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| Mechanical
Pre-Infusion of the Michelangelo Group |
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Group
in standby position:
The infusion piston (1) is in the upper position.
The water doesn’t flow out of the group
because the three way solenoid valve (2) is
closed.
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After a coffee
key has been pressed by the user, the solenoid
valve (2) opens and simultaneously the pump
starts. The 9 bar pressurized hot water flows
from the heat exchanger (inside the boiler)
through the upper thermosyphonical pipe (the
pipe from the boiler to the upper part of
the group) into the group filling all available
room.
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When all available
room has been filled with hot water, the 9
Bar pressurized water
encounters the “resistance” of
the pressed coffee pod (4) inside the metal
filter basket.
If there wouldn’t be the mechanical
piston (1) with its spring (5), this 9 bar
pressurized hot water would pass the coffee
pod right away, allowing almost no “pre-soaking”
of the coffee pod.
Pre-soaking is another word for preinfusion.
It means, giving the coffee pod some 2-3 seconds
to develop best “aroma”, great
“crema” and a consistent “body”.
How is this little delay of 2-3 seconds reached?As
the “resistance” of the piston’s
spring (5) is lower as the resistance of the
pressed coffee pod, the hot water, prior to
go through the coffee, will push down the
infusion piston (1).
This explains why we don’t see the infusion
piston coming out beneath the piston’s
cylinder when there is no coffee in the filter
holder.
Only when the piston is completely down (and
consequently the socalled infusion chamber
is filled with water) the whole water pressure
of 9 bar is built up and hits the coffee pod
(4), penetrating it and dispensing the coffee
into the cup.
This system (called also: “progressive
mechanical preinfusion”) allows a smooth
“gentle” building up of pump pressure
prior to go “full-stroke” through
the coffee.
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When the coffee
dispensing is terminated, the solenoid valve’s
third way opens and the residual pressure
(water) is unloaded to the drain tray.
What other system are available to allow some
kind of preinfusion (presoaking)= delaying
the 9 bar impact on the coffee pod? (The following
list is not complete)
1) Static preinfusion chamber:
just some kind of room inside or aside of
the group which allows expansion of the water
prior to built up the full pressure. Michelangelo’s
group does also have static room to allow
this expansion (in addition to the progressive
infusion piston system).
2) Electronic preinfusion:
this system usually works opening and closing
several times (we’re speaking of some
3 seconds total) the group’s solenoid
valve to release some water for pre-soaking
of the coffee pod prior the solenoid valve
opens definitely and the pressurized water
passes trough the coffee pod dispensing the
product into the cup.
Michelangelo does also come with this electronic
preinfusion. But it’s disabled
ex factory.
So why do we have it?
The reason is linked to possible problems
with unskilled personal who doesn’t
have any care cleaning app. every 4 to 6 weeks
(depending of course on use, type of coffee
etc.) the pre-infusion piston assembly.
What happens if it’s not cleaned?
The dirty piston might block at an intermedium
stage during coffee brewing process. This
will reflect i.e. in uneven coffee portions
(“The left hand group’s automatic
portion control doesn’t work preciselyl!
Come and do something! I’m only 80 miles
away from you and it’s Sunday 10 pm”).
If the operators are reluctant to learn the
super-easy operation to unscrew the cylinder
and clean the piston and the gasket, it might
be better to purchase from us a “blind
piston”, that’s to say a metal
piece which “closes” the cylinder
thus replacing piston and spring.
Disadvantage: you loose the
superior progressive mechanical preinfusion
system.
Advantage: guess!
How do we enable or disable the electronic
preinfusion system (which is disabled ex factory)?Use
only left hand group seen from operator.
Use only the keys for one small cup and one
tall cup: the first and the second key right
side of the “P” key.
Enabling
1 Switch machine off.
2 Switch machine on while
keeping pressed the “1 small cup key”
(the first key right to the “P”
key).
3 Wait 3 seconds.
4 Switch off machine and
on again after another 4 seconds. You’re
done.
Disabling
1 Switch machine off.
2 Switch machine on while
keeping the “1 tall cup key” pressed
(the second key right to the “P”
key).
3 Wait 3 seconds.
4 Switch off machine and
on again after another 4 seconds. You’re
done.
Please note that with electronic preinfusion
the lifetime of the group’s solenoid
valves might be a shorter one.
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