An alert lurker brought this other cutaway photo to my attention, including the diffusion block.

Hi,

Looking at these cutaways, it's not at all clear to me what causes boiler water to circulate in the group. I guess I can see that as water cools in the group, the cooler water will slide down back into the boiler, but by that point the damage has been done, thermally. Barry, I'm sure that you in particular have given this a lot of thought; what's the deal?

Best,
David

DavidMLewis wrote:Looking at these cutaways, it's not at all clear to me what causes boiler water to circulate in the group. I guess I can see that as water cools in the group, the cooler water will slide down back into the boiler, but by that point the damage has been done, thermally.

I don't believe that water does circulate ... rather the arm and the group are essentially part of the boiler volume, and therefore are filled with the same saturated steam that fills any other open space in the group.

Or am I nuts?

HB wrote:An alert lurker brought this other cutaway photo to my attention, including the diffusion block.

i've got several shots of a cutaway group. they had one at the roasterie the last time i was over there, so i took some snaps. when i get home i'll dig them out and email them to you (no broadband at work). there was also a cutaway at intelligentsia a few weeks ago.

DavidMLewis wrote:Hi,

Looking at these cutaways, it's not at all clear to me what causes boiler water to circulate in the group. I guess I can see that as water cools in the group, the cooler water will slide down back into the boiler, but by that point the damage has been done, thermally.

there is bound to be some convective mixing, but i wouldn't think it to be highly organized as one would find in a thermosyphon. it is my understanding (info from people who should know these things) that the hottest, most stable part of the boiler/group system is just under the group lid.


--barry

maddie today: "daddy roast coffee beans. yummy coffee beans!"

skyryders90 wrote:I don't believe that water does circulate ... rather the arm and the group are essentially part of the boiler volume, and therefore are filled with the same saturated steam that fills any other open space in the group.

Or am I nuts?

you're nuts. there is no steam in a marzocco brew boiler.


nadda. zilch. zip.


and you can't not have convective mixing in a tank of water which is hotter in one area than another.

Hello everyone. The pics are great as they clearly show the banjo tube.

AFAIK there are 2 other groups doing the rounds at the moment. The one with the solenoid mounted on the rear of the boiler which was on the proposed Marzocco consumer machine at SCAA and another group I saw some time ago with flowmeter and valve on the group cover. No water left the boiler as far as I could tell. I was under the impression that the GB/5 used this latter set-up but on the machine I had from them it was 3-way valves and flowmeters hanging in space time again. I don't know if it was because my machine was an early one but I have another one coming in a few weeks so I can check again.

Paul

HB wrote:An alert lurker

I like the alert lurkers. It's the spaced-out lurkers that really piss me off.

Well, I'm not a lurker, but I certainly am spaced-out these days...
Don't mean to piss you off though.

Dan asked me to repost this pic of a "semi saturated" E-61... So without further ado.



prototype #1 in cross section

If you look at the x-sec of the E-61, that Dan posted above (previous page?), you can see the differences. Nothing earth shattering, but there is a fairly large new hole in the back of the group that is linked directly to the boiler.

ciao

lino

lino wrote:If you look at the x-sec of the E-61, that Dan posted above (previous page?), you can see the differences. Nothing earth shattering, but there is a fairly large new hole in the back of the group that is linked directly to the boiler.

So how's the coffee taste out of this thing?