What is not obvious about a "K" baffle?

[OldSpook]

It is a form of a Tesla Valve. The K baffle redirects a jet of air across the stream of air exiting the bore. That jet strikes the far wall of the moderator and splits into two streams. Both streams then make their way around the inside of the moderator back to point below the origin of the stream and thence back again into the stream of air exiting the bore. It is in fact a Tesla Valve. Well my version of it is anyway. I suppose some folks would leave off the "mouse hole", Then it is not a form of the Tesla Valve.

When I get time I'll put together a picture unless someone else wants to draw it and post it first.

 

[nervoustrig]

I'm too lazy to sketch up something specifically with a K baffle but the following diagram taken from the Wikipedia page is nicely instructive:

A K baffle exploits the operating principle displayed in the top illustration...think of a pellet being shot from left to right. High pressure gas splits off into the black arrows and red arrows, with the red arrows feeding back onto the black ones, producing turbulence and slowing the rate of flow through the device. Whatever the amount of gas expelled from the barrel, spreading its release over a longer period of time means an attenuated average pressure (read: quieter).

Coming from an electrical background, conceptually I think of it as a leaky diode. Someone from a fluid mechanics background might prefer to think of it as a leaky check valve.

 

[qball]

The "problem" with Tesla's valve is it is designed to be an oneway valve for a continuous flow of liquid or water to be exact, at least the idea is to stop/severely restrict a continuous flow of liquid which is not compressible. The water would circle back 180 degrees and push against the main flow, this relies on the un-compressible property of water pushing against incoming water in the main channel. water being un-compressible it does not need "equalization" of pressure so it travels down the longer side path at basically same speed but even with that the water will not meet the main body of water it split from.

If you look at the path the air to circle back and push against the main airflow is much longer which means it takes longer so the main burst of energy/air could be gone already when the air circling back makes contact. In a continuous flow situation that's not a problem but in airgun situation we have a burst of air/energy to defuse not a stream of energy/air so in theory I've never subscribed to Tesla's valve design because of that. That first burst of energy/air is what we need to defused not what comes after unless your valve opens for a "long" time. Air is compressible and will flow to low pressure area first, if the side path has more restrictions then it would simply compress and flow out the main bore until the pressure at the main bore is higher than the side path before air will flow/equalize. this all happens in milliseconds but could be long enough for the main burst to escape before the air can circle back from size paths to have any affect. However given enough volume any amount of energy/air is redirected has delusion affect but not sure the circling back portion of Tesla valve would work in time in a non-continuous/burst application.

Many people say their STO with the the Tesla valve design works well, they certainly are big enough so the question is can Tesla valve design work better compared to the normal moderator design with same internal volume, number and placement of baffles. In Tesla valve higher the pressure the main flow has the harder the water from side path push back so this could explain STO's performance with higher power applications.

Not saying it can't work but I have my reservations, will run some tests later when I have some time.

 

[bigHUN]

A while back I made a concept for a EU friend with revers porting, he was very positive with the outcome.

 

[OldSpook]

Nice looking baffle design. I've been working on a monocore also. The advantage is "baffle density" the problem is you must keep a certain amount of empty space inside the moderator or it starts to act like a straw basically. I think qball and LDC have done a lot of experimentation.

 

[qball]

Nice looking baffle design. I've been working on a monocore also. The advantage is "baffle density" the problem is you must keep a certain amount of empty space inside the moderator or it starts to act like a straw basically. I think qball and LDC have done a lot of experimentation.

Think people get carried away by all the fancy baffle design and forget that at the end of the day sound is a form of energy. To make muzzle report/energy to defuse it needs room to defuse, volume with certain length is more important.

One of the best small moderator commercially is the Huggett Belita which has a SINGLE nylon flat washer for baffle and ported side, some how it performed better than many bigger moderator with 5-6 baffles. Something to think about.

 

[OldSpook]

Think people get carried away by all the fancy baffle design and forget that at the end of the day sound is a form of energy. To make muzzle report/energy to defuse it needs room to defuse, volume with certain length is more important.

One of the best small moderator commercially is the Huggett Belita which has a SINGLE nylon flat washer for baffle and ported side, some how it performed better than many bigger moderator with 5-6 baffles. Something to think about.

