm bar stock that I reduced to ~1.3mm within the area of the throat, as I always do, this is because I run a .234" throat that support .225" porting ahead of it, which works well with the 1.3mm stem. I have yet to have a stem fail in the 6 years I've used them. Enlarging the throat would require more hammer strike and my build has always been oriented around reducing this as much as possible...so here I am, taking the extreme. DYOR and do so at your own peril!

With the pictured hand made poppet/balance valve I was able to reduce my hammer weight to 14.8 grams, while using only a 7 lb/in hammer spring to reach my valves plateau of ~60 FPE when set at 2000 psi (pretty typical power for a marauder at this setting). The prior valve, same setup but with a 3.175mm valve stem required 18 grams of hammer and 9 lbs of spring to achieve the same power.

The same 14.8 gram hammer with 3 lb/in spring with minimal preload sends 8 grain pellets in .177 out flying at 850, iirc the other 3.175 stemmed valve could only do about 650-700 fps with this spring fully preloaded.

The valves chamber height is adjustable (adding volume allows the valve to open easier, taking more time to fill the chamber, reducing volume does the opposite), but I try to keep my vent and chamber volume harmony to a point where I can tune within my desired range, down to 12 ft/lbs in .177, up to 60~ fpe in .25 cal.


One may ask, why do you still bother with the old marauder, to which I reply, marauder may be old and dumb, however I am young and dumb, and the marauder is a good gun to learn on, and boy have I learned! Prior to running the balanced valve, this gun operated just fine with a 52 gram hammer and the same 7# spring, but I like tinkering, and the result is a gun that operates with very little vibration in the frame with the lowered hammer energy requirement

52 gram hammer with 7 lb spring lock time = 7-8ms
14.8 gram hammer with 7lb spring lock time = 4.3ms

The reduced lock time and vibration in the frame which resonates thru the gun prior to the pellet leaving the barrel definitely doesn't bother me! I may even reduce the weight more...because I can't leave things well enough alone, ever. Thanks for reading.

Poppet OD: .3"
Balance chamber: .234"
Vent diameter: .038"


-Matt

 

[iAMzehTOASTY1]

Excellent work!

 

[Motorhead]

There ya go .... following the path of those before ya can be a good thing

 

[Stubbers]

There ya go .... following the path of those before ya can be a good thing

Most of my work is done in the foot steps of others, save for the few extremes I take to push the envelope, not re-inventing the wheel, more so seeing which tread gets the most traction for my conditions.

For example neither my first bv iteration or this one uses circlip retention for the balance cage. The cage holds itself in place wonderfully due to it balancing a 90 lb load from off the poppet in my case.

Not big on selling the idea of thinned stems to others, as that is entirely application dependent. I am not familiar with anyone that has gone as far down that path as I have, and I've done my own research and calculations as to what works and what probably won't. My 1.3mm~ thinned stem can open up to 100~~ lb valves all day, 200 lbs? Eh...might wanna go 1.55mm, 300~ lbs? Probably need 2mm..however those are rough estimations and I have not calculated 200/300 lb valves. As always DYOR

-Matt

 

[Stubbers]

A look at the reduced stem diameters behavior in an airgun. Left of the chart is their holding/closing force in pounds, bottom is the pressure acting upon the stem, and above are various stem diameters.

One could additionally remove their valve spring or run a lighter valve spring, but the effect / gains are much less impactful than a smaller stem diameter in my findings, as well as I like valve springs for their static holding/closing force which helps produce a bell curve, be that in regulated while falling off the regulator, or unregulated over their usable pressure range, they also help reduce hammer bounce

 

[mackeral5]

Most of my work is done in the foot steps of others, save for the few extremes I take to push the envelope, not re-inventing the wheel, more so seeing which tread gets the most traction for my conditions.

For example neither my first bv iteration or this one uses circlip retention for the balance cage. The cage holds itself in place wonderfully due to it balancing a 90 lb load from off the poppet in my case.

Not big on selling the idea of thinned stems to others, as that is entirely application dependent. I am not familiar with anyone that has gone as far down that path as I have, and I've done my own research and calculations as to what works and what probably won't. My 1.3mm~ thinned stem can open up to 100~~ lb valves all day, 200 lbs? Eh...might wanna go 1.55mm, 300~ lbs? Probably need 2mm..however those are rough estimations and I have not calculated 200/300 lb valves. As always DYOR

-Matt

View attachment 356383

A look at the reduced stem diameters behavior in an airgun. Left of the chart is their holding/closing force in pounds, bottom is the pressure acting upon the stem, and above are various stem diameters.

