Bezzera MITICA TOP Espresso Coffee Machine (2.0L HX Boiler, PID, Rotatary Pump, Plumbable)

Coffee Espresso Machine Terminology Explained

PID VS Pressurestat

A PID has two additional features over the pressurestat.

1. More precise control of the temperature
2. Narrows the deadband of temperature fluctuation

Here is an example of PID versus Pressurestat.

A pressurestat is a mechanical device that uses the temperature to push on a rubber diaphragm and open a switch. In practice, this means that the expanding air from the heated boiler ‘pushes’ open a switch, turning off the heating element and allowing the system to begin to cool.

The PID system solves for the cyclical heating and cooling a pressurestat causes by using mathematical algorithms to predict and counteract the thermal inertia the espresso machine experiences. If you run the hot water tap, the PID system will know that it will be taking in cool water from the fill valve and will begin to micro-fire the heating element, cycling it on and off hundreds of times a second, in order to heat the machine before it has had a chance to cool. The PID system uses a logic panel to identify variation from a set point. This means that when an espresso machine is heating up and approaching the target temperature, the heating element will ‘reduce power’ (increase the “off” time and decrease the “on” time) to less than full power so that it does not over shoot the target temperature. In a perfect world with a perfect espresso machine, this would mean that the temperature remains perfectly constant and you get the right temperature every time. Unfortunately, due to restrictions of the real world, we still see some slight variation from events like boiler filling or loss of steam pressure given that the system cannot always flash-heat water as quickly as it would like (due to heating element wattage restriction). These events can cause dips in temperature, but they are far less pronounced than they are in a pressurestat system.

Dual Boiler / Vs Single Heat Exchanger

Vibration vs Rotary Pump

A rotary vane pump will ramp up to 9 bar quickly and smoothly, whereas the vibration pump will build pressure through a pulsing action that takes a few more seconds. Some will argue this slower build up as as advantage to avoid channeling. others argue the rotary pump provides a more linear build up that promotes consistency. They are different, you can get amazing espresso using either type of pump.

On the cost side of things, rotary pumps are more expensive and if used with high quality water will last seemingly forever. Vibration pumps can fail in as short as one year or can last for decades (water quality really matters here), but they are cheap and easy to replace.

Rotary pumps sound smoother and are a little bit quieter as they don't vibrate and rattle around as much - but which sounds better is sometimes subjective to the individual.