Jake_G wrote:I believe Dan was referring to early Linea machines, which had no gicleur. Our GS/3 machines employ a 0.6mm gicleur (as do modern Lineas, GB5s and FB80s, etc...), so they would behave much like a Slayer that skipped pre-brew if we chose not to profile our shots.

Ah, ok. Just for reference, here's a video showing the ramp from zero to full pressure at the group on my MP:
So it seems like somewhere around 2.5 seconds to get to 9 bar. This is against a steel backflush blank, dry, so the time to fill up the space in the PF is included here.

spressomon wrote:So, no, at least as far as I know from my Slayer 1G experience, you don't get a fast (a couple seconds or quicker) ramp up to full brew pressure by going full brew immediately from zero pressure/flow.

That seems strange to me. I would expect it could go roughly as fast as the video above, unless there's something I'm totally not understanding about how the Slayer works. Which is entirely possible and probable - haha.

Hopefully someone much more knowledgable than I am can comment about how Slayer brew pressure ramps up and also depends upon feedback loop from the resistance at the puck. Even though the maximum brew pressure can be programmed (let's use 9BAR for example), it doesn't always result in a maximum of 9BAR being applied (via the manometer) to the puck.

temp: 93.3
pre-brew: 1.5g/s
dose: 18g
yield: 37g

28 second pre-brew resulting in 2g in cup
full brew until 30g in cup, then back to pre-brew until final weight reached.

total timing is around 60s

light roast natural processed ethiopian coffee

spressomon wrote:... depends upon feedback loop from the resistance at the puck. Even though the maximum brew pressure can be programmed (let's use 9BAR for example), it doesn't always result in a maximum of 9BAR being applied (via the manometer) to the puck.

to my knowledge, i believe there is no feedback loop processing for pressure generated during full brew. the brewing pressure is set via blind disk as a percentage of maximum pump motor RPM.

regardless of the resistance at the puck, the slayer will spin the motor to the % specified during setup which subsequently correlates to a specific and constant RPM.

based on this, i suspect this is why we can see varying brew pump pressures due to different puck densities and pre-brew routines. ex: lower than 9bar brew pressure due to channeling or coarser grind

as far as i'm aware, the only machine that uses a feedback loop to regulate or maintain brew pressure is the strada EP (to her advantage and sometimes disadvantage if you're not careful with puck prep)

I assumed there was a feedback loop...to explain the variable brew pressure reading (manometer) with same brew pressure %. I notice, generally but not absolutely, if a particular bean/bean blend responds to, say, a 10-12 sec pre-brew (medium-dark roast levels typically) with a relatively coarser (not "course" but not as fine as a more typical 20-25 second PB for lighter roasts and/or harder beans), 7.5 to 8BAR is all I get. Whereas with the identical machine settings, finer grind for the lighter/harder beans, and 9BAR is the norm.

Much to learn about my Slayer from a tech standpoint. OTOH, it gives me what I want in the cup so the rest is mostly moot to me.