If you have been shopping for a home espresso machine you have probably come across something called a 3-way solenoid valve. They are usually found on higher quality espresso machines but what do they do and why do you want one?
A three way solenoid valve basically controls the distribution of pressured water from the boiler into the grouphead during the brewing process. It also releases the pressurized water in the brewhead after making a shot and diverts it into the drip tray. This quick release of pressure in the brewhead means you can remove the portafilter right after brewing and you get a nice dry puck that is easily removed.
Without a 3-way solenoid valve you have to wait for the pressure to go down before removing the portafilter or or will get a spray of pressurized water shooting out and the puck of spent coffee grounds will be wet and more difficult to remove.
How Does A 3-Way Solenoid Valve Work?
When you first turn on your espresso machine the 3-way solenoid closes off the water exit from the boiler allowing the water to come up to brew temperature without leaking.
When you turn on the brew switch the valve opens a pathway from the boiler to the brewhead while closing the path to the drip tray. This allows the pump to force the heated water under pressure through the ground coffee in the brewhead and portafilter.
Once the water reaches the coffee grounds the pressure can increase depending on the fineness of the grind and any over pressure triggers a relief valve to open which redirects some of the water back into the water reservoir through a hose maintaining consistent brew pressure.
When your shot is done and you switch off the brew button the 3 way solenoid closes of the water pathway from the boiler and any access pressurized water from the brewhead is redirected into the drip tray.
The pressured water coming through the passage way from the brewhead back into the drip tray can carry some residual coffee grounds which can build up over time so its a good idea to occasionally back flush the brewhead to help keep it clean.
If you are looking to get an espresso machine that makes consistent cafe quality espresso at home you definitely want to get one that has a three way solenoid valve.