Vibiemme Domobar Junior - Manual (Page 7)

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But why sense pressure in the boiler when it is temperature in which we are interested? Pressure is an
indirect measurement, but one that is easy to control and yet accurate without using more complicated electronics.
Heated water at a given pressure is always at a predictable temperature. That is indicated by the left-hand
gauge on the front panel of the Vibiemme espresso machine. As the temperature changes in the boiler
you will see the Boiler Pressure Gauge rise and fall.
3.3. Boiler Pressure Gauge
The Boiler Pressure Gauge on the front left of the machine is calibrated in “BAR”(scale 0,5 to 2,5 );
that is barometric pressure. The boiler works like a pressure cooker in that as the pressure in the boiler
increases the boiling point of water in the boiler increases:
Boiler bar Boiler temp. Approx brew temp
1.0 253 F. (123 C.) 196 F. (91 C.)
1.1 255 F. (124 C.) 199 F. (93 C.)
1.2 257 F. (125 C.) 201 F. (94 C.)
1.3 259 F. (126 C.) 203 F. (95 C.)
A Quick Science Lesson (no homework required)
Gauge readings can be confusing. Let us try to make a bit more sense of it. The Boiler Pressure
Gauge is reading the pressure above the outside pressure, so a reading of 1 BAR is actually a pressure
of 2 BAR in the boiler.
The laws of physics teaches us that at a constant volume, as the pressure of a gas increases or decreases,
by the same factor does its temperature increase or decrease. In plain English, as the pressure in the
boiler rises so does the temperature in the boiler.
Just like in a pressure cooker, the rising pressure of the steam in the boiler allows us to actually raise the
temperature of the water without having it boil. This temperature which is above the boiling point of water
also allows so temperature drop between the boiler and the grouphead so that when the water reaches
the coffee it is at the correct brew temperature.
3.4. Brew Pressure Gauge
The information that Brew Pressure Gauge ( on the front right of the machine calibrated in “BAR”scale
0 to 16 ) displays can actually be confusing. When the machine is at idle (or actually at any time other than
when brewing espresso) the readings of this gauge should be ignored. Its only function is to report brew
force and at any other time the reading is not reporting anything of note at all. During the brew cycle the
reading should be in the range of about 9 to 9.5 bar if everything else is correct. That statement is only
accurate if all other factors are right. More on that later in this manual.
3.5. Back to the Machine
When you need steam you open the steam valve and steam is drawn off the top of the boiler. This will
cause a drop in pressure in the boiler which will again trigger the pressurestat to turn on the heating
element to help maintain the boiler’s temperature. You may also hear the pump occasionally cycle if the
boiler’s water level goes below the sensing wire..
WARNING: The steam comes out with a lot of force and can cause serious burns. Use great care
when using the steam function.
When you need hot water, you open the hot water valve and the pressure of the steam as well as the
pump pushing water into the boiler force hot water through the wand. The machine automatically routes
the water to the boiler or on what mode the machine is in at the time. Limit the dispensing of hot water
to no more than about six ounces at a time. After drawing water allow the pump to refill the boiler and
the boiler to come back up to temperature before further use.
WARNING: The water which is being dispensed can be very near the boiling point, please use great
care when dispensing hot water.