Typically, washing machine pressure switches have a large sensing diaphragm that's about 60mm or so in diameter and three quick-connect male terminals. One connection is common, while the others are for normally open (NO) and normally closed (NC) connections. A set-point adjustment mechanism is built in (it's directly controlled by the 'water level' knob) and the switch opens and closes with audible clicks.
Detecting vehicle movement using a washing machine pressure switch. The switch would be triggered by air pressure when the vehicle crosses a hose. Just remember to plug the end of the hose that's not connected to the switch! So there are four applications but there are lots more. It's certainly worth salvaging these very sensitive switches!