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How Silvia Controls Steam
The
internal wiring
on your Silvia is configured so that all current to the heating element
must pass through the steam thermostat. This is the case while in either brew mode or steam mode.
When the steam switch is turned on, a "jumper" circuit around the brew thermostat is created.
This jumper circuit makes the machine behave as though the brew thermostat is locked in a closed
position, i.e., always calling for heat.
So when the steam switch is on, the temperature is limited only by the steam thermostat, regardless
of the setpoint on the brew thermostat.
Conversely, when the steam switch is off, the temperature is limited by EITHER
the brew thermostat OR
the steam thermostat, whichever has the lower set point.
How a Basic PID Kit Will Improve Steaming
Most MLG kits replace only the brew thermostat, so they control your espresso machine
only when it is in "brew" mode.
Unless you have also installed one of our steam control packages, the original steam thermostat
will continue to control boiler temperatures when the steam switch is on.
But, even though the PID will not directly control the steaming temperature, it still offers a chance to make
significant improvements in your machine's steam quality and capacity.
Without a PID, right after you pull your shot, you will normally turn on the
steam switch and watch the "ready" light. When the light turns off you know that the boiler has
reached steaming temperature. (Although we have seen wide variation in this temperature, the ready light
typically turns off somewhere around 290F-300F.)
Unfortunately, when the ready light is off the heating element is also off.
As you draw down the
steam in the boiler, no new steam is being created to take its place.
Not until the boiler temperature has dropped 40F or more will the stock steam thermostat start calling
for heat again.
A more effective method of steaming would be to open the wand just before the steam thermostat is
"satisfied." This way, as the boiler temperature is dropping, the steam thermostat remains "unsatisfied"
and allows the heating element to remain energized. As steam is used up, more can be created by the
energized heating element.
The trick, obviously, is to find the "satisfaction" temperature for your steam thermostat.
This is where the PID comes in.
Whether in brew or steam mode, you can always read the current boiler temperature on the display
of the PID. After one or two steaming sessions, you will figure out exactly the temperature where the steam
thermostat shuts off the element (on our machine it is a low 285F).
Once you know this temperature for your machine, then for all subsequent steaming adventures you just
watch the PID display,
wait for the boiler to get close to the "magic" steaming temperature, but open the wand
and start steaming
1 or 2 degrees before it gets there.
This procedure maximizes both the steam quantity and quality with your machine. Customers have
told us that following that procedure makes a dramatic
improvement in their stretched milk.
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Sorry, Not Good Enough, I Want More!
Another strategy for improving steam capacity is to make a temporary change to your PID
setpoint, say up to around 295F, instead of turning on the steam switch. This works, but has some
disadvantages.
First, if you recall our earlier description of how Silvia controls steam, regardless of where you set
the PID (i.e. the new brew thermostat), the current must pass through the old steam
thermostat before reaching the heating element. So as soon as that old steam thermostat thinks
things are hot enough, thank you, it will open its switch and turn off the heating element, no matter
what the PID is calling for.
Second, even though all of our customers are unusually bright people,
it would be very easy for the
temporary PID setpoint to become accidentally permanent if you forget to change it back. This
wastes a lot of energy and has the potential for damaging your machine. Even though we pre-set
the PID's in our kits so the maximum setpoint is 300F, there is nothing that can be
programmed into the PID to help you remember to set it back.
The Solutions
We have already discussed how to achieve a significant improvement in steaming using "just"
a basic PID kit. For the vast majority of Silvia owners, this will be enough. But for those of us
(we know who we are) who really obsess over our stretched milk,
MLG can now offer a couple of solutions.
First, and most straightforward, we offer a dual setpoint
Watlow Series 96
controller. By including a
small mechanical relay with your kit, wired directly into Silvia's steam switch,
you will be able
to have the PID take the place of both the brew and the steam thermostats.
This gives you complete
control over the boiler and allows you to set the steam temperature anywhere you want (up to 300F).
The best strategy for steaming with this kit is to begin steaming at between 290F and 295F. As the plot below shows,
the boiler will reach this temperature approximately 100 seconds after turning on the steam switch.
The second option works with our
935A
controllers and is still in the development stage.
Either of these options results in totally transparent steaming operation for the user.
If you follow our
recommendations for installation, you will be able to operate your machine exactly as you do now. When you want
to steam, you flip the switch. (Even the little switch lamp will come on to remind you that
the switch is on). The PID will automatically change setpoint and bring the boiler
quickly to steaming temperature, and
hold it there until you finally find that new carton of soy milk in the fridge, open it, and
prepare your pitcher.
Hang On - This Can Get Tricky
Installation of any MLG steam control package adds complexity and time to your kit installation.
The steam packages are not for everyone!
But, like all of our kits, they are totally reversible. You will need to access the
steam switch to complete the wiring rearrangements. Unless you have unusually long, skinny
fingers, this will almost certainly mean temporarily removing the front panel.
In addition, the 935A steam package introduces another electronic component (power supply).
But if you simply must have the best steam possible you would probably be
satisfied with either of these options.
(Yes, the steam package can be added at any time later, as long as you purchase a compatible
Series 96 or NIB 935A kit).
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