What can make it seemingly more complicated is that there are even more variations of the espresso machine. They all have additional sensors, valves, pumps, and grinders. They generally vary in their additional parts and subsequently, their overall efficacy in terms of automaticity.
The first variation of the espresso machine is the semi-automatic espresso machine. With the espresso machine, water is brought into the machine using a pump, with the pressure of the brewing mechanism being dissipated using a 3-way valve.
The next variation of espresso machine is the automatic espresso machine. With this variation of the espresso machine, there is an addition of a flow meter which lined along with the group head. With this, when a certain amount of water, which has been pre-set, flows through the flow meter, the pump of the espresso machine switches off automatically and consequently, the pressure of the brewing mechanism is also dissipated over a 3-way solenoid type of valve.
Still another variation of the espresso machine would be the super-automatic variation of espresso machine. It works by automatically subjecting the coffee to a process involving grinding, tamping and extracting. It's very convenient in that the operator only has to fill up the bean hopper with coffee beans and either pour water into the reservoir or connect the espresso machine to a water line. What's more, certain models of this variation of espresso machine also have a device that automatically tops the espresso off with a frothy milk later and even an implement for dispensing.
Other such types of espresso machines include the air-pressure driven type and the stove top type. The first one, the air-pressure driven espresso machine, is hand-held and as such, can be used to make excellent crema-topped espresso.
Lastly, there is the stove top espresso machine which makes espresso whose extraction ratio nearly equals that of a conventional machine.