WELCOME
Mirage technical manual
page 9 of 65
A large num
ber of espresso’s
When water in the lower tube is used to brew espresso it is replaced with water from the bottom of the
heat exchanger. This water is initially too hot but is cooled considerably by cross-flow with cold water
flowing from the water supply into the heat exchanger. Cold incoming water is directed upwards in a
copper injector tubing of approximately 20 cm where it heats up along the way. Water is drawn from
the boiler through a brass fitting that completely surrounds the injector tubing such that the hot water
from the boiler is cooled by the incoming cold water. When brewing volume is high, the cross-flow
system, together with the flow restrictor at the top of the heat exchanger warrant a very stable
temperature on the coffee bed (see Figure W 3). Fluctuations in steam boiler water temperature which
result from filling have little effect on coffee water temperature as they are balanced by the large mass
of brass of the group head.
Temperature stability
The entire system allows for very stable water temperature at the coffee bed with low and high
brewing volumes in combination with high steam pressure. The water at the coffee bed can be
adjusted to as low as 88 °C by altering the flow restrictor (either by changing the fixed-opening
restrictors or by regulating the adjustable restrictors).
The temperature in the steam boiler is maintained by a very accurate electronic controller. The
measuring-tip of the temperature sensor is located above the water level in the steam boiler, not in the
boiler water itself. This is done on purpose: when a steam valve is opened, the subsequent pressure
drop in the boiler will immediately lead to a small temperature drop (adiabatic expansion) which results
in activation of the heating element. The controller allows for easy adjustment of boiler temperature.
Boiler fill
An operational level probe in the hot water/steam boiler governs automatic refilling which ensures that
water level remains constant. However, the boiler will not fill when a shot is being pulled as not to
disturb the brewing pressure.
Safety
A safety level probe just above the heating elements ensures that the Mirage heating shuts down
when water level is becoming dangerously low, with LED’s on the touchpads or bastone levers
flashing as visual warning. Overheating is furthermore prevented by a separate sensor which
interrupts power to the heating element when the temperature around the heating element exceeds
145°C (293°F).
The expansion valve in the coffee water system, which is adjusted to 11-12 Bar at our workshop, in
combination with a safety valve of 1.8 Bar on the steam boiler ensure that pressures inside the Mirage
cannot exceed safety values.
When any one of the solenoid valves within the Mirage would ever remain open for longer than 2
minutes, the complete machine will shut
down. At the same time all LED’s on the touch-pads will start
blinking as a visual alarm.
User friendly
All group solenoid valves are located inside the machine and connected to the drain such that no
electric devices are in the splash zone and there is no spattering of discharging valves.
The touchpads or bastone lever units can easily be programmed individually or simultaneously to your
own shot-volume settings with the left-hand side touchpad/bastone (as seen by the barista) as
governing module. A touchpad allows for 4 different volume settings and continuous flow. A bastone
unit allows for 2 different volume settings and continuous flow.
