Due to questions raised on another thread in this forum, the issue of the impact of autofill on shot temperatures and pressure has been discussed. I have started this thread as a repository for any actual observations that might be made on this topic. The original issue raised was what would be the impact on a shot if the autofill was actuated during the shot itself, with particular reference to vibratory pump machines with autofill. There are two issues here, the first being the effect on the shot pressure, and the second being the impact on shot temperatures for both the shot in question and for subsequent shots in a consecutive shot series.
I do not have a vibe pump machine with autofill, although I do have one without it. Testing that machine would probably not produce useful information as the boiler is filled manually. I do have a rotary pump driven plumbed in machine, a Cimbali Junior D model which has been modified with both a PID for more precise boiler temperature control, and a (defeatable) delay timer for inducing preinfusion using regulated water mains pressure of about 3 bar for the initial 6 seconds of each shot. Because of concerns about the delay timer confusing these issues, I elected to bypass the delay timer (it is switched in my installation) leaving the machine in its native configuration other than for the PID.
As the first part of the test I installed the portafilter (PF) manometer and tested shot pressure, which remains as previously set at 9 bar. Then, as a second test I again tested the shot pressure with the PF manometer but after 10 seconds opened the water wand and dumped out 200ml of water which actuated the autofill almost immediately. The shot pressure did not change and remained at around 9 bar. Therefore, with at least this rotary pumped machine, shot pressure was not effected by the autofill coming on during the shot.
The next thing to test was the impact of autofill actuation on measured shot temperatures, both during the shot and in consecutive shots afterwards. I started with a PID boiler temperature setting that I normally use when I'm making milk drinks with the Harrar Horse SO beans I have recently been using for espresso. The Scace Device and an Omega Datalogger were used to record shot temperatures.
As a baseline I performed a 4-shot series without actuating autofill to show the consistency of shot temperatures observed:
Having obtained a baseline, and waiting 45 minutes to allow the machine to return to baseline condition, I performed a six shot series with autofill activating during the 2nd shot. The first shot was pulled, as before, after an initial 50ml cooling flush. Ten seconds into the 2nd shot, I drained 100ml of water out of the water wand while continuing to record the shot. The autofill ran audibly during the 2nd half of this shot and continued into the idle period in between the end of the 2nd shot and the beginning of the 3rd. The shot series continued as before in the baseline series, with 1 shot pulled per 2 minutes, equating to a pause of 90 seconds between the end of one shot and the beginning of the next one:
As you can see, the average shot temperature in the baseline series is a bit higher than that observed in the series where the autofill was actuated. The 2nd shot, during which the water was drained from the boiler and during which autofill was running the last half of the shot, did not appear to have its shot temperature effected by this maneuver. There was a trend towards declining shot temperatures with each subsequent shot, however within the range I have previously observed in this machine as set with this boiler temperature and without the autofill being actuated.
In summary, in my rotary pump driven Cimbali Junior D HX machine, I have observed the following with boiler autofill actuation during a shot series: (1) no effect on measured shot pressure during the shot when autofill was operating, and (2) no effect on shot temperature during a shot in which autofill actuates. Effects of autofill actuation that I DID observe were a trend towards overall lower shot temperatures in the shot series, especially in shots FOLLOWING the shot pulled simultaneous with autofill, and a fairly limited effect overall, all things considered, given the predicted perturbation of the system that I anticipated.
Finally, this is not a test of a vibe pump machine with autofill, and individuals owning such machines will need to test them in order to see how generalizable these observations might be.
ken
