What a Jake Brake actually does is open the exhaust valves just before the piston reaches Top Dead Center, thus dumping all the compression and the cylinder fails to fire. Yeah, I used to fix 'em.
yes, using compression, they use solenoids.
the mechanical end of it, i really cannot say, only what i was taught like 60 years ago in trucking (driving school)...frankly, i could care less what type of engine brakes, or brand name were or were not installed.
i'd get my paperwork, get the trailer, do a pre-trip, and off i went.
the mechanicals were never really my concern, as i said all the companies i ever worked for, forbade us drivers from doing more than a pre-trip, or at the very least a headlamp or tail lamp replacement..they did not want us to climb on top of the tires to replace wiper blades.
when it came to many states DEMANDING we clear snow off of our trailers..??
again, my particular company forbade me from doing so, due to possible severe injury or death..that's what the shop did, and vendors do, not us drivers.
i know for a fact, i was fortunate enough to drive 3 trucks with the 425 CAT, and 15 speed transmissions...gearing..?? WTF cares..???..top speed...1 truck...112 mph, the other 2...110 mph...that's all i ever cared about
i never really talked "trucking" to owner-ops or "diesel in their veins drivers" who knew thier trucks inside out, and could talk specs all day long.
driving safely (which i did for over 40m years) and earning safety awards was where i was at.
i had a family of 6 to take care of, my mind was set on them, not how, or what made that rig.
i pretty much only knew that there were, electrical, hydraulic, and exhaust "Jake" brakes.