Rancilio Silvia + Rocky tips - Page 2

[JimG]

I'm a bit surprised that during the shot that water existing the boiler doesn't fall in temperature due to the influx of cold resevoir water.

Yes, it is surprising. It is also very dependent on flow rate. The shapes of the curves change dramatically if, instead of pulling a shot at a flow rate of around 2-3 ml per second, you allow water to run freely through the group (e.g. flushing). Many people draw poor conclusions about shot temperature and temperature stability by measuring water flushed from the group without significant restriction. The amount of "contact time" between the water and the group, I believe, makes a big difference in the temperature of water coming out of the group.

On a related note, do most pump machines push water in the grouphead by also pushing (cold) resevoir water into the brew boiler? Seems fundamentally like it'd affect the shot temp.

I think so.

Others have concluded that the standpipe inside the Silvia boiler is responsible for preventing much mixing. The theory is that the cold water coming into the boiler, being denser, drops to the bottom. This pushes the hotter water up where it enters the standpipe that leads directly to the group. Sounds like a reasonable explanation to me.

Jim

[Psyd]

2. The second characteristic of a Silvia shot is a rising temperature profile after 15-20 seconds (measured at the puck using a Scace device). adding more heat to the mix (by using the steam switch) does not sound like a step in the right direction to me.

The idea that the quickly dropping temperature at the top of the boiler translates into a dropping temperature in the water hitting the coffee makes sense, but it is wrong.

Nice! I always tell folk that there are people whackier than I on these boards that do all the work, and I just reap the benefits! Thanks! (I'm not saying that you're whacky, they think that I'm whacky...)
I'm curious to find out if this is true after the 100C T-stat turns off the element and the group is flushed til the water dance stops? My technique is to wait for the light to go out, flush til it stops steaming, and wipe the group, lock in, fetch my cup under the PF, set my timer (all in about a four to six second period) and turn on the pump. after about a ten count, I then turn on the steam switch, and let it continue till the end of the pull. Wouldn't the flush counteract the 'thermal flywheel' effect?

[JimG]

My technique is to wait for the light to go out, flush til it stops steaming, and wipe the group, lock in, fetch my cup under the PF, set my timer (all in about a four to six second period) and turn on the pump. after about a ten count, I then turn on the steam switch, and let it continue till the end of the pull. Wouldn't the flush counteract the 'thermal flywheel' effect?

Wow, that's a lot going on.

When the light goes out, the boiler temp is probably around 230F and still rising quickly. The flush will drop the boiler temp considerably, or at least stop the rising. But the flush will also heat the group. I'm not going to venture a guess what the boiler and group temp are when you hit the switch after that procedure, but if it's working for you, then it must be just right.

The only thing I feel fairly confident in is that turning on the steam switch at the 10 second mark is not affecting the shot profile (unless you are pulling shots longer than, say, 30 seconds). The mass of the element sucks up heat, without creating any detectable change in the boiler temp, when it is first powered up. By the time the element has heated to a temperature sufficiently above the surrounding water for heat to start to be transferred, your shot is probably done.

From a "dead stop", it takes somewhere around 25 seconds after the heater turns on to be able to observe any change in boiler temperature.

Jim