Temperature and Pressure

The reason that the temperature and pressure are being discussed together is because La Pavoni are single boiler machines.   The boiler pressure is solely a function of the temperature of the water in the closed system.  When you take a pressure reading as described below, remember this is the pressure generated by the boiler that we’re talking about and not the pressure at the group head.  The final pressure at the group head is much greater due to the pressure exerted by the piston when you push down on the lever.

My machine came with the brew temperature set improperly so I HAD to mess with the device.  It was such that the water wouldn’t go above lukewarm.  That being said, there is likely probably nothing wrong with your temperature setting so if at all possible, don’t mess with thermostat.  There is a definite risk of burning yourself badly or even electrocuting yourself so be advised that I’m not advocating that you play with the internal electrical components.  If the temperature is set properly, the pressure gauge of the La Pavoni Profession should peak out between .7 to .8 bar.  Let the machine heat up, let some steam out of the steaming wand for 5-10 seconds, wait for the pressure to build up again, and then take a reading. 

Although suggestions for the standard temperature varies from 89 to 95C (192 to 203C), mine is set to 91C or 195F as per Dr. Illy, with the boiler 3/4 full. 

Remember, I’m not suggesting that you alter the factory settings.  This is just an account of what I had to do… 

In the base of my La Pavoni Professional, there is an adjustable pressure limiter (which I initially thought was a thermostat).  The partial  pressure of water vapour in the boiler chamber increases proportionally to the increase in temperature of the water.  We use this simple fact to cut off the heating element when the set temperature/pressure is reached.  First I filled the boiler until it was 3/4 full with water.  To get to the innards, I removed the screw underneath the plastic catch tray that holds on the bottom cover.  Inside, I found a brass screw on the right-hand side of the machine which is held in place with a small setscrew.  I loosened the setscrew and turned the adjusting screw a little at a time while checking where the heating elements cuts off.  This can be accomplished by listening to the sound of the water being heated and noting where it cuts out.  Turning it left lowered the cut off point, and turning it right raised it.  I believe that the configuration is different in newer machines (see Michael Stevens’ comments in the Comments/Discussion section).

There is also an issue of temperature instability.  This is my guess as to what happens.  The pressure switch is slow to react.  When the water in the boiler is used up (by pulling several shots in the same session), there is less capacity to hold the constant amount of heat generated by the heating elements.  As a result, the temperature swings are greater with less water than when the boiler is almost full.  You may end up with water that is too hot for the coffee.  I always fill my La Pavoni to about 3/4 full and only pull one or two shots at a time so this isn’t a big deal with me.  However, I thought you should know…

 

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