E61 Thermal Analysis Questions - Page 2

[HB]

Was the E61 designed originally for an HX machine? Makes more sense than a double boiler machine.

The E61 patent ("ALTERNATELY SEATING VALVES") addresses the question of preinfusion and makes no specific mention of the boiler design. It's a safe bet though that it was an HX, as that was pretty much the norm those days as best represented by the Faema E61.

PS: Below is a couple pictures of Ken Nye's Faema E61 Legend from his shop at Ninth Street Espresso:

[Marshall]

Not necessarily because the volume above the dispersion screen on the groups I've looked at provides enough conductance that the off-center water delivery hole has a negligible negative effect on the water dispersion.

-Greg

This has recently become a subject of great interest to me, because I found a very different effect in my Zaffiro. Alt.coffee regulars may recall I had an ongoing problem with "split" pours. The front half would start first, beginning at the very front edge, and turn blonde well before the back half. I tried all sorts of cleanings, adjustments and tests, none of which made any difference.

In frustration, I took it over to Michael Teahan's shop. With some effort, Michael removed the dispersion screw, which I had thought might have a back-end blockage. It was clear. But I discovered for the first time that the E-61 water inlet was at the back of the chamber, not directly above, as I had assumed. We both surmised that the water was jetting forward and exiting the chamber with more force at its front.

Michael opening up the top of the head and found that Isomac was using a 1.0 mm gicleur, instead of the Faema 0.5 mm standard. After trying an intermediate size (0.7), we went with the 0.5. This was over a month ago.

It's hard to measure the improvement that one tweak makes, when my machine has had many others. But, this may rank with the PID installation. I am getting beautiful, even pours with a regularity I had not previously thought possible. This means I can fill my demitasse, and the cup greatly quality exceeds my previous premature short shots.

So, in sum, I think the off-center delivery hole can have a serious negative effect, if the water flow is not adjusted to allow for that fact.

Marshall

[gscace]

This has recently become a subject of great interest to me, because I found a very different effect in my Zaffiro. Alt.coffee regulars may recall I had an ongoing problem with "split" pours. The front half would start first, beginning at the very front edge, and turn blonde well before the back half. I tried all sorts of cleanings, adjustments and tests, none of which made any difference.

In frustration, I took it over to Michael Teahan's shop. With some effort, Michael removed the dispersion screw, which I had thought might have a back-end blockage. It was clear. But I discovered for the first time that the E-61 water inlet was at the back of the chamber, not directly above, as I had assumed. We both surmised that the water was jetting forward and exiting the chamber with more force at its front.

Michael opening up the top of the head and found that Isomac was using a 1.0 mm gicleur, instead of the Faema 0.5 mm standard. After trying an intermediate size (0.7), we went with the 0.5. This was over a month ago.

It's hard to measure the improvement that one tweak makes, when my machine has had many others. But, this may rank with the PID installation. I am getting beautiful, even pours with a regularity I had not previously thought possible. This means I can fill my demitasse, and the cup greatly quality exceeds my previous premature short shots.

So, in sum, I think the off-center delivery hole can have a serious negative effect, if the water flow is not adjusted to allow for that fact.

Marshall

The reduced gicleur size has the effect of increasing the conductance of the volume above the screen. This is a good solution provided that the water debit remains big enough.

-Greg

[Marshall]

Just what I thought! What's "conductance?"

My water debit is a bit more than 60 ml.

Marshall

[gscace]

Conductance in this case is borrowed from vacuum system technology. Imagine that you have a small diameter pipe through which you are trying to cram lots of material (presume a liquid). In order for you to get this stuff through the pipe you have to put a lot of pressure on it upstream. As the liquid goes down the pipe, the pressure drops. If it comes out into the room, then at the end of the pipe the pressure is atmospheric, although to cram lots of liquid through, the pressure will be very high upstream of the exit. This sort of a system is qualitatively "low conductance." A high conductance system is just the opposite. In this case, very low pressure differential pushes a large amount of material. In an espresso machine group, low conductance areas include the tiny holes above the shower screen in the e-61 style groups I'm familiar with (the Astra has a brass diffuser block just above the screen). In order to flow lots of liquid through, the pressure drop along these small holes is relatively high. By contrast, the disc shaped chamber above the diffuser block has a lot of volume and flows the same amount of liquid through it at very low pressure drop and velocity. There's a quantitative value for conductance ( that I'd have to go look up since I don't use it daily). If the ratio of high conductance to low conductance in the group passages I just mentioned is sufficiently big, then the pressure across the entire high conductance volume will be constant. This means that the flow rate through the little holes in the diffuser will be constant throughout the diffuser, and the coffee will get wetted equally. Provided that the conductance ratio is favorable enough, any negative effect of the angled water passage above the diffuser block on water dispersion will be eliminated.

-Greg