The LM's pre-infusion will require a line pressure to be delivered with the water plumbing-in. Otherwise, there is no water out of the brew group during the pre-infusion stage (e.g. plumb-in directly from the bottled water without external pump).

It looks like that the pre-infusion pressure of the LM is just mirroring the line pressure. Does it mean that with a pressure adjustable valve in the line, I can set the pre-infusion pressure of the LM as I wish (e.g. 0 bar to 6 bar)?

It does.

But there is a lower limit of what the pump is expecting to see, in terms of flow. If you set the pressure too low, the pump may cavitate when trying to fill the boiler or when flushing the group.

This doesn't occur when drawing from the reservoir because, while there is no supply pressure, there is ample flow available when the pump runs. Once you feed the machine from line pressure, the available flow from the pressure reducing valve is proportional to the pressure setpoint. For this reason, LM recommends setting the pressure to 45psi^* and ensuring there is at least 2gpm flow available when plumbing in the machine.

^*45 psi is the baseline (3 bar) and the pressure can be adjusted up or down, as you desire, but the 2gpm is key. If you set the pressure to 1 bar or less, be aware that the 2gpm flow rate still needs to be delivered to the machine and this may require a pressure regulator that is physically larger than what would deliver this flow rate at a higher pressure.

Cheers!

- Jake

Thanks for the advice, Jake. It's clear!

I wonder if I add a relatively "big" accumulator tank (e.g. 3 gallons) in the middle, will this solve the issue given the flow rate of the pump is low (e.g. 0.6gpm)?

I'm in a similar boat with setting up my new mobile setup. I'm going with the Shurflo kit since it will send out 1.9gpm in addition to an accumulator. For a few hundred dollars more I think it will be worth it.

The flow rate for espresso is very, very small, so the small Shurflo accumulator will be fine. If you want to run a pitcher rinse too, a larger one makes sense.


From La Marzocoo GS3 MP pressure gauge pointer jumping

Dan,

not sure about that as the smaller accumulators will "trigger" more often. When you consider the rinsing and backflush etc. So yes the smaller ones work but if there is space a 3 gallon means fewer pump accuations I think.

I recently installed the Caffewerks Flojet low volume pump system (Flojet BevJet compact pump with 1/2L accumulator). It's a great pre-assembled package system and works well off a 5 gallon water jug. I installed it soon after the LM firmware release to take advantage of the pre-infusion. It works as advertised but the 1/2L accumulator still kicks in about every first to second espresso pull. It's certainly louder than the built in rotary pump though, so I'd suggest getting a bigger accumulator if space permits to cut down on the noise factor.