I own two Creminas - an '83 and an '89. I pay close attention to the pressure on all my machines, and with the Creminas I get an interesting and consistent behavior which I don't yet understand the reason. Since they are both doing the same thing, I know there is a good reason, and polling the conventional wisdom here for an explanation that jives.

On both, when I start up cold, relieve false pressure, and the machine is up to pressure initially - my pressure is reading 0.9 - 1.1 bar. It will read that way for the first few boiler on / off cycles. Then when the machine "warms" up and sits for, say, 7-10 min, the pressure consistently reads 0.8 - 1.0 bar - which is where I want it. After that, the readings are consistent in the 0.8 - 1.0 bar range.

I will say again - false pressure is relieved in all instances. This is not a one-time phenomenon, it is something I have measured / experienced many times now... and I also have a vac-breaker cap on one of them from Cerini's and it does the same thing. So this has nothing to do with false pressure that I am aware of...

This happens on BOTH Creminas, which leads me to believe this is not unexpected behavior.

My question is - which reading should I be using to set my pressure - cold start up or warmed up? Something tells me the answer is "warmed up" but just seeing what others think, and maybe there is an issue I am not aware of.

NOTE: both machines don't have any leaks, pressure issues - both take about 2 min and 10 sec to cycle the boiler on / off, which is normal with a near full boiler. Just trying to eliminate that there are leaks, etc, there are not. Both machines function / make coffee well.

My Elektra MCAL does basically the same thing. I suspect it is due to the plunger in the pressurestat not being warmed up when the machine is first turned on. When it expands it would seem logical that it would require a lower temperature for it to turn off. It may also be gauge parts expanding too.

Robert - glad to see I am not alone... Kinda suspected this. The real question is if you were setting your pressure - which reading would you use - the higher one on startup or the lower one after it warms up?

The pressure stat is a diaphragm operated pressure switch where a micro switch is actuated by a pin located on the non pressure side of the diaphragm. As the switch heats up the pin gets longer and the setpoint decreases slightly. These pressure stats are not temperature compensated.

SpaceTime wrote:The real question is if you were setting your pressure - which reading would you use - the higher one on startup or the lower one after it warms up?

This is not something exact. As boiler pressure is temperature, you want a temperature low enough to brew the coffees you like that require lower temperature. Higher temperature is easily achieved with half pumps to introduce hot water to the top of the group without infusing the coffee cake. If the temperature is set too low you'll have to do many half pumps to come up to temp. So it's a matter of tuning it to your coffee preferences. I sometimes like dark roasts so I tune mine a bit low and have to do more half pumps to come up to temperature unless pulling several successive shots. I'm thinking of bumping it up a bit. Another way to tune your Cremina (or La Pavoni) is measure the temperature at the outside of the group. I like mine to cruise around 180F and can cool the group slightly with a cool portafilter for darker roasts. Robert measures his brewing temperature more precisely than this as it exits the portafilter.

One might consider it a feature that the boiler reaches higher pressures at the start! It seems to me that the stabilised temperature is what is important.

I do not have a permanently mounted pressure gauge on either of my La Pavonis (1978 and 1999 Europiccolas.) I machined a brass cap fitted with a pressure gauge, and a brass cap fitted with a deep thermometer well. I tend to test both machines' boilers at least fortnightly with the thermometer well cap rather than the gauge. The 1999 Europiccola has a pressurestat, but it does not seem to vary as much as the MCAL. With any of these machines what always seems to me to matter most is the temperature profile of the pull, which requires measuring temperature of the espresso as it emerges from the group. I like it to run from about 50 degrees to 93 degrees. Unless there be a bad grind, bad coffee, or bad roast every shot that has the profile is excellent.

drgary wrote:This is not something exact. As boiler pressure is temperature, you want a temperature low enough to brew the coffees you like that require lower temperature. Higher temperature is easily achieved with half pumps to introduce hot water to the top of the group without infusing the coffee cake. If the temperature is set too low you'll have to do many half pumps to come up to temp. So it's a matter of tuning it to your coffee preferences. I sometimes like dark roasts so I tune mine a bit low and have to do more half pumps to come up to temperature unless pulling several successive shots. I'm thinking of bumping it up a bit. Another way to tune your Cremina (or La Pavoni) is measure the temperature at the outside of the group. I like mine to cruise around 180F and can cool the group slightly with a cool portafilter for darker roasts. Robert measures his brewing temperature more precisely than this as it exits the portafilter.

Gary - yes, that part I get. I am constantly changing SO's on my Creminas and some like it hotter than others and I manage that with at what point I pull during the pressure cycle, along with group head temp I measure with strips and check periodically with a Thermapen. Understood and taken into account.

I also believe you have a permanently mounted digital thermometer on your Cremina - I don't. (I could be wrong, but I recall seeing a prior pic of yours with it). As stated, I have temp strips (mounted toward the back of the bell where it is hotter), and periodically check the back of the group with a Thermapen for verification. I only use a pressure gauge for set up, then remove. Due to this pressure variance I am seeing (and it appears others are too) I am left wondering when I am getting ready to pull a shot if the pressure is actually higher due to it just starting up, or has it been on long enough for it to stabilize to the 1 bar. It wreaks havoc on my OCD'ness LOL and my desire to control the variables... but the temperature measurements I use are really the bottom line, so your point is taken there.

It is not a huge issue, was just trying to understand if others were seeing this difference in pressure between a cold and warmed up machine.... wanted to make sure there was not something that could be tweaked - it doesn't sound like there is.

On a side note - I will say the Teflon heat break has helped out a bit in stabilizing my group faster - can't live without that.

rpavlis wrote:One might consider it a feature that the boiler reaches higher pressures at the start! It seems to me that the stabilised temperature is what is important.

I do not have a permanently mounted pressure gauge on either of my La Pavonis (1978 and 1999 Europiccolas.) I machined a brass cap fitted with a pressure gauge, and a brass cap fitted with a deep thermometer well. I tend to test both machines' boilers at least fortnightly with the thermometer well cap rather than the gauge. The 1999 Europiccola has a pressurestat, but it does not seem to vary as much as the MCAL. With any of these machines what always seems to me to matter most is the temperature profile of the pull, which requires measuring temperature of the espresso as it emerges from the group. I like it to run from about 50 degrees to 93 degrees. Unless there be a bad grind, bad coffee, or bad roast every shot that has the profile is excellent.

Robert - my gauge is only used for set up, then comes off after that. (I have toyed with the idea of a permanent gauge, but have not decided if I want that).

As I replied to Gary, I use a combo of temp strips and a Thermapen as a check point to verify group temp, and have gotten in a groove where I am getting temps in the range I want for the different SO's I try. Still tweaking my method, but satisfied.

I was really just trying to understand if there was something wrong with my machines with the pressure variance between startup and idling, I think I am gathering that the behavior is normal.

SpaceTime wrote:On a side note - I will say the Teflon heat break has helped out a bit in stabilizing my group faster - can't live without that.

If you are using the factory group gasket it is made from an open cell type white foam material not teflon. DR. G corrected me on that fact in a previous thread.

JohnB. wrote:If you are using the factory group gasket it is made from an open cell type white foam material not teflon. DR. G corrected me on that fact in a previous thread.

John - I have seen past posts where Doug has made that clarification too - interesting though -see this link in the Olympia Cremina manual, page 14 - http://www.olympia-express.ch/resources ... 140201.pdf - Olympia says it is made of Teflon and Gore Tex... so I am not sure what to call it anymore!

That being said - it does appear, feel more like open cell foams I have worked with before - definitely not rigid like some of the Teflons.