Cimbali Junior S1 over pressure - Page 2

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
User avatar
civ

#11: Post by civ »

Hello:

Hope you had a nice Xmas. 8^)
Ians wrote: ... cleaned things. replaced stat with a new sirai unit and adjusted.
Right.
If I recall correctly, this is the usual layout of a Cimbali one group single boiler HX of which there are many models, all more or less the same:



See the red circles?
They indicate the places where deposits and scum usually lurk, especially in situations of poor or inexistent maintenance.

As you can see, two pipes lead to the pressurestat and one to the manometer.
They have to be squeaky clean on the inside.

Did you put them in a hot white vinegar bath for a good while and then then checked them out?
There are a lot of how-tos here at HB indicating what/how to do it.
Sometimes the use of acid is required, you may want to have a read.
Ians wrote: ... then the stat brings the pressure up to about 1.5 bar!
Did you run the manometer test I suggested?

The test works because it allows you to compare pressure readings from the same place (boiler) via two locations at the same time.
Replacing the suspicious manometer with another will only tell us something about the manometer and nothing else.

Run the test and tell us how both the manometers read.
You will not be able to adjust boiler pressure properly if the manometer you are using is not reading properly.
Ians wrote: ... valve on the front drips ...
... rubber seal a bit old and hard ...
Not surprised.
Ians wrote: ... patch on the end ...
That is the OVP (over pressure valve), it has a very hard spring against which pump pressure works.
It is supposed to be set to around 8.00/9.00 bars and will open up when the pressure against the coffee grounds in the portafilter basket reaches the set value.

You need to replace the original seal with another the same dimensions and similar material.
A bike patch will not do.
If the OVP leaks, the hydraulic circuit is compromised and pulling a proper shot is not possible.
Ians wrote: ... where to from here?
I'd run the test I suggested after making absolutely sure that the piping in the diagramme above is clean.

Once we know what/if the readings show/match (with the pipes cleaned) we can go forward.

Cheers,

CIV

Ians (original poster)

#12: Post by Ians (original poster) »


thank you for the suggestions again. and happy new year!
i had cleaned those pipes in citric acid but pulled it all off and have done it again and the pressure test as you suggest. I didn't find any blockages, ran some heavy mono fishing line though, soaked in white vinegar, flushed, reassembled, and tested. now Im getting much more consistent pressure and it doesnt seem to be spiking, win. pressures equal on both pics as per your technique.
have ordered the correct OPV seals, luckily good suppliers in Oz
i had one of these machines years ago and thought i could use it but Im learning how little I knew after reading about grinders, tamping, WDT etc etc on here, great resource thanks all who contribute.
picked up a super jolly yesterday for AUD$250 with a 3d printed doserless face mod but my locals are shut so can't buy beans, using reground, 10 sec pours, a LOT to improve.

User avatar
civ

#13: Post by civ »

Hello:
Ians wrote: thank you ...
... happy new year!
You're welcome/likewise.
Ians wrote: ... cleaned those pipes ...
... pressure test ...
... flushed, reassembled ...
... consistent pressure ...
... doesnt seem to be spiking ...
... pressures equal on both pics ...
Right.
Now you know that the on-board manometer is registering properly.
There must have been something in one of the pipes, vinegar took care of it.
Ians wrote: ... ordered the correct OPV seals ...
Good.
The cylindrical one is the most important one and hard to source elsewhere, unlike an 'o' ring.
Once you get the replacement seals for the OVP in place you then have to set it properly.

To do this you have to find a way to measure pump pressure at the brewhead.
One way is with a PF with a manometer attached to it, too expensive to take a reading once in a blue moon.

But ...
You already have an extra manometer which reads properly and you also have an extra port on the OVP where (at some time) Cimbali/Faema machines such as this one attached brew pressure part of a twin reading manometer such as this one:


image courtesy espresso.co.nz
Cost cutting measures brought along its demise.
It is available, but if you have set your OVP properly, not really necessary.

This is the OVP valve in these Cimbali machines:



It is behind the splash screen which you have to remove to do this.
The valve has three threaded ports and one unthreaded port.

The threaded ports are: one opposite the adjustment screw to receive water from the pump and two more at 90° and opposite each other.
One of these threaded ports (pointing up) goes to the brewhead and the other (pointing down) is closed off with a long nut with a block piece inside.
This last one is for taking pump pressure readings on a dual scale manometer.

The unthreaded port points to the back of the machine and takes a silicone hose to dispose or recycle the water output from the valve when it opens.

Taking off the nut/block piece gives you a place to attach a silicone hose to with a manometer on the other end.

