This thread is a continuation of my work with the PID Pavoni: positive-pressure-pid-pavoni-world-domination-begins-t3767.html
It is also a break from my second thread, http://www.home-barista.com/grinders/home-made-grinder-t3880.html
, while I finish the drawings.
In the PID Pavoni thread, I added a PID controller and brew-pressure gauge to my Europiccola. The main defect in that work was the need for an expansion tank in the water circuit. When the lever is raised, about 45ml is displaced from the head back into the boiler. This is, in turn, displaced back into the expansion tank, where hot and cold water may mix. In the robo-Pavoni design, the boiler has enough dead airspace to eliminate the expansion tank. Thus, no mixing and temperature instability.
The other design feature is stability. The Pavoni is not really up to the rigors of 9 bar. It flexes and tries to move. A second hand is nearly always used to hold the machine in place. This design seeks to allow 1-handed operation.
The design itself: take a Pavoni head, build an adaptor to connect to normal plumbing. Add a machined plate with water inlet (this is a plumb-in system), thermometer, and heater. Mount all in a brazed steel base.
This picture shows (left to right) the SSR, the Pavoni head with brew pressure gauge (this is a different head, the PID Pavoni is in service), the PID controller (from auberins.com, no affiliation), the chassis and boiler. Note that the colors are all messed up: the boiler is copper, the base plate brass, and the legs steel.
This picture shows the plate with mounting holes (4), recesses for brazing the boiler, and three threaded holes for water inlet (1/8npt), thermometer (1/8npt, PT100 RTD from auberins.com), and 1kw heater (1/2npt, mcmaster.com). The PID controller is 1/32--a real tiny one. Note how badly I suck at brazing. One of the purposes of the project is to sharpen my fabrication skills for the grinder project above and for building my dream machine from scratch.
This picture shows the adapter for mounting the Pavoni head on the 1.5" k-type copper pipe boiler. Note that the final through-hole will be drilled only after the adapter is soldered or brazed into place. The Pavoni head will screw into the adapter just like on a normal machine, but the adapter will be soldered onto the boiler just above the 2x1.5" flare, about 1/3 of the way up the boiler. The steel chassis is only partly brazed together--I ran out of oxygen over the long weekend and had to stop.
This picture shows the bottom of the plate and a nice view of the brew-pressure gauge.