Isolator for La Pavoniby Simone Forgia, Claudio Santoro
Among the many lever machines for domestic use in the market, the best known and those with a greater number of enthusiasts are certainly the La Pavoni. If you too are one of the owners of these machines, you will surely know that their biggest flaw is the fact that they overheat in no time. This problem, even though over the years the manufacturing company has tried to alleviate it in various ways such as with the introduction of a Teflon sleeve; the transition from steam to water heating and the increase in mass of the grouphead; is still highly relevant today. With the desire to find a definitive solution to this problem, Bong Juachon, John Michael Hauck and Tudor Si Tabita Petriman, a group of well-known enthusiasts in the sector, have developed an isolator that can be easily installed on most models. In this article we will therefore see how they did it.
Bong Juachon, the inventor of this accessory, told us how until now it was not possible to make more espressos one after the other without using boring and unprofessional cooling methods such as the use of a bowl of cold water to be placed under the shower screen, wrapping the grouphead with a cold cloth or similar techniques. Moreover, the second generation models, being steam heated, cannot be left on and extract the coffee when you want because the grouphead stabilises at a temperature higher than 100°C. In the past, solutions like a heat sink to be placed on the brewing unit had already been developed, but in addition to being very aesthetically invasive, they were not always perfectly compatible due to slight differences in size between the groups of each machine. Bong's objective was therefore to design something that would replace the existing heat sinks and also eliminate steam heating for the older models. The requirements were that it should be something easy to install, long-lasting, maintenance-free and with a low aesthetic impact.
Studies carried out by analysing the weights of the various groupheads generations and by heating them individually showed that, if separated from the heat source, they were able to independently cool themselves enough. Starting from this principle, Bong then made a first model of an isolator to be placed between the unit and the boiler with clay and then presented his idea to John. Afterwards a CAD drawing of his idea was made and with a 3D printer the first prototypes were produced.
John told us that before arriving at the final version he made 11 drawings and initially there were two versions, one for the second generation models and another for the third and fourth generation, but then they discovered that the latter could be used for all three models and so only that one was kept. In fact, as can be seen from the image below, mounting a third/fourth generation isolator on a second generation grouphead leaves a few tiny empty spaces but from the tests carried out they did not create any kind of problem.
Rendering of the isolator mounted on a second generation grouphead
Once the final shape was defined and verified that everything was fine, Tudor took care of the production. First of all, they had to choose the material to use and they knew that they would have to rely on someone from outside because a CNC machine was essential. They also knew that the isolator could not be made of stainless steel or chrome-plated brass because it had to be a low conductive material. Tudor remembered some products he had made of POM (polyoxymethylene) and discovered that it had the perfect combination of elements for what they needed. Once the material for the isolator had been chosen, he also took the opportunity to make the screws in stainless steel in substitution of the original iron ones, as they had to be longer due to the increased distance from the grouphead to the boiler.
After a few months, Bong received the final version of his creation and proceeded with the tests to check that everything worked perfectly. First, he tested the performance by checking the temperatures both after a single espresso and after several consecutive extractions. He quickly realised that the small isolators for the screws broke easily and also had no effect on the heat transfer, so he decided to eliminate them and use simple washers instead; everything else worked as expected. Regarding durability, on the other hand, several tests were carried out with extractions at 12 bar (equivalent to 25 kg. of force on the lever) and a 3 mm deflection was measured. This deflection however, was caused by the increased distance of the unit from the boiler and not by the compression of the material itself. The heat resistance, on the other hand, was tested by heating the isolator, which began to deform only after 500°C, meeting the requirements even beyond their expectations. In fact, according to Tudor, the polyoxymethylene had to have a melting point of around 300°C and after contacting the factory he discovered that the isolators had actually been made of Teflon and not as agreed, luckily however, all tests were passed successfully. The only drawbacks with this accessory proved to be a possible reduction in the volume of the espressos and a sometimes "spongy" lever due to the presence of air bubbles. These problems, however, mainly concern the second-generation models and can often occur even without the installation of the isolator. Nevertheless, these issues can be minimised with the right techniques of purging the false pressure and additionally Bong has informed us that he is also working on another mod to definitively say goodbye to these problems.
Following the testing phase and the announcement of this project to the general public, we had the opportunity to personally test the effectiveness of this new isolator on a third generation La Pavoni. From our experience, the biggest inconvenience we encountered was that we had to reverse the orientation of the isolator because on one side it was slightly thicker than on the other and therefore the group was not perfectly level. For everything else we liked it very much; the group adheres better to the boiler than by putting metal against metal as it originally did and the material has a good tactile feeling. Aesthetically speaking, it is really little disturbing, we would only have liked if, in addition to being black, it had also been lacquered like the boiler cap or the lever and portafilter handles. Temperatures have actually dropped and we have not had any more overheating problems, on the contrary they have often proved to be too low for a correct extraction and the use of a thermometer is therefore indispensable. The drastic drop in temperatures, however, has given us the opportunity to raise the boiler pressure from 0.7-0.8 to 1.1-1.2 bar, gaining a lot more steam power for milk frothing and bringing the stabilisation temperature back to an optimal value. We are therefore very satisfied with the result and are grateful to Bong, John and Tudor for this accessory which, from now on, will be difficult to live without.
Final version of the isolator