I think the changes would probably imperceptible in the cup and nothing compared to what you could achieve by:

a) Switching off between shots and watching pressure gauge

b) Flushing portafilter with cold water

c) Wrapping head in cold wet cloth

.... assuming you need to crank out 3 or more shots in a row.

Cheers

Mike

The other alternative is an open-boiler (vintage) machine like my Mini Gaggia or a Caravel or La Peppina. The boilers on these machines aren't under pressure so the temperature in the water in the boiler is the temperature of the water that comes out and the group is mounted directly on the boiler. No overheating. You can also refill the machine while the boiler is on. The big trade-off (besides being a vintage machine and being a bit harder to find parts and get repairs which is really OK since these machines are usually simpler to begin with) is that there is no steaming. So you have to be fine with espresso only.

GB wrote:Now, a crazy idea! If I changed the group head studs and nuts to stainless steel, made the teflon gasket a tight fit on the syphon tube, and changed the syphon tube material to stainless steel would it be worth the effort?

Cheers
Geoffrey

Geoffrey, the stainless steel screws might further prolong the time it takes for (too much) heat to be conducted out to the group. A potable-water-safe high-melt-temp anti-seize coating applied to the SS screws would be a good idea.

Timo,

I think we are both suggesting the same thing for the same reasons but we are using different fasteners? The PVE group head studs are permanently threaded into the group head boiler flange. I would replace those studs with stainless steel and use stainless steel nuts to fasten the group head to the boiler flange but with a thicker teflon gasket.

Your point about using anti seize when fastening stainless to stainless is well taken - thanks.

Soon, I should have access to machine tools and hope to start doing this modification. But, the first job will be to mill the drip tray recess deeper for I am really tired of that thing sliding all over the place and always at the wrong time. The final project is to attach a pressure gauge to the boiler fill cap and tweak the boiler pressure.

Thanks
Geoffrey

michaelbenis wrote:I think the changes would probably imperceptible in the cup and nothing compared to what you could achieve by:

a) Switching off between shots and watching pressure gauge

b) Flushing portafilter with cold water

c) Wrapping head in cold wet cloth

.... assuming you need to crank out 3 or more shots in a row.

Cheers

Mike

+1 ...all work well with my Cremina

To test the theories discussed in my earlier post I performed two temperature tests on the Ponte Vecchio Export (PVE) as shown below:

In both tests the boiler was filled just to the top of the sight glass. The machine turned on, false pressure released and left until the heater idled on and off for about a minute. In each test the water from the grouphead (no filter basket) was collected into a styrofoam cup with a thermometer pierced into its side about 1/8" from the bottom of the cup. This thermometer was tested beforehand in boiling water at about 150 feet above sea level and read 210 degree Fahrenheit. All the numbers are as tested are in degrees Fahrenheit.

TEST 1 (4 oz of water per pull)
1. 2 minutes at idle from startup 191
2. 3 minutes later 188
At this point the water was below the opening in the boiler flange so I waited 30 minutes hoping to prove one of my theories
3. 30 minutes from sample 2 193
4. Last pull because boiler water is below the sight glass 190

Not many data points. Obviously the 4 oz water sample was too large so did a second test this time with less water and after the boiler was rinsed many times with cold water bringing the grouphead back to room temperature. The following test are 2 oz per pull.

TEST 2 (2 oz of water per pull)
1. 2 minutes at idle from startup 186
2. 3 minutes later 189
3. 3 minutes later 186
4. 3 minutes later 190
At this point the water was below the opening in the boiler flange but I did not wait 30 minutes. Just kept on sampling every 3 minutes until the boiler water did not show in the sight glass
5. 3 minutes later 191
6. 3 minutes later 192
7. 3 minutes later 191
8. 3 minutes later and water at bottom of sight glass 190

The experiments are not sophisticated. The numbers are as read and do not have the 2 degree offset due to the thermometer reading 210 degrees instead of 212 in boiling water. Also I would strongly suspect that the temperature the coffee grounds experience is higher due to the evaporative cooling of the water stream as it falls into the cup. Maybe this can be offset by pressure stat adjustment? And speaking of pressure stats, I do not know the boiler pressure but soon will and will post it accordingly.

The numbers are very interesting. There is no evidence to my theory that the water will be cooler when it gets below the opening in the grouphead flange. The flange modifications I suggested in my earlier posts are unnecessary. So much for theories

But I think this shows reasonable evidence that the grouphead of the PVE overheats very little during the of making coffee at regular intervals. Which I hope answers zubinpatrick's original question.

What is also interesting, this data correlates well with peacecup's and my experiences with the PVE. For we have both found from the cup the need to pull a couple of warming shots to get that loverly dark crema on the first shot. And the data also shows that we can most likely can get 5 more

The data in my previous post says more about boiler water temperature than it does about grouphead temperature. A more realistic test of grouphead heating requires thermometry of the water IN the filter basket.

Back to the drawing board.

Geoffrey

A simulation that wanted to approximate an actual duty cycle on the Ponte Vecchio would take into account its relatively small water draw. You shouldn't draw more water than the cylinder can hold + whatever small amount the coffee in the basket can absorb + whatever small amount you allow to dribble into the cup from a Fellini preinfusion. That's for a single. Adjust volume for a two-pull doppio. 40ml, IIRC.

Also, the PV basket is tall and narrow, relative to a broad, shallow 58mm basket. The temperature gradients in the puck will be different according to the basket shapes. So perhaps a tall narrow basket needs more than one probe?

The effects of temperature upon the extraction also vary according to pressure: n° degrees at 6 bar will be different than n° at 9 bar. So we need to bear these differences in mind too, if attempting to compare PV temps to, say, a pump machine's temps.

Timo,

Thanks for the thoughtful response. My reasoning for the 2 oz shot volume was two fold. Get more data points and pull the volume of my typical quick flush and a shot. But it was too crude an experiment to give much meaningful data.

Your points about two probes and pressure gradients are spot on. An ideal experiment probably requires at least two basket temperature probes and at least one pressure probe. And the basket would have to be packed with coffee for each test. Unfortunately such a set up is beyond my resources at present.

Thanks
Geoffrey