This is something Ive been thinking about for a while now. Since rotary pumps have an adjustable bypass, why not just set up a stepper motor to control the bypass valve and use feedback from a pressure sensor to control pressure.

Or am I missing something here.........?

Hi Ross,

There was a thread (that I can't find right now) where someone did just what you are suggesting. I think it was with a solenoid attached to the pressure bypass valve on the pump.

I did it on the cheap, with a T fitting I split the pump output into:

1. [direct] a line going to hx/boiler (i.e. the original line)
2. [shutoff+flow control valve] going to flow control setup (i.e. pressure control line), which is split again into:
   1. [flow control valve] one line goes to refeed rotary input
      
   2. [flow control valve] the other goes to feed general water input:

Here's a quick and dirty drawing I just made to clarify:


I paid ~US$30 for all parts and it works like a charm. The [shutoff+flow control valve] is the only part I adjust pre/during extraction.

This works for my setup. Now, for yours I think the idea to take from what I did is that you can profile extraction pressure by profiling output flow; or to rephrase, by controlling how much restriction you put on the output line over the duration of a shot making session.

And...I think pressure profiling is worth the mess/fuss.

Found it!
Adding preinfusion to a rotary pump machine

Ross,
I was thinking the same thing, ether by bypass on the pump or an addition bypass on the line from the pump that could be manually adjusted with a lever

Also I have the pre-infusion turned on on my linea2av, it seems like alot of people are unaware of this feature. it simply turns the pump on then off then, on but it works

Eric

PRE-INFUSION SETTING
Pre-infusion wets the coffee grinds prior to actually brewing the espresso. The process may
improve the extraction of some coffee blends. To accomplish this the machine opens the brewing
group solenoid valve monetarily, closes it then opens it again. This saturates the coffee grinds and
allows the coffee to swell before the pressure of the brewing cycle is applied to the extraction.
To turn this feature on you must turn the master switch off. Hold the single short dosage button
on the left group (first dosage button on left) while turning the master switch back to the on position.
The LED over the continuous (spiral) switch will light up. Switch the machine off, and then back
to on. To turn this feature off, hold the single normal dosage button on the left group (second dosage
button on left) while turning the master switch back to the on position. The LED over the continuous
(spiral) switch will light up. Switch the machine off, and then back to on. If you program the left
most group in this fashion it will memorize the feature for each group. If you desire this feature for
some groups, but not all the groups, you may program each group individually.

Hi Max,
I want to set this up on my Linea before it goes in to my new shop, so manual controls are out as I want to use a microcontroller to handle the pre-infusion & control the pressure. I want to recreate a spring lever type profile to start with.

Eric,
I cannot do the electronic pre-infusion on my Linea as it is a 1994 model & the brain does not support the on/off style pre-infusion. I have another Linea on the workbench that does support it though, iirc its a 1998 model.

Hi John,
A recreation of a spring lever profile is just what I want to start with, plan to experiment with other profiles from there. I suspect a profile may need to be changed as the coffee degasses to achieve consistency in a commercial setting.

JohnB. wrote:http://www.keesvanderwesten.com/news_idro-matic.html

THAT was the coolest thing I've seen in a while. Amazing.