Binary vs. variable flow control

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bean74

#1: Post by bean74 »

It's been two months of playing with flow control, added by dimmer mod to my Classic in this thread, and I'm beginning to wonder if there's a better way to achieve the desired result.

I've been using the dimmer mod to hold the machine under 1 bar for about 7 seconds from pump charging up, roughly the time it takes to push the first drops of liquid through the puck and into the cup, at that pressure. I actually suspect something less than 1 bar would be even better, but there's really just no way to reliably hold the machine at any lower number with a dimmer switch and reading off a 15 bar gauge. Even targeting 1 bar, my pressure can vary ±50% (ie 0.5 to 1.5 bar), depending on how quick the machine charges up and how quick my response is with the dimmer. Not ideal.

I'm thinking a second OPV set at the lower pressure and solenoid valve are a better solution. Tee this assembly into the line between pump and 9 bar OPV, and switch it in/out at the beginning of the brew, for a more repeatable pre-infusion. Has anyone done this? Are there any machines that use this operating principle?

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Jeff
Team HB

#2: Post by Jeff »

Slayer uses that general approach of a switched, two-rate extraction.

At some point, you should ask yourself what you're trying to achieve and let that guide you, rather what gizmo you can add.

With a machine with highly controllable extraction profile and medium-light and lighter coffees, I'm finding a "zero-flow" hold, monitoring pressure in the basket valuable. Others are using similar approaches. "Slayer shots", while groundbreaking for their time, are not the end game for many coffees and espresso styles.

DeGaulle

#3: Post by DeGaulle »

bean74 wrote:It's been two months of playing with flow control, added by dimmer mod to my Classic in this thread, and I'm beginning to wonder if there's a better way to achieve the desired result.

I've been using the dimmer mod to hold the machine under 1 bar for about 7 seconds from pump charging up, roughly the time it takes to push the first drops of liquid through the puck and into the cup, at that pressure. I actually suspect something less than 1 bar would be even better, but there's really just no way to reliably hold the machine at any lower number with a dimmer switch and reading off a 15 bar gauge. Even targeting 1 bar, my pressure can vary ±50% (ie 0.5 to 1.5 bar), depending on how quick the machine charges up and how quick my response is with the dimmer. Not ideal.

I'm thinking a second OPV set at the lower pressure and solenoid valve are a better solution. Tee this assembly into the line between pump and 9 bar OPV, and switch it in/out at the beginning of the brew, for a more repeatable pre-infusion. Has anyone done this? Are there any machines that use this operating principle?
Have you tried bleeding water from the steam wand during the early stages of the extraction? I can't tell from my own experience whether it is feasible/reproducible or not, but it has been suggested here and there from time to time.
Bert

bean74 (original poster)

#4: Post by bean74 (original poster) » replying to DeGaulle »

Thank you for the recommendation, I should give that another try. I used to use that method, flying blind and just opening it 1/4 turn until I'd see first liquid in the cup, prior to installing the pressure gauge and dimmer mod. Since installing the dimmer and pressure gauge, on the same day, I hadn't really thought to go back to playing with the steam knob.

Since the timing for the pump to charge up is a big variable, and very dependent on dimmer setting, this may improve the process. However, I can't help but think a binary switch from ~0.5 bar to 9 bars might still be preferable to any manual variable control, on a machine where things can happen quickly.

bgnome

#5: Post by bgnome »

Could you not just wire the existing solenoid to a manual switch? If you are looking to pre-infuse at a low pressure, why not use the steam pressure in the boiler?

bean74 (original poster)

#6: Post by bean74 (original poster) » replying to bgnome »

That's an interesting idea. However, the steam pressure in the boiler appears to be highly variable, it reads anywhere from 0 to 4 bar, depending on whether machine is coming up from a cold start or recovering from a prior shot. I actually usually relieve it by cracking open the steam wand for a second and re-closing before I pull a shot, if I see any reading on the pressure gauge, never thought of trying to use that pressure for pre-infusion.

Muscle memory is a funny thing. I've pulled more than a half dozen shots for myself, since DeGaulle suggested trying to play the steam valve, and each time I kick myself half way thru the shot for forgetting to try this. I had been entertaining over the weekend, and had to pull many shots for others, so it wasn't the time to experiment with new technique.

bgnome

#7: Post by bgnome »

As for the variability, the steam pressure should be constant at steady state for a given temperature. It could be reading low from a cold start due to air in the boiler.

bean74 (original poster)

#8: Post by bean74 (original poster) » replying to bgnome »

It actually reads high when the machine has come up from a cold start, due to pressure building with temperature increasing from 23C to 93C.

vas

#9: Post by vas »

If you're modding the machine anyways, why not use some MCU controlled mod for the flow profiling? Like Gaggiuino e.g.

bean74 (original poster)

#10: Post by bean74 (original poster) »

I wasn't even aware that existed. Looks very cool. Will investigate further.