Lots of posts! And some very good ones.
ira wrote:You really need to adjust the frequency if you want to solve the pre-infusion problem.
I concur. To get very slow pre-infusion flow rates out of a vibratory pump (with a pure electrical mod*) you would need to start decreasing the oscillation frequency. However, besides the natural limitation of effective frequencies, Ulka pumps run strictly at 60Hz using simple half-wave rectification of line current. Re-arranging the wave is beyond my current expertise and free time, and chopping it at hard angles can cause huge resistances in the solenoid. I believe rheostats are safer for your pump than simple lamp dimmers which reduce overall power in this manner.
kschendel wrote:A tip on wiring the rheostat:
A good tip! I had read about doing that before, but forgot. I'll probably run a jumper across the two terminals pretty soon.
Frost wrote:So start your shot at 70volts for the first 4-5 seconds, then quickly ramp it up to 108 for the duration of the shot.
mini wrote:I plan to test a lot of shots starting at this lower pressure end and then increasing to my desired "set point." I see no reason not to make the initial flow as gentle as possible
I realize that distribution, dose, tamping, etc. are all the usual culprits in channeling. I also realize that if I practiced enough I could get good, solid pucks at almost any pressure. But, as discussed in the how-to, I really think that this mod will make my machine a lot less critical of puck prep. Why waste coffee while I am still learning?
There are too many factors for me to test currently. I also received a digital scale just before I did my mod, so experimenting with temperature isn't in the fore front of factors currently.
I'm still in the process of getting my bearings with the mod, but everything has been very positive so far. By starting the shot at low pressure, and then quickly ramping up to slightly under full pressure, I have been getting some really nice shots. Blonding has been delayed much longer than my average on all four of the shots done with this technique. The shot I pulled tonight seemed to flow extremely evenly and blond at an almost perfect time. channeling seems to be mitigated a bit as well.
Tomorrow I will do another comparison test - full pressure vs. ramp up - in a little more detail. If anyone has some quick tests they would like to hear about, let me know. This weekend I plan to churn out
some coffee, as well as make some videos. Until then, results will come rather slowly I'm afraid.