TomC wrote:I insulated the case of my old Strega with the generic (cheap) equivalent of Dynamat. It worked extremely well at cutting down noise inside the machine.

The Super Strega: Modifying preinfusion pressures and other functional improvements

Thanks Tom,
read about your action on your Strega, incredibly nicely done!

lars6153 wrote:For a one group lever machine, my boiler is huge. The pressure tank is 6,5 liter (with a content of 3,8l steaming hot water).

So I'm not so sure that the change in temperature, caused by the incoming 0,6 liter of water from the reservoir, will make a big enough pressure drop to engage the pressurestat. Nor do I know if the drop of pressure caused by letting out 0,6 liter to the grouphead chamber will effect the pressurestat.

I'm not even sure a combination of those two events will engage the pressurestat, because we might have an other factor to consider: Added pressure from the pump, filling the boiler (the must be a change (rise) in pressure, otherwise the water will not be able enter to the boiler.

I wouldn't consider that last a factor, but I could be wrong. My La Pavoni is a Bar 2L with a larger boiler (14L?), and the heat routinely comes on after a fill. But I won't say always - if the fill happens just after the heat switched off, and it's a late summer day when the municipal water is a little warmer, I bet it wouldn't switch on. (I don't know how much water introduced in a fill - likely more than 0.6L?)

Thanks for your comments Donn.

Indeed trivia, but lets dig in ;

If we presume a 14L boiler contains 7L 114°C water and we add 0,06L 10°C, we will have a new temperature of 113,1°C. My 6,5L boiler 3,8L 114°C and added 0,06L 20°C will be 112,5°C.

A less than one degree heat reduction for one double espresso.

My mathematics knowledge do not include the ability to calculate pressurised boilers. Will the one degree drop in temperatur cause a drop in pressure big enough to engage the warming element?

But, first thing first. The pressurestat reacts on pressure changes only. When the valve to the grouphead is opened and we let out 0,06L (grouphead chamber contains 52cc) from the boiler, there will be a pressure drop. This will most certainly engage the pressurestat (and warming element), regardless of temperature in the boiler. The solenoid inlet valve will not open/activate pump until the water level drops bellow water level sensor.
If this is correct; in a normal espresso making cycle, the warming element is already activated, when the water from tank/mains enters the boiler.

Another trival thought;
If the solenoid valves would open at the same time as the water starts to escape/is pushed into the grouphead chamber, and the pump/mains filling the boiler has a greater pressure than the present boiler pressure, there will be no drop in boiler pressure. The warming element will not be activated.

As the solenoid valve closes (due to upper water level reached), the temperature (and pressure...) starts to drop and, eventually, the pressurestat will be activated.

(made some mathematics changes, changed 0,6L to 0,06L...)

lars6153 wrote:But, first thing first. The pressurestat reacts on pressure changes only. When the valve to the grouphead is opened and we let out 0,06L (grouphead chamber contains 52cc) from the boiler, there will be a pressure drop. This will most certainly engage the pressurestat (and warming element), regardless of temperature in the boiler. The solenoid inlet valve will not open/activate pump until the water level drops bellow water level sensor.

Apologies for pursuing this so late, I just happened to notice this and have the spare time to think about it a little. Only a little, and with precious little knowledge about the matter, but I'm going to hold out - on the contrary, there's no guarantee that drawing a shot from the boiler will trigger the pressurestat. In the case you used for an example, where the boiler is much larger than shot volume.

One key parameter here is the "deadband" between the pressure at which the switch turns on, and the pressure at which it turns back off. If the pressurestat came on recently and the boiler is near the high end of its range, you can drop the pressure quite a bit before it comes back on.

But maybe more important, I believe the boiler's thermal energy will tend to stabilize the pressure, so the drop won't really be proportional to the volume evacuated for the shot. Rather, as the pressure starts to drop, it will be restored immediately as hot water vaporizes in response. The whole system will certainly lose pressure, and heat, but with a large amount of hot water it's going to maintain that pressure much more effectively, than if we evacuated the same volume from an inflated inner tube for example.