Bezzera Strega Mods: effect on taste and workflow - Page 3

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mrgnomer
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#21: Post by mrgnomer »

Found an Ulka data sheet on the E series. Flow rates from 4 to 7 are interesting. No specs on an 8.

https://cdn.shopify.com/s/files/1/0632/ ... 1679587651
Kirk
LMWDP #116
professionals do it for the pay, amateurs do it for the love

jpaulm
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#22: Post by jpaulm »

So if I'm understanding this correctly, changing the vibe pump is a way to change the pre-infusion pressure? The group head will only pressurize to the maximum capability of the pump - 2 or 4 or 6 or 8 bars, etc.? But you would have to live with that loss of higher capacity from the stock pump - and the (admittedly imprecise) adjustability from timing the pump pre-infusion that goes with it.

So 2.5 bars would be higher than boiler pressure from a dipper, but roughly the same as line pre-infusion. 4 bars might be interesting and allow for a quicker/fuller saturation of the puck while still gentler than stock. Am I right in understanding that the flow rate will not change that much because of the capacity of the tubing carrying the water to the grouphead?

BKH (original poster)
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#23: Post by BKH (original poster) »

I'm not knowledgeable enough to comment on all the technical aspects but I did measure the water debit of about 10ml/sec with the EP8 and no portafilter. This is less than its flow rate on the spec sheets.

What I notice in practice is that I still grind at pretty much the same grind settings with the lower pressure pump. I get drips appearing in about 10 seconds from pump on but it doesn't flow like full pressure shot. I considered a slightly higher rated pressure Ulka pump but wanted to try the more extreme from stock because taste wise.... I'm not sure I'm able to taste the difference from how I was pulling shots before. My weight of shot with a few seconds of drip during preinfusion to end of spring stroke is 50g now. Maybe closer to 60g before.

And if it doesn't work out it's simple to go back to the stock pump. So far I like it.

Marcje
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#24: Post by Marcje »

I have put this pressure regulator between the pump and the group.
This allows you to use any pre-infusion pressure between 1 and 12 bar (between 1 and 3bar I actually use the line pressure btw). Works really well.


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Stephane_Paris
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#25: Post by Stephane_Paris »

Marcje wrote:I have put this pressure regulator between the pump and the group.
This allows you to use any pre-infusion pressure between 1 and 12 bar (between 1 and 3bar I actually use the line pressure btw). Works really well.
Hi, you have to open the Strega to modify each time so ?

Ref of you pressure regulator ?

Thank's ;)
LMWDP #588.

Marcje
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#26: Post by Marcje replying to Stephane_Paris »

I put it under the lid (I don't use the tank anymore, so could use that space).
Here it goes to 9bar, but the regulator goes to 12... (for the spinal tap mode 8) )


doobedy
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#27: Post by doobedy »

jpaulm wrote:So if I'm understanding this correctly, changing the vibe pump is a way to change the pre-infusion pressure? The group head will only pressurize to the maximum capability of the pump - 2 or 4 or 6 or 8 bars, etc.? But you would have to live with that loss of higher capacity from the stock pump - and the (admittedly imprecise) adjustability from timing the pump pre-infusion that goes with it.

So 2.5 bars would be higher than boiler pressure from a dipper, but roughly the same as line pre-infusion. 4 bars might be interesting and allow for a quicker/fuller saturation of the puck while still gentler than stock. Am I right in understanding that the flow rate will not change that much because of the capacity of the tubing carrying the water to the grouphead?
This all sounds right to me. 2.5 bars is a great down-the-middle preinfusion pressure, and brings the Strega much closer to a classic lever machine.

It's just set and forget, and because I am lazy I love that, but it will take your maximum shot weight down to about 50g, which has a lot of implications for how the shot tastes. All for the better as far as I am concerned, because as the shot is ending (for me, around 35-40g usually), the spring is really running out of steam compared to a higher preinfusion pressure, making the whole process more forgiving. Even the last 10g dribbling out of a dialed-in coffee is inoffensive, no bitterness.
BKH wrote:I got the EP8 Ulka pump and like the changes. As mentioned earlier I get the same flow rate, about 50ml total shot volume (without too many drops during preinfusion). And it is very quiet.

I wasn't able to remove the inner spring easily so I just left it. With the new pump the catch is higher so I imagine my peak pressure is closer to 9 bar anyway.

Overall I like this simple change that takes the edge off the Strega and makes a more consistent preinfusion. Maybe some day I will PID the group heaters...
Hey, you actually did it! Glad you didn't find it a waste of time.

I measured the same 10ml/s as you, and that made me curious enough to test the pump connected without the outlet tubing, and it flowed at the rated 20ml/s. The default seems to work fine, but I wouldn't mind a faster grouphead fill. Still tame compared to the firehose of a dipper.

If you ever decide to PID it, hit me up. I will happily answer any questions I can. It is scary stable now, and I have the grouphead a good 3-4C cooler than it was from the factory, at least according to the temperature strip stuck to the front.

As far as the inner spring, you might just need a cheap adjustable pin wrench from Amazon to get it started. It should be a lot easier than switching out the pump! But like you said, the lever catches a little higher up with lower preinfusion pressures, so you are getting lower peak pressures either way. Sounds like bostonbuzz still was hitting 9-bars with no inner spring and 2-bar preinfusion, though, and I definitely prefer the lower pressure.

BKH (original poster)
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#28: Post by BKH (original poster) »

doobedy wrote: If you ever decide to PID it, hit me up. I will happily answer any questions I can.
Will do. It will probably be a while before I PID! For temp I currently am using a metal puck screen that cools the super heated water that initially comes out of the HX and find the stock temperature good for most of what I drink without a flush.

After replacing the pump I do wonder about eventually modding my Strega tank version into a plumbed version that bypasses the pump. Switching pumps is definitely less hassle.

I swear the Strega is a good machine without the mods but it is kinda fun to think of the tinkering one can do!

doobedy
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Joined: 5 months ago

#29: Post by doobedy »

BKH wrote:Will do. It will probably be a while before I PID! For temp I currently am using a metal puck screen that cools the super heated water that initially comes out of the HX and find the stock temperature good for most of what I drink without a flush.
It's probably worth saying that the "95C" thermostat that the Strega ships with is not a precision device, and I'm sure some run hotter or cooler than others. Mine was ruining coffee even using a puck screen and flushing steam before a shot. 99% sure I just got unlucky.

The very first mod I did was installing one of these: https://www.amazon.com/gp/product/B0838RX7P6/ and it actually pissed me off that a $9 part was responsible for me having such a bad time for so long. Now my two temps are with or without flash boil flushing :) PID has been set to 92C since installing.