Pressurestat on la pavoni pre-M

by **audia6** on Tue Dec 27, 2011 9:15 pm

sorry if this has been asked before. After reading many threads I am still not 100% sure how it works.
Older LP has two switch to control different temp for brew and steam. Newer ones has one switch. It uses a pressurestat and it cycles on and off using the green light to indicate readiness.

My question is if that is the case, how does it tell the difference between brewing and steaming. Does it mean that its design goal is have one temp only ? The longer one leaves the machine, the hotter it gets.

If there's only one temp and its rising all the time. Does it mean that one should find the best temp for brewing, do it, then wait for temp to increase and then steam ?

Just got a NOS pre-M euro (2000 model with one switch)

thanks ahead.
** PS : curious if someone has used OE's third shot to control their temp.

Robert

by **jonny** on Tue Dec 27, 2011 9:54 pm

On a lever machine, the boiler is always at steam temperature and that temperature drops when it passes through the massive grouphead. Since the grouphead is directly attached to the boiler, this effect will be diminished over time and become too hot for espresso. A pressurestat keeps the boiler between a set range. This will keep the boiler temperature between a range but ultimately the grouphead will continue to heat until it is in equilibrium with the boiler and far too hot for brewing.

I doubt anyone has used the new OE third shot yet. However it is the same concept as locking in a cold portafilter to absorb some of the heat which has been practiced for some time with success for many.

by **cannonfodder** on Wed Dec 28, 2011 1:32 am

Here is an excerpt from the Gaggia Achille bench thread where I detailed some of the working styles of levers...

Modern Day Lever Espresso Machines

Modern day lever piston espresso machines use three different water supply brew systems and two different piston power designs.

Spring assist and manual lever.

There are two different piston powered systems. The spring assisted lever uses a coiled spring to regulate the extraction pressure of the piston. When the lever is depressed, the piston is cocked. You simply release the lever and the spring delivers the needed pressure for your extraction. The Elektra Microcasa a Leva is one of the most popular spring assisted lever machines.

The second power system is, well, you. The full manual lever relies on the operator to supply the needed pressure to the lever for extraction. These systems require much more time to learn. The operator has to apply steady pressure to the lever during the extraction. The difficult part is training yourself to apply the same amount of pressure for every shot. The La Pavoni Europiccola and the Gaggia Achille are two of these full manual systems.

Water delivery methods.

The most common type of water delivery is the steam pressure driven. In these systems, a single large boiler supplies both brew water and steam power. The machine relies on steam pressure to force water up a brew group supply line and into the group piston chamber. In order for that to work, the water in the boiler must be hot enough to generate steam. Most of these machines operate around .8 bar, or roughly 250F.

Hydraulics diagram from the Olympia Cremina manual

Since the brew water is well beyond the target brew range (195-205F) the water must be cooled prior to the extraction. On these machines, the group acts as a heat sink, leaching heat from the brew water as it enters the piston chamber. This is not a good way to regulate the brew water. Every time you pull a shot, the group absorbs more heat. Most of these will only allow for 3-4 shots before they overheat. Extended idle time also results in an overheated group because the grouphead is directly attached to the boiler. Common machines in this category include the La Pavoni Europiccola, Olympia Cremina and Elektra Microcasa a Leva.

Gravity feed (open boiler) water delivery systems can avoid these overheating problems. A gravity system uses a boiler placed above the grouphead. When the lever is lifted, gravity pulls the water down into the group piston. Because steam pressure is not required to move the water, these systems can operate at much lower temperatures. The water in the boiler can be kept at or slightly above the target percolation temperature. The disadvantage of these systems are two fold:
Because the boiler is located above the grouphead, most of the machines mass is located high off the counter. That tends to make them a bit top-heavy and prone to tipping over if the base is not sufficiently large.
These systems generally have one boiler, the brew boiler. Because these are run at brew temperatures, there is no steam for creating milk drinks.
The La Peppina and Mini Gaggia/Minimoka are popular gravity fed open boiler machines.

Heat exchanger is the third water delivery method. A heat exchanger uses a high pressure (usually 1 bar and up) boiler with a brew water supply line running through it. Most commercial lever machines use a large steam boiler with one heat exchanger per group supplying brew water. As the cold water passes through the heat exchanger tube it is flash heated to brew temperature. The resulting brew water can be adjusted up and down in temperature by the dwell time. The longer the water sits in the heat exchanger, the hotter it gets. The majority of commercial machines use a heat exchanger system. Below is a heat exchanger hydraulics diagram for a pump-driven espresso machine:

For more on how a heat exchanger works see Espresso Machines 202

by **audia6** on Wed Dec 28, 2011 11:42 pm

thanks kindly on both posts. Excellent explanation and comment.

I also received a pharos from OE today. I guess the journey has begun.

thanks again. Much appreciated
Robert

by **drgary** on Thu Dec 29, 2011 1:01 am

jonny wrote:On a lever machine, the boiler is always at steam temperature and that temperature drops when it passes through the massive grouphead. Since the grouphead is directly attached to the boiler, this effect will be diminished over time and become too hot for espresso. A pressurestat keeps the boiler between a set range. This will keep the boiler temperature between a range but ultimately the grouphead will continue to heat until it is in equilibrium with the boiler and far too hot for brewing.

