P.25
4.11 Inlet system
4.11.1 Pressure switch
Working principle
Mechanical pressure switch have two main components that is balloon and electrical
structure. The balloon is fastened sealedly on the pressure switch with hose clamp and
the end of balloon is connected on the bottom of tub using press chamber, plastic pipe.
During flowing water, the bottom of tub is firstly submerged and its space linking the
balloon is closed. With the increase of water level and the pressure of closed air increase
gradually until push the needle of rubber membrane.
Another parts is the electrical structure. With the balloon inflating, a needle top spring
chip to make it conduction and then change the current direction.
Usually, the fault of pressure switch is leakage and contact barrier. It is easy to check
them.
Huff the inlet inflatable with your mouth, and you can clearly hear the clatter sound of
spring chip clicks, if it is multi-level control, several clatters sound can be heard.
There is a group of plastic crosser screw in the side nearly line. These screws are used to
control the height of water level (to avoid adjust it, there is a certain color lacquer to
sign).
Pressure switch is a very important part in the washing machine, which is not only
control water level but also influence the safety of washing machine. Once it is invalid,
water level can’’t be controlled.
Low-frequency analog electronic pressure switch:
its main principle is a group of LC oscillation
circuit, the change of balloon changes the frequency
of LC circuit. Pressure switch feedback to the PCB
signal, and PCB issued in accordance with the
conditions set to decide water level.
The price of low-frequency analog electronic
pressure switch is high and as a result its application
rares.
In a word, pressure switch employs its closed gas
room as the basic condition of normal work. And if
the gas room is damaged, the pressure switch will
be invalid.
In addition, pressure switch is the key part
controlling heating circuit.
4.OVERVIEW OF MAIN COMPONENTS