One could additionally remove their valve spring or run a lighter valve spring, but the effect / gains are much less impactful than a smaller stem diameter in my findings, as well as I like valve springs for their static holding/closing force which helps produce a bell curve, be that in regulated while falling off the regulator, or unregulated over their usable pressure range, they also help reduce hammer bounce

This is all rather eye opening as I never considered the change in closing force, I was only concerned with the gain in throat area when reducing stem diameter... In hindsight I previously credited all gains to gains in flow, I did not consider the changes in dwell...


I've learned a lot following along the various threads on the topic of DIY balanced valves. Your valve is a great example of that evolution and taking certain aspects to the extreme end of design/performance.

Up until this statement I can follow along and understand the forces at play, as described by the collective group of collaborators over the years.

"The cage holds itself in place wonderfully due to it balancing a 90 lb load from off the poppet in my case."

You must have the cage captive between the valve and gauge block???

 

[nervoustrig]

MIke, I recall this was a subject we discussed a few years ago on GTA...the stem's effect on closing force and dwell:

Windy City MKI revisit - Airguns & Guns Forum

Windy City MKI revisit, Air guns, Airgun Forum

www.gatewaytoairguns.org

 

[Stubbers]

This is all rather eye opening as I never considered the change in closing force, I was only concerned with the gain in throat area when reducing stem diameter... In hindsight I previously credited all gains to gains in flow, I did not consider the changes in dwell...


I've learned a lot following along the various threads on the topic of DIY balanced valves. Your valve is a great example of that evolution and taking certain aspects to the extreme end of design/performance.

Up until this statement I can follow along and understand the forces at play, as described by the collective group of collaborators over the years.

"The cage holds itself in place wonderfully due to it balancing a 90 lb load from off the poppet in my case."

You must have the cage captive between the valve and gauge block???

The .234" piston which is secured to the cage via an 8-32 screw is removing 90 lbs of force from the whole assembly. The .3" poppet would normally have 147~ lbs of force keeping it closed at 2000 psi with my 6# valve spring, where the balanced piston takes away 90~ of those lbs, that displaced load is only on the one end of the cage, pulling it into the valve once pressurized. The cage is captive in the same location as the endcap would be. Here is a picture:

It does fit loosely until pressurized , it can't fall out very far due to either a gauge block or plenum block that is nearby, I just fill the gun in a vertical position, has worked fine. The piston end is at ATM pressure until the valve actuates.


You generally have 4 fairly easy to calculate closing forces acting in your conventional and simple balanced valve, those are

- Pressure differential from plenum to throat (there is always more pressure acting upon the plenum side of your poppet, as the throat never meets or exceeds your plenum pressure, even with very small plenums, 5-10% pressure drop is gauranteed due to flow co-efficiency) *except in a blow open valve, or over balanced valve*

- Pressure acting upon the stem of the valve (as shown in the graph in my previous post, however one must take caution depending on their application how thin they go)

- Valve spring force (Easy to modulate from 0-20lbs if one so desires)

-Drag across the poppet / stem, smaller poppets and stems both benefit here as there is much less drag on slimmer profiles. You also achieve reducing the valves holding / closed load by keeping your poppet diameter as small as possible while keeping sealing magins nominal for good poppet life and seal. I am also confident the straight walled poppet has less drag than a tophat style poppet with a spring seat.

 

[bearair]

I always enjoy a good ole marauder thread. I keep learning more and more every time one of these threads pop up. If the envelope was never pushed FX wouldn't have nearly the line up they offer.

 

[mackeral5]

MIke, I recall this was a subject we discussed a few years ago on GTA...the stem's effect on closing force and dwell:

Windy City MKI revisit - Airguns & Guns Forum

Windy City MKI revisit, Air guns, Airgun Forum

www.gatewaytoairguns.org

Yes, Jason, I recall the discussion, but did not recall seeing the chart,

 

[mackeral5]

The .234" piston which is secured to the cage via an 8-32 screw is removing 90 lbs of force from the whole assembly. The .3" poppet would normally have 147~ lbs of force keeping it closed at 2000 psi with my 6# valve spring, where the balanced piston takes away 90~ of those lbs, that displaced load is only on the one end of the cage, pulling it into the valve once pressurized. The cage is captive in the same location as the endcap would be. Here is a picture:

View attachment 356411

It does fit loosely until pressurized , it can't fall out very far due to either a gauge block or plenum block that is nearby, I just fill the gun in a vertical position, has worked fine. The piston end is at ATM pressure until the valve actuates.


