Comparing a few Poppet Valves

[Stubbers]

Before I begin...Many thanks goes to Dave/ @sb327 for his contributions in getting me to where I am today with my current valve arrangement, we worked together closely to dial in versatile pilot valve that works very similarly to the one found in the L2. Also thanks to @csdilligaf for turning me out another one for me for my unregulated marauder. He is a fine gentleman and a machinist whose work is impeccable, honestly out of this world, at this level its an art. The one he turned for me is shown below anodized in a light gun metal grey.

Starting from the Bottom, are a series of poppet valves found in todays pcp's, as we work our way up, the valve designs become more complex but overcoming the force holding the valve shut or shutting the valve is reduced as we ascend. I'll briefly discuss some of their functions and the important numbers acting on each version. All of these have gone through their paces in the same old marauder, as I've experimented over the last 7 years modding and tinkering. I won't be covering hammerless valves here as they are much more complex and not universally retrofittable to most pcp's like the below variety.

A: Standard poppet @ .276" OD, .125" stem, at 2000 psi with 5lbs of valve spring has 129 lbs of force holding it shut, and 29 lbs of peak closing force on the poppet while opened prior to pressure drop. Required 50 grams of hammer and 7.7 lbs of hammer spring .8" hammer travel. .6 FPE / 2 momentum

B) Standard poppet @ .276" OD, .78" stem, at 2000 psi with 5 lbs of valve spring has 129 lbs of force holding it shut, and 14 lbs of closing force on the poppet while opened prior to pressure drop. This valve required 50 grams of hammer and 6 lbs of hammer spring to operate. .8" hammer travel. Roughly .5 FPE / 1.64 momentum

C) Balanced valve, .295" OD, .125" stem, at 2000 psi with 5 lbs of valve spring, it has a .234" balance piston, which reduces the force holding it shut to around 55 lbs of force, with 29 lbs of closing force while opened. This valve required around 20 grams and 7.7 lbs of hammer spring to operate. .8" hammer travel. Roughly .45 FPE. / 1.2 momentum

D) Balanced valve, .295" OD, .078" stem, at 2000 psi with 5 lbs of valve spring, with the same .234" balanced piston and 55 lbs of force holding it shut, it only has a peak of 14 lbs acting upon it while open. This valve required 15 grams and only 5 lbs of hammer spring to operate. ..8" hammer travel. Roughly .384 FPE. / .902 momentum

E) O-ringless Pilot Valve. .315" OD primary which reduces to .276", and .117" OD Pilot head, .125" stem, at 2000 psi the pilot head only has 24 lbs of force holding it shut with a 2 lb valve spring, while the primary has 159 lbs holding it shut. This valve operates with 4.8 grams of hammer, 4 lbs of hammer spring, .044" hammer travel. Roughly .12-.13 FPE / .277 momentum

As you can see, even a balanced valve taken to an extreme degree of balance with a reduced stem diameter to remove as much closing force as possible while remaining tunable, the reduction in hammer energy needed to operate the valve is reduced a fraction of what a pilot valve can accomplish. These above examples are all quite extreme, taken as far as they can be while still being very functional and tameable via hammer strike.

As you ascend through each poppet variation, the design and fabrication that goes into them gets far more complicated, as well as tuning them and setting them up. They all have their pros and their cons, but the benefit to sharing this knowledge is that nearly all pcp's can be retrofitted with the above valves, depending on your guns or personal limitations, its nice to have options if you want to reduce the required hammer strike needed to operate your valve, which results in a smoother shot cycle with less harmonics disturbing your point of aim and thus point of impact.

As you see above, I favor peek. In case you're reading and aren't familiar with the material selection, it's due being less compressible than many counter-parts, which a hammer strike has to over come, the compression of your poppet against the seat, it also stands up to wear and tear much better with this so you're only extending the life of your poppet going with peek or peek filled varieties.

Both Pilot and balanced valves rely on properly sized vents and chambers with ideal volume which can vastly change how they operate, from requiring a lot of hammer strike, to requiring very little, while the latter generally has an unstable or unreachable low end due to not being able to close the valve fast enough (too much volume/not enough vent), and the former is rather undesirable as the whole purpose of going this direction with valves is to reduce hammer strike while retaining tunability, which is why there is the Goldilocks zone for vent sizing and volume within chambers. Both designs for PV and BV above have adjustable height / chamber volume, and adjustable vent sizing (also known as jets) that help one find their Goldilocks zone.

I could write a lot more in regards to the pros or cons of all the versions, or their inner-workings and what makes them tick, but I'll keep this simple to make it more digestible for now and to not clutter this primary post covering some basics.

