I have a question about small single boiler machines design. Why does the boiler intake cold water from the reservoir while brewing? Even the smallest boilers are large enough for doubles and the cold water intake is what's causing the whole temp stability issue on those machine. They can design them in a way that while brewing there is no intake, and immediately after brewing the pump fills the boiler again. If drying the boiler out is an issue they can design a valve that will insert cold water when the water at the boiler reaches a certain level.

What I mean is that they will do 2 switches. One that will do exactly what the brew switch is doing today. This will be used for temp control by the user, and another switch for brewing with no cold water intake. To me that seems like a perfect and cheap solution for a very common problem. Now, I'm sure that I'm missing something here, and it's not that simple. Could someone explain what's the problem with that?

kramerica wrote:Why does the boiler intake cold water from the reservoir while brewing?

Because the boiler is a closed system and the pump has to move water into it to produce pressure. In other words, the space formerly occupied by the water leaving the boiler has to be replaced with something.

However, if the boiler were effectively a cylinder and the pump a screw-type piston reducing the size of the boiler itself, you could do what you suggest. IIRC, the Versalab M3 uses this idea, i.e., it builds steam pressure to drive the boiler/piston. It's mostly trivia now that the M3 never went into production, but that's why it needed 20-30 minutes after pulling less than a dozen espressos - to "recharge" the (steam driven) pump.

The question I've wondered isn't why the boiler intake is cold water, but why isn't it preheated? A few turns of copper tubing around the boiler could preheat the water and improve temperature stability, as has been demonstrated by some Silvia owners.

EDIT: Corrected word glitch per AndyS.

kramerica wrote:I have a question about small single boiler machines design. Why does the boiler intake cold water from the reservoir while brewing? Even the smallest boilers are large enough for doubles and the cold water intake is what's causing the whole temp stability issue on those machine. They can design them in a way that while brewing there is no intake, and immediately after brewing the pump fills the boiler again.

There are several problems with your suggestion:
1. Water will not simply flow out of the boiler. Something has to force it out of the boiler and through the very high resistance provided by the coffee cake. This force is typically provided by pumping fresh water into the boiler. Some people have used compressed air instead, along the lines of what you suggest. This hasn't necessarily produced great espresso.
2. Keeping the boiler temperature constant will not solve "the whole temp stability issue." In a machine like Silvia, the boiler typically runs close to 230F, the group hangs out around 170F, and if you're lucky, water running through the group from the boiler ends up around 200F. But even if the boiler water temp is perfectly stable, the group temperature varies depending on how long it has been since a shot was pulled. This affects the water delivery temperature.
3. The idea that water should be delivered to the coffee cake at an unvarying temperature is itself a controversial one.

HB wrote:the space formally occupied by the water leaving the boiler has to be replaced with something.

Even the space informally occupied by water has to be replaced!

HB wrote:However, if the boiler were effectively a cylinder and the pump a screw-type piston reducing the size of the boiler itself, you could do what you suggest. IIRC, the Versalab M3 uses this idea, i.e., it builds steam pressure to drive the boiler/piston. It's mostly trivia now that the M3 never went into production, but that's why it needed 20-30 minutes after pulling less than a dozen espressos - to "recharge" the (steam driven) pump.

Actually the Versalab machine works quite differently. It uses a boiler open to the atmosphere. A little pump positioned inside the boiler delivers water to the coffee cake. After a dozen or so espressos, the boiler has to be refilled with water.

HB wrote:The question I've wondered isn't why the boiler intake is cold water, but why isn't it preheated?

As you mention, water is preheated in the state-of-the-art machines, eg, LM, Synesso, Schectermatic.

Hey Guys,

You can read all you like about the versalab. Since it's been patented it's public domain.

Versalab M3 Patent App


ciao

lino