If you have a budget semi-automatic espresso machine, you pull a shot and remove the portafilter you may notice it’s like the machine sneezed out a messy, muddy mix of coffee water and grinds. Maybe you’ve seen how easily a freshly brewed but dry coffee puck knocks out of a portafilter on other machines and you’re wondering why you’re stuck bashing your filter over and over. No matter what you do and what you try, it always comes out a wet sloppy mess. While this could be due to needing to clean your machine's brew head, the most likely cause of your machine's problems is simply that it does not have a three-way solenoid valve.
Most of the more basic models of Espresso Machines tend use the aptly named "Group Valve," a spring-loaded rubber check valve which plugs the group head, which is forced open when the pump is switched on, while the higher-end models typically utilize a flow-control valve. In Commercial and Prosumer Espresso machines, manufacturers frequently use an E-61 Brew Heads to control the brew pressure. As these brew groups can often cost more than an entry-level espresso machine ever would, manufacturers have found ways of packaging this same functionality into a smaller hydro-electric solenoid valve. While this sounds like space-age technobabble, this style of brew valve has been used on both home and commercial Espresso Machines for well over 40 years. They're largely standard equipment on higher-end home machines, but almost never found on the entry-level models.
Unlike a simple passive Group Valve, the Three-Way Solenoid Valve is electrically actuated, typically by way of an electromagnet pulling or pushing a metal piston up or down a tube. This allows the valve to selectively allow water to pass between two of its three connections, blocking flow in and out of the third. Most commonly, this produces the following conditions
When espresso machines equipped with a Three-Way Valve are sitting idle or unpowered, this valve sits in the first state; this allows water and air and water to flow freely between the brew head and the drip tray while keeping water neatly contained in the boiler. This keeps the brew head dry.
Toggling the brew button feeds power through the valve's electromagnet, switching it into its operational state; The drain port is sealed shut by the valve's piston. Generally speaking, the pump is powered on as well to force water into the boiler although some manufacturers have added a delay circuit to this process to allow for pre-infusion to occur.
When the shot is finished and the brew button is switched off, the valve returns to the closed position, resealing the boiler and opening the drain port. As the water between the boiler and the brew head ishighly pressurized (roughly 10 bar or 145psi!), it shoots out of the now-opened drain vent into the drip tray. But this water also has inertia and some suction! When it leaves, it pulls with it most of the water that stuck behind.
Beyond less mess and dryer coffee pucks these valves guarantee consistent flow from the boiler through the group head, make back-flushing possible, help stop brew group drips when steaming, and reduce stress on other internal components. So, if you’re looking to purchase a new machine or upgrade consider a machine with a three way solenoid valve. It’s a feature you will definitely appreciate!