This week brought 3 machines for repair in the shop that demonstrate 3 distinct choices for home espresso machines.
The Double boiler was an older Marzocco GS3. This came in with a bad group solenoid and needing adjustment to the expansion valve. Otherwise it is in good shape. The 2 boilers provide steam from the large rear boiler and dedicated espresso from the front boiler. The front boiler is thermostatically controlled at the front mounted led pad. Brew temp is very consistent and predictable.
Heat Exchanger (HX) machines use a different approach to heating. They heat one large boiler for steam and run the espresso supply water through the very hot water in a tube. The conductive energy heats the espresso water. The result is that you do get copious steam on demand and lower temp water for espresso making. The water temp in the HX for espresso is not as predictable as in the double boiler. With an E61 group the water is siphoned & circulated back into the HX system which does provide some temp stability. The HX can be fairly easily mastered so that the operator can produce consistent & great shots. The other choice is Vibe or Rotary pump. The Rotary pump is quiet and extremely reliable. It produces excellent pressure stability. Most Rotary units require plumb-in water. The vibe pumps work well, though they are noisy and have a generally shorter life (though they can last a decade or longer).
These HX units are both Quick Mill units. The Vetrano (LEFT) is a Rotary plumb-in model that had some scale problems throughout the hydraulics. The Andreja Premium (RIGHT) is a Vibe pump model with pour over water tank. This one had a little leak.