The temperature apparently does not wander out of range with the Millennium Pavonis. I did initial tests earlier this year to demonstrate that and plan a more precise test in the new year collaborating with yakster and using a thermocouple in the basket and a group temperature strip. My initial testing is posted here: La Pavoni Millennium Owners, Are Temperature Problems Solved?

Let me put it another way. With my Millennium La Pavoni Europiccola in my office, I can let it idle for hours and pull a good shot. I can pull multiple shots in a row without temperature getting out of control. I deal with the heat in the group in two ways, by my choice of coffee and by cooling the portafilter before inserting it in the group. Some light-roasted coffees need no cooling at all. I can reliably pull shots of other coffees that need a cooler group by dipping the portafilter in room temperature water. The Pavoni itself has its pressurestat set to a level that there is a good compromise between brew temperature and steam pressure. It is not a fast steamer but provides enough steam to do a very good job of milk texturing. The engineers at La Pavoni somehow modified the group and set the pressurestat to make this possible. It is a very welcome advance that makes the machine easy and reliable to use.

This is very different than the pre-Millennium La Pavonis that require more knowledgeable technique to keep the group cool enough to pull multiple shots. I will do a temperature study on a dual switch pre-Millennium Pavoni as well sometime in the first half of the year when I have a bit more time and access to a data logger that can be linked to a thermocouple that will be placed in the basket.

by **dbacks** on Fri Dec 30, 2011 2:13 pm

This is very different than the pre-Millennium La Pavonis that require more knowledgeable technique to keep the group cool enough to pull multiple shots. I will do a temperature study on a dual switch pre-Millennium Pavoni as well sometime in the first half of the year when I have a bit more time and access to a data logger that can be linked to a thermocouple that will be placed in the basket.

Gary, I'm looking forward to your future post on this topic after you've had the time to gather data. I have a pre-millenium Europiccola w/o a pressurestat gadget. Mine has the two position switch (2 heater elements, high/low) + power. I added a pressure gauge to my Europiccola and I find this to be a huge help as the gauge gives me the feedback I need to be able to pull shots and steam/froth milk based on tank pressure.

I do tend to have problems with heat buildup when I try to pull multiple shots (1 pull/shot) unless I take special measures (see below) on my 2nd/3rd shots. Because of high grouphead heat (and therefore high portafilter heat), I can get frothing of the espresso (i.e., it's above the boiling point) as it exits the portafilter toward the end of the pull.

My technique for pulling multiple shots is to:
1. At startup heat with my power switch on the "high" (II) position,
2. Pull the first shot when my pressure gauge reaches about 10psig
for a 2nd shot:
2a. I switch the power to the "low" (I) setting,
2b. take out the portafilter and dip it in ice water to cool it off,
2c. reinstall the portafilter/basket with a fresh load of grounds and pull another shot
2d. for additional shots, repeat 2b. and 2c., cycling power off/on as needed to keep the tank pressure near 10psig
for latte/cappuccino:
3. switch the power back to high (II),
4. as the tank pressure gets close to 20psig, open steam wand to clear any water,
5. steam/froth milk when tank pressure gets to about 21psig. If steaming enough milk for, say, 2 lattes, the tank pressure will drop to as low as 10-12 psig by the end of the milk steaming stage.
6. turn off the power

by **Flasherly** on Fri Dec 30, 2011 3:20 pm

audia6 wrote:sorry if this has been asked before. After reading many threads I am still not 100% sure how it works.
Older LP has two switch to control different temp for brew and steam. Newer ones has one switch. It uses a pressurestat and it cycles on and off using the green light to indicate readiness.

My question is if that is the case, how does it tell the difference between brewing and steaming. Does it mean that its design goal is have one temp only ? The longer one leaves the machine, the hotter it gets.

If there's only one temp and its rising all the time. Does it mean that one should find the best temp for brewing, do it, then wait for temp to increase and then steam ?

Just got a NOS pre-M euro (2000 model with one switch)

thanks ahead.
** PS : curious if someone has used OE's third shot to control their temp.

Robert

Millennium pro here w/ the larger boiler. Between shots for a single person, and that may be awhile, I indulge by running a full boiler out of its water, or to a lower safety limit visible upon the sight glass. In practice, that would be just the opposite. First I heat water in a 2-cup Pyrex measuring glass, in the microwave, thereupon turning on the Millennium or shortly after, for its residual water from last usage to begin heating. The boiler cap is also screwed off for listening in. The Pyrex comes near to boiling within three minutes, when I mix in its contents. Within a few seconds the thermostat is also up, approaching halfway and sufficient for steaming milk;- which I then do, having lifted the lever to run a token amount of hot water through to heat the empty PF, as well emptying hot water I'd added for warming up within the same cup I'll drink from;- extraction follows, also opposite, over frothed milk and using a plastic convenience knife to lightly stir together the lower two layers beneath a macrofoam froth. Indulgence is then flushing out a remainder of the boiler (to a safe sight level), through a now cleaned PF and filter. If anything conceivably were left by way of grinds or fluid coffee in the PF's bell housing, it's flushed out. (The PF also needs to be in and locked or boiler pressure eventually blows out the shower screen and its retainer ring far enough to where the PF won't properly engage.)

