Bezzera Strega mods

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Marcje

#1: Post by Marcje »

Hi,

Our Strega is my everlasting hobby project and I made some mods recently.
Added:
- 2 PID's (boiler & group)
- A manometer on the group head
- A flushing switch (without activating the lever)
- A pressure release switch.

So far it's working ok, time will tell how useful and robust all of this will be.
The coffee does not taste any better with all of this btw!

I want to have better control of the pre-infusion, so the next iteration will involve a rotary pump, and I have some ideas integrating a pressure and flow meter using a Raspberry Pi.
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Cuprajake

#2: Post by Cuprajake »

Some really cool mods there, love the hidden pid controls

My cat also shouts at me like that too :D

jpaulm

#3: Post by jpaulm »

Those changes are amazing. I am in awe! Coffee looks good too.

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bostonbuzz

#4: Post by bostonbuzz »

Very nice! I think the Strega really has legs as a machine due to the group head heaters.

I'm curious about the flushing and group pressure release. I thought the only tube going into the group is covered by the piston seals when the lever is down.

Did you drill a new hole and tap the backside for a solenoid teed to the drip tray line? Surely you won't be selling this as a kit so you could snap a photo or two. :wink:

How did you do the flush with the pump? Maybe teed the pump to the release solenoid and trigger both the solenoid and the pump with the button?

I'm jealous of your group head manometer. I'm fitting one to the brew circuit but I don't have a lathe, so no chance on boring my shaft like you did here.

Question: if you let the group head totally fill does the piston produce the same pressure when you release it or does it change based on the preinfusion pressure?


I have all the parts on order for a bldc gear pump to replace the vibe pump. It will have no programming, just triggered when the pump normally is and controlled by a potentiometer. I plan on using the small auber instruments tachometer and modifying the output to read ml/s. So I will have a little control box that will be under the drip tray with a knob and a flow rate readout - totally manual. Hopefully I'll post a thread on it in a month or so.

I got a little tired of my dimmer vibe pump mod changing the pressure based on voltage fluctuations when the boiler and group heaters come on (by a lot).
LMWDP #353

Marcje (original poster)

#5: Post by Marcje (original poster) replying to bostonbuzz »

I'm not 100% sure, but I think I did the same as what KvdW does on the SlimJim Idrocompresso, the Nurri Leva S.A., or the ACS Vostok.
They use the LSM group (I believe), but you can also do the same with a Strega, with some tweaks.

Yes, pre infusion does influence the spring pressure.
If I use the pump for pre-infusion, which I set at 9 bar, then the shot also starts at 9 bar. So the pump pressure compresses the spring until there is an equilibrium. When I use the line pressure, say 1.5 - 2bar, then the shot starts at 7.5bar (I'm using one spring). When I use the pump for PI, the lever also 'starts lower', and the shot volume is higher.

I'm also not totally happy with a dimmer on the vibe pump. Om working on something with a rotary pump at the moment...

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TomC
Team HB

#6: Post by TomC »

Wow! These are awesome modifications! It blows away the stuff I did to mine back in the day. Jim and the other more electrically-minded moderators helped me tweak mine too. Still kinda miss that machine!

The Super Strega: Modifying preinfusion pressures and other functional improvements
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Marcje (original poster)

#7: Post by Marcje (original poster) replying to TomC »


Thank you. Your thread was actually quite helpful for me when I first got the Strega, and I also did the 'vacuum relief valve drain line modification' you decribed then :wink:

Marcje (original poster)

#8: Post by Marcje (original poster) »

Drilled a hole in the front panel and installed the pressure gauge of a Bezzera Mitica.
Reduntant functionality with the pressure gauge on the group head. The family did not notice a difference, so that's good.

Playing with an Arduino and electronic pressure transducer / thermocouple now, so next project would be to build some sort of a real-time dashboard. Useless, but fun!


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JohnB.
Supporter ♡

#9: Post by JohnB. »

Nice clean looking mods! Your pump sounds a lot quieter then I recall mine was.
LMWDP 267

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bostonbuzz

#10: Post by bostonbuzz »

How are you getting the pressure throughout the shot? You u must have drilled a new hole juuust above the shower screen through the back of the group?
LMWDP #353