sacguy71 So for the powered lever machines, do you have to press and hold down for 30-40 seconds as well to maintain constant 5-9 bars of pressure for the shot like I do on the manual Flair lever machine?
No - the spring provides the brewing pressure, and it does so in a very consistent way, to the point that you don’t even need scales to measure how much liquid is in the cup (if you have a brew chamber manometer).
You pull the lever down all the way, and load the spring “in your own time” - water gets in the brew chamber at “low” pressure (mains/pump) while you are doing that. When you release the lever, the spring force pressurises the water and, as the water gets through the puck, the lever is gradually released back to its vertical position.
If you want, you can ‘pressure profile’ a bit by speeding up/delaying the movement of the lever on its return path, but normally you just let the spring do its job.