The following page gave me a good understanding of the water flow path in the E61 group: http://coffeetime.wikidot.com/the-mystery-of-the-e61-group-mushroom

Thanks to all whose hard work went into making these - these are awesome and extremely helpful for helping me understand what's going on.

I have 2 questions, though:

1. I don't understand how preinfusion works. In Eric's labeled diagram, the bottom section is shown to hold the preinfusion chamber. However, in the youtube animation, it looks like that bottom preinfusion valve is fully closed before the upper brew valve is opened. I thought the way preinfusion works is that when a shot is brewed that the water first fills the preinfusion chamber, then goes up through the neck and down to the dispersion screw, but if I understand the water flow path from the animation I don't see how that's possible. Can someone explain how this works?
2. What's the purpose of the gicleur?

Thanks!

Nevermind my question #1 from above - I now understand from reading the patent. When brewing the shot, as the "cam pocket area" starts to fill, once it reaches ~1.5 bars of pressure it has enough pressure to overcome the preinfusion spring (but not the drain valve spring, which remains closed), thus ensuring that the water hitting the puck will be under relatively low pressure until the preinfusion chamber completely fills.

Wow! Now that I grok it I have even more appreciation for this ingenious device.