I was talking about the flow-meters and solenoids, not the pump, putting such a device into the boiler is about as bad a solution as putting the fuel pump on a car inside the gas tank (you'd be surprised how many makers do that as well). The synesso way is probably the best solution for the pump, only thing is that you're pressurizing the boiler, it would be better to pressurize just the brew path.

It would be real nice to have a proper flow-chart over a La Marzocco since I've never seen one open and I'm familiar enough with their design to make sure I don't sound like an idiot, but it's more fun when there's an certain element of danger involved...

pdx wrote:The group is the highest part of the boiler on purpose- that way there's a coherent convection circuit which includes the group head. Hot water flows up to the group & back down- this makes the group temperature most controllable. Its easier to predict the temperature at the top of this circuit & more difficult to predict the temperature at any other point in the circuit.

Okay, that's something I didn't know, you learn something new every day...

How did they then get the boiler to fill all the way up to the group? The only way I can work out fast in my head is to mount the auto-fill sensor as high as the group, and then bleed out the air from it (as you normally do with the LM machines), but that must be rater bulky...

Stuggi wrote:I was talking about the flow-meters and solenoids, not the pump

Synesso puts all of that on the cold water line- why should any of that be in the boiler? Valves & pump just push cold water into the HX, then into boiler, where it displaces hot water that goes through the group. There's no advantage to burying any of that inside the boiler.

Stuggi wrote:How did they then get the boiler to fill all the way up to the group? The only way I can work out fast in my head is to mount the auto-fill sensor as high as the group, and then bleed out the air from is (as you normally do with the LM machines), but that must be rater bulky...

Again, there's no need to be that complicated. There's no autofill sensor in the brew boiler- its always kept completely full. Remember, the design of the boiler/group is to keep the very top of the boiler/group at a controlled temperature- this means the brew water is drawn from the very top of the group. To fill the boiler you just open the brew valve. The pump (or line pressure) push water through the brew valve, though the steam boiler HX, into the boiler. When water comes out of the dispersion screen the boiler/group is completely full, with no place for air bubbles to hide. The design bleeds itself.

If you want to talk about brew path as the path from the boiler to the dispersion screen it's as short as could be- there's a tube inside the boiler/group that goes from the top of the group (which is the top of the boiler/group body of water) to the dispersion screen.

Stuggi wrote:I was talking about the flow-meters and solenoids, not the pump, putting such a device into the boiler is about as bad a solution as putting the fuel pump on a car inside the gas tank (you'd be surprised how many makers do that as well). The synesso way is probably the best solution for the pump, only thing is that you're pressurizing the boiler, it would be better to pressurize just the brew path.

It would be real nice to have a proper flow-chart over a La Marzocco since I've never seen one open and I'm familiar enough with their design to make sure I don't sound like an idiot, but it's more fun when there's an certain element of danger involved...

The Synesso idea of outboarding the pump to below the counter was, as I understand it, inherited from at least La Marzocco. I wouldn't be surprised if there are a number of other manufacturers that do it. It isolates your pump motor from the heat of the machine (probably not too big a deal), and more importantly isolates pretty much all of the pump's admittedly minimal noise from customers.

As far as flow-meters and solenoids, the same question exists as with the pump: why not just put them prior to the line feed in the boiler? AFAIK, this is what Synesso does.

Every commercial machine I know of puts the pump below the counter.

Right- the image you linked shows flow meters in the Synesso Sabre, which isn't sold in the US to my knowledge. Its just like a Cyncra, but with programmable dosing (& no paddle group). Same idea- all the controls are on the cold water line. This works because the Synesso used individual boilers for each group. The reason LM (and presumably others) have valves in the hot water path is they have multiple groups on one boiler.

There are probably other makers that have multiple brew boilers- I don't know much about some of the makers.

Then what was the problem with the old LM group? If everybody puts everything at the cold water side? But the three-way must be somewhere near the group right?

I believe that some older La Marzocco machines had a water path where the line entered the boiler, exited it, passed through the flowmeter, and re-entered the group to brew, resulting in a pointless flushing requirement to avoid cold first shots.

malachi wrote:Even with the existing dual boiler machines, it is important to understand the relationships between idle times of various durations and brew temperatures. Machines like the Expobar Brewtus have issues with this due to the group design. Automatic Lineas have different issues due to the placement of the flowmeter in the brew pathway. Indeed, semi-auto Lineas provide the best results when flush-managed.

From La Marzocco GS3-Pro's Perspective

If I understand comments I've read lately, newer models don't suffer from this design flaw, and do not have a flushing requirement (at least, to the same extent). La Marzoccos can be confusing to follow (for me at least): While they've changed a lot over the years internally, they still pretty much look the same.

Yeah, that's how I understood it, but why if you just could put it on the cold water line entering the boiler? Weird stuff, now I really want an old LM just to take apart and see how it works...

Stuggi wrote: now I really want an old LM just to take apart and see how it works...

It'll be much cheaper just to look at the parts diagrams
http://www.espressoparts.com/category/03.01.lamarzocco.03/