Trouble adjusting Vibiemme Domobar Super's brew pressure

[miniman]

Ok! Have been using my Domobar for a couple weeks. Great machine! Still do not think all is right. Get the much talked '4' on my initial reading when pulling shot and water comes through coffee. Best the gauge goes to is '8' Have adjusted pressure under cup heating tray with no changes. 3 full turns right 'plus' direction? BEANS always fresh. Grinder Macap MC4. Any suggestions?

[cannonfodder]

What happens when you use a blank basket? Do you still get 8 bar or does it run higher?

[cafeIKE]

Ok! Have been using my Domobar for a couple weeks. Great machine! Still do not think all is right. Get the much talked '4' on my initial reading when pulling shot and water comes through coffee. Best the gauge goes to is '8' Have adjusted pressure under cup heating tray with no changes. 3 full turns right 'plus' direction? BEANS always fresh. Grinder Macap MC4. Any suggestions?

- With a blind basket what is the brew pressure?
Should be around 9.5 to 11? If it's less, the OPV is too low. Look here for adjustment point.
- What is the boiler pressure? This won't affect the shot brew pressure, but it should be ~0.9-1.1bar.
- How fine is the grind? Can you choke the machine?
Try adjusting the RUNNING MC4 until you can just hear the burrs touching, then back off about 1 or 2 numbers on the ring from there.

[Randy G.]

Ok! Have been using my Domobar for a couple weeks. Great machine! Still do not think all is right. Get the much talked '4' on my initial reading when pulling shot and water comes through coffee. Best the gauge goes to is '8'

A low pressure and fast flow is/might be a problem with:
1) the coffee (old, stale, over-roasted...?)
2) the grind (too coarsely ground!)
3) problem with dose/distribution/tamp
4) Not doing a cooling flush before pull and coffee is being fractured by blast of steam

Grind finer and tamp more gently until the machine is choked, and then coarsen up the grind, little by little, until things improve. That's where I would suggest starting.

.... Have adjusted pressure under cup heating tray with no changes. 3 full turns right 'plus' direction? BEANS always fresh. Grinder Macap MC4. Any suggestions?

That screw, under the cup-warming tray and under the black plug, adjusts the pressurestat which raises the pressure in the boiler which gives you a hotter brewing temperature. That is not what you want. Your perceived problem lies with brewing PRESSURE which is adjusted by the overpressure relief valve which is a different part located in a different place.

As cafeIKE stated, put in the blind basket and run the brew function. Tell us what you get on the brew gage then.

[HB]

Have adjusted pressure under cup heating tray with no changes.

The maximum brew pressure is adjusted by the over pressure valve (OPV); it's the valve with the big slotted brass screw below:



See Adjusting brew pressure for background information. The boiler pressure (~boiler temperature) is controlled by the pressurestat; the adjustment on the Super is show below:



Assuming it was correctly adjusted from the factory (1.1 bar max), you should have no need to adjust the boiler pressure.

[miniman]

Ok! I took comments last night and adjusted the OPV, instead of pressurestat. I have just the right screwdriver (LARGE) to get at it. I gave it a 1/2 turn (clockwise) and put everything back together to use this morning. I cranked it up and tried to pull a flushing rinse through the portafilter. I could not move the lever! (Maybe a safety interlock?) I briefly pushed the microswitch and saw the manometer go to 12!
I opened the machine and turned the OPV back 1/4 turn and tried everything again. My boiler runs right near the "1" mark or slightly higher (to the tip of the green zone). Loaded a shot and initially got "4" (like I do when I put the blank in) then went up to "9" Perfect shot! Did another one for my wife and it went between "9-10" I backed the OPV off another 1/4 and will re-try tomorrow.
Moral: a little turn on the OPV makes big changes unlike the pressurestat screw.

P.S. Make sure you unplug your machine BEFORE poking around with a screw driver!
Ha, ha, Yeoooowwww! Ha, Ha!

