As I understand, there're two main configuration for commercial spring lever groupheads (of course this is a broad generalization) - either a dipper (single inlet port) or a thermosyphon (double inlet port) config.

Here's a dipper grouphead cross section pic that had been circulated on HB for more than a few times.


However, I can't find the equivalent diagram for a thermosyphon grouphead.

I guess the main question I'm trying to answer is - does water actually flow(dynamically) and circulate throughout the entire grouphead (which results in faster heat up), or is the water flow just limited to the cavity near the inlet port entrance?

Further extension of the question would be is it possible to easily mod a dipper head to a thermosiphon head, and vice versa. But I better not get ahead of myself.

This image shows the best view I've found showing the thermosiphon group connections. On the new CMA heavy head group are two stacked connection ports for the thermosiphon instead of the one, central connection port for the dipper configuration.
https://hankua.files.wordpress.com/2015/03/nc7i5460.jpg

However, I can't find the equivalent diagram for a thermosyphon grouphead.

Here ya go . . . Londinium I:

Thanks Curtis. That's exactly my question - what happens after the inlet port? Are the water mixed immediately upon entrance or are they mixed in the jacket surrounding the main grouphead?

A quick & dirty pic to illustrate what I'm after - pardon the lousy pic - it's a top view of the grouphead and the arrows of cold water are inverted :

Awesome, thanks Erics!! That's exactly what I want to know. Just notice your post after posting mine.

EricS, do you think the L1-P is the same Group configuration and just different HX configuration?

BTW, very nice illustration of the Thermosyphon Group.

The best answer I can give is "I don't know".

I've attached some thermocouples to my Salvatore Compact Lever to measure the inlet and outlet temperatures of the thermosyphon loop at the head as well as the surface temperature near the portafilter collar.

The average of the two thermosyphon temperatures is ~96C which was the target temperature I used for my E61 to get ~92C for the brew temperature. With ~75C at the exterior of group, I am thinking this may lead to a low brew temperature, especially with too long a pre-infusion time.
Has anyone looked at the optimum pre-infusion time for this type of lever?

On my President my preinfusion varies greatly depending on the coffee, anywhere from 10 to 30 seconds or so. I do start to struggle with keeping the brew temp hotter with the longer preinfusion, though.

I do start to struggle with keeping the brew temp hotter with the longer preinfusion

I've noted that after 10 second pre-infusion on my machine (my ususal time), both thermosyphon tubes are about 89C. I'd guess I would get a sour extraction with a longer pre-infusion, but I need to try it to verify. I tried shorter pre-infusion (~2 sec), but noted some boiling/bubbling on the grouphead screen and a pretty acidic extraction.