You generally have 4 fairly easy to calculate closing forces acting in your conventional and simple balanced valve, those are

- Pressure differential from plenum to throat (there is always more pressure acting upon the plenum side of your poppet, as the throat never meets or exceeds your plenum pressure, even with very small plenums, 5-10% pressure drop is gauranteed due to flow co-efficiency) *except in a blow open valve, or over balanced valve*

- Pressure acting upon the stem of the valve (as shown in the graph in my previous post, however one must take caution depending on their application how thin they go)

- Valve spring force (Easy to modulate from 0-20lbs if one so desires)

-Drag across the poppet / stem, smaller poppets and stems both benefit here as there is much less drag on slimmer profiles. You also achieve reducing the valves holding / closed load by keeping your poppet diameter as small as possible while keeping sealing magins nominal for good poppet life and seal. I am also confident the straight walled poppet has less drag than a tophat style poppet with a spring seat.

No questions about filling, etc. i have a loose poppet in a modified .457 extreme, I have never had any adverse effects due to this. As you said, fill from empty muzzle up, with no hammer preload against the valve.

i can clearly understand the reduction in pressure against the poppet, how the balance chamber affects that.

But I am still having difficulty understanding how the balance system(chamber, vent, spring) are influencing opening rate/speed/dwell, if the cage is not captive in some way and not allowed to travel with the poppet.

Is the 90lb of force removed from the poppet now 90lb acting against the piston, and in turn the piston is pulling the cage tightly against the valve? If that is the case, then awesome, I am relieved to finally understand this. If it is not the case, then I will remain in this perplexed state, with regards to this topic, lol.....

 

[Long_Shot]

Good job showing your work. Very intersesting valve stem size info. I failed to test that.
I made a balance valve for a .25 cal. that works suprisingly good shooting 78 - 84 FPE @ about 128 bar.
I see your spring behind the poppet looks rather strong in the photo. Maybe I'm wrong.
I tried several different springs behind the poppet. With different vent sizes, HS weights, reg. setings and slug weights in mine.
Ended up using a very light weight spring, .040" vent that makes the system have better adjustability with a light HS.
Just curious if you tried different springs.

 

[Stubbers]

No questions about filling, etc. i have a loose poppet in a modified .457 extreme, I have never had any adverse effects due to this. As you said, fill from empty muzzle up, with no hammer preload against the valve.

i can clearly understand the reduction in pressure against the poppet, how the balance chamber affects that.

But I am still having difficulty understanding how the balance system(chamber, vent, spring) are influencing opening rate/speed/dwell, if the cage is not captive in some way and not allowed to travel with the poppet.

Is the 90lb of force removed from the poppet now 90lb acting against the piston, and in turn the piston is pulling the cage tightly against the valve? If that is the case, then awesome, I am relieved to finally understand this. If it is not the case, then I will remain in this perplexed state, with regards to this topic, lol.....

Your last statement about the 90 lb load removal which technically acts upon the cage and pulls it tight is correct, and that fluctuates some during the valve actuation however I feel once its sealed down that force increases once pressed against the valve by whatever sealing margin that has, likely quite a bit considering the diameter.

 

[Stubbers]

Good job showing your work. Very intersesting valve stem size info. I failed to test that.
I made a balance valve for a .25 cal. that works suprisingly good shooting 78 - 84 FPE @ about 128 bar.
I see your spring behind the poppet looks rather strong in the photo. Maybe I'm wrong.
I tried several different springs behind the poppet. With different vent sizes, HS weights, reg. setings and slug weights in mine.
Ended up using a very light weight spring, .040" vent that makes the system have better adjustability with a light HS.
Just curious if you tried different springs.

I have tried various springs, but reality is the light spring is 3-4 lbs and this spring is 6-7 lbs (force required to open valve 3mm), not a huge difference...no major change other than a bit more hammer strike required. I have my hammer weight / spring dialed in so no need to go lighter, although I haven't tested how it acts off the reg yet, may be beneficial to go lighter, time will tell.

Your vent size is spot on imo! .035"-.04" vent is a great place for 1900-2100 psi or 120-140 bar.

Curious what your hammer weight is fully dressed?

Your barrel must be 23.5"+?

-Matt

 

[mackeral5]

Your last statement about the 90 lb load removal which technically acts upon the cage and pulls it tight is correct, and that fluctuates some during the valve actuation however I feel once its sealed down that force increases once pressed against the valve by whatever sealing margin that has, likely quite a bit considering the diameter.

That was a missing link for me, for quite some time. Thank you for clarifying. It doesn't quite reconcile some related thought processes I have, but I clearly understand what is preventing the balance system from moving with the poppet now.

 

[Airgunmann]

Nice I've taken regular marauder valve stems down to .090 thousandths it definitely helps the valves breath better nice work . Peek can be a real pain to get to seal especially in a balance valve

 

[Long_Shot]

I have tried various springs, but reality is the light spring is 3-4 lbs and this spring is 6-7 lbs (force required to open valve 3mm), not a huge difference...no major change other than a bit more hammer strike required. I have my hammer weight / spring dialed in so no need to go lighter, although I haven't tested how it acts off the reg yet, may be beneficial to go lighter, time will tell.

