WHAT IS A PRESSURESTAT / P-STAT?
A pressurestat is a mechanical device that uses the temperature to push on a rubber diaphragm and open a switch. In practice, this means that the expanding air from the heated boiler ‘pushes’ open a switch, turning off the heating element and allowing the system to begin to cool. The pressurestat can be adjusted to open at different pressures depending on the machine in question but is typically set to open somewhere around 1 to 1.2 bar.
Now once the machine begins to cool via the natural process of radiation, losing heat to the surrounding environment. This continues until the pressure on the rubber diaphragm is no longer enough to hold open the switch. The switch closes, completing the circuit and turning on the heating element. Now the espresso machine heats up again until the temperature can again ‘push’ open the switch.