Modern Day Lever Espresso Machines
Modern day lever piston espresso machines use three different water supply brew systems and two different piston power designs.
Spring assist and manual lever.
There are two different piston powered systems. The spring assisted lever uses a coiled spring to regulate the extraction pressure of the piston. When the lever is depressed, the piston is cocked. You simply release the lever and the spring delivers the needed pressure for your extraction. The Elektra Microcasa a Leva is one of the most popular spring assisted lever machines.
The second power system is, well, you. The full manual lever relies on the operator to supply the needed pressure to the lever for extraction. These systems require much more time to learn. The operator has to apply steady pressure to the lever during the extraction. The difficult part is training yourself to apply the same amount of pressure for every shot. The La Pavoni Europiccola and the Gaggia Achille are two of these full manual systems.
Water delivery methods.
The most common type of water delivery is the steam pressure driven. In these systems, a single large boiler supplies both brew water and steam power. The machine relies on steam pressure to force water up a brew group supply line and into the group piston chamber. In order for that to work, the water in the boiler must be hot enough to generate steam. Most of these machines operate around .8 bar, or roughly 250F.
Hydraulics diagram from the Olympia Cremina manual
Since the brew water is well beyond the target brew range (195-205F) the water must be cooled prior to the extraction. On these machines, the group acts as a heat sink, leaching heat from the brew water as it enters the piston chamber. This is not a good way to regulate the brew water. Every time you pull a shot, the group absorbs more heat. Most of these will only allow for 3-4 shots before they overheat. Extended idle time also results in an overheated group because the grouphead is directly attached to the boiler. Common machines in this category include the La Pavoni Europiccola, Olympia Cremina and Elektra Microcasa a Leva.
Gravity feed (open boiler) water delivery systems can avoid these overheating problems. A gravity system uses a boiler placed above the grouphead. When the lever is lifted, gravity pulls the water down into the group piston. Because steam pressure is not required to move the water, these systems can operate at much lower temperatures. The water in the boiler can be kept at or slightly above the target percolation temperature. The disadvantage of these systems are two fold:
- Because the boiler is located above the grouphead, most of the machines mass is located high off the counter. That tends to make them a bit top-heavy and prone to tipping over if the base is not sufficiently large.
- These systems generally have one boiler, the brew boiler. Because these are run at brew temperatures, there is no steam for creating milk drinks.
The La Peppina and Mini Gaggia/Minimoka are popular gravity fed open boiler machines.
Heat exchanger is the third water delivery method. A heat exchanger uses a high pressure (usually 1 bar and up) boiler with a brew water supply line running through it. Most commercial lever machines use a large steam boiler with one heat exchanger per group supplying brew water. As the cold water passes through the heat exchanger tube it is flash heated to brew temperature. The resulting brew water can be adjusted up and down in temperature by the dwell time. The longer the water sits in the heat exchanger, the hotter it gets. The majority of commercial machines use a heat exchanger system. Below is a heat exchanger hydraulics diagram for a pump-driven espresso machine:
For more on how a heat exchanger works see Espresso Machines 202
Commercial lever heat exchanger machines are plumbed into a water supply. The lever machine's heat exchanger uses the mains water pressure to force the brew water through the heat exchanger and into the brew group. This system gives the barista much more control over the brew water temperature. In the event the grouphead overheats, the barista can cool the unit by pulling a long flush of cool water through the group. These machines are intended for all day use. Our Gaggia Achille lever uses this same principle to overcome the inherent overheating problems of the steam pressure driven systems while still providing steam for milk based drinks.
So the question is, can the Gaggia Achille run all day like a commercial heat exchanger without overheating? Over the next few days, I plan to answer that question.
