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From: "Andy Schecter" <schec...@rochester.rr.com>
Newsgroups: alt.coffee
References: <lYha6.145498$P82.17780626@news1.rdc1.ct.home.com>
Subject: Re: "Aftermarket" idea
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Date: Sat, 20 Jan 2001 21:31:36 GMT
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Jack Denver <nunuv...@netscape.net> wrote:
> Here is my proposal for the world's first aftermarket espresso enhancement
> part:

Well, certainly not the first (I've already replaced my Silvia portafilter
basket with a La Morozzco (sp?)and the plastic tamper with a Reg Barber), but I
get your drift.

> An electronic brew thermostat that would serve as a drop in replacement for
> the brew thermostat found on the Silvia and almost every other single boiler
> machine.  The "basic" model would be adjustable by means of a control
> mounted on the thermostat.  The "deluxe" would be adjustable without opening
> the machine case and would require the purchaser to drill a hole in their
> machine in order to mount the control knob. The "super" would include a
> digital temperature display. All would offer much closer control of
> temperature than the standard model.

I have to smile upon reading your post. I was out at Whole Latte Love this
morning (with Todd, their service manager) replacing the thermostat on my
three-week-old Silvia. We had a conversation about doing exactly what you've
suggested, replacing the stock thermostat with one that is more accurate and
adjustable.

Todd's concerns were about the liability for a company like WLL to get involved.
Since our whole government nowadays is run by damn lawyers, it gives one pause
before jumping into a situation where you modify the controls for a boiler that
runs as high as 320 degrees / 70 psi.

My concern is more technical. Unfortunately, I don't think this kind of
modification will work as well as you would like it to.

The stock t-stat measures temperature on the upper surface of the boiler shell.
You can replace it with as fancy a PID controller as you like, but if it still
senses temperature at that spot, you will never achieve good temperature
regulation where it counts: at the portafilter.

Although the Rancilio engineers, designing to a price point, obviously used a
thermostat that could be improved upon, I don't believe their design is all that
bad. To get really good water temperature regulation you'd have to have a very
fast-acting sensor inside the boiler shell, not on the outside surface. You'd
want to place it right by the siphon tube where the water exits on its way to
the portafilter. You'd have to account for the cooling and averaging effect that
occurs on the way to and through the portafilter. You'd have to account for the
conductive and convective cooling of the portafilter and gruppo. You'd have to
install a much larger electric heater element that could deliver massive amounts
of heat.

And when all this is said and done, you still haven't overcome the basic
limitation of the Silvia: although its boiler is larger than most home units,
it's still way too small to keep the temperature really steady as you draw off
water to make your shot. This is why Schomer claims that you should have at
least a three group commercial machine (with a boiler perhaps ten times the
Silvia's boiler) before you can expect good temperature regulation. And I don't
believe that the Silvia provides a true pre-infusion, where the water is
introduced gently to the portafilter at the beginning of the extraction.

I still think the stock t-stat can and should be improved upon. If I keep my
Silvia I intend to do it. Just don't expect miracles.

BTW, it seems to me that the ultimate design for a good home machine would have
no heat exchanger, just separate large boilers for brewing and steaming. With
hefty heater elements and high tech controls to provide big-time heat when
needed. Oops!. I guess the ultimate home machine is probably a state of the art
commercial machine.   :-)

One last thing: I certainly do not doubt Whole Latte Love's committment towards
servicing their customers. Both Todd and Gary seem genuinely concerned at
getting the Silvias (that they've sold) to perform properly.
--



-Andy