Sorry,Peter,you're a bit off base on this one..
Brakes,intended to reduce muzzle rise and/or recoil,DO work on pcp's and co2 rifles.Strictly speaking even just a weight on the barrel will function as a brake in that sense on a springer (reduce felt recoil and muzzle movement)
One problem is that common terms in airgunspeak mean different things to different people..Springer "recoil" isn't real recoil,i.e. it's not a reaction (primarily) to the accelerating pellet and rocket effect of the muzzle blast,as in true recoil.A high power pcp or co2 gun does have true recoil,to a greater or lesser extent.Most airgun hammers are strikers..(a hammer swings in an arc,a striker moves in a straight line) a dump valve may be the same as a blockade valve, or pop open valve,but some consider the term to mean the way the valve is intended to fuction(i.e. dump the charge instead of meter part of it) " plenum" is sometime used to describe the storage area in a valve body,but that area is actualy a reservoir.The term valve is commonly used to describe the entire valve assembly,often including an intake,(or inlet,or check) valve ,one or 2 springs,a reservoir,one or 2 valve seats, an outlet valve,and both inlet and exhaust ports.
"Brake" means different things to different folks.Often mostly "bling" (though I've seen some designs that should be very effective)sometimes code for a moderator,sometimes "just" a weight (just a weight can be an effective acuracy enhancer,if used to tune barrel harmonics)It would be nice if we all agreed on the meaning of the terms we use,but it hasn't happened yet...