The isolated steam boiler is located at the rear of the machine and has a total capacity of 10.5 litres. (Duette and Triplette, about 75% filled with water). An electronic temperature controller gets its information through a probe located above the water level and activates the heating element via 3 solid state relays. The heating element provides a powerful total of 4.800 Watt (normal) or 6.000 Watt (high power). This is divided over 3 heating spirals mounted on one flange. There are no moving parts in the complete heating system. Each heating spiral is connected to a control light at the bottom of machine. Combined with the machine`s display this enables for a quick visual control to check from the outside of the machine whether all parts in the heating system function as intended.

The steam boiler is made in stainless steel 316L, which is more resistant against aggressive water than stainless steel 304 and has a long life expectancy in an espresso machine.
The controller offers a programmable ECO mode, lowering the temperature of the steam boiler to about 70 °C during longer periods of idle or overnight.

Steaming

As standard, the steam valves have a turning knob. From closed to fully open requires less than half a turn. As an option, the mechanical steam valves at left and/or right can be activated with a toggle type lever or even by foot activation: an air bulb on the floor activates an electrical switch inside the machine which in turn activates a solenoid valve with a large passage. This solenoid valve is either fully open or fully closed. The steam flow/power can be decreased by the use of the original steam valve to match the size of the pitcher. When adjusted, the foot-activated valve opens always immediately at the preferred flow, enabling speedy steaming.

Hot water dispensing

Hot water can be dispensed in two manners:
1. Pressing the push button switch results in dispensing mixed water for an adjustable number of seconds. The switch activates two solenoid valves and the pump simultaneously: hot water from the steam boiler passes through one valve, the other valve supplies cold water at pump pressure. Cold water addition is restricted by an adjustable needle valve in the manifold such that the temperature of the water dispensed can be adjusted between approximately 60 and 100 °C. This mix of hot and a bit of cold water results in a steady, non-spattering stream from the hot water spout and can be adjusted to be excellent for making Americanos or green tea.
2. When the toggle switch is pressed downwards only the hot water valve opens which results in water flowing directly from the steam boiler to the spout. Releasing the toggle switch will stop the flow immediately. At the moment the toggle switch is pressed down the temperature of the water dispensed quickly rises to boiling point and will start to sputter. The boiling water is excellent for making black tea.

Steam boiler fill

Filling of the steam boiler is prohibited while a group is active. This setting eliminates flow-rate decrease and subsequent variations in brew-pressure during the infusion phase. The disadvantage of this setting is that the steam boiler may never start to top-up in a high-volume location where at least one of the groups is active for uninterrupted periods of time while also dispensing hot water and, with minor impact, steaming milk.  For extremely high-volume locations the setting can be changed such that the steam boiler starts filling as soon as the water level drops below operational.

The Slim Jim`s lever group is a fully newly developed system. The first and foremost improvement is the elimination of the danger of the spring-loaded lever accidentally jumping upwards and hitting a part of the barista`s body. To lock the lever, it is no longer necessary to pull it all the way down. With the new lock, the lever remains at a much higher position. This means the lever always moves away from, not towards, the barista. When the lever is pulled, water immediately flows up into the brewing chamber under the piston and down onto the coffee puck . Total down-travel of the piston will result in approximately 60 ml of water being pushed through the coffee-bed, enough for two single espressos. Un-locking only requires pressing a knob with ones thumb.

The moment the lever is pulled, its shot-timer starts counting. Each individual group has a large 3-digit display that functions as a shot timer during brew (and shortly thereafter) before changing to display the group temperature. The actual pressure at the puck is displayed at the gauge, showing infusion- and afterwards the diminishing extraction pressures. Optical feedback is also provided by the movement of the big levers, offering the classic theatrical true espresso-drama.

Flushing the group screen is very easy, just hit the small lever next to the group. The time water will run through the screen is adjustable. This same small lever can be used to stop an extraction in progress at any given moment. The large lever will leisurely move to its original rest position and the remaining water in the cylinder will disappear through the machine`s discharge system. No waiting or sneezing.

The piston V-ring can be easily replaced, the piston can be taken apart by undoing one centre bolt.
The lower part of the piston is made from PEEK, which is heat neutral as to not disturb the temperature of the water and reduces fouling. The cylinder sits inside the saturated group and is completely surrounded by the water that will be used to brew.

