In the summer of 2008, Richard Penney designed a prototype boiler-neck pressure gauge adapter for Olympia Express espresso machines in response to requests from fellow home barista. This adapter mounts on the boiler neck in place of the OEM boiler cap, and is threaded to accept pressure gauge with a 1/4 NPT (National Pipe Thread) mount. In effect, it allow home users to calibrate the pressurestat on their espresso machine in much the same fashion as they were originally calibrated back in the factory. The adapter fits all Olympia-made machines: Cremina, Maximatic, Club, Coffex and the re-branded Pasquini Livietta.
The pressurestat on Olympia espresso machines is mounted under the back cover alongside the boiler. The pressurestat is adjustable via a knurled brass knob, which you can see here:
Turning this knurled knob toward the boiler increases the pressure (and water temperature) inside the boiler; turning it away from the boiler decreases the pressure within the boiler. (Note that very early Cremina models may have a different pressurestat orientation than shown here.)
In order to set the pressurestat to the factory recommended settings—or to your preferred setting—you need a way to mount a high accuracy pressure gauge on your machine. At the factory, this is accomplished by temporarily installing a pressure gauge on the boiler neck in place of the boiler cap. A technician will then refer to the manometer readings as the heating element cycles on and off, and adjust the pressurestat accordingly.
With the Richard Penney boiler-neck pressure gauge adapter, you can not only ensure that the pressurestat on your vintage espresso machine is set properly and verify its deadband, but you can also optimize the setting to your brewing style. Most people agree that something in the 0.7–1.2 bar range is ideal. However, people who want to steam milk efficiently may want their machine to cycle at the top of that range, whereas some espresso purists prefer to to set their machine at the lower end of this range.
To set the pressurestats on my machines, I purchased a high accuracy 30-psi liquid-filled pressure gauge from Valworx with a 1/4 NPT fitting for $45. This particular gauge is 2.5″ in diameter, has a stainless case and stainless sensing components, and is rated for 212°F media temperatures. (You can find 2% to 3% accurate pressure gauges for under $15, but they my not be rated for 212°F media temperatures.) For good measure, I also installed a perforated cooling tower between the pressure gauge and the Penney adapter. This cooling tower tempers the steam temperature before it comes into contact with the pressure gauge, which improves measurement accuracy and prevents damage due to high temperatures. (Note that you also have to protect the gauge against the vacuum that the boiler draws during cool down by venting the boiler as it cools.)
Armed with my high accuracy pressure gauge, I learned that the pressurestat on my 1991 Pasquini Livietta was set too high, whereas the one on my Cremina was set too low—in spite of the fact that both were calibrated using an inexpensive pressure gauge a few years ago. Now that they are calibrated properly, both machines are brewing better espresso.
If you are tired of brewing blind, check out the CoffeeBOS shop on Etsy to pick up your own adapter!