Expanding plenum volume

[antithesis]

This pertains to an umarex gauntlet or by extension, a qb79 or similar bottle gun...regged.

I was a tiny bit inspired by the fx innovation of incorporating a provision for a auxiliary plenum, improving overall cycle pressure.

By the same token, I was considering using a crosman gauge block to mount in the existing plenum tube and routing a little stock material out to add a short closed tube containing additional air to supply the plenum air via high pressure fittings .

My question is would the additional air supplying the main tube from the secondary source justify the space taken up by something like a slightly hogged out prod gauge block, flowing enough extra air to the plenum faster than the bottle and block?

And if such a modification were worth doing, what would be the best location for the air to be piped in? I think closer to the valve cage the better but that may also choke flow from the rest of the air behind it? This idea is in its infancy and I would like to consider the degree of potential benefit and if worth doing what would be the best way to go about it from an airflow standpoint?

[PikeP]

I essentially did similar in my mrod with a tee at the gauge block allowing the stock gauge to still remain as well as tubing that goes forward and hides within the stock, acting as a secondary / auxiliary plenum. My secondary plenum flow path intersects forward of my primary plenum, I see no need for concern if it were before or after.

Your question really depends on a few variables, such as obtainable volumes via hogging things out (such as gauge block/valve/ect) versus obtainable volume by doing the same plus adding your auxiliary plenum...and how close or far away either are from roughly 1 cc per desired fpe.

So the answer isn't so cut and dry...but in most cases, with smaller air tube guns that are regulated, or guns with mono-blocks and limited plenum volume in between bottle and valve, its certainly beneficial to consider ways to increase said volume, and it certainly is best to increase volume in increments between 50-100% or otherwise you may find the resulting increase rather insignificant.

[antithesis]

I essentially did similar in my mrod with a tee at the gauge block allowing the stock gauge to still remain as well as tubing that goes forward and hides within the stock, acting as a secondary / auxiliary plenum. My secondary plenum flow path intersects forward of my primary plenum, I see no need for concern if it were before or after.


And finally most people may tell me that this is a redundancy given that this is a .22 call gauntlet, which has a plenum volume of roughly twice my desired fpe. But if any significant efficiency benefit can be had from this relatively simple add on I see no reason not to.
Your question really depends on a few variables, such as obtainable volumes via hogging things out (such as gauge block/valve/ect) versus obtainable volume by doing the same plus adding your auxiliary plenum...and how close or far away either are from roughly 1 cc per desired fpe.

So the answer isn't so cut and dry...but in most cases, with smaller air tube guns that are regulated, or guns with mono-blocks and limited plenum volume in between bottle and valve, its certainly beneficial to consider ways to increase said volume, and it certainly is best to increase volume in increments between 50-100% or otherwise you may find the resulting increase rather insignificant.

So point 1....you're basically saying that as long as the air volume gained by said apparatus is greater than the air volume occupied by the same, it's ok....and

2. That lets say I have about 70cc plenum give or take, that practical performance benefits would be insignificant unless my secondary cylinder is minimum 35- 70 cc or more?

And also, naturally I would be trying to maximize flow into plenum main as much as possible, I believe I have been told that any restrictions larger than the smallest post valve flow area essentially become plenum. My only concern left really is placement. Logic tells me that the most ideal place to try to keep pressure up is where it would drop most, immediately behind the valve ... but if you were to see the spring retainer "cage" that is a part of the gauntlet valve, butting the two together could be overall detrimental to air flow supplying the valve ... although that is probably an easy work around

[PikeP]

I essentially did similar in my mrod with a tee at the gauge block allowing the stock gauge to still remain as well as tubing that goes forward and hides within the stock, acting as a secondary / auxiliary plenum. My secondary plenum flow path intersects forward of my primary plenum, I see no need for concern if it were before or after.