[cafeIKE]

Ok! I took comments last night and adjusted the OPV, instead of pressurestat. I have just the right screwdriver (LARGE) to get at it. I gave it a 1/2 turn (clockwise) and put everything back together to use this morning. I cranked it up and tried to pull a flushing rinse through the portafilter. I could not move the lever! (Maybe a safety interlock?) I briefly pushed the microswitch and saw the manometer go to 12!
I opened the machine and turned the OPV back 1/4 turn and tried everything again. My boiler runs right near the "1" mark or slightly higher (to the tip of the green zone). Loaded a shot and initially got "4" (like I do when I put the blank in) then went up to "9" Perfect shot! Did another one for my wife and it went between "9-10" I backed the OPV off another 1/4 and will re-try tomorrow.
Moral: a little turn on the OPV makes big changes unlike the pressurestat screw.

P.S. Make sure you unplug your machine BEFORE poking around with a screw driver!
Ha, ha, Yeoooowwww! Ha, Ha!

If you are getting a large shot to shot variation on the brew manometer, you could have a sticky OPV. Over the course of a year, the shot to shot brew pressure variation on my machine has varied ±½ pointer width or ±¼bar.

From what Cannonfodder and others have said, a blind basket setting of 10bar should give great shots.

[DavidinVT]

Moral: a little turn on the OPV makes big changes unlike the pressurestat screw.

Yes, this is exactly what I've found (and noted on an earlier thread) -- very slight turns of the OPV screw make for VERY BIG changes in brew pressure.

And also remember, whereas the pressurestat adjustment is counterclockwise for MORE boiler pressure, the OPV adjustment is exactly the opposite -- it's clockwise for GREATER brew pressure.

Best wishes,

David

[Randy G.]

Ok! I took comments last night and adjusted the OPV, instead of pressurestat. I have just the right screwdriver (LARGE) to get at it. I gave it a 1/2 turn (clockwise) and put everything back together to use this morning. I cranked it up and tried to pull a flushing rinse through the portafilter. I could not move the lever! (Maybe a safety interlock?) I briefly pushed the microswitch and saw the manometer go to 12!
I opened the machine and turned the OPV back 1/4 turn and tried everything again. My boiler runs right near the "1" mark or slightly higher (to the tip of the green zone). Loaded a shot and initially got "4" (like I do when I put the blank in) then went up to "9" Perfect shot! Did another one for my wife and it went between "9-10" I backed the OPV off another 1/4 and will re-try tomorrow.
Moral: a little turn on the OPV makes big changes unlike the pressurestat screw.

Well, you took some of the comments.....

Better Moral 1: make sure that the problem is with the machine before changing settings
Better Moral 2: if you are not absolutely sure what you are doing, do not adjust anything

Your assumption seemed to be that there is a problem with the machine- if that was the case then the best thing would have been to find the problem instead of making adjustments of which you were not sure. Why? if there is a problem with the OPV, then adjusting it to a higher pressure may cause damage or premature wear to the machine. (EXAMPLE: OPV sticking open causes low pressure. You adjust to a high pressure and now it sticks closed)

I am not stating that there is not a problem with the machine- there could be. Your sticking operating lever indicated that there may be a bit of something in the brewhead causing problems. BUT, a safer set of guesses as to the cause of a low indicated brew pressure are too coarse of a grind or poor distribution or tamping. Maybe even a cracked basket.

Simply finding screws to turn and fiddling with them on a $1300+ machine is generally not recommended.

The advice you received earlier was to use the blind filter and check the reading on the brew pressure gage. That is the easiest and best (and safest) way to judge whether or not the OPV is operating properly.

The advice I originally gave was to grind so fine that the machine is choked and slowly adjust the grind a little at a time to a more coarse setting to find the correct grind (and thus eliminate that as a possible cause of your problem). IIRC, you originally said that the flow was too fast and the pressure reading was too low- those two occurrences together could indicate that the OPV was set TOO HIGH, not too low.

Your original adjustment of the pressurestat, mistakenly thinking it would control brew pressure, seems to indicate that you may not have a full understanding on how the machine works. Please proceed carefully.

[HB]

Your original adjustment of the pressurestat, mistakenly thinking it would control brew pressure, seems to indicate that you may not have a full understanding on how the machine works. Please proceed carefully.

Also check out the site's FAQs and Favorites, Resources, and especially the recommended reading.

[jesawdy]

Don't forget you have that nifty three-position power switch. If you need a session to dial in your brew pressure, use the 'Fill" position so that that you don't have to contend with a hot machine between testing OPV settings. And use the blind basket to test as others have said.