-Matt

 

[Stubbers]

I left out the stock Marauder poppet, which is .34" OD with .125" stem with a heavy 30lb/in valve spring, closed it has around 200-280 lbs of force holding it shut at 2000-3000 psi and 34lbs or so of closing force acting on the stem, made from unknown thermoplastic similar to black delrin, this poppet required a 78 gram hammer stock with 10-11 lbs of hammer spring (at my power level .25 cal/60 fpe) and .75" hammer travel. .7 FPE / 2.79 momentum.

Above stock setup has a lock time of around 6 MS, which means it takes 6 MS for the hammer to reach the valve from the moment its released from the triggers sear.

The Fastest lock time out of all the above valves is by far the pilot valve with .44" hammer travel, having just 1.2 ms of lock time. Lock time is very important as it produces harmonics through the rifle prior to the pellet even moving down the barrel which may or may not influence deviation from your intended point of aim.

One may argue, there is very little difference between 1.2 MS and 6 MS of lock time, that it takes 250 ms for the information to travel to your brain and that its moot, but one must realize while your brain is living in the past reacting to information that is 250ms old your nervous system feels the duration/lock time of the hammers travel in real time, so ultimately both your nervous system and brain will observe the difference and it will effect your shot cycle. It also feels the .7 fpe and 2.8 momentum happening within the action far greater than .13 and .28 momentum, nearly 1/10th of the overall energy compared to stock, with 1/5th the lock time combined its not only very perceptible and impacting shooters performance, its far more pleasant with reduced noise and harmonics making for a softer shot, which pcp's are well known for already compared to say springers or pb's.

Next, I'll briefly discuss what makes a these valves tick...stay tuned.

-Matt

 

[Stubbers]

Standard/Conventional valves:

Seen above as version A and B, nothing fancy, hammer goes bong, valve opens, the valve's spring (if present), plus air going by the valve through the throat and the force acting on the area of valve stem which terminates into atmospheric air return the poppet to its seat. Generally a high density/modulus thermoplastic seated against the valve body.

These can be used in both regulated and unregulated guns and are very tunable and quite consistent.


Balanced Valve:

Seen in the Original post as version C and D, these rely on a piston contained within a chamber be it built within the poppet or within the insert that retains/secures the piston or bore and its load to the valve body, a chamber that can breathe to atmospheric air, and its this magic that exposes the chamber's surface area to atmospheric air opposed to the high pressure air within your airguns reservoir that allows the 'balance valves' reduced force to transfer the load that was once on the poppet, to the piston which keeps the chamber shielded until the guns fired.

The balance valve also relies on venting, which once fired, is activated by pressure within the throat that allows the chamber that was once at atmospheric pressure to fill, and depending on your vent sizing, it can fill slow, allowing for light hammer strikes or longer dwells, or with bigger vents it can fill very quickly, ultimately reverting it to a conventional valve very briefly after the poppet leaves the valves seat.

The biggest caveat to balanced valves is their reliance on an o-ring that sits between your valves pressure and atmospheric pressure, and as it sits the o-ring succumbs to an effect that increases break out friction. Pressure is building on just one side of the o-ring, forcing it into a corner of its gland, and while this is occurring, it has its own pressure and system pressure acting on it, and what occurs here is the o-ring begins to 'push out' lubricant that normally resides between it and its bore, and sort of adhering microscopically into little nano/micro grooves. This can mostly be addressed by tuning towards the rifles plateau or even sacrificing a bit of efficiency and just going a bit over. Best suited in regulated actions.



Pilot Valves:

Seen above as exhibit E, pilot valves are essentially a 'dual poppet' system that primarily relies on a small poppet with a greatly reduced surface area to activate another poppet or piston that resides in a bore with a tight tolerance else advisable to use an o-ring, which when activated allows air to begin to flow through your valve. These valves do not need exposure to atmospheric air, nor o-rings, one may use an o-ring and it shouldn't cause stiction issues as the above balanced valves as the piston the o-ring can reside on is not activated by the hammer, rather pneumatically with great force. There are quite a few ways one could go about building one, but I will explain the one pictured above, which relies on 2 chambers with somewhat specific volumes, a vent that is ideally activated by the piston that allows air to flow through your valve, and to keep the chamber volumes modest, a reduction/step on the piston that allows flow through the valve on the end that seats to the valve body.

