In designs that use pressure, the water changes the air pressure trapped in a chamber and tube. The sensor turns that change into a signal that the control interprets as level.
From water to signal
As the water rises in the area connected to the chamber, the pressure of the air linked to the sensor changes. A mechanical pressure switch can change contacts under set conditions; an electronic sensor provides a signal that is interpreted according to its calibration. They are not interchangeable devices.
The control uses that information to limit filling and coordinate operations that depend on the wash bath. In a design with a heater, the signal can take part in the conditions that allow heating. The release of stages and protections depends on the specific logic.
Level, load, and flow are not the same
- Level: state of the wash bath in the measurement system.
- Flow: amount of water that passes per unit of time when measured.
- Load: estimate of laundry or the mechanical and hydraulic response of the assembly.
An absorbent load may require additional water even if the target level does not change. The cycle adaptation combines information only when the appliance has those functions.
What you cannot infer by looking at the drum
Water located below the visible holes or absorbed in the laundry can be part of the wash bath. For that reason, a glass with no visible water does not by itself prove a lack of filling.
An overflow detector, if present, can add independent protection. To investigate inconsistent signals, you need system level diagnostics, without blowing into tubes or adjusting sensors as a universal home test.
Interpret the signal within its complete circuit: chamber, tube, sensor, and control, not as an isolated reading from the glass.