La Marzocco micra Serie Manuel page 22

Coffee group
pressure gauge
When the coffee group heats up and reaches the operating temperature, pressure inside it increases. An expansion valve
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allows a small amount of water to flow out during this process, to ensure that pressure inside the coffee group does not
exceed 12 bar. The coffee group pressure gauge will reach about 12 bar during the initial stage of the process, then it will
stop.
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Steam boiler
pressure gauge