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Plenum Questions
- Thread starter Hylander
- Start date
- Latest activity Latest activity:
- Replies 27
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BenjeneerJohn
HAM Sniper
Plenum is the regulated volume of air. If the plenum is too small it is harder to make power. You can also get an increasing or decreasing shot string velocity.
If the plenum is sized correctly for the power you can get a very flat and consistent shot string. Bigger plenum allows you to make bigger power.
John
If the plenum is sized correctly for the power you can get a very flat and consistent shot string. Bigger plenum allows you to make bigger power.
John
PasadenaMike
Grand HAMster
Simply put, a plenum is the amount of potential energy reserved inside the regulated volume of air inside an airgun, measured by volume.
More plenum = more energy potential, however the potential of energy greatly tapers off once you exceed about 1.5CC per FPE.
See below as an example, given the same .25 cal gun with 90% bore porting and a 19.5" barrel, at 2000 psi the power curve here greatly tapers off after 1.5cc per fpe and almost flat lines above 2cc per fpe. A conservative goal would be around .8-1cc per fpe, but as you see, even .5 cc per FPE can go quite the long way...But with todays day and age of chasing dragons / peak performance, most manufacturers probably aim for greater than 1:1.
More plenum = more energy potential, however the potential of energy greatly tapers off once you exceed about 1.5CC per FPE.
See below as an example, given the same .25 cal gun with 90% bore porting and a 19.5" barrel, at 2000 psi the power curve here greatly tapers off after 1.5cc per fpe and almost flat lines above 2cc per fpe. A conservative goal would be around .8-1cc per fpe, but as you see, even .5 cc per FPE can go quite the long way...But with todays day and age of chasing dragons / peak performance, most manufacturers probably aim for greater than 1:1.
- Original poster
- #5
Thank you,
I'm going to have study this as it is mostly above my head at the moment.
I'm shooting a 26" barrel with 18.1gr. Pellet at about 960 FPS and a 23gr. Slug at I think about 930 FPS.
So, not sure how to figure if a plenum would be of any benefit.
What you will find is you will get the same FPE with a lower regulated air pressure. The plenum provides air to keep the pellet under acceleration longer in the barrel.
Upshot is, keep the same current reg pressure and more power
Or
More shots because you can lower the reg pressure to keep the same FPE.
Optimal plenum is 3-4x barrel volume.
The issue with poppet valve guns is that the effective maximum plenum size varies. Depends upon a lot of variables
Poppet dwell
Poppet diameter
Transfer Port diameter
Turns between regulator and barrel
Etc.
The longer the poppet stays open, dwell, the larger a plenum can be used. Hammer spring and poppet spring are the two big variables there. But longer dwell means more air so shot count goes down.
Too big of a plenum could have hysteresis issue, where the plenum does not refill from a shot and the next shot has less air and less energy. But I have not encountered that and have some very big plenums 120cc and 240cc tubes...
Danman
Grand HAMster
I'll add this, it may be obvious to many but maybe it will be helpful to your questions:
-An unregulated gun has obviously no regulator and therefore no plenum.
-The entire air tank is technically 'potential plenum space' (think AirForce pcps) and how much air is used per shot is controlled by the hammer weight, the hammer spring, your tanks current pressure, and lastly the valve orifice size exhausting the air itself behind the ammo and out the barrel.
-A regulated pcp will have a plenum, some are very small, hence the add on plenums offered for some pcps when chasing power.
-The plenum can be a power limiting factor and if so is a good idea to add one if going for more power, whereas (already mentioned by @SpindleB) in some guns it may do little or nothing to help.....like putting a 3inch exhaust on a 4cyl engine when a 2 1/4" is plenty.
"there is no replacement for displacement" holds mostly true for plenum sizes but its just one part of many that makes a regulated pcp work.
Last edited:
The 1st GEN Avenger 25 cal as shown had a 12cc plenum which was very small so at the time there was an extender you could buy and I think it was 16cc so with the 2 it gave me 28cc of plenum along with making the valve port, barrel port and other work, was to make more air flow to take full advantage of the added plenum cc, started with a 42 fpe in stock form and ended up with 100 fpe, It was a laser beam.
phone-(412) 780-3024https://www.facebook.com/alienairguns/
Attachments
AirForce are the easiest when it comes to plenum. No poppet valve and a direct line from regulator to barrel.
Most poppet guns don't make adding a plenum the easiest unless there is an OEM plenum available. There are some aftermarket plenum that screw into the gauge hole. Be careful there as the diameter of the air hole is critical with them. Too small and the plenum will be a nice paper weight
Yeah,go ahead and brag how big yours is!
And it gets bigger, 120cc plenum and 1.1L bottle.Yeah,go ahead and brag how big yours is!
What do we have ?
Condor and Talon
1.1L Acecare Fat CF Bottle
Trajectron angled adapter
Huben Power U Adapter
Regulator 1/2 of a Cricket
20CM Shan Bao 3000psi (120cc) tube
M18-M18 extension
High Flow 8mmx5.5 Tophat
I have another version uses the Cricket Max-ATH with a 1.1L and a high flow tophat. That is 50cc plenum in the regulator.
The Dream Universal with the 19.5cc plenum was effective but the .25 with 24" barrel like a bigger plenum.
Very nice! Thank you for the info.
Nice combination of parts brother! You should get quite a few shots as well as max power.
On the .22 with the 18" barrel I think I was getting 160 shots from 4500 to 3500 with the reg at 1750psi. So 400 or so before I fall off the regulator.
I cannot imagine 400 shots in one sitting through a Talon...
My hand is sore just thinking about that many shots on a Airforce rifle! Better to have more than not enough.
Billm
Grand HAMster
That is awesome.
Cantona256
HAM Expert
If you added a plenum to your barra it would let you drop reg pressure by 500psi to get the same speed as before.
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