I own a La San Marco Flexa 85 (pour over version) and recently tested it with a pressure gauge PF. Noticed that it would go way past the 10 bar mark without anything coming from the return line in the tank so I said to myself "no problem, time to clean a bit the OPV".

I opened the machine (first time) and to my surprise found I this:



Both are ODE solenoid valves. The one at the front gets water from the group head and discharges it to the dip tray when pressing the button to end the brewing process, so it's doing what a 3way valve would do in a "classic" system.
The one at the back is getting water from the top of the brew boiler (the machine being a DB system) and discharges it inside the water tank via a soft plastic water line. The machine does not have a classic OPV valve (spring type) - the pump (ULKA, vibe pump) delivers the pressure directly to the brew boiler via a hard plastic line.


I did some testing and this second solenoid valve is discarding a small amount of water back in the tank when stopping the brew process. This would suggest that the solenoid is working. However, I can let the pump choke itself on a blind PF for 20 seconds at well above 12 bar (didn't had the guts to try it longer and don't know how high the pressure actually went as the gauge is 0-12 bar) and nothing would come out of the return line going to the tank.

The question is: should the second solenoid valve (the one at the back) act as an OPV at the command of some pressure sensor located in the brew boiler? And if yes is there any way to test the pressure sensor?

I presume it to be this little bugger:



Thanks a lot.

You have a unique machine there not readily available in the market over here.

There exists some machines "out there" that do not have an OPV but instead rely on an orifice(s) between the pump and the coffee to reduce the effective pressure presented to the coffee to AROUND 9.0 bar. When you test a machine (that may have an orifice and no OPV) with zero flow from the pump, your reading is not relevant.

The item you identify as a "little bugger" is likely a temperature sensor which regulates the temperature of the brew boiler.

Certainly an email to La San Marco requesting a parts catalog would explain a lot. A "Google search" brings them up quite quickly using your machine as a subject line.

Eric,

The "little bugger" is located al 6 o clock on the boiler. However at 9 o clock there's another probe which I believe to be the one regulating the water temperature in the brew boiler. (it appears to be designed to simply cut the power to the heating element, whose ports are located at 11 and 1 o clock on the boiler)

Indeed, the one at 6 o clock looks very much like the temperature probe found in many hot water boilers but...

I understand the concept that you're describing, but wouldn't it be much more suitable for a manual machine? In one that relies on a pump for brewing it's certainly possible to choke the pump by grinding too fine and I don't see the pump lasting too long if there isn't some sort of pressure relief system.

I'll mail LSM but while waiting for an answer from them(probably tomorrow at best) I'll have to reassemble the machine, so I was hoping that maybe someone is familiar with the model. The Flexa is being sold in the US(not sure if it would be OK to share the link) for a whopping 4295$

What puzzles me is the second solenoid, which definitely could play the role of an OPV if paired with a pressure sensor.