The way these work, the brew circuit should idle at just under 12 bar. If nothing is leaking or letting pressure off, they'll hold this pressure for quite a long time. If it drops quickly, then something is letting the pressure escape. It will of course, drop somewhat with time and there's no getting around that.

There is nothing in the manual about a "minimum" pressure reading for idle brew pressure. My experience is that it produces best results when the 12-bar value is nominally present and the brew circuit is "primed" (as in flushed with some water). It should not be higher than 12-bar.

My machine is over a year old. I had a check valve stop holding pressure, and LM was very good about sending me a new one. In addition, some of the fittings in the brew boiler showed traces of very, very slow leakage, just mineral build up around them. Resealing these got mine to hold pressure very well, as it did when new.

erics wrote:That is a lot of work . . . thanks. I would like to receive a copy of your drawing(s) and/or sketches. My email is below my sig.

I'll be happy to share it. Had intended to make a Visio drawing of it, but corporate dropped our site license.

I can quickly sketch it out on paper and scan it and share it with everyone. It's pretty fascinating how complex it is.

I have the LMLM hydraulics from their parts manual. Your info would be most helpful.

My intent (should I find the time) would be to create something similar to this:

RockyIII wrote:The same guide says that the brew boiler gauge "should never read above 12 bars of pressure," but I do not see a minimum. Mine runs about 9.0 or slightly higher while brewing, and then goes to 12.0 immediately after I move the paddle to the off position. I tried letting it idle a couple of times to see what would happen to the pressure. One time it fell to 7.0 after 30 minutes, and the next time it fell to 9.0.

Rocky

That's exactly the pressure pattern I see on my GS/3, and I believe it's quite normal for an LM machine.

The 12 BAR ceiling is set by the expansion valve and it looks like you have it set correctly. The brew pressure is set by the pump bypass valve, and it looks like yours is set correctly or close to it. The gauge should read exactly 9 BAR with the portafilter removed (free flow) and should max out a little higher when brewing. How much higher is a function of the puck density and the flow restrictor (gicleur) size, which I believe is 0.8mm by default but some owners have replaced it with a 0.6mm for more gentle preinfusion. Most likely you'll see pressure in the 9.5-10.5 BAR range when pulling a shot. The pressure at the puck will be 0.5-1.5 BAR lower due to the pressure drop across the gicleur. In other words, the machine is designed so that when you adjust the pump for 9 BAR boiler pressure at free flow, the pressure at the puck will be very close to the desired 9 BAR.

The idle pressure at any given time is a function of how recently you pulled a shot (i.e., it takes some cooling time to come down from 12 BAR) and the ambient temperature, which determines how often the heater cycles on and off. 7-9 BAR sounds normal. If it was below 6 BAR I'd be concerned.

If I may append a quick question to this - do any of you notice some dripping of water from the brew head when then paddle is in the off position? Occasionally I see drops coming out when the machine has been on for a while.Is this normal?

I get this as well. Hopefully it's normal!

nuketopia wrote:When the machine is idle, the brew pressure gauge should indicate 12-bar. There is a pressure relief valve just behind the drip tray that can be adjusted to maintain this pressure. It should be adjusted so that at idle, the pressure does not exceed 12-bar, but should be right at or just under that value. You can adjust it easily with a wrench (17mm as I recall) or even with your fingers if it isn't hot. Adjust, flush water with the brew padle for a second or so, then watch the pressure after you turn off the brew paddle. It should quickly rise and settle at 12-bar. It should hold this pressure for a considerable amount of time, like 30-minutes or longer. (if it doesn't hold the adjusted pressure for long, then a check valve or something is leaking and you should contact LM for service - they were quite helpful when I had a check valve go bad and the indicated pressure would drop in a short time idling).

I've found that the idle pressure is an important setting on the LMLM, as it greatly effects the next thing you mentioned, pre-infusion.

Thanks for this information. I just tested my machine and it goes to 10 bars of pressure after switching the paddle off and within 10 seconds is back down to 9 bars. I'm going to reach out to LM Home. Was it an easy part to replace?

Learninginlondon wrote:If I may append a quick question to this - do any of you notice some dripping of water from the brew head when then paddle is in the off position? Occasionally I see drops coming out when the machine has been on for a while.Is this normal?

Nigel,

I get a few drops after flushing some water through the brew head, but it stops fairly soon.

Rocky

if it doesn't hold the adjusted pressure for long, then a check valve or something is leaking and you should contact LM for service . . .

Or the AC just turned on directing cold air in the vicinity of the machine.

This is a very, very small "brew boiler" compared to other double boiler (DB) machines and so any changes in temperature have a more dramatic effect on the brew pressure reading. In addition, the Linea Minea manual DOES NOT state to set the max pressure to 12.0 bar. It simply says that the pressure should not exceed same.

Another addition would be that this is the same steam boiler as is used in the GS/3 so variations in steam boiler pressure (and thus temperature) play an equally important role in the brew boiler's behavior due to the heat exchanger in the steam boiler. This is a complex situation but the brew pressure readings when the machine is at idle are meaningless as LM implies in their manual.

erics wrote:Another addition would be that this is the same steam boiler as is used in the GS/3 so variations in steam boiler pressure (and thus temperature) play an equally important role in the brew boiler's behavior due to the heat exchanger in the steam boiler. This is a complex situation but the brew pressure readings when the machine is at idle are meaningless as LM implies in their manual.

I can definitely see the Linea Mini brew boiler pressure cycling some while idling, more or less in unison with the steam boiler, but with a narrower range of pressure.

Rocky