As the pilot valve is struck by the hammer, the pilots chamber which is equal in surface area to the entire piston sealed against the valve body begins to dump in another chamber which is a somewhat specific volume within the piston itself, the dumped air is momentarily semi self-contained by tight tolernace between the pilot stem and the piston's bore out. This protects the projectile from budging from the pilot chambers dump prior to the piston activating and allowing metered air through. The pressure differential once acting in favor of closing the piston within the pilots chamber is reduced and the pressure differential then favors the step/reduction and the piston launches from the valves seat. The pilot valve's vent acts similarly as a balanced valve, once the pilot valve returns to its seat against the piston, the vent reverses the pressure differential by refilling the pilots chamber, while the force acting on the stem in the throat also tugs both the pilot and the piston its seated against back to the valve seat.

These valves work very well in regulated and unregulated applications as they are a bit less vent dependant than balanced valves. More info about them available in my signature.

-Matt

 

[Long_Shot]

Great info. !!!
I've been using a balance valve in a custom gun with surprisingly good results for about 1.5 years now.
Took a bit of time to get things right. Now that I'm in the "Goldilocks zone" with it. Just trigger time now.
More velocity and power.
Less cocking force, less plenum pressure. less shot sound.
The perfect platform for a slug gun.

 

[Stubbers]

Great info. !!!
I've been using a balance valve in a custom gun with surprisingly good results for about 1.5 years now.
Took a bit of time to get things right. Now that I'm in the "Goldilocks zone" with it. Just trigger time now.
More velocity and power.
Less cocking force, less plenum pressure. less shot sound.
The perfect platform for a slug gun.

With less cocking force comes less tension against the hammer and thus the sear which results in a slightly lighter trigger pull too, which many favor.

-Matt

 

[Long_Shot]

Looking forward to what info. you might share about the Pilot Valve design.
You gave a very nice description so far.
I want to use that type of valve in my next build.

Here's the style Balance valve I made for a Cricket that can get a .25 cal. 50.4 gr. slug going 950 FPS @ 135 bar reg. pressure.
This isn't my design, I did change a few things. The poppets on the right have a hole in the stem.
I did the vent through the Peek, instead of weakening the valve stem.
Shot many thousands of rounds with it so far............without any maintenance.

 

[Stubbers]

Looking forward to what info. you might share about the Pilot Valve design.
You gave a very nice description so far.
I want to use that type of valve in my next build.

Here's the style Balance valve I made for a Cricket that can get a .25 cal. 50.4 gr. slug going 950 FPS @ 135 bar reg. pressure.
This isn't my design, I did change a few things. The poppets on the right have a hole in the stem.
I did the vent through the Peek, instead of weakening the valve stem.
Shot many thousands of rounds with it so far............without any maintenance.

View attachment 478982

Nice looking poppets, clean work.

There are a lot of devils in the details to pilot valve designs. Quite a bit of info available in my signature about them. I'll gloss over some more details in the future.

Today, for a giggle I tossed in my conventional valve/poppet, 50 gram hammer and 9 lb spring, what a terrible, awful experience, it's like my senses were numb after some time using such valves in the marauders not long ago, so many harmonics going on from a heavy spring going boing-oing-oing to a heavy hammer slamming around in the action, compared to a 4 gram hammer and 4 lb spring used for the same power in my piloted valve version, I almost felt sick that many pcp's out there still rely on conventional valves.

Here is a gif I made showing how I envision a pilot valve works internally.

-Matt

 

[Star7]

I GREATLY appreciate this thread, thank you all.

 

[Stubbers]

Lift and Dwell, how do they tie into these valves.

What is lift. Lift is the distance your poppet travels from the valve seat.

What is dwell? Valve dwell is the duration the poppet remains off of its seat.

Lighter hammers with heavier springs create slightly more lift and slightly less dwell, and heavier hammers with lighter springs create more dwell and less lift, it takes extremely huge shifts in hammer/spring weight to see noteworthy changes provided you tune both setups to equal power.

Both balanced and conventional/standard poppet valves require similar lift, generally 3-4mm, while pilot valves require a bit less, 2.5-3.5mm, even with their extremely light hammer weights and springs. Conventional valves require hammer's energy to maintain dwell through the majority of the shot cycle, up until the moment it begins to reverse, while balanced valves and pilot valves only partially so, depending on vent size and chamber volumes the vent flow rate partially determines the length of dwell, which on top of the reduced force holding the poppet shut, helps reduce the required hammer energy needed to keep a valve open as it flows. The initial bit of lift in a pilot valve interestingly has an entirely different job than a conventional or balanced, where its purpose is to dump the pilot valves chamber to activate the main piston/poppet, this initial lift contributes (ideally, in my version, some version will contribute flow and cause loss of peak/plateau power potential) no flow towards the guns power output, and this action takes just a fraction of a MS (unless you do not fabricate one correctly, it may not dump fast enough to activate the main poppet), once activated, the pilots job is to carry on based on the hammer energy put into it to create hammer assisted dwell, and once the hammer energy dissipates, the pilot seats to the main poppet, and the chamber refills. Where as in both conventional and balanced valves, the moment the hammer strikes the poppet, your creating lift that contributes to air flow through the valve.


