Bosch TCA640 Series Repair Instruction page 37

4.4.4.2 Brewing position
When the gears move into the brewing position, the drive shaft rotates
with the actuator (D) in an anti-clockwise direction.
The brewing unit is moved upwards. The connection to the drainage
valve is closed with the water
coupling in the brewing unit. The switch cam on tripping device (D)
reaches into the drainage valve control line and closes it. Water can
flow from inlet (A) through drainage valve (B) to outlet (C).
58300000120060_ARA_en_c.doc – 18.09.09
4.4.4.3 Drainage position
Once the brewing process is complete, the water pump switches off.
The transmission motor turns the input shaft with tripping device (D)
back through about 8° and opens the drainage valve.
The pressure is relieved and the water can drain into the expansion
chamber and then into the drip tray. To prevent underpressure, air can
flow back through valve (B).
Then the transmission turns back in a clockwise direction until it is in
the basic position again.
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