Aside from an above ackbasswards procedure, making multiple shots for another present is actually simpler, although for the most I'd agree with those that feel the La Pavoni is basically a two-shot getter-upper.

by **drgary** on Fri Dec 30, 2011 11:36 pm

dbacks and Flasherly, welcome to these forums!

SF Dave, have you tried bringing your machine up to temperature with full power and then just turning it off before toggling power switches on to pull a shot? I'm still learning my -2K but find when I do this and cool the portafilter in water I have no problem keeping the group cool for multiple shots. In other words, once it's warm, it heats so fast that I don't usually keep it idling on the low power.

Gabriel, with your 2K machine, that seems like a really nice way to heat it up fast but awfully complicated after that. My 2K Pavoni takes all of 13 minutes to fully heat on its own power, including a warm portafilter. The OPV (over pressure valve) hisses a little on the way to getting warm, then it hisses slightly from time to time. No need to keep the boiler cap open to listen for anything. To keep the group cool enough I only need to dip the portafilter in water and sometimes don't have to do that if I'm using a coffee that tolerates more heat. The steam pressure seems perfectly adequate on mine once it's warm for getting microfoam with no need to mix layers other than some tapping on the counter and swirling of milk in the pitcher. In another thread here, I read that Richard Penney uses a sponge in the portafilter to do a gentle backflush. I use a group brush and then a sponge in the portafilter to clean it when I'm ready to shut down the machine. Coffee retained in the group and pushing out the shower screen may be a sign of overfilling the basket.

For both machines I disagree that they're limited to two shots given adequate and relatively simple technique. They're not my choice for a party, though because of limited tank size, although once most of the water is out, shutting the machine off and opening the steam valve until there's no more steam emerging depressurizes enough to open the boiler (carefully please, at your own risk) and refill/reheat. At that point your preheated water refill seems like a great idea.

by **Flasherly** on Sat Dec 31, 2011 2:32 am

Gary: Gabriel, with your 2K machine, that seems like a really nice way to heat it up fast but awfully complicated after that. My 2K Pavoni takes all of 13 minutes to fully heat on its own power, including a warm portafilter. The OPV (over pressure valve) hisses a little on the way to getting warm, then it hisses slightly from time to time. No need to keep the boiler cap open to listen for anything. To keep the group cool enough I only need to dip the portafilter in water and sometimes don't have to do that if I'm using a coffee that tolerates more heat. . . .

Hey, Gary -- the complicated part, the 'after that,' is from rummaging around related coffee sightings in South America. An espresso, rather latte or cappuccino, thereabouts, is served up in three layers from a long, tall glass with a spring of mint, imaginatively, for topping. Extracted over, of course. Never been there, but I liked the idea (after reading and sightings from coffee the world over) well enough to have adopted it for a "routine".

But, hey, espresso's is after all espresso, and I've just gotten off work, half an hour ago, driven home in time already to tossed one down before meandering over to the terminal. (Thirteen minutes being more along with having made a shot to sit sit down and finish up that last delicious sip from the bottom of the glass.)

The top off the boiler is sufficient to timing the process conveniently for the microwave to finish up, for a few bubbles formed and boiling in a Pyrex measuring glass, at three minutes plus some, for an added care to pre-conditioning, turning on the La Pavoni, that the surrounding ceramic to the boiler element absorbs heat, as not to shock or risk a crack and disastrous repair through dissimilar temperatures by suddenly adding scalding water from the microwave. Skipping the middle part in preparation and on to cleaning, the final flush, all that is basically spare water in the boiler I may as well blast through.

The few times I've left the Pavoni on over [by some for] a recommended 30 minutes, I like the operation and results from a stabilized temperature it reaches. I see a difference, but, ah well, hasn't but for the occasional exception worked out -- for when and how I want it in impetuous sense of now. (I'd have to dig out my IR thermometer and put black tape strategically on the Pavoni to look for comparisons to what I like about the machine's sitting up at temperature.)

Can't say, though, I've experienced a point of having developed a taste for S/O temperature tolerances;- nope, figure I'm doing well enough watching over a roaster to catch beans ($5lb. budget greens) at critical times when attempting to enhance the roast flavors.

For a La Pavoni party of, say, 40 ravenous espresso drinkers, probably take at least a bank of three machines, one person might proficiently man, that or some fittings and brass pipe fitted to the top of the boiler for piping in very hot water, at better one to a operator.

by **drgary** on Sat Dec 31, 2011 4:22 am

Man, oh man!

Just shows there's no one "right" way to do this.

What I wrote, then, isn't for you, but for readers who might think learning to use these machines has to be complicated.


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