And finally most people may tell me that this is a redundancy given that this is a .22 call gauntlet, which has a plenum volume of roughly twice my desired fpe. But if any significant efficiency benefit can be had from this relatively simple add on I see no reason not to.
Your question really depends on a few variables, such as obtainable volumes via hogging things out (such as gauge block/valve/ect) versus obtainable volume by doing the same plus adding your auxiliary plenum...and how close or far away either are from roughly 1 cc per desired fpe.

So the answer isn't so cut and dry...but in most cases, with smaller air tube guns that are regulated, or guns with mono-blocks and limited plenum volume in between bottle and valve, its certainly beneficial to consider ways to increase said volume, and it certainly is best to increase volume in increments between 50-100% or otherwise you may find the resulting increase rather insignificant.

So point 1....you're basically saying that as long as the air volume gained by said apparatus is greater than the air volume occupied by the same, it's ok....and

2. That lets say I have about 70cc plenum give or take, that practical performance benefits would be insignificant unless my secondary cylinder is minimum 35- 70 cc or more?

And also, naturally I would be trying to maximize flow into plenum main as much as possible, I believe I have been told that any restrictions larger than the smallest post valve flow area essentially become plenum. My only concern left really is placement. Logic tells me that the most ideal place to try to keep pressure up is where it would drop most, immediately behind the valve ... but if you were to see the spring retainer "cage" that is a part of the gauntlet valve, butting the two together could be overall detrimental to air flow supplying the valve ... although that is probably an easy work around

1) Yes, The value of increasing plenum volume is relative to how far away from 1-2 cc per fpe you currently are.

2) Yes, although any gain in volume is greatly beneficial the further below 1 fpe/cc you are, in general its a good idea to aim for a roughly 50-100% increase in volume.  For example, increasing from 10 cc to 11 cc in a 12 fpe gun will leave you disappointed if you expect big gains. That same gun would benefit a lot if its current plenum was 2 cc and you increase the same 1 cc volume to 3cc. The closer to 1 fpe per cc you currently are the less impact small increases will have. That is not to say a 10%,20%,or 30% increase should be disregarded, but the closer to 1 fpe/cc you currently are, the less you should expect to gain unless adhering to a 50%-100% optimal increment of increase. That is why this answer is really not cut and dry, and many are told to aim for 1 fpe per cc.

The pressure within your plenum, will act fairly uniformly provided you have no restriction within the flow paths moving backwards from the valve exit. The only decrease in cross section for any flow path from valve seat to regulator seat should be the regulator seat/piston/feed

[rsterne]

A simple way to think about plenum volume is to aim for 1 cc per FPE if possible.... This is because the gains in going larger are reduced.... If you cannot achieve that plenum goal, you can use a smaller plenum, but the penalty will be a drop in efficiency, and the need to increase the regulator setpoint pressure to compensate for the smaller plenum.... In guns that are restricted in space, you can do just fine with 1/2 cc per FPE with about a 10% increase in regulator setpoint.... If your plenum volume (including the valve volume, you are really looking at the amount of air "on deck" and available for the shot) is less than 1/2 cc per FPE, any increase is likely worthwhile, and worth striving to achieve....

Bob

[antithesis]

A simple way to think about plenum volume is to aim for 1 cc per FPE if possible.... This is because the gains in going larger are reduced.... If you cannot achieve that plenum goal, you can use a smaller plenum, but the penalty will be a drop in efficiency, and the need to increase the regulator setpoint pressure to compensate for the smaller plenum.... In guns that are restricted in space, you can do just fine with 1/2 cc per FPE with about a 10% increase in regulator setpoint.... If your plenum volume (including the valve volume, you are really looking at the amount of air "on deck" and available for the shot) is less than 1/2 cc per FPE, any increase is likely worthwhile, and worth striving to achieve....