The group screen is held in place by the group gasket, not a screw blocking part of the surface. To pull out the gasket with screen for controlling, cleaning or replacing, a special tool is provided with each machine in the Barista Kit. The gasket ring sits against the group bottom that has a small downward ridge. This ridge is pushed into the gasket each time the filter holder is locked into the group, thus providing excellent sealing. The slight moving up of the gasket ring, because of the flexibility of the material and the ridge, provides an ergonomically correct, soft comfortable feel for the barista. Full sealing is achieved without having to pull the filter holder firmly. The group gasket is made in a heat resistant material that does not harden and go brittle but remains flexible.
The group screen’s circumference is pushed against the bottom of the group making the screen robust. Together with the gasket surrounding the screen, it is impossible for coffee grounds to ever reach the insides of the group. The supporting horizontal base of the screen is extra-thick to resist deformation. This base is perforated and covered with a stainless-steel membrane, not a woven mesh. This membrane provides a very even dispersion of the water during extraction. It also strongly filters the water sucked up when the pressure is discharged at the end of the shot.

Our approach is to create an exact water temperature and then make sure it does not lose any heat on its way to the coffee puck.

The coffee boiler is fed with preheated water from the heat-exchanger in the steam boiler. All parts are stainless steel (316L where in contact with water). Stainless has a roughly ten times less heat transferring capability, compared to brass, so heat is not lost to surrounding metal.

Brew-water pick-up is at the highest location within the group. Air within the coffee boiler is thus relieved every time you activate the group valve; it has no chance to accumulate.

Law of nature demands that a thermo-syphon flow will commence when changes in water temperature are present. Water heated by the heating element will rise.  In the coffee system the warmer water will flow up to the very end of the group head where it will cool slightly and travel downwards again to the bottom of the boiler. The boiler and group are specifically designed to offer ample space allowing the warmer and cooler flows to pass each other. The “sweet spot”, the most stable temperature in this system, will develop at the highest point, right underneath the group top. The pick-up tube is positioned exactly in that sweet spot. During brewing, the water never leaves the coffee water boiler/group on its path towards the coffee.
Coffee boiler and group are one large piece, temperature is PID controlled. The Idrocompresso’s cylinder with piston sits inside the group and is fully surrounded by a generous amount of the very same water that will flow into the chamber when pulling the lever. The bottom of the piston is made in PEEK. This is fully heat neutral, so the water does not lose any of its heat and the piston does not become dirty.

Infusion pressure can be adjusted by the pressure reducer that comes with the machine.
If there is any doubt regarding the reliability of the line pressure of the building, we recommend to order the optional pump. People usually are unaware of the large fluctuations happening in any water mains, because of toilets flushed, dish washing machines, ice-machines, washing hands, etc. These fluctuations do have an effect on the infusion phase and therefore may deliver a different result in the cup. The optional pump together with the reducer allows for a larger range of infusion pressures and will increase consistency between shots .

Spring pressure can be adjusted by turning the disc on top of the spring. With the old classic machines one was not able to notice, but two or three fully mechanical spring-loaded systems will very likely differ slightly in pressure. The main reason to add this feature is to be able to calibrate the groups to have them generate identical extraction pressures. A special tool to turn the disc comfortably comes with the machine. One may also experiment with different extraction pressures, adjustment is possible from approx. 8 to 11 bar starting pressure.

The steam boiler has two probes to monitor the level of the water inside. The lower probe ends just above the heating element. When the machine is being filled and fired for the first time, the brain only switches on all heating elements, when the lower probe detects water. During filling, the coffee boilers fill quicker than the steam boiler because filling starts immediately when the water connection is opened and the coffee boilers are smaller. When the lower probe in the steam boiler detects water the elements inside the coffee boilers are already submerged. This system ensures the elements cannot be turned on while not being cooled by surrounding water.
If the steam boiler level would ever fall under the safety probes tip, the led under each flush lever starts blinking as an alarm.

If the steam boiler fill solenoid remains open for longer than 2 minutes, the machine will disconnect the steam boiler heating elements and stop filling. The machine can be re-set by switching it off and on again to resume further filling.

When one of the group solenoids is activated by the lever continuously for longer than 3 minutes, it will close automatically.
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A moment after the higher probe contacts water the fill solenoid and pump are de-activated. Filling starts as soon as the water level drops and the higher probe no longer detects water, provided that no group is active at that time (or fill-setting is adjusted to “fill during brew possible”).

All temperature settings have a restricted upper temperature programmed. When this temperature is reached no more signal to the solid-state relay is sent. Each boiler is equipped with a temperature cut-out switch. When this switch detects too high a temperature, it will disconnect power to the element.
The steam boiler is equipped with an over-pressure relief valve. The coffee system, including the heat-exchanger, is equipped with an expansion valve.
Each group solenoid valve may act as a second expansion valve, rated at 15 bar, in the event the original expansion valve would fail.