malachi wrote: I checked brew pressure on the machine and it was higher than I like (10.25BAR). But I didn't really want to bother with it. Today I decided to suck it up and dial the brew pressure in to where I like it (right between 9BAR and 9.25BAR).
So even with the Flojet pressure variations (described in the "Flojet and rotary pump questions" thread), with this setup you are able to dial in the brew pressure and maintain it within 0.25 bar?
malachi wrote:I got it dialed in and pulled a shot of the Hairbender that was all I wanted it to be. Dense, rich, heavy in chocolate but with all the fruit and acidity desirable. Layered and complex but with great definition of flavour.
After some more work I had an idea. I did a quick re-plumb to get rid of the FloJet and the water filtration unit. Clarity gone. I then hooked up the FloJet without the water filtration unity. Ah Hah!!! Clarity still gone!! Excited now, I replumbed with no FloJet and no filtration and logged brew pressure. Flutter!! Same with the FloJet and no filtration!! And then with the FloJet and the filtration unit... No Flutter!!!! And clarity!!!
So... new theory (just waiting for Jim or Barry or someone to disprove it) is that it's the combination of brew temp profile and consistent brew pressure profile that creates this clarity.
In trying to understand your theory...do I understand you correctly that you are talking about two distinct pressure parameters:
1. brew pressure profile, a curve that defines the nominal brew pressure value through the course of a shot
2. brew pressure flutter, a description of the fraction-of-a-second water pressure vibrations produced by the pump?
Concerning flutter, vibe pumps produce their eponymous pressure waves at 60 hz. Rotary pumps produce pressure pulses each time a vane passes by the outlet pipe. This works out (in N America) to be about 115 times a second (115 hz).
It's possible to greatly reduce flutter using a "water hammer arrestor" (part number 2522K14 at Mcmaster.com). Also, running the brew water through a gicleur reduces flutter.