Worth nothing, pilot valves: Limited lift

One of the requirements of pilot valves is that you must limit the lift of the primary piston/poppet that flows air. Poppet valves only need to lift approximately 1/4 of the throats flow-able surface area to hit peak flow, this is called the curtain, Any lift beyond this doesn't add flow rate, only extends duration (creates more dwell) in a typical conventional valve. Pilot valves rely on an insert that encases the main poppet with a sliding fit. This insert can be arranged so that the main poppet can only lift off the seat 1/3-1/4 of the valves flow-able surface area. The caveat/downside to this is that it limits the low end of power as the valve will have to lift that distance prior to the pilot/vent doing its job in reversing the main poppet to the valve seat. So one must rely on transfer path chokes or externally adjustable regulators if they really want to dial the power down super far, OR reduce the distance the main poppet can open, which then hurts your top end. This doesn't mean a pilot valve is not tunable via hammer strike, quite the contrary, it just has limited range on the low end without introducing other means such as a choke as previously mentioned.


Over venting or poorly dumped Pilot Valves:

If one decides to run a lot of vent, or an unchecked vent that is open all the time, you can lose power, albeit not much, but loss is loss.. This is why its best, much like the L2, to have the vent only active/open while the main piston/poppet is off of its seat, while being closed prior to it activating.

Poorly made pilot valves can contribute to a lot of power loss by dumping the pilots chamber into the throat opposed to a shielded hollowed out main piston/poppet that slowly releases it, as well as running vents that are left unchecked and are always flowing, or are just generally over-vented.

Side note:
The time it costs to dump the pilot chamber is a fraction of the reduction of hammer travel/lock time, meaning you're still reducing the time in large from the moment the hammer leaves the sear, to the moment the pellet begins to move. Dump time must be between a tenth and two tenths of a MS or its likely the pilot will fail to activate the main, where as the reduction in hammer lock time is 2-5 MS.

-Matt

 

[Stubbers]

Peak inside a Pilot Valve (and out) (long read)

Here you can see the internal components. The pilot poppet is made from an externally threaded 18g titanium barbell intended for piercings, and the .125" stem is stainless steel tubing pressed and epoxied onto it using a .062" to .047" bushing in between. I got pretty creative in the design and lucky finding something that works so well without having to machine it, as having the pilots head be removable via threads is rather ideal opposed to a press fit which not only is likely to fail over time if pressed, it makes for a pain if you want to resurface either side of the pistons sealing faces. Threading hard steels at these small diameters is rather tough with caveman tools and even for seasoned machinists. The pilot head is a 3mm titanium spike that threads on, there are quite a few options with piercings for different head shapes/sizes. This version is used in my regulated marauder that is using very little return spring, where as pictured below you'll see a version used in my unregulated marauder with an added external spring. The inside of the insert has a .125" bored hole roughly .25"-.3" deep for the pilot return spring and 3mm pilot head to reside in, allowing space for spring compressing and pilot valve lift.

The longer spring seen is for the checked vent that activates once the peek piston opens, with it, ideally after .01" to .02" of peek piston travel, a .056" piston going into a .059" bore making for a surface area equal to .019"/.5mm begins venting. One of the goals in this build was to keep volumes very minimal within the pilots chamber, while leaving enough volume to allow the peek piston to fully open/compress the air that does not dump. Thanks to this, not much vent is needed (bonus here as well). The two springs (Credit to Dave/sb327) are from a tire valve core (pilot spring) and a bic lighter (check valve spring). The check valves spring bore is .103" and threaded for a 6-32 screw to retain all those bits. The insert also has 7 .103" bored holes allowing enough flow for 120% of the flow from a full ported 25 cal, or 150% the flow of my .225" ported valve. The throat for the pilot is opened to .09", where the .118" head sits with .014" sealing margin, things being aligned here are quite critical. However one could simply run a 3.5 or 4mm head and achieve similar results, however pilot throats smaller than .08" with a .047" stem may not fire, the dump time may be too slow to activate the peek piston/poppet. I recommend a throat CSA of around .0175 at minimum. So for a .062" stem that would be a .097" throat. I find it a bit funny that the pilot head is fractionally smaller than the stem, meaning the force holding the valve shut is less than the force trying to shut the valve once that time arrives.