Yep. You are right about over doing the baffle count. I put three baffles in the front half of a 30x83 mm tube and got a 4 dB reduction in noise level. That's not bad for something that is 3.5" long and just over an inch in diameter... but then I added another three behind the first without changing anything else and only got about 1.5 more dB of reduction. All total in that space I got about 5 dB reduction. Then I doubled the length of that moderator and left the 6 baffles in the front. Doubled the length so doubled the volume. Net reduction went to 13 dB. The rifle was registering about 83 dB (but the phone was not tracing the peak noise well). It was probably more like 90 dB for that little rifle. The net reduction on that loooonnnnng moderator was around 13 dB. Not bad but 166mm long. That's too long for a squirrel hunter unless he stand hunts.. It is all about the compromises. That's a 30 caliber capable moderator on a .177 rifle though (has a big hole in it).

I have been thinking about that quite a bit the last couple of days. Hours on the spread sheets and half a dozen moderators where I only changed one thing at a time. I am beginning to understand. Long way to go though.

 

[TheWhiteBreath]

Dang, yall put a lot of though into this. ...I just hogged out the threads on a rainbird sprinkler, pounded a 1/2-20 nut in there, drilled some holes and screwed it on the end of my gun. Make my shooty boi more quieter....

 

[Franklink]

So I guess it's not obvious to me.....I understand the creation of a tortuous path for the air to follow, essentially with the goal of keeping that air from leaving the muzzle (or moderator) and making a report/sound. But I'm curious about the asymmetrical method of the porting and keyhole.....

The blue circle I added is the pellet path correct? That beveled, rectangular "port" for the air to be stripped away from the pellet is entirely on one side. I've always thought one of the supreme goals was to make sure nothing is asymmetrically effecting the pellet (crown, leade, airflow, etc).

The opposite of this, something like radially located ports (for example, 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock or even more if going past 4 wouldn't be too complicated) to allow the air to enter the baffle from all sides seems like it would prevent the pellet from being influenced a certain direction. ie, keep it moving straight down the chute.

Quiet is good, accuracy is better. Are you far enough along in your testing to see if you are adversely affecting accuracy with this design?

What am I missing?

 

[OldSpook]

So I guess it's not obvious to me.....I understand the creation of a tortuous path for the air to follow, essentially with the goal of keeping that air from leaving the muzzle (or moderator) and making a report/sound. But I'm curious about the asymmetrical method of the porting and keyhole.....
View attachment 291823
The blue circle I added is the pellet path correct? That beveled, rectangular "port" for the air to be stripped away from the pellet is entirely on one side. I've always thought one of the supreme goals was to make sure nothing is asymmetrically effecting the pellet (crown, leade, airflow, etc).

The opposite of this, something like radially located ports (for example, 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock or even more if going past 4 wouldn't be too complicated) to allow the air to enter the baffle from all sides seems like it would prevent the pellet from being influenced a certain direction. ie, keep it moving straight down the chute.

Quiet is good, accuracy is better. Are you far enough along in your testing to see if you are adversely affecting accuracy with this design?

What am I missing?

You are not missing anything, sir.

Take this with a lot of salt 'cause it's just feeling but I think what must be happening there is the air strikes the entire surface of the baffle and gets redirected around that rim into the slope. That must happen after the pellet has passed or it would knock the skirt to one side. After that the air pressure is always "playing catchup" with the pellet, but never can. Tom and his brother are reporting "good" (not necessairly match grade) accuracy with most of the moderators I have sent them to test. Although they did place #1 and #2 in one match and Tom's rifle was wearing one of my moderators that day.

There is a modification to that baffle which some people call a "mouse hole". The mouse hole is under the top of the baffle at the top of the cone and beneath the "ramp" which directs air across the path of the pellet. It is about half the size of the large port on the opposite side of the ramp. What that mouse hole does is allow the pressure from the ramp to feed back into the bullet path and complete a "feed back" loop. I have not tested that modification as much as I would like to have done.


I completely agree with your ideas on distributing that port around the clock. The "Tesla Baffle" which is also called a "Tesla Diode" works on that principle when you apply it to gasses.



In that baffle the pressure vents around the circumference of the top cone and builds against the second cone which has only the hole for the bore. It is then redirected up into the air stream from the muzzle blast. In that baffle all this also happens after the passage of the projectile. I think that baffle is easier to make accurate than the K baffle, not sure but that seems to be the case. It also seems to be more efficient than the K design.

