Not really similar in the details, but kinda sorta, sure.

Trying to turn the pump pressure down to 2 or 3 bar on the pump itself is likely a fool's errand. I say likely, because I haven't tried, so it may work just fine, but the idea is fraught with challenges.

The bypass valve in the pump uses a compressed spring and a plunger to determine the pressure. When you increase the brew pressure at the pump, you are putting more preload on the spring, and when you lower it, you are putting less pressure on the spring. There is a limit to how low you can go before the threaded plug that is pressing on the spring simply falls out. Experiencing this point while trying to pull a shot of espresso would be... annoying, to say the least. On top of this, it would take several full turns of the pump adjustment screw to move between a desired preinfusion pressure and brew pressure.

The GS/3 MP leaves the pump pressure alone and controls the brew pressure by taking manual control of the 3-way valve in the group. This gives you a range of about 45 degrees on the paddle where the group is somewhere in between being connected to the pump and the drain tray. Thus you can control the pressure by controlling how much brew water you are sending to the drain tray. Of course, nobody is actually looking at the drain tray to surmise their brew pressure, since there is a handy dandy brew pressure gauge sitting right on top of the group.

One thing I'm surprised I haven't seen in pretty much any pump machine is a dedicated pressure reducing valve for preinfusion. There is certainly room on the micra to install one on the pump discharge. If you really wanted a repeatable 2 or 3 bar preinfusion pressure with the reservoir, just install an OPV and a solenoid valve after the pump with the discharge running back to the pump inlet. When the solenoid is closed. The OPV does nothing and you have your primary pump pressure. When you open the OPV with a switch mounted somewhere convenient, like the mid position of the paddle, the OPV comes on line and limits the pressure to whatever your preferred preinfusion pressure might be. You could even use a delay on make relay with a timer and have rock-solid consistency, if that's your prerogative. It might cost $100-$150 in parts, but it would work much better than a long screwdriver.

Cheers!

- Jake

Thanks for response. Yeah, I was making a diagram of the Micra flowpaths yesterday for a heat transfer class I'm teaching and realized the steam boiler feed pressure would be a limiting factor with this arrangement vs. Jake's needle valve mod which reduces pressure at the grouphead inlet. So max steam boiler pressure is about 2 bar plus some head losses would probably limit it to 3-4 bar.

I'm beginning to think I'll holdoff for plumb-in or Jake mod. With the Jake mod, I'd prefer to figure out a way to stick with the "stock or equivalent" piping between the feed manifold and the grouphead/pressure gauge. Previous experience from my own mods or others on here has ingrained a conservative approach to avoid expensive leaks.

Thanks Jake for the bypass valve operation details. This was one of my biggest unknowns.

My initial idea was just to be able to more easily adjust extraction pressures to allow, 6 bar extractions for example. The preinfusion was an afterthought.

6 bar is no issue.

Beware there is a solid rail under the cup tray impeding access to the pump pressure adjustment. This rail must be removed to adjust the pressure currently, but a properly-placed hole in the rail would work just fine.

Thanks Jake!!! That was another unknown.

Linea Micra plumb-in kit already available in Austria.

Price: 318,00€ (incl. 53,00€ VAT)

So I'm wondering, on my La Marzocco App (for controlling the Micra), the brew tank temperature usually displays in green, but sometimes it displays in red...I thought this might have something to do with an indicator of the machine warming up, but the actual red light on the machine is showing a solid red light, so it shouldn't be that.

Can anyone explain the meaning of the two colors on the app?

Thanks!

I believe it works like this. The numbers show the brew boiler temperature and steam boiler water temperature (number) setpoint selected. Green means actual brew boiler or steam boiler water temperature are at or above setpoint. Red means they are below setpoint. Without a way to read actual temperatures; hard to verify. Does it always respond immediately..... ehhh.

Red can also indicate over temp. When reducing the brew temp recently from 203 to 200 the displayed app temp remained red for several minutes before going green.

That would make senese, however, when I first turn on the machine it starts in red...then at some point goes green. None of the changes are associated with the blinking red light on the machine.