Passing March into April, on this super quiet weekend we decide to take the group head apart on the Bosco Spring lever espresso machine.
top part of group head is held down by 4 screws
Once they are undone then it can be lifted carefully straight upwards, perpendicular to ground plane.
Looking into the cylinder wall of group head with shower screen. It has a think coat of coffee oil.
You can see the construction of the spring piston. Brass plate at base coated with coffee oil, the O-rings with lubrican
Complete over view of top part: Spring with piston and lever. It is rather heavy but straight forward simplicity.
Correct us if we are wrong, normal pump machine dispersion plate gets worst than this in a day’s operation? It is perhaps down to the fact that water only travels downwards with spring lever machine, so not as much back flow of coffee comes through the shower screen reduce the amount of coffee oil accumulated here. Advantage of spring lever?
After a simple wipe with paper, dark mark is patination only.
Some heavy brass machining and plating here.
In case you are curious of how brew water gets to the brew chamber: it has 4 +/- 0.8mm holes towards the base of chamber. When you pull the lever it lifts the piston (the above piece) so water flows into the chamber as shown above.
The four jet rushes water horizontally into chamber and drops down to the shower screen, thus onto the coffee cake. The horizontal jet seems to make water drops softly onto coffee cake, and build up pressure as it fills (to the boiler pressure with dipper system or to pump pressure with HX system)
We have 2 group on our Bosco, while having one in stand by mode, the other can be cleaned by simply shuting down the flow restrictor at the back of the group outside the machine with a Philips screw driver.
Once clean and lubricated with food grade lubrican, the piston is simply dropped back vertically into chamber, tightened 4 screws, and back in action!
It is very basic and simple without the worries of waiting for service personel and down time, with simple care we assume everyone can do it! Just make sure the group is not too hot!