A solenoid does work on a really simple principle, magnetism. You have 2 types of solenoid valves, a normally open and a normally closed. In espresso machine you mainly find normally closed, seen it is a pressurized system. But with a normally closed solenoid valve a spring pushes a plunger against a valve seat, which closes off the valve. When the coil of the solenoid valve is energized the piston is also lifted. When the power is taken off the valve, the valve closes automatically
On espresso machines there are in total 4 brands which make solenoid valves, which areParker,Asco(sirai), Lucifer and ODE. The valves of Parker and Lucifer do look similar, but that has to do because they are part of the same company.
There are various types of solenoid valves available, in various configurations. They are defined into a 2 way solenoid valve and a 3 way solenoid valve. The solenoid valves come in 2 versions, one which has a flat flange and the other one is a threaded version.
A other important feature is also what kind of Voltage they use, seen there are some brands which use 24V DC solenoid valve coils. But the most common ones still remain 220/230V AC.
The brewing group solenoid valve is used on basically every modern espresso machine, except for the E61 manual brewing groups. These solenoid valves are 3 way valves, in most cases with a flange connection but also with threaded fittings. In this case you see that the nozzle inside the solenoid valve can change from brand to brand, but the main thing is that they are the smallest in diameter of all solenoid valves used on coffee machines.
Which type of solenoid valve used on the water inlet valves does depend on how they are mounted. Seen you have espresso machine brands which use valve blocks, where a flange solenoid valve can be mounted to. But you have also ones which are installed against tubing, for that the threaded ones are used. The nozzle on these valves is normally quite big, which makes sense seen you are able to fill the boiler faster.
A solenoid valve can also be used on water and steam valves, this does mainly depend on the brand. Seen a lot of manufacturers still use a manual operated valve, which is easier to control. This can be especially handy when you are using your milk pitcher to froth up milk.
The most common one is a 2 way valve, used on for instance a water outlet. In the case of frothing up milk, you can find it on automatic milk frother or on temperature controlled milk frothers. Such as with La Cimbali Turbosteam.
