Astoria 1GR Use And Maintenance Manual page 16

2.9.1 Heating unit
The heating unit is made of copper sheet metal (1). The heat
exchangers are assembled onto this unit and are in turn con-
nected to the dispensing group. The water used for dispensing
coffee is taken directly from the heat exchanger. During the
dispensing process, cold water is sent inside the exchanger
by means of the motor pump. Cold water and the pre-exist-
ing hot water are mixed together inside the heat exchanger,
in order to obtain the optimal water temperature for coffee
infusion.
1
Electric heating
The heating unit is electrically heated by an electric heating
element immersed in the water (2).
Gas heating
Gas heating is obtained by feeding the burner flame which is
located under the heating unit.
Electric + gas heating
In machines equipped with both systems, it is possible to
combine the two heating types.
Overflow device
2.9.2
The cover installed on the pressure relief valve makes it possi-
ble to collect any water and steam which may leak from the
heating unit due to a malfunction and channel it to the drain
tray, via a special hose.
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of
2.9.3
The pressure relief safety valve has a calibration
of 0.19 MPa (1.9 bar) in order to ensure that the
pressure in the steam heating unit does not exceed
0.21 MPa (2.1 bar). Should a fault occur, the capac-
ity of the valve is such as to be able to eliminate all
the excess pressure in the heating unit.
2.9.4
This is a valve consisting of an expansion valve and a check
2
valve.
• Expansion valve (A):
the cold water sent from the pump to the heat exchangers
is heated. This heating causes an increase in the volume
of water. To limit pressure increases in
the hydraulic circuit, the valve limits
the maximum internal pressure of the
circuit to 1.2 MPa (12 bar).
• Check valve (B):
its function is to prevent the water
from back-flowing into the hydraulic
circuit exchangers.
2.9.5
The purpose of the negative pressure valve is to pre-
vent liquids from back-flowing through the steam
nozzle when they are being heated. Furthermore, the
excess air inside the heating unit is removed during
the machine's heating phase.
2.9.6
The pressure switch makes it possible
to control the heating unit pressure by
activating or bypassing the heating
element in the heating unit. Any pres-
sure switch calibration can be carried
out with the machine in operation by
turning the screw (6) located on the
body of the component.
Pressure relief safety valve
The safety valve should be checked regularly as
indicated in Chap. "7. MAINTENANCE AND
CLEANING" on page 46.
Two safety valves are installed on all machines
with 4 groups.
Expansion valve + check valve
Negative pressure valve
Pressure switch
A
B
6
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