The peek piston is hollowed, on the bottom side that sits within the throat is a 'boring hole' made from a 10-24 plug or the like. The peek is drilled to thread the plug and prior to that must be bored a bit larger internally unless you run an even taller poppet, the plug resides in the throat in case it ever develops a leak. Rubberized superglue or the like is probably a reasonable sealant to use here but I am sure there is better although it doesn't matter terribly much. The internal volume here is quite critical, although there is no such thing as too much, more times than not space is a constraint, hence why the poppet is quite tall. There is roughly roughly .4cc of empty volume waiting for the pilots chamber to dump inside that peek piston/poppet, and the pilots chamber is roughly .11 cc when closed and setup at ideal height from the valve seat.

There is a step on the bottom of the peek poppet going from .315" to .276". At this step, I need 75% pressure drop within the pilots chamber for the pressure differential to activate the peek poppet. If the step were not present, I would need 98% pressure drop. If the step were say .315" to .25", I would only need 61% pressure drop. I made a pretty cool calculator via spreadsheets to arrive at these numbers that I have personally tested to be tried and true. The more pressure drop you need, the more volume you need for it to even be possible, likewise the less pressue drop you need, the less volume you need for it to be possible.

In my version, I run a .062" to .047" bushing press fit into the piston for the .047" pilot stem to have a tight sliding fit. This allows me to run a bore that is taller than the poppet allows, allowing for really good alignment that inhibits the pilot from pivoting at angles, you can even witness this in the picture above as the peek piston sits horizontally and the pilot remains central to the throat. This tight tolerance between the .047" stem and the .0475" or so bore into the peek piston/poppet helps eliminate reopening of the valve via hammer bounce by temporarily retaining the pilot chambers pressure drop, provided all volumes are within their optimal range. Once the initial pilot chambers dump takes place, it takes 100-150 ms for the peeks hollowed out chamber to evacuate entirely, a volume that is critical and unless empty, won't allow the peek piston to 're-activate'. Any hammer bounce occurring is like trying to blow air in to an empty non-deformed bottle with your lungs.

The Edgun L2 pilot valve utilizes an o-ring on the piston/poppet, while this o-ring doesn't create as much hassle as balanced valve o-rings, I had a hunch these valves would fire just fine without one present provided good tolerances between the piston and its bore. Dave tested my theory in one of his versions by removing the o-ring, and what do ya know, the valve fired! So that remained in the design to allow more space with the hollow peek poppet and reduce a wearable item that may or may not impact cold/hot shots (o-rings change a lot based on temperature) / or long sitting shots (break out friction) ect.

Shown below is the unregulated version setup. I left the threaded end of my 18g barbell for a 4mm (or 5mm if I wish in the future) ball that retains an external spring. I put a flat spot for the hammer to contact which isn't shown below. The presence of the added spring helps reduce the pressure variation over the unregulated guns bell curve. The internal valve core spring only adds 1 lb of resistance at best, where this spring adds another 4. While its not a lot, neither are the opening/closing over the guns pressure range. At 3000 psi there is 35lbs holding valve shut, and 37 lbs of force pneumatically trying to shut the valve, and 2000, that drops to 24 lbs and 25, a 39% drop. With 1lb of spring added, that is 37.5%. With 5 lbs, that is now 33%. I can always add more if I feel necessary as well, but a 5% difference is quite a lot. Initial tests show promise and I can't even tell its there by needing a hair more hammer strike on this valve. The unregulated version I have .5" hammer travel, 8 grams of hammer and 3 lbs of hammer spring, ya heard that right, an unregulated gun with 8 grams of hammer and 3 lbs of spring opening just fine even at at 3.2k psi, even with only 66% of the travel a stock marauder uses.

-Matt

 

[RScott]

Wow. I'm overwhelmed by your insightful understanding, design/analytical skills, execution, and ability to explain all of this. And while I'm envious of your capabilities, I'm grateful that you are sharing your accomplishments which might help the industry move faster to offering devices to less skilled people like me who would love to use them.

Your animation helped me much better understand the concepts. But it, and your write-up, also helped me appreciate the complexities.

