follow the link is information about E61group head. it is very details about the legend.

http://www.home-barista.com/espresso-machines/can-anyone-explain-preinfusion-on-e61-t5472.html#p63406

http://www.home-barista.com/espresso-machines/e61-group-truth-and-lies-t724.html#p5272

http://www.home-barista.com/espresso-machines/e61-group-espresso-machine-detailed-interior-schematics-t397.html#p2308

http://www.home-barista.com/espresso-machines/e61-group-espresso-machine-is-its-reputation-justified-t376.html

enjoy.