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The Group
Every group is independently thermoregulated, with its own separate
" THERMOSIPHON CIRCULATION ".
The following devices are found on the front of the machine where the filter-holder
is inserted:
- the flow block (M)
- the spout (N)
- the under cup gasket (P)
On the rear are the water entry and exit perforations (A and B respectively) for
the themosiphon circulation water and for the coffee.
The three group valves perform the following functions:
1.
The dispensing valve (E). When the group is operating this valve is
open and allows the passage of water to the ground coffee.
The valve is closed when the group is not operating and allows the
thermosiphon circulation.
2.
Infusion valve (I). Determines the "cooking" of the coffee thanks to a
play on the pressure.
3.
Drainage valve (S). This valve is closed during dispensing. It opens
and drains the group at the end of the dispensing, controlled by the
command lever cam wheel.
HOW THE GROUP FUNCTIONS
A.
Group at rest.
1.
Group command lever (2) - horizontal.
2.
Thermosiphon circulation - the water circulates in the changer around
the central head (G) .(metal tube), maintaining the group thermoregulated.
3.
Dispensing valve (E) - Closed.
4.
Infusion valve (I) - Kept open by the cam (C).
5.
Drainage valve (S) - Kept open by the cam (C).
6.
Filter-holder - Inserted and containing the previous coffee grounds.
7.
Pump - Standstill.
B.
Group in operation
1.
Filter-holder - Inserted with freshly ground coffee.
2.
Group command lever (2) - Vertical.
3.
Pump - In operation.
4.
Dispensing valve (E) - Kept open by the cam (C).
5.
Infusion valve (I) - Closed.
6.
Drainage valve (S) - Closed.
Group command lever (2) in vertical position acts on the cam shaft which
presses on the microswitch button of the pump motor.
INFUSION TIME
- The pressure in the thermosiphone circulation reaches the pump delivery
head value (8 ÷ 9 bar).
- The water under pressure enters the chamber above the nozzle (H) via the 4
perforations in the central head.
- Nozzle (H) permits the passage of a small calibrated quantity of water into the
group (cam chamber, dispensing chamber, ducts and space on the ground
coffee) which gradually fills up until the level of pressure is reached that opens
the infusion valve (I).
- At this point, the infusion chamber (L) is filled.
- While the infusion chamber is being filled, the air contained therein has contact
with the ground coffee. Steam is formed in this air bubble.
- The entire group is now at infusion pressure and remains at this level until the
entire infusion chamber is filled. At this point, the pressure rises to reach the
pump delivery head value.
- Completion of the infusion requires about 6 seconds from the moment the
group command lever (2) rises. This is the "INFUSION PERIOD".
- During this period hot water comes into contact with the ground coffee at a
pressure that is not sufficient to overcome the resistance.
- The water pressure gradually increases on the ground coffee, causing its
preliminary swelling and "cooking".
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34
COFFEE DISPENSING
- At the end of the infusion period, i.e. when the water pressure on the ground
coffee has reached the pump delivery head, dispensing of the "coffee cream"
commences and continues until the group is halted. Dispensing of a normal
coffee must last about 25 seconds.
- These times are based on the type of coffee (blend) used, its correct roast
level and above all to its grinding degree.
NOTE: The closure of the group must be made quickly so that the cushion of
steam that forms upon contact with the coffee grounds can contribute to an
effective drainage from the group and consequently the drying of the coffee
grounds.
Upon completion of the dispensing, the group drains automatically to remove the
pressure and thus making it safe to remove the filter-holder.
C. DISPENSING COMPLETION
1.
All the group components return to the point A position.
2.
The opening of the infusion valves (I) and drainage valves (S) via the
cam (C) empties the spaces under the dispensing valve.
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