I have a few questions:
1- After the pilot opens to reduce the air pressure holding the piston against the valve head, what causes the piston to move? There is still some net pressure keeping it closed. It would seem you would want another nodule along the stem that would push the piston open shortly after the pilot poppet opens into the small pressure chamber.
2- I read that the action of pushing the pilot poppet to bring air into the piston chamber takes only 0.1 - 0.2 ms. That adds to the cycle time. Where does the reduction come from? Is it that it takes a long time in a conventional valve for the poppet to be separated from the valve seat due to the compression from back pressure, whereas the 1/5 amount of back pressure in the pilot valve design doesn't have that decompression action/time? Or is it that a lighter hammer in the pilot valve design moves faster than a heavy hammer in a conventional valve?
3- Once optimized, will a pilot valve lead to lower or higher standard deviation of muzzle velocity compared to conventional valve design? (I realize it will provide far less vibration, shorter cycle time, and potentially lighter trigger pull). Is the activity in the valve a key determinant of SD, or is it more due to friction of sear and hammer movement?

Regards,

 

[Stubbers]

Wow. I'm overwhelmed by your insightful understanding, design/analytical skills, execution, and ability to explain all of this. And while I'm envious of your capabilities, I'm grateful that you are sharing your accomplishments which might help the industry move faster to offering devices to less skilled people like me who would love to use them.

Your animation helped me much better understand the concepts. But it, and your write-up, also helped me appreciate the complexities.

I have a few questions:
1- After the pilot opens to reduce the air pressure holding the piston against the valve head, what causes the piston to move? There is still some net pressure keeping it closed. It would seem you would want another nodule along the stem that would push the piston open shortly after the pilot poppet opens into the small pressure chamber.
2- I read that the action of pushing the pilot poppet to bring air into the piston chamber takes only 0.1 - 0.2 ms. That adds to the cycle time. Where does the reduction come from? Is it that it takes a long time in a conventional valve for the poppet to be separated from the valve seat due to the compression from back pressure, whereas the 1/5 amount of back pressure in the pilot valve design doesn't have that decompression action/time? Or is it that a lighter hammer in the pilot valve design moves faster than a heavy hammer in a conventional valve?
3- Once optimized, will a pilot valve lead to lower or higher standard deviation of muzzle velocity compared to conventional valve design? (I realize it will provide far less vibration, shorter cycle time, and potentially lighter trigger pull). Is the activity in the valve a key determinant of SD, or is it more due to friction of sear and hammer movement?

Regards,

1) Correct there is still force resisting the pistons opening however there is a pressure differential once the pilots chamber evacuates into the hollowed piston, the step on the piston (from .315" to .275" in my example) amplifies the differential, there is a minor force acting upon the step always trying to open the piston, it's only able to overcome the force holding the valve shut once that pilots chamber pressure drops enough to overcome the .315" vs .275" difference. The step isn't necessary as I explained however, the more step you have, the more extreme the opening may become, to the point it may be destructive to the pilots head or even itself. No step present would require much more piston volume / throat cross sectional area to accommodate a bigger pressure dump, basically 99% of the pilot chamber volume has to dump to activate the piston if no step is present.

2) The reduction in time comes from reduced hammer lock time, which is the time it takes for the hammer to travel from its rested position at the sear, to the valve stem. The time gained here is far greater than the time lost towards activating the main piston/poppet. So you lose .1-.2ms in piston activation time but gain 1ms+ in hammer lock time, which overall means less time before pellet moves once trigger is pulled. A stock marauder hammer lock time is around 6-7ms, where as the pilot valve version is 1-2 ms.

3) Loaded question. For unregulated, I would say a pilot valve has more potential in being a better 'self regulating valve', this is due to allowing the use of much heavier valve spring without compromising too much on the light hammer strike these valves require. You can achieve valve spring force to poppet holding force ratios that no standard valve can. For regulated, a pilot valve opens to full power more consistently even with a lot of regulator creep, and mitigates reg creep better due to the reduction in pressure delta when the regulator creeps to its maximum state. Outside of regulator creep there I'd say all things are potential equal unless you design a pilot valve that requires too light of a strike, it does start to become more vulnerable to minor changes in hammer energy which can result in poor consistency if tuned below plateau, however plateau will be consistent in such a version.


-Matt

 

[Stubbers]

It's hard to put into words how soft the shot cycle of a well made pilot valve feels next to a standard valve...not even an electronic valve could compare unless it utilized similar force reduction. I degas my pilot valve with my thumb, well my regulated one, unregulated at 2500+ psi is a tall order for me, I am a smaller guy, however your average guy could definitely degas unregulated by hand too.

The best and maybe a bit extreme comparison I can make is...it's like trying to hammer a nail into ice (standard valve) vs slush (pilot valve), or a baseball vs a tennis ball, except you're using a real steel hammer for the ice and baseball and a plastic child's hammer for the slush and tennis ball, and the swing into ice and baseball must be full where the slush and tennis ball is half a swing...yep.

