Brew pressure is around 6 bar - Tweak pump or leave it?

[bdbayer]

I have purchased a Vibiemme Domobar Super that makes great espresso. I love the machine and am just trying to improve my technique. I've had the machine just a couple of weeks. It was an upgrade from a Silvia, so I am loving the ability to read some of what is going on with the meters.

The question I have regards the pump pressure meter. I grind at "5" on a Rocky doserless and have tried tamping well beyond 30 lbs. The best I get from that meter is around 6 bar. This really doesn't go much higher even if I grind at "3" and tamp like a brick. When I put a blank in the portafilter the highest it goes is about "10". I am using home roasted coffee only a few days old. I have tried older packaged beans and get about the same.

Boiler pressure is at 1.2 bar.

Is this a normal reading for this machine or do I need to start tweaking the valve? Is it totally dependent on my grind and tamp or do people usually have to make these adjustments?

Thanks for your input in advance.

Barry D. B.

[HB]

As shown in this diagram, for a vibratory pump, the actual pressure is the lesser of the pump's maximum pressure, puck resistance, OPV resistance, and flow rate (the pressure drops for wee little vibe pumps as the flow rate increases). If you're reading 6 bar during an extraction and 10 bar against a blind filter, the puck is offering only that much resistance. The crema production will be lower and the flavor profile will be quite difference (many lever owners and some single origin espresso lovers would argue it improves).

What grinder are you using? How much coffee? Are you pulling single or doubles? While I'm asking questions, would you post a video?


From How can I adjust the brew pressure of a vibe pump espresso machine?

[bdbayer]

Thanks for the diagram. I never understood the 2 hoses. I've seen this before, but never soaked it in.

As for the grinder, Rocky doserless.
Coffee amount, 2 full scoops, tamped below the line on the basket with a flat Bumper tamper.
Pulling doubles.
Video... maybe when my son gets home for spring break, my wife is afraid of the camera.

The crema looks great though and the taste is better than what I can get at any chain shop around here (MI). The double shots takes about 20 to 24 seconds, depending on how fine I have tried to grind. The number on the meter just makes me think I can do better.

Thanks,
BDB

[erics]

Well BDB,

That is one nice tamper you've got there, in addition to the machine of course. I would recommend you go one notch finer on the Rocky and see what the brew pressure/shot timing/volume do with that setting.

I would also recommend you get a nice pocket scale like this:

http://www.amazon.com/Polder-932-...cale/dp/B0002EXVH8

This way you will know how much coffee you are using as coffee density can vary.

A blind basket reading of 9.0 Bar gets you about 8.7-8.8 during brew conditions so you might end up turning the OPV adjustment screw about 1/4 turn CCW after changing the grind on Mr. Rocky.

Skol,

Eric S.

[bdbayer]

Thanks Eric S.

The scale is a great suggestion. Before I got your reply I tried updosing and grinding finer. I was able to get the meter to ramp up to 9.5 and then start going back down to around 8 on a few tries. The scale will help me at least be consistent on the dose when I find the right one.

What that gave me was anything from a double shot that took 40 seconds to one that took 27 seconds. I will play with an accurate measure and lower tamp pressure. That may be the answer. I will say that the shots had a much deeper red/brown crema like I've not seen before, either on the Silvia or the Domobar. I've seen pictures and thought the color on my monitor was off, but this looks great.

thanks,
BDB

[erics]

If you have not undressed Mr. Domobar as of yet, here is an excellent link to what he looks like:

http://www.espressocare.com/InsideVibiemme.html

This link was provided by Ian in another recent post.

Eric S.

[bdbayer]

I actually did take the cover off to check things out, but that page really shows some good detail. That page is now bookmarked under "coffee". Thank you.

Just to update my progress, I am now grinding at 3 with Rocky and not tamping as hard. I get the pump pressure meter up to 9 at times. If I tamp too hard it will go that high (not much above though) but it can take 30 to 40 seconds for a double.

I really like what I am getting now, the flavor, crema, and everything is great. I still need to buy a scale to know exactly what I am feeding the thing, but other than that...I'm a happy camper.

Thanks to all

BDB