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9.9 Flow
meter
Some models of solenoid valves have a built-in flow sensor which measures the quantity of water in litres
that is loaded into the appliance.
If the sensor malfunctions, the water level is controlled by the analogue pressure switch.
Solenoid valve – exploded view
Main board
Turbine
1-Circuit
board 4-Diffuser
2-Turbine 5-Double
filter
3-Deflector
6- Reed switch
7-Magnet
9.9.1 Operating principle of flow meter
The main components of the flow sensor are:
1. Turbine (with magnet and
counterweight mounted on the
outside)
2. Reed switch (normally open)
3. Magnet
4. Counterweight
Water entering the solenoid valve rotates the turbine (1) and magnet (3), which passes in front of the reed
switch (2), thus closing it. As this contact opens and closes, it generates pulses at a frequency that is a
function of water flow.
The turbine completes 230 revolutions for each litre of water. The operating range of the flow sensor is 0.2-
10 bar.
Using the signal it receives, the microprocessor can calculate the number of litres of water passing through
the solenoid valve.
Contact closed
Contact open
Signal 0
Signal 1
