What does a external plenum actually do ?
Does it mean you can run the gun at a lower bar and gain more FPS?
Does it mean you can run the gun at a lower bar and gain more FPS?
Plenum
- Thread starter villaman
- Start date
Pretty much. It gives you a wide varietys of tunes too. When my gun was stock it had a very heavy hammer, long stroke, and hit the valve quite hard at 150 bar for 850fps ( .25 34gr) for 40-45 shots. Now, with a 150cc plenum, I run a super light short stroke hammer that just burps the valve, get 930fps, and about 80 shots and improved accuracy. Also, if I wanted to, I could drop down to 100 bar with little baby strikes on the valve and get 890fps with 25gr pellets with an insane shot count.
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All it does is contain a larger volume of regulated pressure air. When a shot is fired the pressure on the regulated side drops less as the pellet moves down the barrel allowing a more efficient burst of relatively consistent pressure air to be used, rather than a needing to use a large volume of air with rapidly dropping pressure.
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It is a little odd that while it can cost very little to produce a larger volume plenum in the original design of the rifle, that the manufacturers choose not to do that. Downsides? The Impact could easily have a larger plenum tube (as is done by the aftermarket supplier in Poland), but FX chose not to do this, adding only 5cc to the Mark II.
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I guess for most guns it is a compromise between saving space, and have enough plenum for the given caliber, and what most owners will use the gun for. If the gun use the tube and the area behind the reg as a plenum, one can make it bigger by moving the reg and breath hole forward in the tube. But bigger plenum would in this case mean smaller reservoir for the high pressure air. A .25 caliber gun will probably benefit more from a bigger plenum, than a .177. Same will probably a high power slug shooter, in comparison to a medium powered pellet shooter. A gun with the plenum inside the block, would probably require a bigger block, for a bigger plenum.
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What is an external plenum? I have been out of airguns for a bit and just hopping back in. I'm familiar with what a standard plenum is...
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G
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It's added regulated air volume between the regulator and valve. Too much and you get a shot curve as if it weren't regulated. Too little and you get scavenging which causes erratic velocity changes.
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