Your vent size is spot on imo! .035"-.04" vent is a great place for 1900-2100 psi or 120-140 bar.

Curious what your hammer weight is fully dressed?

Your barrel must be 23.5"+?

-Matt

Not sure what my HS cocking weight is. I don't have a way to measure that. It's been called "pinky cocking".
As a lame reference - feels like 50% of my stock .25 cal. Cricket.
The hammer itself is a stock .35 cal. Cricket hammer.
You nailed it - my barrels are 24" and 25". Just finnishing a 29.5" too.
My poppet OD: .390" with a .325" hole ("throat") it seals leading to a .300" transfer port with a .118" (3mm) valve stem.
The main reason I probably got better results with a light poppet spring. Very curious now about that .118" stem diameter in a .325" hole.
I only have .235" diameter balance end vented to the transfer port.
Which sould be about 80.5 lbs. @ 1856 PSI reduction in force needed to crack the poppet open.
I've been thinking about getting a Vulcan 3 to put a balance valve in, along with several other things.
Could be a good place to experiment with your reduced valve stem concept.
Thanks again, for the interesting info.

 

[Stubbers]

Not sure what my HS cocking weight is. I don't have a way to measure that. It's been called "pinky cocking".
As a lame reference - feels like 50% of my stock .25 cal. Cricket.
The hammer itself is a stock .35 cal. Cricket hammer.
You nailed it - my barrels are 24" and 25". Just finnishing a 29.5" too.
My poppet OD: .390" with a .325" hole ("throat") it seals leading to a .300" transfer port with a .118" (3mm) valve stem.
The main reason I probably got better results with a light poppet spring. Very curious now about that .118" stem diameter in a .325" hole.
I only have .235" diameter balance end vented to the transfer port.
Which sould be about 80.5 lbs. @ 1856 PSI reduction in force needed to crack the poppet open.
I've been thinking about getting a Vulcan 3 to put a balance valve in, along with several other things.
Could be a good place to experiment with your reduced valve stem concept.
Thanks again, for the interesting info.

Your throat is is fine with the .118" stem to support .3" ports. I wouldn't change that up. In another build you could go with a smaller stem and smaller throat which leads to smaller poppet and overall easier to operate valve when all factors are considered. For example a 2mm / .078" stem would only need a .315" throat. Not a huge difference but it all adds up, especially the thinned stem.

I meant your hammer weight itself, not the cocking force. Pinky cocking is always nice!

 

[Stubbers]

Few tweaks. Took my poppet's OD down from .3" to around .295", mostly to remove some run-out from my hand job (pun intended). I also re-faced the poppet, changing the angle a bit so the face is slightly concave, and it impressively made a difference in ease of opening the valve. As such my 7 lb spring started plateauing my valve at minimum preload.

I took my hammer weight down from 14.8 to 10.9 grams dressed, something like 8.8 grams naked. Very little meat left, although I could see getting it down a scoche more. I plan to try to get it down to 8 or 9 gr dressed.

At roughly 145 bar the valve is slinging 33.4 grs out at 920 fps on the 7 lb hammer spring, 920 fps being where both my valve limiter and plateau both are. That is with just .05" preload, ideally I want to be around 870-890~ with a tiny bit of pre-load so I will probably reduce my chamber height the slightest to get it there if taking the hammer weight down further doesn't do the trick.

That said, I appear to have found the end game when it comes to lightening a marauder hammer, I will be hard pressed to shave off any more significant weight.

Lock time decreased from 4.3 ms on the 14.8gr hammer to 3.7ms on the 10.9 gr according to my spreadsheet. I must say with this data I have accumulated, the effect of hammer weight is not proportional to the % change in weight, which I poorly assumed going in...rather removing 4gr from a 14 gr hammer is seemingly no different than removing 4 gr from a 50 gram hammer in terms of its relationship with the valve. Also noted very little change in lift requirement on the valve going from 30 gram down to 10 gram, and even less change going from 15 to 10, as I assumed, it takes very large shifts in hammer weight to have even the remotest effect on your valves lift thats deemed notable. A statement I strongly stand behind, and a hill I don't mind dying on!

-Matt

 

[Stubbers]

Got my hammer weight down to 10gr dressed, and have a peek cocking lug on the way that will drop it down further to about 9gr. Taking the weight down to 10gr allowed me to get just a hair off the plateau, bringing fps down to 895-900 shooting 33.4's, so the 9gr should do the rest of the trick, if not I have another .5-1gr I can shave off the hammer.

Pictured is the stock 78gr hammer, along with a 25 gr, 18gr, and my current 10gr hammer. The 10 gram hammer fits and slides in the tube without any weird side to side play or wobble, makes me wonder how thin one can really go before that becomes an issue.

Matt