Coffee Data Science
New Decent Dispenser Unit Test for Espresso
Airlock Defect
A year after I got the Decent Espresso machine, I performed a unit test on the water dispenser part which sits above the water diffuser above the shower screen. I found major issues with how it distributed water, and when I made some modifications, I was able to get more even water flow. I recently bought the new Decent diffuser and inlet (v2.0), and I repeated the same unit test.
I found the dispenser’s design suffers from three main issues:
- Airlock in the main water path
- Airlock in the 6 exit paths
- Uneven water flow among the holes.
I performed this test using a piece of clear tape and milk so I could clearly see where the liquid was going. I also sat the part on top of a disk so the water could exit the holes.
The water comes in from one side and goes around the ring before filling the exit holes.
Here is a single frame of the full video which shows the water is uneven for the different holes.
This is the start of the water entering the exit holes.
More water progresses, and you can see the air bubble by each hole blocks the water from entirely filling the hole.
Even with the most pressure, some bubble remains. More importantly, two of the exit paths are flowing unevenly.
This does not get better.
The other revealing part of this test is that an air bubble gets trapped in the ring because of the design. I’m not sure how that interferes with water flow, but I’m sure it could cause some uncertainty.
The main symptom I have seen is an uneven flow in people’s shots usually with a eccentric cone when using a bottomless portafilter.
I hope this part could get redesigned. I otherwise like the Decent. I think water input is the key variable of good espresso.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