Bob

Well Bob, considering this is a .22 gauntlet and I know you have some familiarity with the QB79 on hpa, how much approximate volume does the tube have as is? Consider that the gauntlet valve is a QB valve with no piercing pin and the little "can" replaced with an aluminum cage that doesn't take up any appreciable space? I don't need any more than say 30-35 ftlbs from this gun,  and I already understand that the volume is somewhere in the neighborhood of 60-70 cc...and I plan on running the reg at around 1500-1600. I know after I'm done opening the throat to maybe .240 so I can come close to the transfer and barrel port size ( don't ask me what they were thinking making it all between .160- .170 ish , and running a .120 stem through a .210 throat), that is easily achievable, but if I can get a further efficiency bump with a relatively simple mod I'll do it

[PikeP]

Bob can certainly answer the QB79 questions. But I'll touch in a bit on the stem/throat and port size.

I would personally aim for .1" stem within the throat and its likely typical .125" in its stem bore. With that...you could port up to .1875" (85% of barrel / bore) with a .218"~ throat...even with the full .125" stem you could keep the throat to just .231" and still support porting up to .1875"...going all the way to .240 on the throat will make the valve quite a bit more difficult to knock open, hence why I suggest the slight reduction of stem within the throat, similar to what a lot of 'elite' air gun manufacturers have done for years. HTH.

[antithesis]

Bob can certainly answer the QB79 questions. But I'll touch in a bit on the stem/throat and port size.

I would personally aim for .1" stem within the throat and its likely typical .125" in its stem bore. With that...you could port up to .1875" (85% of barrel / bore) with a .218"~ throat...even with the full .125" stem you could keep the throat to just .231" and still support porting up to .1875"...going all the way to .240 on the throat will make the valve quite a bit more difficult to knock open, hence why I suggest the slight reduction of stem within the throat, similar to what a lot of 'elite' air gun manufacturers have done for years. HTH.

I was concerned about that being that my throat was originally around. .205 or thereabouts, minus the .120 stem it seemed way too tight for a ( iirc) .159 valve outlet and barrel intake...barrel port may have been closer to .170 actually I can't remember....but that is definitely not optimal airflow so I'm now at about .235 throat and think I'll stay there. As for the stem I was a little Leary to take it down much further even for a short stretch....does a 3/8 section above the poppet face turned down to .110 or so sound like it'd hold up against a .230-.235 throat at 1600 psi?   

[scion19801]

fwiw the plenum volume on the gauntlets are 24cc. i have the .25 cal. pretty much identical to the .22 cal, except they punched out the barrel from .22 to .25. and changed the pellet probe. biggest improvement is to put in an aftermarket poppet. you'll see huge gain in performance. I have done all hajimotos mods to mine except the high travel valve stop.
I have my barrel port at .1875. everything else is stock port wise.
valve exhaust is .194"
valve throat is .219" ? where poppet seals ?
valve stem is .078"
custom tp that is .194" on exhaust side to .1875 on breech side.
receiver port is .1875
poppet is aftermarket peek with a dia of .338"
had my jsar spring die on me and had to put stock spring setup back in. replaced hammer spacer with a washer stack for less length than factory spacer(temporary fix to keep FPS down). lowered my Flex regulator to 1700 psi and getting 882 fps with 25.4 gr for 44.3 FPE currently.
there are a few specs on the valve that i forgot to write down.  like my id of the valve body to poppet od clearance.

[Samcirrus]

We take our poppet stems down to .072 or2mm....for the liberty and freedom...they are fine! Valve throat....250. TP hole .217....works great.

[PikeP]

Bob can certainly answer the QB79 questions. But I'll touch in a bit on the stem/throat and port size.

I would personally aim for .1" stem within the throat and its likely typical .125" in its stem bore. With that...you could port up to .1875" (85% of barrel / bore) with a .218"~ throat...even with the full .125" stem you could keep the throat to just .231" and still support porting up to .1875"...going all the way to .240 on the throat will make the valve quite a bit more difficult to knock open, hence why I suggest the slight reduction of stem within the throat, similar to what a lot of 'elite' air gun manufacturers have done for years. HTH.

I was concerned about that being that my throat was originally around. .205 or thereabouts, minus the .120 stem it seemed way too tight for a ( iirc) .159 valve outlet and barrel intake...barrel port may have been closer to .170 actually I can't remember....but that is definitely not optimal airflow so I'm now at about .235 throat and think I'll stay there. As for the stem I was a little Leary to take it down much further even for a short stretch....does a 3/8 section above the poppet face turned down to .110 or so sound like it'd hold up against a .230-.235 throat at 1600 psi?   