Having a lock time that is 1 ms is incredibly beneficial, the greater the distance between you and your target, the greater the movement your crosshair can potentially veer off target before pellet leaves your barrel, the overall lock time from sear release to pellet exit is critical in long range shooting, I am sure quite a few br shooters have lost a point here and there due to this exact potential margin of error.

-Matt

 

[RScott]

1) Correct there is still force resisting the pistons opening however there is a pressure differential once the pilots chamber evacuates into the hollowed piston, the step on the piston (from .315" to .275" in my example) amplifies the differential, there is a minor force acting upon the step always trying to open the piston, it's only able to overcome the force holding the valve shut once that pilots chamber pressure drops enough to overcome the .315" vs .275" difference. The step isn't necessary as I explained however, the more step you have, the more extreme the opening may become, to the point it may be destructive to the pilots head or even itself. No step present would require much more piston volume / throat cross sectional area to accommodate a bigger pressure dump, basically 99% of the pilot chamber volume has to dump to activate the piston if no step is present.

2) The reduction in time comes from reduced hammer lock time, which is the time it takes for the hammer to travel from its rested position at the sear, to the valve stem. The time gained here is far greater than the time lost towards activating the main piston/poppet. So you lose .1-.2ms in piston activation time but gain 1ms+ in hammer lock time, which overall means less time before pellet moves once trigger is pulled. A stock marauder hammer lock time is around 6-7ms, where as the pilot valve version is 1-2 ms.

3) Loaded question. For unregulated, I would say a pilot valve has more potential in being a better 'self regulating valve', this is due to allowing the use of much heavier valve spring without compromising too much on the light hammer strike these valves require. You can achieve valve spring force to poppet holding force ratios that no standard valve can. For regulated, a pilot valve opens to full power more consistently even with a lot of regulator creep, and mitigates reg creep better due to the reduction in pressure delta when the regulator creeps to its maximum state. Outside of regulator creep there I'd say all things are potential equal unless you design a pilot valve that requires too light of a strike, it does start to become more vulnerable to minor changes in hammer energy which can result in poor consistency if tuned below plateau, however plateau will be consistent in such a version.


-Matt

I've been thinking a bit more about the much lower lock time for the pilot valve and how it is due to shorter hammer throw time. I realize the use of a lighter hammer increases its acceleration and thus shortens lock time, but for such a dramatic reduction, wouldn't you also have to reduce the distance between the the valve stem and the hammer face when it is cocked? Does this mean you use a longer hammer/striker or a longer valve stem to help reduce the throw distance? (I've tried to estimate the hammer lock time for a couple of my guns using a Microtrack sound recorder and estimate it is 5.6 to 4.4 ms for my USFT (with the lower value when I switch to a shorter, stronger hammer spring and turn in the hammer tension screw) and 1.5 ms for my Daystate Pulsar (i.e., time between when solenoid starts to move and pellet starts to move)

 

[Stubbers]

I've been thinking a bit more about the much lower lock time for the pilot valve and how it is due to shorter hammer throw time. I realize the use of a lighter hammer increases its acceleration and thus shortens lock time, but for such a dramatic reduction, wouldn't you also have to reduce the distance between the the valve stem and the hammer face when it is cocked? Does this mean you use a longer hammer/striker or a longer valve stem to help reduce the throw distance? (I've tried to estimate the hammer lock time for a couple of my guns using a Microtrack sound recorder and estimate it is 5.6 to 4.4 ms for my USFT (with the lower value when I switch to a shorter, stronger hammer spring and turn in the hammer tension screw) and 1.5 ms for my Daystate Pulsar (i.e., time between when solenoid starts to move and pellet starts to move)

You're correct, the hammer travel is GREATLY reduced in the pilot valve version, this is because if I used OEM hammer travel, I would need to lighten my hammer spring even more than it is now (4lb/in) which then makes for too light of a hammer strike for a mechanical gun imo, where minor variability in hammer energy results in wider deviation in fps. Heck I could even reduce it further if I wanted lol, lots of room. The 4lb/in spring is only needed for plateau in .25 cal otherwise I run a 3lb/in spring for sub 50 fpe. The more distance a light strike travels the more variability presents itself, for sure.

To reduce the throw, yes my valve stem does stick out a bit further, that alone would suffice but I also notched the face of my hammer where it engages the sear by about .2". This pictured hammer is for an unregulated action that sees 3000 psi and is only 8gr and didn't need extra weight loss so much, but my super light one I run regulated at 4 grams I wanted to remove as much material as possible to see how light I could get it.