Thanks for asking the question, sir. I hope I gave you a useful answer. It is mostly opinion though.

 

[OldSpook]

Dang, yall put a lot of though into this. ...I just hogged out the threads on a rainbird sprinkler, pounded a 1/2-20 nut in there, drilled some holes and screwed it on the end of my gun. Make my shooty boi more quieter....

Sometimes it is the destination, sometimes it is the trip.

 

[qball]

Personally I’m a fan of even/uniform baffles to uniformly strip air away from the projectile, granted not at the same level as a ununiform crown but My preference is not to take any chance on possibly affecting accuracy. Granted an inaccurate gun is the quietest gun ever made even without a moderator because I won’t shoot it! LOL

 

[steve-l]

I have been making silencers for many, many years and I tried all kinds of different designs. Much of what I read here is old wives tales. I good moderator never hurts accuracy. Even the very best moderators are not whisper quiet. You do not get more measurable benefit with more than 3 baffles. The best baffle design deflects the accelerating air charge from racing past the pellet after barrel exit. That turbulence can disturb the projectile's flight path. That is why the the K baffle does not work well. Its deflection is not symmetrical. This same principal is why a uniform barrel crown is critical. Just as important as the baffle is the available charge expansion space. The more space you have, the quieter the moderator is. However, please remember that a good moderator attenuates the rushing air column both in front and behind the projectile. Therefore changing the differential pressure around the projectile slowing the projectile somewhat. In my experience my best performing moderators usually cost about 40 FPS in comparison to not having the moderator mounted. The best baffles I feel is the inverted cone for good symmetry. Do not underestimate the amount of force that is applied to these baffles, it is substantial. 3D printed plastic baffles do not hold up well.

 

[lbc_PSI]

When talking baffle symmetry, does this mean they must be concentric around the center hole?

 

[OldSpook]

When talking baffle symmetry, does this mean they must be concentric around the center hole?

How are those K baffles working out in your Prophets?

 

[lbc_PSI]

Finally got the chance to experiment with the baffles. couldn't use the spacers, so I improvised with a .85 spring from ACE hardware. I could cut the spring in half and fit the 5th baffle.

Using a rather generic DB meter from the app store I got the following results. Phone set at 10' from the front of the barrel and 8' to the right Test barrel was a 16" CZ .22 shooting 16gr PM Shorts @ 930fps. Ambient background was 55dB-60dB

90dB - airgun without baffles..baseline
85dB - airgun with DonnyFL Tatsu .25
86dB - 4 K-baffles
83dB - 4 K-baffles and DonnyFL Tatsu .25

With just the baffles installed the dB signature was just 1dB less efficient thatn the Tatsu. The results may have bee different with a .22 Tatsu..as the .25 is somewhat "over caliber"..so it's letting out more air..not sure that matters that much.

I'll redo the test when I have more time and a better dB app. I'm sure there's a good one out there. I'll also add a .25 and .22 Huma30mm to the test. I have a 20" .25 CZ barrel I can swap to check with 4 baffles..since they're sized for .25.

Initial impression is that the baffles are very effective..at least to my old ears. The affect on accuracy..is nil up to 20yds..hole on hole before..hole on hole after Will test further out next week.

 

[steve-l]

When talking baffle symmetry, does this mean they must be concentric around the center hole?

Yes, that is why I like the inverted cone baffle best, (small diameter facing the muzzle) This deflects the accelerating air charge away from the pellet's path through the center hole.

 

[lbc_PSI]

Yes, that is why I like the inverted cone baffle best, (small diameter facing the muzzle) This deflects the accelerating air charge away from the pellet's path through the center hole.

I can understand how concentric baffles might be best in theory, but if that's the case, I struggle to understand how the offset Edgun baffles are effective as they are.

 

[BlackICE]

I can understand how concentric baffles might be best in theory, but if that's the case, I struggle to understand how the offset Edgun baffles are effective as they are.

To get a larger shroud volume, Edgun uses an offset shroud that requires offset baffles. The reason the baffles are not cone shaped, are linear ones are cheaper/easier to mass produce. IMO they still work quite well.

 

[steve-l]

The disadvantage of the cone baffle is cost. They are more expensive to make.