How A Washer Pressure Switch Works

A clothes washing machine pressure switch, is also called the water level control switch, because it controls the amount of water that enters the washer during fill. Molded into the side of the washer outer tub is a plastic chamber with a small outlet at the top where a small flexible tube mounts.

When the washing machine fills with water, the air within this chamber wants to exit out the top where the small tube is attached. The tube is connected to the back of the washing machine pressure switch. As the washer fills with water, it forces air out of the chamber on the side of the washer tub, up the tube to the pressure switch. The amount of pressure in the tube is determined by the amount of water in the washing machine tub.

The water level control switch has an airtight diaphragm that senses the pressure in the tube and applies pressure to a set of switch contacts. The switch contacts are in series with the washer fill valve and regulate the amount of water that enters the tub.

Some water level control switches are not adjustable and the amount of water that goes into the washing machine is determined by the engineers at the factory. In most cases however, a water level control switch is adjustable to allow the user to wash smaller loads of laundry. Washing machine manufactures use pressure switches instead of a timing mechanism, because water pressure can vary widely.