---> Be very careful and don't lose these two: they are unobtanium Serto brand parts. <---

You will be measuring ~ 9.0/10.0 bar instead of 1.6 bar, so secure both ends of the silicone tube tightly with pair of small zip ties.

You would need a blind basket but if you don't have one you can close off the holes of a plain basket with some duct tape or similar.
Doesn't have to last long and it is not a problem if it leaks a wee bit.

With everything in place, seal the basket, put the PF in place and start the pump.
Read the manometer and stop the pump.

Screw in/out the OVP valve adjustment screw and repeat till you get a reading just below 8.5 bar.

That's about it.
Once you have this done, you should be able to enjoy your Cimbali.

Best,

CIV

Ians (original poster)

#14: Post by Ians (original poster) »

thanks CIV once again!
Ive found a 10 bar gauge and once the OPV parts arrive I will set it. may be a bit slow given time of year but will report back,
best
ian

User avatar
civ

#15: Post by civ »

Hello:
Ians wrote: thanks ...
You're welcome.
Ians wrote: ... found a 10 bar gauge and once the OPV parts arrive I will set it.
... will report back,
Right.
Keep us posted.

Best,

CIV

Ians (original poster)

#16: Post by Ians (original poster) »

finally the pressure gauge arrived so have replaced the OVP seals (both) and connected up to monitor as shown in the pic. initially the gauge oscillated so fast i couldn't read it so sealed up the gauge with hot glue, drilled a small hole, filled it up with oil and sealed then take 2. it was over 10 bar, now its 8.5bar, so I ground, tamped and poured a 60ml shot thinking it would be slower but it poured in 10 seconds. the OVP has water pour out of it now at this pressure setting. grinder is super jolly set very fine and burrs are good.

thanks in advance!

User avatar
civ

#17: Post by civ »

Hello:
Ians wrote: ... pressure gauge arrived ...
... replaced the OVP seals ...
... connected up to monitor ...
Good.
Ians wrote: ... gauge oscillated ...
... sealed up the gauge with hot glue ...
... filled it up with oil ...
Very ingenious of you.

This unsteadiness is due to the viberation pump which oscillates at line frequency.
ie: on/off at 50/60 Hz. depending on your location.

It can also be be solved with a (much) longer, spiraled tube which will absorb the vibrations.
Ians wrote: ... was over 10 bar, now its 8.5bar ...
Is this 8.5 bar measured while actually pulling the shot?
Ians wrote: ... poured a 60ml shot thinking it would be slower ...
... poured in 10 seconds.
Roughly 15/20s short.

Ideally, you would measure the pressure with a loaded portafilter in place while pulling a shot.
If you are too full of caffeine or don't have old coffee to test, you can use a blind filter.

If not, you are not measuring brew pressure.
ie: there is no resistance (to the pump at the basket) to be measured.

Best,

CIV

Ians (original poster)

#18: Post by Ians (original poster) »

thanks CIV, its measured with a blind protafilter. the oil has made the pressure measurement quite steady, I was pleased with that!

the amount of water pouring out the vent arm of the OVP in the picture, is that normal? seems like a lot. that's with vibe pump running and blind portafileter basket and set at 8.5bar brew pressure.

its nighttime here, more experiments in the morning...

User avatar
civ

#19: Post by civ »

Hello:
Ians wrote: thanks ...
You're welcome.
Ians wrote: ... measured with a blind protafilter.
Right.
Ians wrote: ... amount of water pouring out the vent arm ...
While pouring a shot, the pump sends water to the PF, slowly ramping up.
If the pressure reaches the OVP set point, it opens up reducing the pressure and closing up again as it is reduced.

Now, this is a 30s long dynamic process in which the OVP is regulating / throttling its output to keep the pressure at the PF at the set point.
ie: think a centrifugal speed governor.

Now, with a blind basket, no water is going past the PF so whatever the OVP pressure is set to, the water will run off the OVP output.
ie: nowhere else to go.

Your pressure is now set at an approximate value and what you need to do now is mimic a loaded portafilter to rule out grinding issues.
ie: bad setting, stale coffee or whatever.

Wipe clean of oils with some alcohol and tape up the bottom of a basket with duck tape or similar.
Once you do that, with a thin sewing needle punch 3 or 4 holes in the duck tape and measure the output in 30s.

It should be ~ 70/75cc.. I am allowing for ~ 10/15cc which would be absorbed by the ground coffee in the basket.

Adjust the amount of holes as needed to get that value and then try the OVP experiment again.

Best,

CIV

Ians (original poster)

#20: Post by Ians (original poster) »

making consistently satisfactory coffee now. thanks CIV. I hope this thread is as useful to others as it has been to me.