The Basic Layout Of an Espresso machine with a 3-Way Valve
Here we see a diagrammatic layout of an espresso machine that is equipped with a 3-way valve.*1 The 3-Way valve controls the flow of water from the boiler to the brewhead, and from the brewhead into the drip tray.*2 It is called "3-way" because there are three water paths connected to the valve:
- Boiler to 3-Way
- Brewhead to 3-way
- 3-Way to drip tray
In this image the machine is "at rest." The red square between the boiler and the 3-way valve represents the gate controlled by the 3-way valve. The valve works by applying an electromagnetic field to a metal plunger inside the valve. When power is applied it pulls the valve open. When no power is applied (the valve is "at rest") the plunger blocks the passage as shown above.
As shown here, the brew switch is in the off position and the 3-way is not energized. It blocks the flow of water, essentially keeping the boiler closed at its exit. Click "NEXT" or "BACK" at the bottom of each page to move through the presentation
*1 - Note that all these illustrations are designed to show how an espresso machine operates and are not an actual representation of how the parts actually interface or to indicate their actual position in the machine.
*2 - WARNING - There are some machines that, for some reason, are designed with the 3-way valve between the pump and the boiler— not in the brewhead as shown above (one example may be some home machines manufactured by Gaggia). If you suspect that you machine is so designed, refer to your owner's manual before attempting to backflush.