Espresso machines, to scale

Single boiler 100 machines

One boiler does both jobs, so the machine brews, then heats up to steam, then cools down to brew again.

1. 1 Casing The shell and cup tray; lift it and the whole system is three parts and a pump. 100 machines
2. 2 Boiler One small tank with one element, switched between brew temperature and steam temperature. 100 single-boiler machines
3. 3 Group head Where the portafilter locks in and hot water meets the coffee. 100 machines
4. 4 Pump Pushes water through the coffee at brewing pressure, about 9 bar. 17 vibratory · 1 rotary
5. 5 PID controller Holds the boiler at a set temperature instead of letting a thermostat swing it. 23 with PID
6. 6 Reservoir The water supply: a tank you fill, a mains line, or a choice of both. 68 reservoir · 1 plumbed · 2 both

Heat exchanger 68 machines

A big steam boiler with a tube running through it: fresh brew water is flash-heated on its way to the group, so it steams and brews at once.

1. 1 Casing The shell and cup tray; under it, one large boiler sits across the machine. 68 machines
2. 2 Steam boiler Held well above brewing temperature, so it always has steam ready. 68 heat-exchanger machines
3. 3 Heat-exchange tube A pipe through the steam boiler; brew water crosses it in seconds and leaves near brewing temperature. 68 machines
4. 4 Group head Often an E61: a thermosiphon loop circulates water from the tube to keep this heavy brass group hot. 68 E61 groups and others
5. 5 Pump Vibratory pumps are compact and loud; rotary pumps are quieter and can run from the mains. 19 vibratory · 13 rotary
6. 6 Water supply A tank you fill, a mains line, or a choice of both. 22 reservoir · 20 plumbed · 13 both

Dual boiler 83 machines

Two boilers, two jobs: a brew boiler held at brewing temperature and a steam boiler held hot, each with its own control.

1. 1 Casing The shell and cup tray; two boilers side by side sit under it. 83 machines
2. 2 Steam boiler The larger tank, run hot for steam and hot water. 83 dual-boiler machines
3. 3 Brew boiler A smaller tank feeding the group, held at the brewing temperature you set. 83 machines
4. 4 Group head Fed straight from the brew boiler, often saturated: bolted to it and full of its water. 83 machines
5. 5 Pump Most dual boilers use a rotary pump, quiet and fit for a mains line. 6 vibratory · 27 rotary
6. 6 PID controllers One per boiler, so brew and steam temperatures are set independently. 54 with PID

Thermoblock 108 machines

No standing boiler: water is heated on demand as it runs through a hot metal block, so the machine is ready in a minute or two.

1. 1 Casing The shell and cup tray; most thermoblock machines are compact home designs. 108 machines
2. 2 Thermoblock A heated metal block with a water channel cast through it; water leaves it hot without being stored. 108 thermoblock machines · 8 thermocoil
3. 3 Pump Usually a vibratory pump drawing from the tank and pushing through the block. 24 vibratory · 13 rotary
4. 4 Group head Often a light group with its own small heater, since no hot boiler water flows round it. 108 machines
5. 5 Temperature control A PID or a thermostat governs the block; the better ones hold within a degree. 41 with PID
6. 6 Reservoir Nearly always a tank you fill by hand. 86 reservoir · 4 plumbed · 9 both

Multi-boiler 107 machines

The café bar: one large steam boiler plus an independent brew boiler for every group, each group at its own temperature.

1. 1 Casing A wide commercial chassis, two to four groups across. 48 two-group · 35 three-group · 10 four-group
2. 2 Steam boiler Shared by both wands and the hot-water tap; large enough for a rush. 107 multi-boiler machines
3. 3 Group boilers One small brew boiler per group, so two groups can brew two coffees at two temperatures. 107 machines
4. 4 Group heads Each bolted to its own boiler. 107 machines
5. 5 Rotary pump Mains-fed and usually mounted under the counter or in the base. 6 rotary · 43 plumbed
6. 6 PID per boiler Independent control of every boiler from the front display. 45 with PID

Spring lever 14 machines

No pump at all: pulling the lever compresses a spring, and the spring pushes a piston that presses water through the coffee.

1. 1 Casing The shell; the lever and group stand proud of it. 14 machines
2. 2 Boiler Usually a single or heat-exchanger boiler feeding hot water to the group. 14 spring-lever machines
3. 3 Spring and piston The spring sets the pressure curve: it starts near 9 bar and falls as the shot runs. 14 machines
4. 4 Lever Pulled down it loads the spring and lets water into the chamber; released, it rises as the shot pours. 14 machines
5. 5 Group head A tall brass group: the piston chamber sits above the portafilter. 14 machines