Bezzera Strega mods - Page 2

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Marcje (original poster)
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#11: Post by Marcje (original poster) »

bostonbuzz wrote: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?
In short: For the manometer on the grouphead, I drilled a hole through the piston + rod, and I had to do some machining in the head to get 'to the ouside world'.
For the manometer in the front cover (+ pressure release), I removed the 2 bottom seals of the piston (only using the top one) and filled them up with teflon rings. Then I put 2 solenoid valves in the feed line, between the HX and the grouphead. One valve open/block the flow from the HX to the grouphead, and one valve release the pressure (into the drain).
Not sure if I would do all of that with a new machine, but ours is quite old and decided to take the risk. So far it's working ok...

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bostonbuzz
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#12: Post by bostonbuzz »

I just fully understood what you wrote, thanks for the explanation. Quite a mod to change the bottom 1/2 of the piston!

I was wondering how you got a reading on the gauge and the solenoid to function given that the piston covers the water hole quite soon in the stroke. I just installed one on mine and it's really only useful for preinfusion. That makes sense that the hole being open all the time through to the portafilter would allow for that. The flush function would be important since the group water tube may have some coffee from the exhaust still in there, as there is no back-flushing a lever. Cheers.
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Stephane_Paris
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#13: Post by Stephane_Paris »

I thought when lever down until the pump fill the group the pressure will go to 9 or 10 bar.. look like around 2 bar on you two videos.
LMWDP #588.

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baldheadracing
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#14: Post by baldheadracing »

Marcje wrote:... For the manometer in the front cover (+ pressure release), I removed the 2 bottom seals of the piston (only using the top one) and filled them up with teflon rings. Then I put 2 solenoid valves in the feed line, between the HX and the grouphead. One valve open/block the flow from the HX to the grouphead, and one valve release the pressure (into the drain). ...
That's a very impressive mod. Kudos.

Do you have any tips on making the hole in the machine's faceplate for the additional gauge?
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

Marcje (original poster)
Posts: 97
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#15: Post by Marcje (original poster) »

Thank you! I used this drill and lots of lubricant.
It was a bit nerve wrecking to be honest...


Marcje (original poster)
Posts: 97
Joined: 5 years ago

#16: Post by Marcje (original poster) »

Stephane_Paris wrote:I thought when lever down until the pump fill the group the pressure will go to 9 or 10 bar.. look like around 2 bar on you two videos.

The machine is plumbed and I was using the line pressure, not the pump.

Marcje (original poster)
Posts: 97
Joined: 5 years ago

#17: Post by Marcje (original poster) »

Next useless, but fun mod: First step of connecting the Strega to a pressure monitoring dashboard/app.

Marcje (original poster)
Posts: 97
Joined: 5 years ago

#18: Post by Marcje (original poster) »

Since I can adjust the temperature of both the boiler and the group individually, I was curious what the actual shot temperature was. So I machined a 'custom' piston on the mini lathe and glued a thermocouple in it (leaving the head exposed) to see if I could measure it. Getting the wire out of the group head was a bit of a puzzle, but it worked. Not sure how long it will last, maybe the wire is damaged after a few days, maybe not :wink:

The boiler was set at 122 deg C and the group on 88degC. Funny enough, the shot temperature was lower that I thought. For the second shot I raised the group temperature to 91degC. Understandably the pressure was highest at the Pre-infusion, but there was also a small 'bump' when the lever was released. Next few days I'll be experimenting a bit more and will also add a pressure transducer so I get the actual pressure and temperature for each shot.
And the espresso did not taste any better 8)




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bostonbuzz
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#19: Post by bostonbuzz »

I found similar things when I made my own scace device a couple weeks ago. A bit inconclusive as I couldn't get a consistent reading with a bare k-type thermocouple and a needle valve in an epoxy-filled basket. However, shot temperature did appear low. I raised my group temperature to 194F / 90C. Interested to see what you find.

Since you are on a modding streak, I had a crazy idea to make a dual boiler. Get a spare HX from the strega (I think it's around 150ml?) and attach it an inch from the grouphead. Put a 100-300W cartridge heater in it, a temperature sensor, and an over temp switch. Then you want a little mixing of the HX water and the cold pump water to get something close to brew temp to fill this new boiler when pulling a shot (like La Marzocco Linea Mini/Micra). Run the gouphead temp around 200F. Should be dead stable! What do you think?
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BKH
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#20: Post by BKH »

Interesting setup and measurements. I just have a stock Strega but still find this cool. I remember seeing a temperature reading of the front of the group, away from the cartridge heaters, settling around 83°C. Where are you measuring the group to get your temperature reading of 88°C? With a group at that temp and boiler at 122°C, I find it surprising that the measured water temp would be so low.