How to measure brew pressure on Bezzera Strega

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royi_klein
Posts: 26
Joined: 9 years ago

#1: Post by royi_klein »

Hi all
Since I am having troubles with my shots (overdose + fine grind and still the flow is to quick), I would like to measure the pressure on my Strega.
I was thinking of connecting a pressure gauge to my PF but I will need to drain the water in order to release the pressure somehow, was thinking of connecting a T splitter to the PF and a to it on one side the gauge and some kind of a tap to the other.
Anyone have an example of such/similar thing?
many thanks guys
-Roy

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rpavlis
Posts: 1799
Joined: 12 years ago

#2: Post by rpavlis »

I suspect the tee is the best way to do this. HOWEVER, there is a problem. There are entirely too many kinds of threads for things in the world today.

Portafilters tend to be BSPT, tapered threads with a 55 degree thread profile angle. Other things use BSPP, parallel threads with a 55 degree thread profile angle. Others will use the US NPT, tapered threads with a 60 degree thread profile. Of course to make matters worse the thread pitch varies between NPT and BSPP and BSPT. Strangely much of the world likes to use the British threads on all sorts of products. Of course there are standard metric pipe threads too. Had everyone the sense to use just those there would not be this problem!

One approach is to take a bar of brass perhaps 10x10x25mm in dimensions and drill it on 3 sides with appropriately sized drill bits and then use dies to cut appropriate threads for whatever you need. You probably will need a gauge that goes up to at least 15 bar. (1.5 MPa) You do not one that goes too high, because then there will not be enough deflexion to read accurately.

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naked-portafilter
Posts: 698
Joined: 10 years ago

#3: Post by naked-portafilter »

Hi Royi,

You can do it that way (as described) but you should buy a pressure gauge designed for high temperatures (stainless steel bourdon tube is a must) or use a cooling cycle to bring down temperatures for a low cost pressure gauge. I did it that way (low cost) with an Olympia Cremina a bit differently (Olympia Cremina monitored/controlled pressure profiling [video])

Cheers

Gábor

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radudanutco
Posts: 147
Joined: 11 years ago

#4: Post by radudanutco »

I just wish these brew pressure measurements at the PF level will help you find the clue;

I've made some rough measurements:
as I've found it, the PI pressure is zero, for the first 5-6 secs, as the pump fills the chamber;
then enters the ramp, up to an 10-11 bar (as limited by OPV); mine was at about 10,2 bar;
then follows extraction, with pressure under springs, which takes from 10-11 bar, down to about 5 bar when lever hits the upper resting position;
then the residual pressure decrease towards a final 0 with the remains of gases exiting eventually the cylinder;

this is the "tool" I've used (being in Europe, I do not think any details about components are useful for you, however all - execept the gauge - are 3/8" fittings):


and this is a roughly "simulated" shot:
https://youtu.be/Rvowykmtd7w

currently, the pressure gauge is connected to the pump output and is showing the PI profile: