Creating Teflon Gasket for Pre-Millennium La Pavoni - Page 2

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atjong
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#11: Post by atjong »

What about the black group gasket, did you omit that one Drgary?

Where would one buy such a sheet of teflon?

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rpavlis
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#12: Post by rpavlis »

Sheets and rods of various polymers are available from many online sources. Some industrial supply places carry such things too, especially places that sell metal stock.

Heat is transferred from the boiler to the 1974-2000 type La Pavoni group by several means:

(1) Heat comes into the group with the hot water from the boiler!

(2) It is transferred from the boiler to the group by direct conduction from the hot boiler walls. (This is what is reduced with a insulating gasket.

(3) It is transferred from the boiler to the group by condensation of steam in the tube like structure leading from the flange to the walls of the cylinder, and then conduction onward through the group.

(4) The primary means of keeping the group hot between shots and before the first one is by having steam pass through the small hole at the top of the cylinder and condense inside. This does not function much until one clears the air out of the space by raising the group handle during the air purge.

One can tell that modes 2 and 3 are far smaller than 4 because until you first raise the handle the group is only perhaps 35 to 40 degrees, after doing this within seconds the top of it is well above 100 degrees!

I suspect an insulating gasket would be most helpful if one leave the machine idling for long periods. I wonder if there would be a good way to insulate the walls of the inside of the large channel leading to the cylinder of the group?

Note that the 1960 to 1973 and 2001 onward models do not use method 4 at all, and instead flood the space around the cylinder inside group with hot water from the boiler. (It is too bad that La Pavoni decided to use trash plastic for the liner required in the 2001 onward models. It might not be too difficult to make a decent one by machining brass.)

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drgary (original poster)
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#13: Post by drgary (original poster) »

atjong wrote:What about the black group gasket, did you omit that one Drgary?

Where would one buy such a sheet of teflon?
Arne:

I left the black group gasket in place because otherwise the group wouldn't seal well to the boiler. The Teflon gasket becomes a new surface on the group and it seals against that. I checked prices on McMaster-Carr and eBay and found them more expensive than on Amazon.com, but that wasn't a wide search. I don't know where I would recommend in the EU but it's worth a search. I found the prices varied a lot and that Teflon was affordable with a competitive source.
rpavlis wrote:I suspect an insulating gasket would be most helpful if one leave the machine idling for long periods. I wonder if there would be a good way to insulate the walls of the inside of the large channel leading to the cylinder of the group?

Note that the 1960 to 1973 and 2001 onward models do not use method 4 at all, and instead flood the space around the cylinder inside group with hot water from the boiler. (It is too bad that La Pavoni decided to use trash plastic for the liner required in the 2001 onward models. It might not be too difficult to make a decent one by machining brass.)
Robert:

I don't leave my dual switch Pavoni idling because this would gradually dissipate steam through the pressure release valve, and it could idle a bit hot anyway. You ask an intriguing question about insulating the walls of the channel between the boiler and cylinder but that seems difficult. If one were to want that much temperature regulation it's probably time to PID the machine. Speaking with Christopher Cara about the plastic liner inside the Millennium model, it has an isolation function similar to my Teflon gasket. I don't know if you've tried a Millennium model. If you can live with the lower build quality temperature regulation is quite easy. The machine can be left on for hours and successive shots can be pulled without overheating if you cool the portafilter in water. I really like my Millennium machine and have replaced the plastic sightglass fittings and piston with metal parts. I've economized by keeping plastic parts that don't affect the operation of the machine. I'm thinking of adding a group thermometer for more shot-pulling precision to dial in specific coffees.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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rpavlis
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#14: Post by rpavlis »

The polyphenylene sulphide liner used in 2001 and later models also has a lower total heat capacity. I wonder whether the insulating capacity or the heat capacity in these machines really matters much, because the 1961-1973 seem to have been the best La Pavoni machines. I wonder if anyone have made a brass liner for the 2001 and later models and tested it?

I suspect that if the design change made in 2001 had been to replace brass with stainless and keep the actual design the same, we would also have close to the ideal machine. Stainless is, for a metal, a very poor conductor of both heat and electricity. As it is they make a machine filled with trash plastic! There must be a way to make a machine without lining it with trash!

coelcanth
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#15: Post by coelcanth »

probably would be easiest to add a pressurestat to an early switch-controlled machine

or PID



but that's probably getting carried away...

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