With .235 throat, and .12 stem, you can port up to .195" (89% of bore) which I honestly highly recommend leaning towards if your valve throat is already that big... and you can leave the stem as is. (A .235" throat could also support up to a .217" port others mention with a .072" stem"..)

[rsterne]

I don't know how much length there is between the tank block stem and the front of the valve in a Gauntlet, in a QB79 there is very little (1/8" ? ).... QB tubes are 0.44 CI (7.2 cc) per inch of inside length.... A full length QB78 tube is only about 50-51 cc including the valve volume (6-7 cc)....

The QB stem is 3mm (0.118"), I would imagine the Gauntlet is the same?.... If the Gauntlet has a 24 cc plenum, plus another 6-7 cc for the valve, you probably don't need to increase it for a .22 cal.... I would just use drilled 0.166" (75%) ports for a pellet shooter, which with the stock 3mm stem means a throat of about 0.203" would be the minimum, drilling it to 7/32" (0.219") would be better if you don't slim the stem.... Using a 7/32" throat and 0.166" porting I got 35 FPE at 1600 psi with 18 gr. JSBs, with a 3" long (22 cc) plenum (30 cc with a slotted/hogged out valve body)....

If you are looking at shooting heavier than 18 gr. pellets, and are willing to take the time to make an oblong barrel port, and then increase the rest of the porting to match, you can get more power, or by limiting the dwell, more efficiency.... If the gun is using a bolt probe, if you calculate the annular chamber area around that, there is no point in making any of the porting larger than that....

Bob

[antithesis]

I don't know how much length there is between the tank block stem and the front of the valve in a Gauntlet, in a QB79 there is very little (1/8" ? ).... QB tubes are 0.44 CI (7.2 cc) per inch of inside length.... A full length QB78 tube is only about 50-51 cc including the valve volume (6-7 cc)....

The QB stem is 3mm (0.118"), I would imagine the Gauntlet is the same?.... If the Gauntlet has a 24 cc plenum, plus another 6-7 cc for the valve, you probably don't need to increase it for a .22 cal.... I would just use drilled 0.166" (75%) ports for a pellet shooter, which with the stock 3mm stem means a throat of about 0.203" would be the minimum, drilling it to 7/32" (0.219") would be better if you don't slim the stem.... Using a 7/32" throat and 0.166" porting I got 35 FPE at 1600 psi with 18 gr. JSBs, with a 3" long (22 cc) plenum (30 cc with a slotted/hogged out valve body)....

If you are looking at shooting heavier than 18 gr. pellets, and are willing to take the time to make an oblong barrel port, and then increase the rest of the porting to match, you can get more power, or by limiting the dwell, more efficiency.... If the gun is using a bolt probe, if you calculate the annular chamber area around that, there is no point in making any of the porting larger than that....

Bob

Bob, ultimately I'm finding that the throat minus (yes 3mm) stem was smaller than the (iirc) already larger than necessary barrel port and valve exhaust, which I believe was .168 by my calipers. My plan is to bump up the ninja to around 1600 and choke flow area to around .130 to .140 like a disco, possibly smaller, and lay into the preload for maximum consistency and tunability via hajis preload adjuster..the plenum thing was to exploit the already high shot count the new 22ci tank by further optimizing the shot cycle keeping pressure up.



I want around 25 to 30 ftlbs, trying to go with 18 to 21 gr pellets,. I'm thinking something along the lines of hunter ft class type performance, if I understand that term correctly.  longer range target , silhouette and larger pesting gun

[Rohmpm]

How I did it. Additional 28cc. Quite a chore.

[antithesis]

Did I inspire that or did you beat me to it?

