Profitec Pro 600 2 bar pressure drop

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#1: Post by homeslice »

My Profitec Pro 600 machine is dropping from 9.5 bar to below 8 bar during 25 second extractions. I've adjusted the grind level to much finer and raised the bar pressure 1.5 bars and it still drops significantly. Screen and basket are cleaned every other week. Needle tool is used to break up clumps to basket. Been going on for about 3months. Machine is about 9 months old. Any ideas why?

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#2: Post by Jeff »

OK, let's back up a bit

The pressure gauge on the machine usually reads pump pressure. If the OPV is activating, then it will be close to that pressure. If the OPV is opening, the water that bypasses the brew chamber usually goes through a tube back into the tank or into the drip tray (on vibe-pump machines -- rotary-pump machines use a "bypass valve" on the pump to control the brewing pressure limit).

There is a lot of discussion about what is "right" for the OPV pressure. My own opinion is that over 9 bar is too high. There are many people that have tried lower pressures and prefer the results. Once we get the "pressure drop" figured out, you might want to try a week or two at a conventional 8 or 9 bar, then a week or two at maybe 2 bar lower, so you have an idea of what the difference might be. From there you can adjust to your own preferences.

If the resistance of the puck to flow is high, the the OPV will open and the pressure will be limited to that value. If that resistance is lower, then the pressure may not rise to the point where the OPV opens. What I am guessing is that the puck has "enough" resistance until it starts to dissolve into your coffee. Then its resistance drops. In a well-extracted espresso, somewhere around 20% of it dissolves. This is natural. If your pressure is being limited by the OPV, the flow will increase as the puck erodes. If the flow rate increases enough, the pressure will drop as the pump can't keep up.

A pressure drop, in and of itself, isn't a bad thing. It is a problem if you can't control it and make it an intentional choice.

If that's what is going on, then "grind finer" is the first step. But why didn't that help?

Stale coffee and espresso is a bad combination. Shots that flow too fast are often a sign of stale coffee.

Too fine and it gets very hard for water to move through the puck. It can find weak spots and start to run through those, "channeling". Increasing the pressure only makes things worse, as it has to sustain even higher pressures.

I'm guessing it is not a machine problem or a pump problem, as the pumps tend to last several years. You can check it by finding the outlet of the OPV and measuring the output when using a blind basket. As I recall, the typical Ulka E5 pumps are rated at roughly 180 to 320 cc/min at 9 bar.

I would suggest:

* Confirm that you have fresh coffee from a respected roaster that hasn't been open too long
* Set your OPV pressure no higher than 9 bar
* DIal in the coffee, starting from the coarse side of things and going finer

If you're still having problems, a video of your shot might help