Your estimations seem spot on! (5ms USFT lock time and 1.5ms lock time on the daystate) I can run the math with all the right data/variables provided to me on mechanical actions.

This is my current regulated pilot valves data: (.44" hammer travel, 4.8 gram hammer, 4lb spring, .6" preload)

This would be stock conventional valve in a marauder: (.75" hammer travel, 78 gram hammer, 8 lb spring with .6" preload)

Knowing the above hammer FPE needed to plateau on my pilot, I could reduce travel further like this...

.3" hammer travel, 4.8 gram hammer, 7 lb hammer spring, .55" preload)

Oh you have a side lever and can manage 18lb/in hammer spring? Lets have a giggle...

.14" hammer travel, 4.8 gram hammer, 18 lb/in spring, .55 preload....

Down to basically a tenth of a ms....and this is very much feasible with a side lever action.

Actually, heck the above cocking force is only 12.4 lbs so one could do this with bolt action, a side lever with 3:1 would make it 4lbs.


-Matt

 

[Scotchmo]

I haven’t (yet) gotten into pilot valves as the assisted (balanced) type has been working well in my big bore airguns. I used Cothran valves in my 160fpe .257 (stock Cothran valve) and 260fpe 7mm (slightly modified Cothran valve). My latest build is an all custom 500fpe (maximum) .308. The Cothran valves and my valve are not tunable via hammer strike. It is possible to strangle the transfer port, but generally, once I get the dwell about where I want it, I use regulated plenum pressure to vary the fpe/velocity.

The .308 will initially be shooting 171gr slugs at 1060fps on 3300psi.

It uses an electronic “hammer” (34 grams) with an adjustable voltage and adjustable stroke length. Lock time is variable but currently about 0.0015 seconds. Dwell is determined by the balance chamber volume and vent size. Dwell is probably a little under 0.004 seconds.

Custom .308 assisted valve on left. 2mm (0.078”) stem diameter, 9/32” piston, 5/16” ports, 0.332” throat. Stock Marauder valve on right.

 

[Stubbers]

I haven’t (yet) gotten into pilot valves as the assisted (balanced) type has been working well in my big bore airguns. I used Cothran valves in my 160fpe .257 (stock Cothran valve) and 260fpe 7mm (slightly modified Cothran valve). My latest build is an all custom 500fpe (maximum) .308. The Cothran valves and my valve are not tunable via hammer strike. It is possible to strangle the transfer port, but generally, once I get the dwell about where I want it, I use regulated plenum pressure to vary the fpe/velocity.

The .308 will initially be shooting 171gr slugs at 1060fps on 3300psi.

It uses an electronic “hammer” (34 grams) with an adjustable voltage and adjustable stroke length. Lock time is variable but currently about 0.0015 seconds. Dwell is determined by the balance chamber volume and vent size. Dwell is probably a little under 0.004 seconds.

Custom .308 assisted valve on left. 2mm (0.078”) stem diameter, 9/32” piston, 5/16” ports, 0.332” throat. Stock Marauder valve on right.

1.5ms lock times are pretty common its seems with electronic / solenoid driven hammers.

Pilot valves do that with ease and can crush those times, of course there are diminishing returns with lock time reduction, but .15-.5ms lock times are very realistic and imo probably reaching the point of said diminishing returns. I don't even know if an electronic signal can travel from trigger through all the needed circuits prior to actuating the solenoids 'hammer' faster than .15 ms.

Tune-ability (via hammer strike) could easily be brought back into your balanced valve with a .125" stem diameter vs .078" however if only concerned for near plateau dwell, .078" stems are quite magnificent in many applications, and even partly tunable in others. The hammer strike was so light running a pilot valve with a .078" stem it was comical and no amount of vent really restored tune-ability as well as a .125" stem did, because you can't amplify the peak closing force with vent size in either balanced or pilot valves, which is mostly determined by your stem diameter. My balanced valve with .078" stem was mildly tunable via hammer strike.

It's hard to imagine a hammer driven valve that could actuate as fast as a pilot valve taken to the extreme simply due to how little energy is required to activate them thus allowing incredibly brief hammer travels. They aren't perfect by any means, but they are unique and incredibly easy to open.

As to hammerless valves, I wonder how quick their locktimes are, uncharted territory for me.

-Matt


-Matt

 

[Scotchmo]

1.5ms lock times are pretty common its seems with electronic / solenoid driven hammers.

….

-Matt

It would be possible to get below 1ms if I thought there were any significant benefits. Higher voltage and shorter stroke.