And now that I'm looking, did you make that shroud ....idk ..."thimble" ....where it mates the breech recess.    I'd like a closer look if you got a pic

[Rohmpm]

I don't know, about six months ago I did it for a slug gun and it's very accurate with a variety of .25 slugs, really liking Nielsen 29's at 980fps I've shot them at 1040 but lost the soft cocking. . Of course it has an SSG, porting, peek etc, It can make a lot of power with light cocking effort, much lighterr than stock. I used a JSAR adjustable reg to tune the gun, replaced it with a preset at 1900 psi. Yes I made the shroud support, and moderator,  it's very quiet. Also note the extra barrel mount grub screw holes in the receiver....no longer loses zero when I've purposely banged it around. I deleted most of my build pics but I pm shared several with a member whose name I can't recall. Perhaps he'll share. I have to credit Bob and Motorhead for opinion, advice and help as I was working on my valve along with the world of knowledge they have shared which I scoured for ideas.

[antithesis]

I don't know, about six months ago I did it for a slug gun and it's very accurate with a variety of .25 slugs, really liking Nielsen 29's at 980fps I've shot them at 1040 but lost the soft cocking. . Of course it has an SSG, porting, peek etc, It can make a lot of power with light cocking effort, much lighterr than stock. I used a JSAR adjustable reg to tune the gun, replaced it with a preset at 1900 psi. Yes I made the shroud support, and moderator,  it's very quiet. Also note the extra barrel mount grub screw holes in the receiver....no longer loses zero when I've purposely banged it around. I deleted most of my build pics but I pm shared several with a member whose name I can't recall. Perhaps he'll share. I have to credit Bob and Motorhead for opinion, advice and help as I was working on my valve along with the world of knowledge they have shared which I scoured for ideas.

How did you do up an ssg on this platform?

I had considered something closer to a tss in a front to back configuration might be more feasible but then I am still trying to pick the brains of guys like you who already went well outside the box....it's a important one to me bc you can really hear the bounce in these guns and anything I can do to reduce it I'm happy.

My primary issues are making the space in the stock for the secondary plenum tube, reducing hammer bounce, and stabilizing the barrel and bottle.  Since I'll be using a stainless custom PCP tube from mountain air, I'll be putting the bottle and block further forward too and I need to figure out what to do with the extra space in the stock and to support the bottle more

[Rohmpm]

I'll check Monday. May have some pics at the shop. The extra plenum easily fits in the stock. Just grind clearence in the thin webs .i

[elaerico]

Hi. I'm new in the forum. I'm from Argentina, and I own a SPA P15, and I want to increase it plenum volume. Currently has 12cc, and I want 30 fpe. I have a lathe, so I can manufacture the plenum extension. I was thinking in making an extension of the tube, where it connects with the valve. But I have some questions about sizing. I never before worked with pieces who holds this much pressure. I used an online calculator for strain, and came up with using 1045 steel, and a cylinder with wall thickness of 0.157", and an OD of 1.260" ,it will hold up to 772bar , near six times the working pressure.
Can you give me an advice in the manufacturing, calculing, or something else?
Thanks a lot!

[antithesis]

Hi. I'm new in the forum. I'm from Argentina, and I own a SPA P15, and I want to increase it plenum volume. Currently has 12cc, and I want 30 fpe. I have a lathe, so I can manufacture the plenum extension. I was thinking in making an extension of the tube, where it connects with the valve. But I have some questions about sizing. I never before worked with pieces who holds this much pressure. I used an online calculator for strain, and came up with using 1045 steel, and a cylinder with walls of 4mm,it will hold up to 480 bar, three times the working pressure.
Can you give me an advice in the manufacturing, calculing, or something else?
Thanks a lot!

First, welcome to the mad house my friend.   

Truthfully I think you may be better off looking in the machine shop section of the forum...but I myself am unfamiliar with the model you are speaking of, maybe if I find anything out about it I will offer some conjecture about methods and implementation, but I definitely need more info. You are on the right track with the 3 to 1 safety margin though.you also may want to consider what else needs done to prep for these pressures.  What kind of pressure is it currently rated for? ( Meaning factory recommended operating pressure)